Method and apparatus for providing peak detection circuitry for data communication systems

[0001] This application claims priority under 35 USC §119(e) to Application No. 60/466,243 filed Apr. 28, 2003 entitled “Method and Apparatus for Providing Peak Detection Circuitry for Data Communication Systems” and assigned to TheraSense, Inc., assignee of the present application, and the disclosure of which is incorporated herein by reference for all purposes.

[0002] The present invention relates to communication systems. More specifically, the present invention relates to radio frequency (RF) communication systems for data communication between portable electronic devices such as in continuous glucose monitoring systems.

[0003] Continuous glucose monitoring systems generally include a small, lightweight battery powered and microprocessor controlled system which is configured to detect signals proportional to the corresponding measured glucose levels using an electrometer, and RF signals to transmit the collected data. When the microprocessor is active or when the system is in the process of processing or transmitting data, the battery power supply may display a loading effect commonly referred to as “drooping” due to the current consumption of the microprocessor operation or the transmit function compared to the average current draw level.

[0004] The voltage drooping may occur when the processor (or controller) for the transmitter initiates and performs a configured procedure, or alternatively, in the case where the RF transmitter initiates data transmission. For example, the processor may draw a small amount of current in idle state (for example, 1 μA), while in active processing mode, it may draw as much as 2 mA. Additionally, the RF transmitter may draw approximately 10 mA during data transmission state.

[0005] The drooping effect is particularly prominent after a portion of the available battery energy has been consumed (that is, the battery energy is partially discharged) and is typical for small batteries where size, weight and power density are optimized versus peak current capacity. This, in turn, may have a negative impact on the processing of detected signals such as by signal degradation or data loss, and importantly, may adversely affect the delicate electrometer and the analog circuitry in the transmitter unit of the monitoring system. More specifically, when the analog front end circuitry in the transmitter of the monitoring system is disturbed, there may be a several second delay when the data may be unusable and a longer delay (for example, on the order of 10 seconds) when the data may be unreliable or beyond the tolerance range of desired accuracy.

[0006] In view of the foregoing, it would be desirable to isolate the delicate electrometer and the analog circuitry of the monitoring system, for example, in the transmitting side, from the adverse effects of battery voltage drooping using simple, low cost and low noise approaches, in contrast to the existing techniques using, for example, a DC to DC converter which typically has higher cost as well as higher noise.

[0007] Accordingly, in one embodiment of the present invention, there is provided a peak detection circuit comprising a diode including an input terminal and an output terminal the input terminal of the diode configured to receive an input signal, a capacitor operatively coupled to the output terminal of the diode, and an output terminal operatively coupled to the capacitor and the output terminal of the diode for outputting an output signal.

[0008] The diode may include a Schottky diode switch, and further, the input signal may include a voltage signal from a power supply.

[0009] Moreover, in one embodiment, a voltage droop may be detected at the input terminal of the diode, and where the diode and the capacitor may be configured to compensate for the voltage droop.

[0010] In a further embodiment of the present invention, there is provided a data communication system including peak detection circuit comprising a peak detection circuit configured to receive a power supply signal, and further to output a detected signal, and a low pass filter operatively coupled to the detection circuit, the detection circuit configured to receive the detected signal, where the peak detection circuit may be configured to detect a voltage droop in the power supply signal and further, to compensate for the voltage droop.

[0011] In a further embodiment, the peak detection circuit may be configured to electrically isolate the detected voltage droop.

[0012] Additionally, the peak detection circuit may in an alternate embodiment include a passive switching configuration.

[0013] Also, the peak detection circuit may in one embodiment include a diode operatively coupled to a capacitance, where the diode may include a Schottky diode switch.

[0014] In accordance with yet another embodiment of the present invention, there is provide a method of providing a peak detection circuit, comprising the steps of providing a diode having an input terminal and an output terminal the input terminal of the diode configured to receive an input signal, operatively coupling a capacitor to the output terminal of the diode, and operatively coupling an output terminal to the capacitor and the output terminal of the diode for outputting an output signal.

[0015] Also, the input signal may include a voltage signal from a power supply.

[0016] Moreover, in a further embodiment, the method may further include the steps of detecting a voltage droop at the input terminal of the diode, and compensating for the voltage droop by the diode and the capacitor.

[0017] In accordance with still another embodiment of the present invention, there is provided a method of providing peak detection in a data communication system, comprising the steps of configuring a peak detection circuit to detect a voltage droop in a power supply signal and to output a compensated signal, low pass filtering the compensated signal from the peak detection circuit.

[0018] In one embodiment, the step of configuring the peak detection circuit may further include the step of electrically isolating the detected voltage droop.

[0019] Moreover, the step of providing the peak detection circuit may include providing a passive switching configuration.

[0020] Additionally, the step of configuring the peak detection circuit may include the step of operatively coupling a diode to a capacitance.

[0021] Indeed, in accordance with the various embodiments of the present invention, there is provided a peak detection circuit in the transmitter of a data communication system which is configured to detect a voltage droop from its power supply such as a battery configured to power the transmitter, and to effectively compensate for the detected voltage signal droop such that the delicate circuitry of the electrometer and the analog front end circuitry of the transmitter unit may be electrically isolated (for example, by switching off the connection between the electrometer and the analog front end circuitry, and the power supply source) from the detected voltage drooping while the necessary current is drawn from another source such as a capacitor to support the required voltage level of the electrometer and the analog front end circuitry.

[0022] The peak detection circuit in one aspect may include passive switching configurations with a diode and a capacitor combination. In addition, a low pass filter may be operatively coupled to the peak detection circuit to filter out any switching noise transients. In an alternate embodiment, the peak detection circuit may include active components such as a relay switch, a BJT or FET transistor switch. In this case, the switching mechanism is controlled by the processor to turn the switch on or off, in case of power supply voltage drooping, as opposed to the passive component configuration with the diode, in which case such voltage drooping is automatically detected and the switching mechanism of the peak detection circuit accordingly operated in response thereto.

[0023] Furthermore, as discussed above, the diode used for the peak detection circuit may include a Schottky diode switch. Moreover, the peak detection circuit in one embodiment may be provided between the power supply and the analog front end circuitry of the transmitter unit in the continuous glucose monitoring system such that in the case where power supply voltage drooping occurs, the peak detection circuit may be configured to isolate the delicate circuitry of the analog front end of the transmitter unit from the power supply, and rather allow the electrometer and the analog front end circuitry of the transmitter to draw the necessary power from a capacitor of the peak detection circuit to ensure continuous and proper operation.

[0024] Accordingly, in accordance with the various embodiments of the present invention, by using a peak detection circuit with a tuned low pass filter, an effective, low cost and low noise approach to isolating the battery droop, even that in excess of 0.5 volts, may be achieved such that in the monitoring system discussed above, the detected and processed data values are not substantially effected, and the delicate analog circuitry of the transmitter is not adversely effected by the fluctuation in power supply signal.

[0025] Applicants herein incorporate by reference application Ser. No. 09/753,746 filed on Jan. 2, 2001 entitled “Analyte Monitoring Device and Methods of Use”, and Application No. 60/437,374 filed Dec. 31, 2002 entitled “Continuous Glucose Monitoring System and Methods of Use” each assigned to the Assignee of the present application for all purposes.

[0032] FIG. 1 illustrates a data communication system such as, for example, a continuous glucose monitoring system 100 in accordance with one embodiment of the present invention. In such an embodiment, the continuous glucose monitoring system 100 includes a sensor 101, a transmitter 102 coupled to the sensor 101, and a receiver 104 which is configured to communicate with the transmitter 102 via a communication link 103. The receiver 104 may be further configured to transmit data to a data processing terminal 105 for evaluating the data received by the receiver 104. Only one sensor 101, transmitter 102, communication link 103, receiver 104, and data processing terminal 105 are shown in the embodiment of the continuous glucose monitoring system 100 illustrated in FIG. 1. However, it will be appreciated by one of ordinary skill in the art that the continuous glucose monitoring system 100 may include one or more sensor 101, transmitter 102, communication link 103, receiver 104, and data processing terminal 105, where each receiver 104 is uniquely synchronized with a respective transmitter 102.

[0033] In one embodiment of the present invention, the sensor 101 is physically positioned on the body of a user whose glucose level is being monitored. The sensor 101 is configured to continuously sample the glucose level of the user and convert the sampled glucose level into a corresponding data signal for transmission by the transmitter 102. In one embodiment, the transmitter 102 is mounted on the sensor 101 so that both devices are positioned on the user's body. The transmitter 102 performs data processing such as filtering and encoding on data signals, each of which corresponds to a sampled glucose level of the user, for transmission to the receiver 104 via the communication link 103.

[0034] In one embodiment, the continuous glucose monitoring system 100 is configured as a one-way RF communication path from the transmitter 102 to the receiver 104. In such embodiment, the transmitter 102 transmits the sampled data signals received from the sensor 101 without acknowledgement from the receiver 104 that the transmitted sampled data signals have been received. For example, the transmitter 102 may be configured to transmit the encoded sampled data signals at a fixed rate (e.g., at one minute intervals) after the completion of the initial power on procedure. Likewise, the receiver 104 may be configured to detect such transmitted encoded sampled data signals at predetermined time intervals. Alternatively, in accordance with a further embodiment of the present invention, the continuous glucose monitoring system 100 may be configured with a two-way RF communication path between the transmitter 102 and the receiver 104 using transceivers.

[0035] Additionally, in one aspect, the receiver 104 may include two sections. The first section is an analog interface section that is configured to communicate with the transmitter 102 via the communication link 103. In one embodiment, the analog interface section may include an RF receiver and an antenna for receiving and amplifying the data signals from the transmitter 102, which are thereafter, demodulated with a local oscillator and filtered through a band-pass filter. The second section of the receiver 104 is a data processing section which is configured to process the data signals received from the transmitter 102 such as by performing data decoding, error detection and correction, data clock generation, and data bit recovery.

[0036] In operation, upon completing the power-on procedure, the receiver 104 is configured to detect the presence of the transmitter 102 within its range based on, for example, the strength of the detected data signals received from the transmitter 102 or a predetermined transmitter identification information. Upon successful synchronization with the corresponding transmitter 102, the receiver 104 is configured to begin receiving from the transmitter 102 data signals corresponding to the user's detected glucose level. More specifically, the receiver 104 in one embodiment is configured to perform synchronized time hopping with the corresponding synchronized transmitter 102 via the communication link 103 to obtain the user's detected glucose level.

[0037] Referring again to FIG. 1, the data processing terminal 105 may include a personal computer, a portable computer such as a laptop or a handheld device (e.g., personal digital assistants (PDAs)), and the like, each of which may be configured for data communication with the receiver via a wired or a wireless connection. Additionally, the data processing terminal 105 may further be connected to a data network (not shown) for storing, retrieving and updating data corresponding to the detected glucose level of the user.

[0038] FIG. 2 is a block diagram of the transmitter of the overall communication system shown in FIG. 1 in accordance with one embodiment of the present invention. Referring to the Figure, the transmitter 102 in one embodiment includes an analog interface 201 configured to communicate with the sensor 101 (FIG. 1), a user input 202, and a temperature detection section 203, each of which is operatively coupled to a transmitter processor 204 such as a central processing unit (CPU). Further shown in FIG. 2 are a transmitter serial communication section 205 and an RF transmitter 206, each of which is also operatively coupled to the transmitter processor 204. Moreover, a power supply 207 such as a battery is also provided in the transmitter 102 to provide the necessary power for the transmitter 102. Additionally, as can be seen from the Figure, clock 208 is provided to, among others, supply real time information to the transmitter processor 204. Also shown in FIG. 2 is a peak detection unit 210 operatively coupled to the analog interface 201, the processor 204 and the power supply 207.

[0039] In one embodiment, a unidirectional input path is established from the sensor 101 (FIG. 1) and/or manufacturing and testing equipment to the analog interface 201 of the transmitter 102, while a unidirectional output is established from the output of the RF transmitter 206 of the transmitter 102 for transmission to the receiver 104. In this manner, a data path is shown in FIG. 2 between the aforementioned unidirectional input and output via a dedicated link 209 from the analog interface 201 to serial communication section 205, thereafter to the processor 204, and then to the RF transmitter 206. As such, in one embodiment, via the data path described above, the transmitter 102 is configured to transmit to the receiver 104 (FIG. 1), via the communication link 103 (FIG. 1), processed and encoded data signals received from the sensor 101 (FIG. 1). Additionally, the unidirectional communication data path between the analog interface 201 and the RF transmitter 206 discussed above allows for the configuration of the transmitter 102 for operation upon completion of the manufacturing process as well as for direct communication for diagnostic and testing purposes.

[0040] As discussed above, the transmitter processor 204 is configured to transmit control signals to the various sections of the transmitter 102 during the operation of the transmitter 102. In one embodiment, the transmitter processor 204 also includes a memory (not shown) for storing data such as the identification information for the transmitter 102, as well as the data signals received from the sensor 101. The stored information may be retrieved and processed for transmission to the receiver 104 under the control of the transmitter processor 204. Furthermore, the power supply 207 may include a commercially available battery.

[0041] The transmitter 102 is also configured such that the power supply section 207 is capable of providing power to the transmitter for a minimum of three months of continuous operation after having been stored for 18 months in a low-power (non-operating) mode. In one embodiment, this may be achieved by the transmitter processor 204 operating in low power modes in the non-operating state, for example, drawing no more than approximately 1 μA of current. Indeed, in one embodiment, the final step during the manufacturing process of the transmitter 102 may place the transmitter 102 in the lower power, non-operating state (i.e., post-manufacture sleep mode). In this manner, the shelf life of the transmitter 102 may be significantly improved.

[0042] Referring yet again to FIG. 2, the temperature detection section 203 of the transmitter 102 is configured to monitor the temperature of the skin near the sensor insertion site. The temperature reading is used to adjust the glucose readings obtained from the analog interface 201. The RF transmitter 206 of the transmitter 102 may be configured for operation in the frequency band of 315 MHz to 322 MHz, for example, in the United States. Further, in one embodiment, the RF transmitter 206 is configured to modulate the carrier frequency by performing Frequency Shift Keying and Manchester encoding. In one embodiment, the data transmission rate is 19,200 symbols per second, with a minimum transmission range for communication with the receiver 104.

[0043] Additional detailed description of the continuous glucose monitoring system, its various components including the functional descriptions of the transmitter are provided in application Ser. No. 09/753,746 filed on Jan. 2, 2001 entitled “Analyte Monitoring Device and Methods of Use”, and in application No. 60/437,374 filed Dec. 31, 2002 entitled “Continuous Glucose Monitoring System and Methods of Use”, each assigned to the Assignee of the present application, and the disclosures of each of which are incorporated herein by reference for all purposes.

[0044] FIG. 3 is a block diagram illustrating the peak detection unit 210 in the transmitter of FIG. 2 in accordance with embodiment of the present invention. Referring to the Figure, there is shown a peak detection circuit 301 operatively coupled between the power supply 207 and a low pass filter 302. As further shown in FIG. 3, the power supply 207 is further operatively coupled to the processor 204 and the RF transmitter 206. The low pass filter 302 is additionally operatively coupled to the analog interface 201 (FIG. 2) which includes delicate circuitry for detecting and processing signals corresponding to the glucose level detected by the sensor unit 101 (FIG. 1), and powered by the power supply 207.

[0045] The processor 204 may draw a small amount of current in idle state (for example, 1 μA) as described above, while in active processing mode, the processor 204 may draw as much as 2 mA of current. Additionally, the RF transmitter 206 may draw approximately 10 mA of current during data transmission state. Either case of the processor 204 in active processing mode or the RF transmitter 206 in data transmission mode may result in voltage drooping from the power supply 207.

[0046] Accordingly, the peak detection circuit 301 in accordance with one embodiment is configured to detect the occurrences of the power supply voltage drooping, and to switch off the connection of the power supply 207 to the analog interface 201. In this case, the analog interface 201 may be configured to draw the necessary current from, for example, a capacitor of the peak detection circuit 301 to support the voltage necessary for operation. This will be discussed in further detail below in conjunction with the embodiments illustrated in FIGS. 4 and 5A-5C. Additionally, the low pass filter 302 in one embodiment may be configured to filter out any resulting switching noise transients also discussed in further detail below.

[0047] FIG. 4 illustrates the peak detection circuit and the low pass filter of the peak detection unit shown in FIG. 3 in accordance with one embodiment of the present invention. Referring to the Figure, the peak detection circuit 301 in one embodiment includes a diode 401 operatively coupled to a capacitor 402. The diode in one embodiment may be a Schottky diode configured to operate as a switch, while the capacitor 402 may, in one embodiment have a value of approximately 10 μFarads.

[0048] Referring back to FIG. 4, the low pass filter 302 in one embodiment may include a resistor 405 operatively coupled between the peak detection circuit 301 and the interface to the analog front end circuitry, and a capacitor 406 further operatively coupled to the resistor 405. In one embodiment, the resistor 405 may have a value of 1 kOhms, while the capacitor 406 may have a value of approximately 1 μFarads. In this manner, the configuration of the resistor 405 and the capacitor 406 effectively establishes a low pass RC filter.

[0049] Referring again to FIG. 4, while any suitable diode may be used for diode 401 in the peak detection circuit 301, the Schottky diode as shown in the Figure may be used to take advantage of its properties including a lower forward voltage drop as compared to conventional diodes. This, in turn, allows the capacitor 402 of the peak detection circuit 301 to charge to a higher value, as there is a smaller voltage drop from the voltage at the input terminal 403 and the output terminal 404 of the peak detection circuit 301 under steady state conditions. In accordance with one embodiment of the present invention, the low pass RC filter 302 shown in the Figure may be implemented for each chip connected to the power supply of the analog front end circuitry.

[0050] Furthermore, in one embodiment, the diode 401 of the peak detection circuit 301 may be directly coupled to the battery or to a switched power supply source (for example, power supply 207 (FIGS. 2 and 3)). Also, the output of the processor 204 in one aspect may be used to drive the diode 401 of the peak detection circuit 301 such that the analog front end circuitry may be switched off to increase the storage (for example, post manufacture sleep mode) period when the system is being transported to the users. This approach is possible when the processor 204 output drive signal level is sufficient to power the analog front end circuitry with no noticeable output voltage droop due to loading.

[0051] Additionally, it should be noted that the low pass filter 302 in one embodiment may be configured to prevent the high frequency switching noise of the processor 204 from adversely affecting the analog front end circuitry. More specifically, since the processor 204 displays high frequency switching noise on the order of 1 MHz, a low pass filter with a cut-off frequency of, for example, 1 kHz would reduce the switching nose to approximately 0.1% or less. For example, with a 1 kOhm resistor 405 and a 1 μFarad capacitor 406 forming the low pass filter 302, the cut-off frequency is established at 1 kHz such that any signal of higher frequency than the cut-off frequency will be attenuated. In one embodiment, the low pass filter values (i.e., the values of the resistor 405 and the capacitor 406) may be varied or optimized for a given processor 204 and circuit implementation.

[0052] In the manner described above, in accordance with one embodiment of the present invention, the peak detection circuit 301 and the low pass filter 302 may be configured to provide an effective safeguard against any potential perturbation in the outputs of any circuitry operatively coupled to the analog front end circuitry (e.g., at terminal 407 shown in FIG. 4) resulting from voltage drooping of the power supply 207. In the case of the continuous glucose monitoring system discussed above, this translates to less than one least significant bit (lsb) of data change on the electrometer output as measured by an analog to digital converter during processor 204 activity or during a data transmit occurrence. In a further embodiment, the low pass filter values (i.e., the values of the resistor 405 and the capacitor 406) may be further varied or optimized for a given Power Supply Rejection Ratio (PSRR) of the analog circuitry.

[0053] FIGS. 5A-5C illustrate the signal levels at the input to the peak detection circuit, between the output of the peak detection circuit and the input to the low pass filter, and at the output of the low pass filter, respectively, in accordance with one embodiment of the present invention. Referring to FIGS. 5 and 5A-5C, the signal waveform at the input terminal 403 to the peak detection circuit 301 (FIG. 4) is shown in FIG. 5A over the time period t₀ to t₁, while the signal waveform at the output terminal 404 of the peak detection circuit 301 is shown in FIG. 5B, and the low pass filtered signal at the output terminal 407 of the low pass filter 302 (FIG. 4) is shown in FIG. 5C.

[0054] FIGS. 6A-6C illustrate the peak detection circuits implemented using active components in accordance with alternate embodiments of the present invention. More specifically, FIGS. 6A-6C respectively illustrate a relay circuitry 601, a pnp bipolar junction transistor (BJT) switch 602, and a PMOS field effect transistor (FET) switch 603, each configured to operate as active peak detection circuits in accordance with alternate embodiments of the present invention. In the embodiments shown in FIGS. 6A-6C, the peak detection circuits 601-603 are implemented as an inverter so that a low input signal closes the switch, and charges the capacitor, driving the load circuit (e.g., the analog front end circuitry), and a high input signal causes the switch to open and the load circuit in such case is powered by the energy stored in the capacitor.

[0055] As each of the switches shown in FIGS. 6A-6C are active switches, they each must be actively switched on and off by the processor 204 each time a voltage drooping is anticipated. By contrast, the passive peak detection circuit using the diode switching system does not require active switching by the processor 204, but rather, is configured to automatically detect such voltage drop due to processor 204 activity or based on the detection of data transmit activities.

[0056] By way of example, in the case of using the relay switch 601 or the FET switch 603 as the peak detection circuit 301, the voltage drop between the power supply 207 voltage coupled to the input terminal 403 of the peak detection circuit 301, and the voltage supplied to the analog front end circuitry (for example, at terminal 407 in FIG. 4). may be in the order of 5 mVolts, while the embodiment discussed above using the diode 401 (FIG. 4) may have a 100 mV drop.

[0057] In the manner described above, in accordance with the various embodiments of the present invention, there is provided a method and apparatus for isolating potential voltage droop from the power supply 204 to the delicate circuitry of the analog front end in a simple, and cost effective manner while maintaining the level of noise to a minimum.

[0058] More specifically, there is provided in one embodiment, a peak detection circuit in the transmitter unit of a data communication system which is configured to detect a voltage droop from its power supply such as a battery configured to power the transmitter, and to effectively compensate for the detected voltage signal droop such that the delicate circuitry of the electrometer and the analog front end circuitry of the transmitter unit may be electrically isolated (for example, by switching off the connection between the electrometer and the analog front end circuitry, and the power supply source) from the detected voltage drooping while the necessary current is drawn from another source such as a capacitor to support the required voltage level of the electrometer and the analog front end circuitry.

[0059] The peak detection circuit may include passive switching configurations with a diode and a capacitor combination. In addition, a low pass filter may be operatively coupled to the peak detection circuit to filter out any switching noise transients. In an alternate embodiment, the peak detection circuit may include active components such as a relay switch, a BJT or FET transistor switch. In this case, the switching mechanism is controlled by the processor to turn the switch on or off, in case of power supply voltage drooping, as opposed to the passive component configuration with the diode, in which case such voltage drooping is automatically detected and the switching mechanism of the peak detection circuit accordingly operated in response thereto.

[0060] In one embodiment, the diode used for the peak detection circuit may include a Schottky diode switch. Moreover, the peak detection circuit in one embodiment may be provided between the power supply and the analog front end circuitry of the transmitter unit in the continuous glucose monitoring system such that in cases where power supply voltage drooping occurs, the peak detection circuit may be configured to isolate the delicate circuitry of the analog front end of the transmitter unit from the power supply, and rather allow the electrometer and the analog front end circuitry of the transmitter to draw the necessary power from a capacitor of the peak detection circuit to ensure continuous and proper operation.

[0061] Accordingly, in accordance with the various embodiments of the present invention, by using a peak detection circuit with a tuned low pass filter, an effective, low cost and low noise approach to isolating the battery droop, even that in excess of 0.5 volts, may be achieved such that in the monitoring system discussed above, the detected and processed data values are not substantially effected, and the delicate analog circuitry of the transmitter is not adversely effected by the fluctuation in power supply signal.

[0062] Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.