Abstract:
A device and method to regulate an electronic device in response to temperature changes is shown and described. For example, the present invention can control devices that are operable in different operational modes. The method and the device can be used so as to include 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 corresponds to the sensed temperature; and operating the device in the proper one of the operational modes that corresponds to the operational mode indicator.

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1A is a block diagram of a temperature-controlled variable resistor; 
     FIG. 1B is a more detailed block diagram of the temperature-controlled variable resistor of FIG. 1A; 
     FIG. 1C is a circuit diagram of the variable resistor component shown in FIG. 1A; 
     FIG. 2A is a block diagram of a temperature-controlled variable voltage source; 
     FIG. 2B is a circuit diagram of the variable voltage source shown in FIG. 2A; 
     FIG. 3A is a block diagram of a temperature-controlled variable current source; 
     FIG. 3B is a circuit diagram of the variable current source shown in FIG. 3A; 
     FIG. 4A is an illustration of an electronic device with an integrated temperature-controlled regulation device; and 
     FIG. 4B is a block diagram of a temperature controlled regulation device as shown in FIG.  4 A. 
    
    
     DETAILED DESCRIPTION 
     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. 
     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. 
     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. 
     Although the device of FIG. 1A can be implemented in a variety of ways, a preferred embodiment is illustrated in FIG.  1 B. 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.  1 A), two variable resistors  102   a  and  102   b , a temperature sensor  116  and a control logic  108 . 
     Referring first to the I/O interface  110 , in this embodiment, it is a two wire interface with eight communication pins. These pins include: 
     V cc —Power Supply Terminal. 
     GND—Ground Terminal. 
     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. 
     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. 
     H a , H b  —High-end terminals (e.g., high-end terminal  104 ) of the variable resistors  102   a ,  102   b , respectively. For both variable resistors  102   a  and  102   b , 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. 
     L a , L b —Low-end terminals (e.g., low-end terminal  106 ) of the variable resistors  102   a ,  102   b . 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. 
     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 cc  if write protection is desired. 
     A 0 , A 1 , A 2 —Address Inputs. These input pins specify the address of the device when used in a multi-dropped configuration. 
     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: 
     
       
         
               
               
               
             
           
               
                   
               
               
                   
                 Memory 
                   
               
               
                 Name of Location 
                 Location 
                 Function of Location 
               
               
                   
               
             
             
               
                 User Defined Lookup 
                 00h to 47h 
                 This block contains the 
               
               
                 Tables 120 
                   
                 user defined temperature 
               
               
                   
                   
                 settings of the variable 
               
               
                   
                   
                 resistors 102a and 102b. 
               
               
                   
                   
                 Values between 00h and FFF 
               
               
                   
                   
                 can be written to either 
               
               
                   
                   
                 table to set the 256 
               
               
                   
                   
                 different resistance 
               
               
                   
                   
                 levels. The first address 
               
               
                   
                   
                 location, 00h, is used to 
               
               
                   
                   
                 set the resistance level 
               
               
                   
                   
                 for −40° C. Each successive 
               
               
                   
                   
                 memory location will 
               
               
                   
                   
                 contain the resistance 
               
               
                   
                   
                 level for the previous 
               
               
                   
                   
                 temperature plus 2° C. For 
               
               
                   
                   
                 example, memory address 01h 
               
               
                   
                   
                 is the address that stores 
               
               
                   
                   
                 the resistor setting for a 
               
               
                   
                   
                 −38° C. environment. 
               
               
                 Table Select Byte 
                 E0h 
                 Writing to this byte 
               
               
                 122 
                   
                 determines which of the two 
               
               
                   
                   
                 user defined lookup tables 
               
               
                   
                   
                 120 is selected for reading 
               
               
                   
                   
                 or writing. 
               
               
                   
                   
                 00h (Table A selected) 
               
               
                   
                   
                 01h (Table B selected) 
               
               
                 Configuration Byte 
                 E1h 
                 The configuration Byte 124 
               
               
                 124 
                   
                 contains three data items: 
               
               
                   
                   
                 TAU - Temperature/Address 
               
               
                   
                   
                 Update; 
               
               
                   
                   
                 TEN - Temperature Update 
               
               
                   
                   
                 Enable; and 
               
               
                   
                   
                 AEN - Address Update 
               
               
                   
                   
                 Enable. 
               
               
                   
                   
                 The DEFAULT setting is 03h, 
               
               
                   
                   
                 TAU = 1, TEN = 1 and AEN = 
               
               
                   
                   
                 1. 
               
               
                   
                   
                 TAU becomes a 1 after a 
               
               
                   
                   
                 temperature and address 
               
               
                   
                   
                 update has occurred as a 
               
               
                   
                   
                 result of a temperature 
               
               
                   
                   
                 conversion. The user can 
               
               
                   
                   
                 write this bit to 0 and 
               
               
                   
                   
                 check for a transition from 
               
               
                   
                   
                 0 to 1 in order to verify 
               
               
                   
                   
                 that a conversion has 
               
               
                   
                   
                 occurred. 
               
               
                   
                   
                 If TEN = 0, the temperature 
               
               
                   
                   
                 conversion feature is 
               
               
                   
                   
                 disabled. The user sets 
               
               
                   
                   
                 the resistance level for 
               
               
                   
                   
                 the variable resistor 102 
               
               
                   
                   
                 in “manual mode” by writing 
               
               
                   
                   
                 to addresses F0h and F1h 
               
               
                   
                   
                 (Resistor A setting and 
               
               
                   
                   
                 Resistor B setting 140) to 
               
               
                   
                   
                 control variable resistors 
               
               
                   
                   
                 A, 102a and B, 102b, 
               
               
                   
                   
                 respectively. 
               
               
                   
                   
                 With AEN = 0 the user can 
               
               
                   
                   
                 operate in a test mode. 
               
               
                   
                   
                 Address updates made from 
               
               
                   
                   
                 the temperature sensor will 
               
               
                   
                   
                 cease. The user can load a 
               
               
                   
                   
                 memory location into E4h 
               
               
                   
                   
                 and verify that the values 
               
               
                   
                   
                 in locations F1h and F2h 
               
               
                   
                   
                 are the expected user 
               
               
                   
                   
                 defined values. 
               
               
                 Temperature MSB 126 
                 E2h 
                 This byte contains the MSB 
               
               
                   
                   
                 of the 13-bit 2&#39;s 
               
               
                   
                   
                 complement temperature 
               
               
                   
                   
                 output from the temperature 
               
               
                   
                   
                 sensor 116. 
               
               
                 Temperature LSB 128 
                 E3h 
                 This byte contains the LSB 
               
               
                   
                   
                 of the 13-bit 2&#39;s 
               
               
                   
                   
                 complement temperature 
               
               
                   
                   
                 output from the temperature 
               
               
                   
                   
                 sensor 116. 
               
               
                 Address Pointer 130 
                 E4h 
                 This pointer is the 
               
               
                   
                   
                 calculated, present 
               
               
                   
                   
                 resistance level address 
               
               
                   
                   
                 (0h - 47h). The user- 
               
               
                   
                   
                 defined resistor setting at 
               
               
                   
                   
                 this address in the 
               
               
                   
                   
                 respective look-up table 
               
               
                   
                   
                 120 will be loaded into F1h 
               
               
                   
                   
                 and F2h (Resistor A 
               
               
                   
                   
                 setting, Resistor B 
               
               
                   
                   
                 setting) to set the 
               
               
                   
                   
                 resistance two level 
               
               
                   
                   
                 resistors 102a, 102b. 
               
               
                 User Memory 132 
                 E5h to E6h 
                 This block is general 
               
               
                   
                   
                 purpose user memory. 
               
               
                 Internal Address 
                 E7h 
                 This byte allows the user 
               
               
                 Select 134 
                   
                 to use the external address 
               
               
                   
                   
                 pins (A 0  A 1  A 2 ) or an 
               
               
                   
                   
                 internal register location 
               
               
                   
                   
                 to determine the address of 
               
               
                   
                   
                 the temperature-controlled 
               
               
                   
                   
                 variable resistor 100. The 
               
               
                   
                   
                 byte is configured as 
               
               
                   
                   
                 follows: 
               
               
                   
                   
                 A 2  A 1  A 0  ENB 
               
               
                   
                   
                 When ENB = 0 and external 
               
               
                   
                   
                 A2, A1, A0 are grounded, 
               
               
                   
                   
                 the temperature-controlled 
               
               
                   
                   
                 variable resistor 100 will 
               
               
                   
                   
                 use internal address bits 
               
               
                   
                   
                 (A 2 , A 1 , A 0 ) in this 
               
               
                   
                   
                 register 134. 
               
               
                   
                   
                 When ENB = 1, external A2, 
               
               
                   
                   
                 A1, A0 = any setting of the 
               
               
                   
                   
                 temperature-controlled 
               
               
                   
                   
                 variable resistor 100 will 
               
               
                   
                   
                 use external address pins 
               
               
                   
                   
                 (A 0  A 1  A 2 ). 
               
               
                   
                   
                 The DEFAULT setting is 01h. 
               
               
                   
                   
                 The temperature-controlled 
               
               
                   
                   
                 variable resistor 100 uses 
               
               
                   
                   
                 external pins (A 0  A 1  A 2 ) to 
               
               
                   
                   
                 determine its address. 
               
               
                 User Memory 134 
                 E8h to Efh 
                 This block is general 
               
               
                   
                   
                 purpose user memory. 
               
               
                 Resistor A Setting 
                 F0h 
                 In the user-controlled 
               
               
                 138 
                   
                 setting mode, this block 
               
               
                   
                   
                 contains the variable 
               
               
                   
                   
                 resistance level for 
               
               
                   
                   
                 resistor 102a. 
               
               
                 Resistor B Setting 
                 F1h 
                 In the user-controlled 
               
               
                 140 
                   
                 setting mode, this block 
               
               
                   
                   
                 contains the resistance 
               
               
                   
                   
                 level for the variable 
               
               
                   
                   
                 resistor 102b. 
               
               
                 User Memory 142 
                 F2h to FFh 
                 General purpose user 
               
               
                   
                   
                 memory. 
               
               
                   
               
             
          
         
       
     
     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 E 2 h and E 3 h (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. 
     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. 
     Referring now to FIG. 1C, there is illustrated a circuit diagram of the variable resistor  102  shown in FIG.  1 A. 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 . 
     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. 
     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 N  times the value of the individual resistors  180 ,  182  and  184 , where N equals ½ the number of input bits. 
     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. 
     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 . 
     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. 
     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.  1 A. 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.  1 A). 
     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 out  can 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.  1 A. As the resistance value is changed, the voltage drop is changed and the value of V out  is changed. 
     Another embodiment of the variable voltage source  210  is illustrated in FIG.  2 B. 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 in  and 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 in  and V out  will be the value of resistor  226  plus the value of resistor  228 . Resistor  230  will not impact the total resistance. Accordingly, V in  will be dropped according to resistors  226  and  228 . 
     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. 
     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.  3 B. 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. 
     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. 
     The temperature-controlled regulation device  402  is shown in greater detail in FIG.  4 B. This embodiment reflects a generic version of the devices shown in FIGS. 1A,  2 A, and  3 A. 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. 
     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.