Radio frequency data communications device

[0008] The drawings for this patent are the same as those in U.S. Pat. No. 6,130,602, which has been incorporated by reference.

[0009] The invention provides a radio frequency identification device comprising an integrated circuit including a receiver, a transmitter, and a microprocessor. The integrated circuit is preferably a monolithic single die integrated circuit including the receiver, the transmitter, and the microprocessor. Because the device includes an active transponder, instead of a transponder which relies on magnetic coupling for power, the device has a much greater range.

[0010] One aspect of the invention provides a radio frequency identification device comprising a monolithic integrated circuit including a receiver, a transmitter which can operate at frequencies above 400 MHz, and a microprocessor.

[0011] Another aspect of the invention provides a radio frequency identification device comprising a monolithic integrated circuit including a receiver, a transmitter which can operate at frequencies above 1 GHz, and a microprocessor.

[0012] Another aspect of the invention provides a radio frequency identification device comprising a monolithic integrated circuit including a transmitter, a microprocessor, and a receiver which can receive and interpret signals having frequencies above 400 MHz.

[0013] Another aspect of the invention provides a radio frequency identification device comprising a monolithic integrated circuit including a transmitter, a microprocessor, and a receiver which can receive and interpret signals having frequencies above 1 Ghz.

[0014] Another aspect of the invention provides a radio frequency identification device comprising a monolithic integrated circuit including a receiver, a microwave transmitter, and a microprocessor.

[0015] Another aspect, of the invention provides a radio frequency identification device comprising a monolithic integrated circuit including a microwave receiver, a transmitter, and a microprocessor.

[0016] Another aspect of the invention provides a radio frequency identification device comprising a single die including a receiver, a transmitter, and a microprocessor, the die having a size less than 90,000 mils². In accordance with a more preferred embodiment of the invention, the die has a size less than 300×300 mils². In accordance with a more preferred embodiment, of the invention, the die has a size less than 37,500 mils². In accordance with a more preferred embodiment of the invention, the die has a size of 209 by 116 mils².

[0017] Another aspect of the invention provides a radio frequency identification device comprising a single die integrated circuit including a receiver, a transmitter, and a microprocessor.

[0018] Another aspect of the invention provides a radio frequency identification device comprising a single die with a single metal layer including a receiver, a transmitter, and a microprocessor.

[0019] Another aspect of the invention provides a radio frequency identification device comprising a single die integrated circuit including a receiver, a transmitter, and a microprocessor formed using a single metal layer processing method.

[0020] Another aspect of the invention provides a radio frequency identification system comprising an integrated circuit including a receiver, and a transmitter; and an antenna coupled to the integrated circuit, the integrated circuit being responsive to radio frequency signals of multiple carrier frequencies.

[0021] Another aspect of the invention provides a radio frequency identification device comprising transponder circuitry formed in a monolithic integrated circuit comprising both transmitting and receiving circuits of the transponder circuitry; a power supply operably associated with the transponder circuitry; and an antenna operably associated with the transponder circuitry.

[0022] Another aspect of the invention provides a radio frequency identification device comprising a monolithic semiconductor integrated circuit including a receiver and a transmitter; means for applying a supply of power to the integrated circuit device from a battery; and means for configuring the integrated circuit to receive and transmit radio frequency signals.

[0023] Another aspect of the invention provides a method for producing a radio frequency identification device, the method comprising the following steps: providing a monolithic integrated circuit having a receiver and a transmitter; and providing a package configured to carry the integrated circuit.

[0024] Another aspect of the invention provides a method for adapting a radio frequency data communication device for use at a desired carrier frequency for use in a radio frequency identification (RFID) device, the method comprising the following steps: providing an integrated circuit having tunable circuitry, the integrated circuit comprising a receiver and a transmitter; configuring the integrated circuit for connection with a power supply to enable operation; configuring the integrated circuit to receive and apply radio frequency signals, via an antenna, the antenna and the tunable circuitry cooperating in operation there between; and tuning the tunable circuitry and the antenna to realize a desired carrier frequency from a wide range of possible carrier frequencies. A method for adapting a radio frequency data communication device for use at a desired: carrier frequency for use in a radio frequency identification device, the method comprising the following steps: providing an integrated circuit having tunable circuitry, the integrated circuit comprising a receiver and a transmitter; configuring the integrated circuit for connection with a power supply to enable operation; configuring the integrated circuit to receive and apply radio frequency signals via an antenna, the antenna and the tunable circuitry cooperating in operation there between; and tuning the antenna to realize a desired carrier frequency from a wide range of possible carrier frequencies.

[0025] Another aspect of the invention provides a radio frequency communications device comprising an integrated circuit including a transmitter and a receiver, the integrated circuit including a clock recovery circuit recovering a clock frequency from a signal received by the receiver, the clock recovery circuit having a phase lock loop including a voltage controlled oscillator, and a loop filter having a capacitor storing a voltage indicative of a frequency at which the voltage controlled oscillator is oscillating, the integrated circuit using the voltage stored on the capacitor to generate a clock frequency for the transmitter.

[0026] Another aspect of the invention provides a method of recovering a clock frequency from a received radio frequency signal, storing the clock frequency, and using the clock frequency for radio frequency transmission by a transmitter, the method comprising: providing a clock recovery circuit recovering a clock frequency from a signal received by the receiver, the clock recovery circuit having a phase lock loop including a voltage controlled oscillator, and a loop filter having a capacitor; using the clock recovery circuit to recover a clock frequency from a received radio frequency signal; storing on the capacitor a voltage indicative of frequency at which the voltage controlled oscillator is oscillating; using the voltage stored on the capacitor to generate a clock frequency for use by the transmitter.

[0027] Another aspect of the invention provides a method of recovering and storing a clock frequency from a received radio frequency signal in a radio frequency identification device including a transmitter and a receiver, the method comprising providing a clock recovery circuit recovering a clock frequency from a signal received by the receiver, the clock recovery circuit having a phase lock loop; using the clock recovery circuit to recover a clock frequency from a received radio frequency signal; storing in analog form a value indicative of frequency at which the voltage controlled oscillator is oscillating; and using the analog value to generate a clock frequency for use by the transmitter.

[0028] Another aspect of the invention provides a radio frequency communications device comprising an integrated circuit including a transmitter and a receiver, the transmitter being switchable between a backscatter mode, wherein a carrier for the transmitter is derived from a carrier received from an interrogator spaced apart from the radio frequency communications device, and an active mode, wherein a carrier for the transmitter is generated by the integrated circuit itself.

[0029] Another aspect of the invention provides a radio frequency communications device comprising an integrated circuit including a transmitter and a receiver, the transmitter selectively transmitting a signal using a modulation scheme, the transmitter being switchable for transmission using different modulation schemes.

[0030] Another aspect of the invention provides a method for adapting modulation schemes of a radio frequency data communication, device in a radio frequency identification device, the method comprising the following steps: providing an integrated circuit having switching circuitry, a receiver, a transmitter, and a processor; the integrated circuit having a plurality of transmitting circuits including a first transmitting circuit configured to realize an active transmitter scheme and a second transmitting circuit configured to realize a modulated backscatter scheme; configuring the integrated circuit for connection with a power supply to enable operation; configuring the integrated circuit to receive and apply radio frequency signals via an antenna, the antenna and the tunable circuitry cooperating in operation; and switching the switchable circuitry with respect to the antenna to enable one of the transmitting circuits to realize one of the modulation schemes.

[0031] Another aspect of the invention provides a method for adapting modulation schemes of a radio frequency data communication device in a radio frequency identification device, the method comprising the following steps: providing an integrated circuit having switching circuitry, a receiver, a transmitter, and a processor, the integrated circuit including a plurality of transmitting circuits, the plurality of transmitting circuits configured to selectively realize a plurality of modulated backscatter schemes; configuring the integrated circuit for connection with a power supply to enable operation; configuring the integrated circuit to receive and apply radio frequency signals via an antenna, the antenna and the tunable circuitry cooperating in operation; and switching the transmitting circuits with respect to the antenna to enable one of the transmitting circuits to realize one of the modulation schemes.

[0032] Another aspect of the invention provides a radio frequency identification device comprising: an integrated circuit including a transmitter and a receiver, the integrated circuit being adapted to be connected to a battery, and further including a comparator comparing the voltage of the battery with a predetermined voltage and generating a low battery signal if the voltage of the battery is less than the predetermined voltage.

[0033] Another aspect of the invention provides a method for detecting a low battery condition in a radio frequency data communication device for use in a radio frequency identification device, the method comprising the following steps: providing an integrated circuit having switching circuitry, a receiver, and a transmitter, the integrated circuit including a comparator configured to compare the battery voltage with a predetermined voltage and generate a low battery signal if the battery voltage is less than the predetermined voltage; configuring the integrated circuit for connection with the battery to enable operation; configuring the integrated circuit to receive and apply radio frequency signals via an antenna, the antenna and the tunable circuitry cooperating in operation there between; determining a predetermined voltage for the battery; comparing the voltage of the battery with the predetermined voltage; and generating a low battery signal if the voltage of the battery is less than the predetermined voltage.

[0034] Another aspect of the invention provides a radio frequency communications device comprising an integrated circuit including a transmitter and a receiver, the integrated circuit periodically checking if a radio frequency signal is being received by the receiver, the integrated circuit further including a timer setting a time period for the checking, the timer having a frequency lock loop.

[0035] Another aspect of the invention provides a radio frequency communications device comprising an integrated circuit including a transmitter and a receiver, the integrated circuit being configured to periodically check if a radio frequency signal is being received by the receiver, the integrated circuit further including a timer setting a time period for the checking, the timer having a phase lock loop.

[0036] Another aspect of the invention provides a method for calibrating a clock in a radio frequency data communication device for use in a radio frequency identification device, the method comprising the following steps: providing an integrated circuit having a receiver and a transmitter, the integrated circuit including a timer having a frequency lock loop configured to set a time period for periodically checking if a radio frequency signal is being received by the receiver; configuring the integrated circuit for connection with a battery to enable operation; configuring the integrated circuit to receive and apply radio frequency signals via an antenna, the antenna and the integrated circuit cooperating in operation therebetween; and periodically checking whether a radio frequency signal is being received by the receiver.

[0037] Another aspect of the invention provides a radio frequency identification device for receiving and responding to radio frequency commands from an interrogator transmitting a radio frequency signal, the device comprising an integrated circuit including a receiver, a transmitter, and a connection pin, the integrated circuit being switchable between a radio frequency receive mode wherein the receiver receives commands via radio frequency, and a direct receive mode wherein commands are received via the connection pin.

[0038] Another aspect of the invention provides a radio frequency identification device for receiving and responding to radio frequency commands from an interrogator transmitting a radio frequency signal, the device comprising an integrated circuit including a receiver, a transmitter, and a digital input pin, the integrated circuit being switchable between a radio frequency receive mode wherein the receiver receives commands via radio frequency, and a direct receive mode wherein commands are received digitally via the digital input pin. Another aspect of the invention provides a radio frequency identification device for receiving and responding to radio frequency commands from an interrogator transmitting a radio frequency signal, the device comprising an integrated circuit including a receiver, a transmitter, and a connection pin, the integrated circuit being switchable between a radio frequency receive mode wherein the receiver receives commands via radio frequency, and a direct receive mode wherein a modulation signal without a carrier is received via the connection pin.

[0039] Another aspect of the invention provides a radio frequency identification device for receiving and responding to radio frequency commands from an interrogator transmitting a radio frequency signal, the so device comprising an integrated circuit including a receiver, a transmitter, and a connection pin, the integrated circuit being switchable between a radio frequency transmit mode wherein the receiver transmits responses to the commands via radio frequency, and a direct transmit mode wherein responses are transmitted via the connection pin.

[0040] Another aspect of the invention provides a radio frequency identification device for receiving and responding to radio frequency commands from an interrogator transmitting a radio frequency signal, the device comprising an integrated circuit including a receiver, a transmitter, and a digital output pin, the integrated circuit being switchable between a radio frequency transmit mode wherein the receiver transmits responses to the commands via radio frequency, and a direct transmit mode wherein responses are transmitted digitally via the digital output pin.

[0041] Another aspect of the invention provides a radio frequency identification device for receiving and responding to radio frequency commands from an interrogator transmitting a radio frequency signal, the device comprising an integrated circuit including a receiver, a transmitter, and a connection pin, the integrated circuit being switchable between a radio frequency transmit mode wherein the receiver transmits responses to the commands via radio frequency, and a direct transmit mode wherein a modulation signal without a carrier is transmitted via the connection pin.

[0042] Another aspect of the invention provides a method comprising the following steps: providing an integrated circuit having a receiver, a transmitter, and a connection pin, the integrated circuit including a switchable circuit configured to switch between a radio frequency receive mode wherein the receiver receives commands via radio frequency, and a direct receive mode wherein commands are received via the connection pin; configuring the integrated circuit for connection with a battery; configuring, the integrated circuit to receive and transmit radio frequency signals via an antenna, the antenna and the integrated circuit cooperating in operation; and switching to one of the radio frequency receive mode and the direct receive mode to enable receipt of radio frequency commands or commands received via the connection pin. Another aspect of the invention provides a method comprising the following steps: providing an integrated circuit having a receiver, a transmitter, and a connection pin, the integrated circuit including a switchable circuit configured to switch between a radio frequency transmit mode wherein the transmitter transmits information via radio frequency, and a direct transmit mode wherein data is transmitted via the connection pin; configuring the integrated circuit for connection with a battery; configuring the integrated circuit to receive and transmit radio frequency signals via an antenna, the antenna and the integrated circuit cooperating in operation; and switching to one of the radio frequency transmit mode and the direct transmit mode to enable transmission of information via radio frequency or via the connection pin.

[0043] Another aspect of the invention provides an integrated circuit comprising a radio frequency receiver; a unique, non-alterable indicia identifying the integrated circuit; and a radio frequency transmitter configured to transmit a signal representative of the indicia in response to a command received by the receiver.

[0044] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit, including a receiver for receiving radio frequency commands from an interrogation device, and a transmitter for transmitting a signal identifying the device to the interrogator, the transmitter and receiver being formed on: a die having a lot number, wafer number, and die number, the integrated circuit including non-alterable indicia identifying the lot number, wafer number, and die number, the transmitter being configured to transmit the non-alterable indicia in response to a manufacturer's command received by the receiver, the transmitted non-alterable indicia being different from the identifying signal.

[0045] Another aspect of the invention provides a method of tracing manufacturing process problems by tracing the origin of a defective radio frequency identification integrated circuit, the method comprising: forming a non-alterable indicia on a die for the integrated circuit, the indicia representing the wafer lot number, wafer number, and die number on the wafer, the indicia being not readily ascertainable by a user; and causing the integrated circuit to transmit the non-alterable indicia via radio frequency in response to a manufacturer's command.

[0046] Another aspect of the invention provides a method of tracing stolen property including a radio frequency identification integrated circuit, the method comprising: forming a non-alterable indicia on a die for the integrated circuit, the indicia representing the wafer lot number, wafer number, and die number on the wafer, the indicia being not readily ascertainable by a user; and causing the integrated circuit to transmit the non-alterable indicia via radio frequency in response to a manufacturer's command.

[0047] Another aspect of the invention provides a method of tracing manufacturing process problems in the manufacture of a radio frequency integrated circuit by tracing defect origin, the method comprising the following steps: providing a detectable signature on the integrated circuit, the signature indicative of one or more of the wafer lot number, wafer number, and die number of a die for the integrated circuit; and enabling the integrated circuit to transmit the signature via radio frequency responsive to an inquiry command.

[0048] Another aspect of the invention provides a radio frequency identification device comprising: an integrated circuit including a microprocessor, a receiver receiving radio frequency commands from an interrogation device, and a transmitter transmitting a signal identifying the device to the interrogator, the integrated circuit switching between a sleep mode, and a microprocessor on mode, in which more power is consumed than in the sleep mode, if the microprocessor determines that a signal received by the receiver is a radio frequency command from an interrogation device.

[0049] Another aspect of the invention provides a method for conserving power during operation, of a radio frequency identification device, the method comprising the following steps: providing a receiver, a transmitter, microprocessor, and wake-up circuitry, the wake,-up circuitry configured to selectively supply clock signals to the processor and thus control power consumption of the processor; configuring the receiver with an antenna to receive radio frequency signals from an interrogation device; configuring the transmitter to transmit a signal identifying the device to the interrogator; selectively enabling powered wake-up of the receiver to periodically check for presence of radio frequency signals; detecting whether a radio frequency signal is valid; and depending on whether a radio frequency signal is valid, supplying clock signals to the processor.

[0050] Another aspect of the invention provides a method for conserving power during operation of a radio frequency identification device, the method comprising the following steps: providing a receiver, a transmitter, microprocessor, and wake-up circuitry, the wake-up circuitry configured to selectively supply power to the processor; configuring the receiver with an antenna to receive radio frequency signals from an interrogation device; configuring the transmitter to transmit a signal identifying the device to the interrogator; selectively enabling powered wake-up of the receiver to periodically check for presence of radio frequency signals; detecting whether a radio frequency signal is valid; and depending on whether a radio frequency signal is valid, supplying power signals to the processor.

[0051] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a microprocessor, a transmitter, and a receiver, the integrated circuit being switchable between a sleep mode, and a microprocessor on mode in which more power is consumed than in the sleep mode, the integrated circuit being switched from the sleep mode to the microprocessor on mode in response to a direct sequence spread spectrum modulated radio frequency signal, which has a predetermined number of transitions within a certain period of time, being received by the receiver.

[0052] Another aspect of the invention provides a method for conserving power in a radio frequency identification device, the method comprising periodically switching from a sleep mode to a receiver on mode and performing the following tests to determine whether to further switch to a microprocessor on mode because a valid radio frequency signal is present: (a) determining if any radio frequency signal is present and, if so, proceeding to step (b); and, if not, returning to the sleep mode; and (b) determining if the radio frequency signal has a predetermined number of transitions per a predetermined time period of time and, if so, switching to the microprocessor on mode; and, if not, returning to the sleep mode.

[0053] Another aspect of the invention provides a radio frequency identification device switchable between a sleep mode and a mode in which more power is consumed than in the sleep mode, the radio frequency identification device comprising a transponder including a receiver and a transmitter; means for periodically checking whether any radio frequency signal is being received by the receiver; and means for determining if a radio frequency signal has a predetermined number of transitions within a predetermined period of time.

[0054] Another aspect of the invention provides a method for conserving power in a radio frequency identification device, the method comprising periodically switching from a sleep mode to a receiver on mode and performing the following tests to determine whether to further switch to a microprocessor on mode because a valid radio frequency signal is present: (a) determining if any radio frequency signal is present and, if so, proceeding to step (b); and, if not, returning to the sleep mode; (b) determining if the radio frequency signal is modulated and has a predetermined number of transitions per a predetermined period of time and, if so, proceeding to step (c); and, if not, returning to the sleep mode; and (c) determining if the modulated radio frequency signal has a predetermined number of transitions per a predetermined period of time different from the predetermined time of step (b) and, if so, switching to the microprocessor on mode; and, if not, returning to the sleep mode.

[0055] Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing a p-type substrate; defining an n-type region relative to the substrate; forming an insulator over the n-type region; removing an area of the insulator for definition of a contact hole, and removing an area encircling the contact hole; forming n+regions in the n-type regions encircling the contact hole; depositing a Schottky metal in the contact hole; and annealing the metal to form a silicide interface to the n-type region.

[0056] Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing a substrate; defining a p-type region relative to the substrate; forming an insulator over the p-type region; removing an area of the insulator for definition of a contact hole, and removing an area encircling the contact hole; forming p+regions in the p-type regions encircling the contact hole; depositing a Schottky metal in the contact hole; and annealing the Schottky metal to form a silicide interface to the p-type region.

[0057] Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing a p-type substrate; defining an n-well region relative to the substrate; forming a BPSG insulator over the n-well region; etching away an area of the BPSG for definition of a contact hole, and etching an area encircling the contact hole; forming n+regions in the n-well regions encircling the contact hole; depositing titanium in the contact hole; and annealing the titanium to form a silicide interface to the n-well region.

[0058] Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing an n-type substrate; defining a p-well region relative to the substrate; forming a BPSG insulator over the p-well region; etching away an area of the BPSG for definition of a contact hole, and etching an area encircling the contact hole; forming p+regions in the p-well regions encircling the contact hole; depositing titanium in the contact hole; and annealing the titanium to so form a silicide interface to the p-well region.

[0059] Another aspect of the invention provides a radio frequency communications system comprising an antenna; an integrated circuit including a receiver having a Schottky diode detector including a Schottky diode coupled to the antenna; and a current source connected to drive current through the antenna and the Schottky diode.

[0060] Another aspect of the invention provides an integrated circuit for radio frequency communications comprising an inductorless radio frequency detector.

[0061] Another aspect of the invention provides a system comprising an antenna; a transponder including a receiver having a Schottky diode detector including a Schottky diode having a first terminal coupled to the antenna and having a second terminal; and means for driving current through both the antenna and the Schottky diode in a direction from the first terminal to the second terminal.

[0062] Another aspect of the invention provides a system comprising an antenna;

[0063] a transponder including a receiver having a Schottky diode detector including a Schottky diode having a first terminal coupled to the antenna and having a second terminal; and means for driving current through both the antenna and the Schottky diode in a direction from the second terminal to the first terminal. Another aspect of the invention provides a system comprising an antenna;
a transponder including a receiver having a Schottky diode detector including a Schottky diode having an anode coupled to the antenna and having a cathode; and means for driving current through both the antenna and the Schottky diode in a direction from the anode to the cathode.

[0064] Another aspect of the invention provides a radio frequency communications system comprising: an antenna; an integrated circuit including a receiver having a Schottky diode detector including a Schottky diode having an anode coupled to the antenna and having a cathode, the Schottky diode detector further including a capacitor connected between the cathode and ground, and including a capacitor having a first contact connected to the cathode and having a second contact defining an output of the Schottky diode detector; a current source connected to the cathode to drive current through the antenna and the Schottky diode in a direction from the anode to the cathode.

[0065] Another aspect of the invention provides a radio frequency communications system comprising an antenna; an integrated circuit including a receiver having a Schottky diode detector including a Schottky diode having a cathode coupled to the antenna and having an anode, the Schottky diode detector further including a capacitor connected between the anode and ground, and including a capacitor having a first contact connected to the anode and having a second contact defining an output of the Schottky diode detector; and a current source connected to the anode to drive current through the antenna and the Schottky diode in a direction from the anode to the cathode.

[0066] Another aspect of the invention provides a system comprising an antenna; a transponder including a receiver having a Schottky diode detector including a Schottky diode having a cathode coupled to the antenna and having an anode; and means for driving current through both the antenna and the Schottky diode in a direction from the anode to the cathode.

[0067] Another aspect of the invention provides a method for realizing an improved radio frequency detector for use in a radio frequency identification device, the method comprising the following steps: providing an integrated circuit and an antenna, the integrated circuit having a receiver and a transmitter, the integrated circuit further having a Schottky diode and a current source, with the Schottky diode in operation being coupled to the antenna and the current source, the Schottky diode and antenna cooperating there between to form an inductorless radio frequency detector; applying a supply of power to the integrated circuit device from a battery; and applying a desired current across the Schottky diode to impart a desired impedance there across relative to the impedance of the antenna.

[0068] Another aspect of the invention provides a frequency lock loop comprising a current controlled oscillator including a plurality of selectively engageable current mirrors, the frequency of oscillation of the frequency lock loop varying in response to selection of the current mirrors, the current mirrors including transistors operating in a subthreshold mode.

[0069] Another aspect of the invention provides an integrated circuit comprising a receiver, a transmitter, and a frequency lock loop including a current source having a thermal voltage generator, a current controlled oscillator having a plurality of selectively engageable current mirrors multiplying up the current of the current source, the frequency of oscillation of the frequency lock loop varying in response to selection of the current mirrors, the current mirrors including transistors operating in a subthreshold mode.

[0070] Another aspect of the invention provides a timing oscillator that consumes less than one milliAmp.

[0071] Another aspect of the invention provides a method of constructing a frequency lock loop including a current controlled oscillator having a plurality of selectively engageable current mirrors, the frequency of oscillation of the frequency lock loop varying in response to selection of the current mirrors, the method comprising selecting current mirrors to vary frequency of operation, and operating transistors in the current mirrors in subthreshold mode.

[0072] Another aspect of the invention provides a method of operating an integrated circuit including a receiver, a transmitter, and a frequency lock loop including a current source having a thermal voltage generator, a current controlled oscillator having a plurality of selectively engageable current mirrors multiplying up the current of the current source, the frequency of oscillation of the frequency lock loop varying in response to selection of the current mirrors, the method comprising engaging selected current mirrors and operating transistors in the current mirrors in a subthreshold mode.

[0073] Another aspect of the invention provides an amplifier powered by a selectively engageable voltage source, the amplifier comprising first and second electrodes for receiving an input signal to be amplified, the input electrodes being adapted to be respectively connected to coupling capacitors; a differential amplifier having inputs respectively connected to the first and second electrodes, and having an output; selectively engageable resistances between the voltage source and respective inputs of the differential amplifier and defining, with the coupling capacitors, the high pass characteristics of the circuit; and second selectively engageable resistances between the voltage source and respective inputs of the differential amplifier, the second resistances respectively having smaller values that the first mentioned resistances, the second resistances being engaged then disengaged in response to the voltage source being engaged.

[0074] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a microprocessor, a receiver receiving radio frequency commands from an interrogation device, and a transmitter transmitting a signal identifying the device to the interrogator, the integrated circuit switching between a sleep mode, and a microprocessor on mode, in which more power is consumed than in the sleep mode, if the microprocessor determines that a signal received by the receiver is a radio frequency command from an interrogation device, the integrated circuit further including an amplifier powered by a selectively engageable voltage source engaged in the microprocessor on mode but not in the sleep mode, the amplifier including first and second electrodes for receiving an input signal to be amplified, the input electrodes being adapted to be respectively connected to coupling capacitors, a differential amplifier having inputs respectively connected to the first and second electrodes, and having an output, selectively engageable resistances between the voltage source and respective inputs of the differential amplifier, second selectively engageable resistances between the voltage source and respective inputs of the differential amplifier, the second resistances respectively having smaller values that the first mentioned resistances, the second resistances being engaged then disengaged in response to the integrated circuit switching from the sleep mode to the microprocessor on mode. Another aspect of the invention provides a method of speeding power up of an amplifier stage powered by a selectively voltage source and including first and second electrodes for receiving an input signal to be amplified, the input electrodes being adapted to be respectively connected to coupling capacitors; a differential amplifier having inputs respectively connected to the first and second electrodes, and having an output; and selectively engageable resistances between the voltage source and respective inputs of the differential amplifier, the method comprising: shorting around the selectively engageable resistances for a predetermined amount of time in response to the voltage source being engaged.

[0075] Another aspect of the invention provides a radio frequency communications system comprising an antenna; an integrated circuit including a receiver having a Schottky diode detector including a Schottky diode having an anode coupled to the antenna and having a cathode, the Schottky diode detector further including a capacitor connected between the cathode and ground, and including a capacitor having a first contact connected to the cathode and having a second contact defining an output of the Schottky diode detector, the integrated circuit further including a clock recovery circuit recovering a clock from rising edges only of a signal at the output of the Schottky diode detector; and a current source connected to drive current through the antenna and the Schottky diode in a direction from the anode to the cathode.

[0076] Another aspect of the invention provides a radio frequency communications system comprising an antenna; an integrated circuit including a receiver having a Schottky diode detector including a Schottky diode having a cathode coupled to the antenna and having an anode, the Schottky diode detector further including a capacitor connected between the anode and ground, and including a capacitor having a first contact connected to the anode and having a second contact defining an output of the Schottky diode detector, the integrated circuit further including a clock recovery circuit recovering a clock from falling edges only of a signal at the output of the Schottky diode detector; and a current source connected to drive current through the antenna and the Schottky diode in a direction from the anode to the cathode.

[0077] Another aspect of the invention provides a method of recovering a clock in a radio frequency communications system, the method comprising: providing an antenna; providing a receiver having a Schottky diode detector including a Schottky diode having an anode coupled to the antenna and having a cathode, the Schottky diode detector further including a capacitor connected between the cathode and ground, and including a capacitor having a first contact connected to the cathode and having a second contact defining an output of the Schottky diode detector; driving current through the antenna and the Schottky diode in a direction from the anode to the cathode; and recovering a clock from rising edges only of a signal at the output of the Schottky diode detector.

[0078] Another aspect of the invention provides a method of recovering a clock in a radio frequency communications system, the method comprising: providing an antenna; providing a receiver having a Schottky diode detector including a Schottky diode having a cathode coupled to the antenna and having an anode, the Schottky diode detector further including a capacitor connected between the anode and ground, and including a capacitor having a first contact connected to the anode and having a second contact defining an output of the Schottky diode detector; driving current through the antenna and the Schottky diode in a direction from the anode to the cathode; and recovering a clock from falling edges only of a signal at the output of the Schottky diode detector.

[0079] Another aspect of the invention provides a stage for a voltage controlled oscillator, the stage comprising a first transistor having a control electrode defining a first input, and having first and second power electrodes, the first power electrode defining a first node; a second transistor having a control electrode defining a second input, and having first and second power electrodes, the first power electrode of the second transistor defining a second node; a current source connected to the second power electrodes of the first and second transistors and directing current away from the second power electrodes of the first and second transistors; and means defining a variable resistance connecting the first and second nodes to a supply voltage.

[0080] Another aspect of the invention provides a stage for a voltage controlled oscillator, the stage comprising a first p-channel transistor having a gate defining a control node, having a source adapted to be connected to a supply voltage, and having a drain; a second p-channel transistor having a gate connected to the control node, having a source connected to the supply voltage, and having a drain; a first n-channel transistor having a gate defining a first input, having a drain connected to the drain of the first p-channel transistor and defining a first node, and having a source; a second n-channel transistor having a gate defining a second input, having a drain connected to the drain of the second p-channel transistor and defining a second node, and having a source; a current source connected to the sources of the first and second n-channel transistors directing current from the sources of the first and second n-channel transistors; a first resistor connected between the supply voltage and the drain of the first n-type transistor; a second resistor connected between the supply voltage and drain of the second n-type transistor; a first source follower having an input connected to the first node and having an output defining a first output of the stage; and a second source follower having an input connected to the second node and having an output defining a second output of the stage.

[0081] Another aspect of the invention provides a transmitter including a ring oscillator having a chain of stages, each stage comprising a first p-channel transistor having a gate defining a control node, having a source adapted to be connected to a supply voltage, and having a drain; a second p-channel transistor having a gate connected to the control node, having a source connected to the supply voltage, and having a drain; a first n-channel transistor having a gate defining a first input, having a drain connected to the drain of the first p-channel transistor and defining a first node, and having a source; a second n-channel transistor having a gate defining a second input, having a drain connected to the drain of the second p-channel transistor and defining a second node, and having a source; a current source connected to the sources of the first and second n-channel transistors directing current from the sources of the first and second n-channel transistors; a first resistor connected between the supply voltage and the drain of the first n-type transistor; a second resistor connected between the supply voltage and drain of the second n-type transistor; a first source follower having an input connected to the first node and having an output defining a first output of the stage; and a second source follower having an input connected to the second node and having an output defining a second output of the stage.

[0082] Another aspect of the invention provides a method of varying frequency in a stage of a voltage controlled oscillator having two input transistors having gates defining input nodes and having drain to source paths adapted to be connected between a supply voltage and a current source, the method comprising providing an impedance between the input transistors and the supply voltage, and varying the impedance.

[0083] Another aspect of the invention provides a frequency doubler comprising a first Gilbert cell; a second Gilbert cell coupled to the, first Gilbert cell; a frequency generator configured to apply a first sinusoidal wave to the first Gilbert cell; and a phase shifter applying a sinusoidal wave shifted from the first sinusoidal wave to the second Gilbert cell.

[0084] Another aspect of the invention provides a frequency doubler comprising a first Gilbert cell including a first pair of transistors having sources that are connected together, a second pair of transistors having sources that are connected together, a first one of the transistors of the first pair having a gate defining a first input node and a first one of the transistors of the second pair having a gate connected to the first input node, a second one of the transistors of the first pair having a gate defining a second input node and a second one of the transistors of the second pair having a gate connected to the second input node, the first transistor of the first pair having a drain, and the second transistor of the second pair having a drain connected to the drain of the first transistor of the first pair, the second transistor of the first pair having a drain, and the first transistor of the second pair having a drain connected to the drain of the second transistor of the first pair, a third pair including first and second transistors having sources coupled together, the first transistor of the third pair having a drain connected to the source of the second transistor of the first pair, the second transistor of the third pair having a drain connected to the source of the second transistor of the second pair, and a current source connected to the sources of the third pair and forward biasing the third pair, the second transistor of the third pair having a gate defining a third input node, and the first transistor of the third pair having a gate defining a fourth input node; and a second Gilbert cell including a first pair of transistors having sources that are connected together, a second pair of transistors having sources that are connected together, a first one of the transistors of the first pair of the second cell having a gate defining a first input node and a first one of the transistors of the second pair of the second cell having a gate connected to the first input node of the second cell, a second one of the transistors of the first pair of the second cell having a gate defining a second input node of the second cell and a second one of the transistors of the second pair of the second cell having a gate connected to the second input node of the second cell, the first transistor of the first pair of the second cell having a drain, and the second transistor of the second pair of the second cell having a drain connected to the drain of the first transistor of the first pair of the second cell, the second transistor of the first pair of the second cell having a drain, and the first transistor of the second pair of the second cell having a drain connected to the drain of the second transistor of the first pair of the second cell, a third pair including first and second transistors having sources coupled together, the first transistor of the third pair of the second cell having a drain connected to the source of the second transistor of the first pair of the second cell, the second transistor of the third pair of the second cell having a drain connected to the source of the second transistor of the second pair of the second cell, and a current source connected to the sources of the third pair of the second cell and forward biasing the third pair of the second cell, the second transistor of the third pair of the second cell having a gate defining a third input node of the second cell, and the first transistor of the third pair of the second cell having a gate defining a fourth input node of the second cell; the drain of the second transistor of the first pair of the second cell being connected to the drain of the second transistor of the first pair of the first cell, the drain of the second transistor of the second pair of the second cell being connected to the drain of the second transistor of the second pair of the second cell, the first input node of the second cell being connected to the fourth input node of the first cell, the third input node of the second cell being connected to the second input node of the first cell, and the fourth input node of the second cell being connected to the first input node of the first cell.

[0085] Another aspect of the invention provides a method of doubling frequency without using a feedback loop, the method comprising: providing a first Gilbert cell; providing a second Gilbert cell coupled to the first Gilbert cell; applying a first sinusoidal wave to the first Gilbert cell; and applying a sinusoidal wave shifted from the first sinusoidal wave to the second Gilbert cell.

[0086] Another aspect of the invention provides a pseudo random number generator comprising a linear feedback shift register switchably operable in a first mode, and in a second mode wherein the shift register consumes more power than in the first mode.

[0087] Another aspect of the invention provides a method of generating a pseudo random number, the method comprising providing a linear feedback shift register; providing an oscillator which generates clock signals used by the linear feedback shift register for shifting; and providing a first power level to the oscillator when a pseudo random number is required, and providing a second power level, lower than the first power level, to the oscillator at other times. Another aspect of the invention provides a method of generating a pseudo random number, the method comprising: providing a linear feedback shift register; providing an oscillator which generates clock signals used by the linear feedback shift register for shifting; and operating the oscillator at a first frequency in response to a request for a pseudo random number, and operating the oscillator at a second frequency lower than the first frequency after the pseudo random number is generated.

[0088] Another aspect of the invention provides a system comprising a microprocessor operating at a frequency; a linear feedback shift register operable in a low power mode, wherein the shift register operates at a frequency below the frequency of the microprocessor, and a high power mode wherein the shift register consumes more power than in the low power mode, operates at the frequency of the microprocessor, and shifts data into the microprocessor.

[0089] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a receiver, a transmitter, a thermal voltage generator, a microprocessor operating at a frequency, a linear feedback shift register operable in a low power mode, wherein the shift register operates at a frequency below the frequency of the microprocessor, and a high power mode wherein the shift register consumes more power than in the low power mode, operates at the frequency of the microprocessor, and shifts data into the microprocessor, an oscillator supplying clock signals to the shift register, and current mirrors supplying current to each stage of the shift register, the current mirrors being referenced to the thermal voltage generator when the shift register is in the low power mode, and, when the shift register is in the high power mode, connected to a supply voltage potential greater than the potential provided by the thermal voltage generator.

[0090] Another aspect of the invention provides a method of generating a pseudo random number, the method comprising: providing a thermal voltage generator, a linear feedback shift register, an oscillator supplying clock signals to the shift register, and current mirrors supplying current to each stage of the shift register; referencing the current mirrors to the thermal voltage generator when no pseudo random number is required; and connecting the current mirrors to a supply voltage potential greater than the potential provided by the thermal voltage generator when a pseudo random number is required.

[0091] Another aspect of the invention provides an integrated circuit comprising a receiver and a transmitter sharing a common antenna.

[0092] Another aspect of the invention provides a method of using an integrated circuit including a receiver and a transmitter, the method comprising connecting the receiver and transmitter to a common antenna.

[0093] Another aspect of the invention provides an integrated circuit comprising:

• [0094] a die including a transmitter having an antenna output and a detector having an antenna input; a package housing the die; a first contact connected to the antenna output and accessible from outside the package; a second contact connected to the antenna input and accessible from outside the package; and a short electrically connecting the first contact to the second contact outside the package.

[0095] Another aspect of the invention provides a method of using an integrated circuit including a die having a transmitter including an antenna output and a detector including an antenna output, the integrated circuit further including a package housing the die, a first contact connected to the antenna output and accessible from outside the package, and a second contact connected to the antenna input and accessible from outside the package, the method comprising: electrically shorting the first contact to the second contact outside the package.

[0096] Another aspect of the invention provides a transceiver comprising an antenna having a first end connected to a bias voltage, and having a second end; a detector including a Schottky diode having an anode connected to the second end of the antenna; and a transmitter having an output connected to the second end of the antenna.

[0097] Another aspect of the invention provides a radio frequency identifications device comprising an integrated circuit including both a receiver and a transmitter; a first antenna connected to the receiver; and a second antenna connected to the transmitter.

[0098] Another aspect of the invention provides a transceiver comprising a loop antenna having a first end connected to a bias voltage, and having a second end; a second antenna; a detector including a Schottky diode having an anode connected to the second end of the antenna; and a transmitter having an output connected to the second antenna.

[0099] Another aspect of the invention provides a transceiver comprising an antenna having a first end connected to a bias voltage, and having a second end; a detector including a Schottky diode having an anode connected to the second end of the antenna; and an active transmitter having an output connected to the second end of the antenna.

[0100] Another aspect of the invention provides a transceiver comprising an antenna having a first end, and having a second end; a detector including a Schottky diode having a cathode connected to the second end of the antenna and defining a potential at the second end of the antenna; the first end of the antenna being connected to a potential lower than the potential of the second end of the antenna; and a backscatter transmitter including a transistor having a first power electrode connected to the first end of the antenna, a second power electrode connected to the second end of the antenna, and a control electrode adapted to have a modulation signal applied thereto.

[0101] Another aspect of the invention provides a transceiver in accordance with claim and further comprising a current source directing current in the direction from the anode to the cathode.

[0102] Another aspect of the invention provides a transceiver comprising a loop antenna having a first end connected to a bias voltage, and having a second end; a detector including a Schottky diode having an anode connected to the second end of the antenna; a backscatter transmitter having a first output and having a second output; a capacitor connected between the first output and the first end of the antenna, and a capacitor connected between the second output and the second end of the antenna.

[0103] Another aspect of the invention provides a method of configuring a transceiver including a backscatter transmitter having first and second outputs, and a detector having a Schottky diode including an anode, the method comprising: applying a bias voltage to a first end of an antenna; connecting a second end of the antenna to the anode; connecting a capacitor between the first output and the first end of the antenna; and connecting a capacitor between the second output and the second end of the antenna.

[0104] Another aspect of the invention provides a method of arranging a transceiver including a backscatter transmitter and a detector having a Schottky diode including a cathode, the method comprising: connecting a first end of an antenna to a ground potential; connecting a second end of the antenna to the cathode; and connecting a first power electrode of a transistor to the first end of the antenna; connecting a second power electrode connected to the second end of the antenna; and connecting a control electrode of the transistor to a modulation signal.

[0105] Another aspect of the invention provides a method of determining when a phase lock loop achieves frequency lock relative to a desired frequency, the phase lock loop including a voltage controlled oscillator having a control node and oscillating at a frequency responsive to the voltage applied to the control node, the method comprising: crossing the voltage that would result in the phase lock loop tracking the desired frequency in a first direction; crossing the voltage that would result in the phase lock loop tracking the desired frequency in a second, direction opposite the first direction; and indicating that frequency lock has been achieved.

[0106] Another aspect of the invention provides a method of determining when frequency lock occurs relative to a desired frequency, the method comprising:

• [0107] providing a phase lock loop including a voltage controlled oscillator that oscillates at a frequency responsive to voltage applied to the voltage controlled oscillator; applying a voltage to the voltage controlled oscillator to produce a frequency of oscillation less than the desired frequency; increasing the voltage applied to the voltage controlled oscillator using one or more steps of a first size; increasing the voltage applied to the voltage controlled oscillator using one or more steps of a second size smaller than the first size; decreasing the voltage applied to the voltage controlled oscillator using one or more steps of a third size smaller than the second size; increasing the voltage applied to the voltage controlled oscillator using a step of the third size; and indicating that lock has occurred in response to the increase of the step of the third size.

[0108] Another aspect of the invention provides a method of determining when a phase lock loop achieves frequency lock relative to a desired frequency, the phase lock loop including a voltage controlled oscillator having a control node and oscillating at a frequency responsive to the voltage applied to the control node, the method comprising: increasing the voltage applied to the control node to a voltage above the voltage that would result in the phase lock loop tracking the desired frequency; decreasing the voltage applied to the control node to a voltage below the voltage that would result in the phase lock loop tracking the desired frequency; and increasing the voltage applied to the control node and indicating that frequency lock has been achieved.

[0109] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a microprocessor, a transmitter, and a receiver, the integrated circuit periodically switching between a sleep mode, and a receiver-on mode in which more power is consumed than in the sleep mode, and further including a selectively engageable timer preventing switching from the sleep mode to the receiver-on mode for a predetermined amount of time.

[0110] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a microprocessor, a transmitter, and a receiver, the integrated circuit periodically switching between a sleep mode, and a receiver-on mode in which more power is consumed than in the sleep mode, and further including means for selectively preventing switching from the sleep mode to the receiver-on mode for a predetermined amount of time.

[0111] Another aspect of the invention provides a radio frequency identification device comprising an integrated circuit including a microprocessor, a transmitter, and a receiver, the integrated circuit being switchable between a sleep mode, and a mode in which more power is consumed than in the sleep mode, the integrated circuit being switched from the sleep mode to the mode in which more power is consumed in response to a direct sequence spread spectrum modulated radio frequency signal being received by the receiver which has a predetermined number of transitions within a certain period of time, the integrated circuit further including a selectively engageable timer which prevents switching from the sleep mode for a period of time regardless of whether a signal is subsequently received by the receiver which has the predetermined number of transitions within a certain period of time.

[0112] Another aspect of the invention provides a method for conserving power in a radio frequency identification device, the method comprising: periodically switching from a sleep mode to a receiver on mode and performing tests to determine whether to further switch to a microprocessor on mode because a valid radio frequency signal is present; and selectively disabling the periodic switching from the sleep mode for a predetermined amount of time.