Temperature-controlled variable resistor

[0002] The present invention relates to temperature-responsive electronic devices and methods of operation. More particularly, but not by way of limitation, the present invention relates to temperature-controlled variable resistors, temperature- controlled variable current sources and temperature-controlled variable voltage sources.

[0003] Many modern electronic devices require very precise current and/or voltage sources for proper operation. Temperature variation, however, can change the operation of a part and thereby change, for example, a required level of operating current/voltage. Present systems compensate for temperature variations in a variety of ways—none of which are completely satisfactory. In particular, these present systems often lack the necessary resolution and cannot be adjusted with enough frequency and/or accuracy.

[0004] One electronic device that requires a current source that varies with changes in temperature is a laser diode driver. Laser diodes are notoriously fickle and require a very precise operating current that will generally vary with temperature. For example, the efficiency and optical power of a laser diode above threshold increase with decreasing temperatures. This means that a laser diode that has its operating current configured at room temperature will have reduced output once it warms up past room temperature. Conversely, if the operating current is set up after the laser diode has warmed up, the laser diode may overdrive when it is operated at room temperature. Thus, a laser diode driver would be enhanced by a temperature-controlled regulation device that can adjust current or at least aid in adjusting current. Such a device would allow a laser diode to operate efficiently over a wide range of temperatures to maintain a constant output power.

[0005] Of course, laser diode drivers are not the only electronic devices that require temperature-controlled current/voltage sources. For example, transceivers may require a temperature-controlled current source, and those of skill in the art can readily identify numerous other devices that require temperature-controlled current/voltage sources. Thus, a device and method are needed to adjust or aid in adjusting current/voltage sources in response to changes in temperature.

[0006] To remedy the deficiencies of existing systems and methods, the present invention provides, among other things, a method and apparatus to regulate an electronic device in response to temperature changes. For example, one method of the present invention can control a device operable in different operational modes. This method can include the steps of sensing a temperature; accessing a table using the sensed temperature; reading an operational mode indicator from the table, wherein the operational mode indicator can, for example, correspond to the sensed temperature; and operating the device in a proper one of the operational modes, which corresponds to the operational mode indicator.

[0007] Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein:

[0008] FIG. 1A is a block diagram of a temperature-controlled variable resistor;

[0009] FIG. 1B is a more detailed block diagram of the temperature-controlled variable resistor of FIG. 1A;

[0010] FIG. 1C is a circuit diagram of the variable resistor component shown in FIG. 1A;

[0011] FIG. 2A is a block diagram of a temperature-controlled variable voltage source;

[0012] FIG. 2B is a circuit diagram of the variable voltage source shown in FIG. 2A;

[0013] FIG. 3A is a block diagram of a temperature-controlled variable current source;

[0014] FIG. 3B is a circuit diagram of the variable current source shown in FIG. 3A;

[0015] FIG. 4A is an illustration of an electronic device with an integrated temperature-controlled regulation device; and

[0016] FIG. 4B is a block diagram of a temperature controlled regulation device as shown in FIG. 4A.

[0017] Although the present invention is open to various modifications and alternative constructions, a preferred exemplary embodiment that is shown in the drawings is described herein in detail. It is to be understood, however, that there is no intention to limit the invention to the particular forms disclosed. One skilled in the art can recognize that there are numerous modifications, equivalences and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.

[0018] Referring now to FIG. 1A, it is a block diagram of a temperature-controlled variable resistor 100 that can be used for, among other things, adjusting current/voltage sources in response to changes in temperature. This embodiment includes a variable resistor 102 with a high-end resistor terminal 104 and a low-end resistor terminal 106. The variable resistor 102 is responsive to inputs from a control logic 108 that can communicate with the variable resistor 102 in a serial and/or a parallel fashion.

[0019] Furthermore, the control logic 108 is connected to an I/O interface 110, a lookup table 112, a memory device 114 and a temperature sensor 116. In operation, the control logic 108 reads a temperature from the temperature sensor 116 and accesses the lookup table 112 to determine a resistance value that corresponds to the temperature read from the temperature sensor 116. This resistance value is then communicated to the variable resistor 102 so that the resistance between the high-end terminal 104 and the low-end terminal 106 can be changed accordingly.

[0020] Although the device of FIG. 1A can be implemented in a variety of ways, a preferred embodiment is illustrated in FIG. 1B. This embodiment includes an I/O interface 110, a combined memory block 118 (which can include the lookup table 112 and memory device 114 of FIG. 1A), two variable resistors 102aand 102b, a temperature sensor 116 and a control logic 108.

[0021] Referring first to the I/O interface 110, in this embodiment, it is a two wire interface with eight communication pins. These pins include:

[0022] V_cc—Power Supply Terminal.

[0023] GND—Ground Terminal.

[0024] SDA—2-wire serial data interface. The serial data pin is for serial data transfer. The pin is open drain and may be wire-ORed with other open drain or open collector interfaces.

[0025] SCL—2-wire serial clock interface. The serial clock input is used to clock data in on rising edges and clock data out on falling edges.

[0026] H_a, H_b—High-end terminals (e.g., high-end terminal 104) of the variable resistors 102a, 102b, respectively. For both variable resistors 102aand 102b, it is not required that these high-end terminals be connected to a potential greater than the low-end terminal of the corresponding variable resistor.

[0027] L_a, L_b—Low-end terminals (e.g., low-end terminal 106) of the variable resistors 102a, 102b. For both variable resistors, it is not required that these low-end terminals be connected to the potential less than the high-end terminal of the corresponding variable resistor.

[0028] WP—Write Protect. Write Protect should be connected to GND before either the data in memory or resistance level may be changed. Write Protect is pulled high internally and must be either left open or connected to V_ccif write protection is desired.

[0029] A0, A1, A2—Address Inputs. These input pins specify the address of the device when used in a multi-dropped configuration.

[0030] Now referring to the combined lookup table and memory device 118 of FIG. 1B, it can be divided into sections. For example, in one embodiment the memory can be divided as follows:

[0031] Still referring to FIG. 1B, the temperature sensor is a direct-to-digital temperature sensor that measures temperature through the use of an on-chip temperature measurement technique. Temperature measurements are initiated upon power-up, and the most recent result is stored in address locations E2h and E3h (that is, temperature MSB 126 and temperature LSB 128) of the combined memory block 118. New measurements are taken every 10 milliseconds except during reads or writes to memory.

[0032] The embodiment of the present invention illustrated in FIG. 1B is the presently preferred embodiment, and the invention should not be limited thereto. For example, the I/O interface 110 could be a one-wire interface, a two-wire interface, a parallel communication interface, etc. Similarly, the combined memory block 118 could be arranged in virtually any fashion—with additional data items being included or some of the listed items being omitted. For example, the combined memory block 118 could be configured to include any number of lookup tables for driving any number of variable resistors. Further, the temperature sensor 116 is not necessarily limited to a direct-to-digital temperature sensor. Any type of temperature sensor can be used.

[0033] Referring now to FIG. 1C, there is illustrated a circuit diagram of the variable resistor 102 shown in FIG. 1A. This embodiment of the variable resistor 102 includes a MSB (most significant bit) decoder 144 and a LSB (least significant bit) decoder 146. Each of these decoders operates a set of associated switches (which can include parallel CMOS devices, FETs, BJTs, etc.) responsive to signals received from the control logic 108. The most significant bits of the signal from the control logic 108 are received at the MSB decoder 144 on lines 150 and 152, and the least significant bits of the signal are received at the LSB decoder 146 on lines 154 and 156.

[0034] Still referring to FIG. 1C, the MSB decoder 144 is configured to operate switches 158, 160, 162, and 164, and the LSB decoder 146 is configured to operate switches 166, 168, 170, and 172. By turning certain switches off or on, individual resistors are connected and disconnected from the pathway between terminal 104 and terminal 106 such that the resistance level therebetween is varied.

[0035] In this particular embodiment, sixteen different resistance levels (from 0 to 15X) can be achieved. The maximum resistance of 15X is obtained because the resistance value of individual resistors 174, 176, and 178 is four times the value of individual resistors 180, 182, and 184. Thus, the resistance of 15X is obtained by connecting all of the resistors between terminal 104 and terminal 106. The relationship between the resistors is best described in that the value of the individual resistors 174, 176, and 178 should be 2_Ntimes the value of the individual resistors 180, 182 and 184, where N equals ½ the number of input bits.

[0036] Still referring to FIG. 1C, the operation of the variable resistor 102 can be illustrated by an example. Assume that a signal of binary “1101” is received from the control logic 108 with the left most bit being the most significant bit. The MSB decoder should receive binary “11” and the LSB decoder 106 should receive binary “01”. Next, the MSB decoder 144 should turn switch 164 on and switches 158, 160, and 162 off. Similarly, the LSB decoder 146 should turn switch 170 on and switch 166, 168, and 172 off. This configuration of switches causes resistors 174, 176, 178, and 184 to be connected between terminal 104 and terminal 106 and gives a total resistance of 13X.

[0037] Further, the variable resistor 102 also includes resistors 186, 188, and 190 as well as a capacitor 192. These components are designed to minimize switching noise within the variable resistor 102. The present invention can also be configured with the switches on the inside of the resistors 174, 176, 178, 180, 182, and 184 relative to terminals 104 and 106. That is, resistors 174, 176, and 178 are located between terminal 104 and the switches 158, 160, 162, and 164 and resistors 180, 182, and 184 are located between terminal 106 and switches 166, 168, 170, and 172.

[0038] In this embodiment, only four inputs 150, 152, 154, and 156 are used, thereby giving the part 16 different resistance levels. One skilled in the art, however, can recognize that the number of inputs could be altered or varied to provide virtually any number of different resistance levels. Additionally, one skilled in the art can recognize that the variable resistor 102 could be designed with any number of decoders and banks of resistors. For example, a variable resistor with 16 different resistance levels could be designed with a single, four-input/16 output decoder. Such a variable resistor could include 16 switches and 15 resistors arranged in a single bank. In another embodiment, the variable resistor could include 3 decoders—each with three inputs. This embodiment of the variable resistor would include three banks of eight switches and would provide 512 different resistance levels.

[0039] Now referring to FIG. 2A, it is a block diagram of a temperature-controlled variable voltage source 200. This embodiment of the present invention is similar to the temperature-controlled variable resistor 100 shown in FIG. 1A. For example, the temperature-controlled variable voltage source includes an I/O interface 200, a lookup table 202, a memory 204, a control logic 206 and a temperature sensor 208. The temperature-controlled variable voltage source 200, however, includes a variable voltage source 210 rather than the variable resistor 102 (shown in FIG. 1A).

[0040] In operation, the temperature sensor 208 senses a temperature and provides that information to the control logic 206, which accesses the lookup table 202 to determine a proper setting for the variable voltage source 210. This setting is then communicated to the variable voltage source 210 so that the output voltage at V_outcan be adjusted. In one embodiment, the voltage output from the variable voltage source 210 is varied by varying an internal resistance. For example, in one embodiment, the variable voltage source 210 includes a variable resistor such as the variable resistor 100 shown in FIG. 1A. As the resistance value is changed, the voltage drop is changed and the value of V_outis changed.

[0041] Another embodiment of the variable voltage source 210 is illustrated in FIG. 2B. In this embodiment, a 2-input decoder 212 is connected to four switches 214, 216, 218, and 220. Depending upon the value of the input at lines 222 and 224, at least one of the four switches will be turned on, thereby setting the resistance value between V_inand V_out. For example, if the input into the decoder is binary “10”, then switch 218 will be turned on (and switches 214, 216, and 220 will be turned off), and the resistance between V_inand V_outwill be the value of resistor 226 plus the value of resistor 228. Resistor 230 will not impact the total resistance. Accordingly, V_inwill be dropped according to resistors 226 and 228.

[0042] Now referring to FIG. 3A, it is a block diagram of a temperature-controlled variable current source 300. The temperature-controlled variable current source 300 includes an I/O interface 302, a lookup table 304, a memory 306, a control logic 308, a variable current source 312 and a temperature sensor 310. In operation, the temperature sensor 310 senses a temperature and provides that information to the control logic 308, which accesses the lookup table 304 to determine a proper setting for the variable current source 312. This setting is then communicated to the variable current source 112 where the output current is adjusted accordingly.

[0043] Although the variable current source 312 can be designed in a variety of ways, good results have been achieved with the circuit shown in FIG. 3B. In this embodiment, the variable current source 312 includes a two-input decoder 314 with one output 316 left unconnected and three outputs connected to switches 318, 320, and 322. Each switch is associated with one of current sources 324, 326, and 328. When a switch is on, the associated current source can contribute to the current at I_out, and when a switch is off, the associated current source cannot contribute to the current at I_out. Additionally, in this embodiment, any combination of switches 324, 326, and 328 can be on. For example, if a current of 1¾ X is desired at I_out, switches 324, 326, and 328 should be on simultaneously.

[0044] Now referring to FIG. 4A, it is an illustration of an electronic device with an integrated temperature-controlled regulation device 402 such as the temperature controlled resistor 102, the temperature controlled voltage source 210 and/or the temperature controlled current source 312. The electronic device 400 can be any type of electronic device that requires temperature based regulation, including laser diode drivers, wireless devices, power sources, etc.

[0045] The temperature-controlled regulation device 402 is shown in greater detail in FIG. 4B. This embodiment reflects a generic version of the devices shown in FIGS. 1A, 2A, and 3A. For example, the temperature-controlled regulation device 402 includes an I/O interface 404, a lookup table 406, a memory 408, a control logic 410, and a temperature sensor 412. Additionally, the temperature-controlled regulation device 402 includes a regulator 414 that could be a variable resistor, a variable current source, a variable voltage source, or any other type of regulator. Moreover, when the temperature-controlled regulation device 402 includes the variable resistor, the overall device does not necessarily need to be associated with temperature-controlled voltage/current source.

[0046] Although the present invention is described with relation to the illustrated embodiments, those skilled in the art can readily recognize that numerous variations, substitutions or deletions may be made from the embodiments shown and described, however the invention use and its configuration would achieve substantially the same or similar results as achieved by the specific exemplary embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary form. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.