Abstract:
A thermally stabilized device is described. Single or multiple input ports are accommodated and single and multiple power ports are described. The variation of resistance of a resistor subject to varying power dissipations is minimized by injecting complementary power dissipation and thermally linking it to the resistor. In this manner the temperature of a resistor may be maintained constant even though it dissipates varying amounts of power.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to the field of electronic components. More particularly, this invention relates to a resistor or a dissipative network where resistance change resulting from self-heating is objectionable.  
       BACKGROUND  
       [0002]     The variability of electronic component characteristics with environmental changes is basic to practical applied electricity. The performance of electrical and electronic circuits depends directly on constituent component characteristics, such as resistance and capacitance, and when these characteristics change as a result of temperature or humidity operation of the parent circuit also changes.  
         [0003]     There are many characteristics of electronic components which are commonly of interest to the designer. As an example, a resistor has characteristics such as resistance, tolerance, operating temperature range, power rating versus temperature, inductance, capacitance, temperature coefficient, humidity, aging, and so forth. Capacitors and inductors have similar performance characteristics, as do transistors and diodes and in general every electrical and electronic component.  
         [0004]     A common example is a circuit where the frequency or a voltage level may depend on the value of resistance of a specific resistor. If the value of resistance changes the frequency or voltage also changes. This may not be what the designer intends, as in many cases such variability causes unacceptable circuit operation. Attempts to rectify this problem may range from securing if possible a better grade resistor to a complete circuit redesign.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however, both as to organization and method of operation, together with objects and advantages thereof, may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawings in which:  
         [0006]      FIG. 1  is an exemplary simplified block diagram of a thermally stabilized device with one signal port and one power port, in accordance with certain embodiments of the present invention.  
         [0007]      FIG. 2  is an exemplary block diagram of a thermally stabilized device with up to N signal ports and one power port, in accordance with certain embodiments of the present invention.  
         [0008]      FIG. 3  is an exemplary block diagram of a thermally stabilized device with one signal port and up to M power ports, in accordance with certain embodiments of the present invention.  
         [0009]      FIG. 4  is an exemplary block diagram of a thermally stabilized device with up to N signal ports and up to M power ports, in accordance with certain embodiments of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0010]     A method and structure for automatically keeping a resistor or a dissipative network at a constant temperature increment above ambient is presented, in accordance with certain embodiments of the present invention. This is achieved by maintaining the power dissipated in the thermally stabilized device at a constant total value.  
         [0011]     Many variations, equivalents and permutations of these illustrative exemplary embodiments of the invention will occur to those skilled in the art upon consideration of the description that follows. The particular examples above should not be considered to define the scope of the invention. For example networks containing large numbers of resistors may be stabilized using techniques of the present invention. A further example would be a network which contains electrical components other than resistors (a dissipative network). Another example would be not calculating total network power as the summation of all signal component powers, but including only the most significant. A still further example would be including active devices in the network wherein power dissipated in these devices may or may not be included in the power calculations.  
         [0012]     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals may be used to describe the same, similar or corresponding parts in the several views of the drawings.  
         [0013]     For purposes of this document, the exact mechanical and electrical parameters of equipments are unimportant to an understanding of the invention, and many different types of electrical and mechanical components may be utilized without departing from the spirit of the invention. An example is that resistors utilized in the network may differ as to power rating and physical size. This document uses generalized descriptions by way of example only. Many variations for these constituent items are possible without departing from the spirit and scope of the invention.  
         [0014]     Refer to  FIG. 1 , which is an exemplary simplified block diagram of a thermally stabilized device with one signal port and one power port, in accordance with certain embodiments of the present invention. Resistor  135  receives power from signal port  145 . This power may be AC, DC, or a combination thereof. Signal port  145  consists of high signal line  115  and low signal line  120 , and the signal applied to the port is the difference between these two lines. The power that signal port  145  delivers to resistor  135  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry  
         [0015]     Resistor  140  receives power from power port  150 . This power may be AC, DC, or a combination thereof. Power port  150  consists of high power line  125  and low power line  130 , and the signal applied to the port is the difference between these two lines. The power that power port  150  will deliver to resistor  140  is known or calculated, as will be explained later.  
         [0016]     Thermally stabilized device  105  contains resistor  135 , resistor  140 , and thermal linking agent  110 . The purpose of thermal linking agent  110  is to provide low thermal resistance between resistor  135  and resistor  140 . This may be accomplished in a number of ways, such as thermal compound, a common substrate, a common heat sink, physical contact between resistors, or any combination of these. There are many thermal management techniques available in the industry. Physical co-location of resistors is not required given adequate thermal linking.  
         [0017]     The maximum and minimum power to be dissipated in resistor  135  must be known, measured, or assumed. These powers may be known from system design characteristics, or may be measured under maximum and minimum power conditions using techniques known to the industry. In operation as maximum and minimum power dissipations occur in resistor  135  the temperature of resistor  135  varies. This variation of temperature will cause resistor  135  to change resistance and possibly affect loading on signal port  145 , which in turn may introduce errors. For example, if the current through resistor  135  is to be measured, any variation of resistance will produce a variation in current thus introducing a measurement error. If the temperature of resistor  135  can be maintained constant, the resistance will remain constant and this problem may be avoided. To accomplish this, complementary power is applied to resistor  140  in a manner such that the power dissipated in the combination of resistor  135  and resistor  140  is a constant. If the total power dissipated is constant, and if thermal linking agent  110  is utilized, the operational temperature of each resistor will be constant and equal. If the temperature of resistor  135  is maintained constant its resistance will remain constant. As an example, assume that resistor  135  operates between 1 watt and 10 watts power dissipation. A constant power dissipation for the overall device will occur if resistor  140  is caused to dissipate between 9 watts and 0 watts in a manner such that the total power is always 10 watts. In other words, Pdiss140=10−Pdiss135 and the total power dissipated will always be 10 watts. A value larger than the maximum dissipation of resistor  135  may also be chosen, such as Pdiss140=35−Pdiss135 wherein resistor  140  would dissipate between 34 watts and 25 watts depending on the value of dissipation in resistor  135 , and the total power dissipated would be constant at 35 watts, and the temperature for both resistors would remain constant. Note that ambient temperature variations are not corrected. The minimum power can optionally be used to improve overall device efficiency since that power is always present and does not need to be supplied at the power port.  
         [0018]     Refer to  FIG. 2 , which is an exemplary block diagram of a thermally stabilized device with up to N signal ports and one power port, in accordance with certain embodiments of the present invention. Resistor  235  receives power from signal port  245 . This power may be AC, DC, or a combination thereof. Resistor  280  receives power from signal port  290 . This power may be AC, DC, or a combination thereof. Resistor  285  receives power from signal port  295 . This power may be AC, DC, or a combination thereof. Signal port  245  consists of high signal line  215  and low signal line  220 , and the signal applied to the port is the difference between these two lines. Signal port  290  consists of high signal line  260  and low signal line  265 , and the signal applied to the port is the difference between these two lines. Signal port  295  consists of high signal line  270  and low signal line  275 , and the signal applied to the port is the difference between these two lines. There may be any number of signal power resistors, designated by resistor  235 , resistor  280  . . . . resistor  285 , and are shown as R 1 , R 3  . . . Rn in the figure for clarity. The power signal port  245  delivers to resistor  235  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry. The power signal port  290  delivers to resistor  280  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry. The power signal port  295  delivers to resistor  285  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry. Similar descriptions apply to intermediate resistors and signal ports.  
         [0019]     Resistor  240  receives power from power port  250 . This power may be AC, DC, or a combination thereof. Power port  250  consists of high power line  225  and low power line  230 , and the signal applied to the port is the difference between these two lines. The power that power port  250  will deliver to resistor  240  is known or calculated, as will be explained later.  
         [0020]     Thermally stabilized device  205  contains resistor  235 , resistor  240 , resistor  280 , resistor  285 , all intermediate resistors, and thermal linking agent  210 . The purpose of thermal linking agent  210  is to provide low thermal resistance between all resistors in thermally stabilized device  205 . This may be accomplished in a number of ways, such as thermal compound, a common substrate, a common heat sink, physical contact between resistors, or any combination of these. There are many thermal management techniques available in the industry. Physical co-location of resistors is not required given adequate thermal linking.  
         [0021]     The maximum and minimum power to be dissipated in the combination of resistor  235 , resistor  280  . . . resistor  285  and all intermediate resistors must be known, measured, or assumed. These powers may be known from system design characteristics, or may be measured under maximum and minimum power conditions using power measurement techniques known to the industry. In operation as maximum and minimum power dissipations occur in resistor  235 , resistor  280  . . . resistor  285 , the temperature of the resistors varies. This variation of temperature will cause the resistors to change resistance and affect loading on signal port  245 , signal port  290  . . . signal port  295  which in turn may introduce errors. For example, if the current through resistor  280  is to be measured, any variation of resistance will produce a variation in current thus introducing a measurement error. If the temperature of each resistor can be maintained constant, resistance will remain constant and this problem may be avoided. To accomplish this, complementary power is applied to resistor  240  in a manner such that the power dissipated in the combination of resistor  235 , resistor  280  . . . resistor  285 , and resistor  240  is a constant. If the total power dissipated is constant, and if thermal linking agent  210  is utilized, the operational temperature of each resistor will be constant and equal. If the temperature of any resistor is maintained constant its resistance will remain constant. As an example, assume that signal resistor combination operates between 1 watt and 10 watts power dissipation. A constant power dissipation for the overall device will occur if resistor  240  is caused to dissipate between 9 watts and 0 watts in a manner such that the total power is always 10 watts. In other words, Pdiss240=10−Pdiss(comb) and the total power dissipated will always be 10 watts. A value larger than the total maximum dissipation of the signal resistor combination may also be chosen, such as Pdiss240=35−Pdiss(comb) wherein resistor  240  would dissipate between 34 watts and 25 watts depending on the value of dissipation in the signal resistor combination, and the total power dissipated would be constant at 35 watts with the temperature of all resistors remaining constant. Note that ambient temperature variations are not corrected. The minimum power can optionally be used to improve overall device efficiency since that power is always present and does not need to be supplied at the power port.  
         [0022]     Refer to  FIG. 3 , which is an exemplary block diagram of a thermally stabilized device with one signal port and up to M power ports, in accordance with certain embodiments of the present invention. Resistor  335  receives power from signal port  345 . This power may be AC, DC, or a combination thereof. Signal port  345  consists of high signal line  315  and low signal line  320 , and the signal applied to the port is the difference between these two lines.  
         [0023]     Resistor  340  receives power from power port  350 . This power may be AC, DC, or a combination thereof. Power port  350  consists of high power line  325  and low power line  330 , and the signal applied to the port is the difference between these two lines. The power that power port  350  will deliver to resistor  340  is known or calculated, as will be explained later. Resistor  380  receives power from power port  390 . This power may be AC, DC, or a combination thereof. Power port  390  consists of high power line  360  and low power line  365 , and the signal applied to the port is the difference between these two lines. The power that power port  390  will deliver to resistor  380  is known or calculated, as will be explained later. Resistor  385  receives power from power port  395 . This power may be AC, DC, or a combination thereof. Power port  395  consists of high power line  370  and low power line  375 , and the signal applied to the port is the difference between these two lines. The power that power port  395  will deliver to resistor  385  is known or calculated, as will be explained later. Similar descriptions apply to intermediate resistors and power ports.  
         [0024]     Thermally stabilized device  305  contains resistor  335 , resistor  340 , resistor  380 , resistor  385 , all intermediate resistors, and thermal linking agent  310 . The purpose of thermal linking agent  310  is to provide low thermal resistance between all resistors in thermally stabilized device  305 . This may be accomplished in a number of ways, such as thermal compound, a common substrate, a common heat sink, physical contact between resistors, or any combination of these. There are many thermal management techniques available in the industry. Physical co-location of resistors is not required given adequate thermal linking.  
         [0025]     The maximum and minimum power to be dissipated in resistor  335  must be known, measured, or assumed. This power may be known from system design characteristics, or may be measured under maximum and minimum power conditions using techniques known to the industry. In operation as maximum and minimum power dissipations occur in resistor  335  the temperature of resistor  335  varies. This variation of temperature will cause resistor  335  to change resistance and possibly affect loading on signal port  345 , which in turn may introduce errors. For example, if the current through resistor  335  is to be measured, any variation of resistance will produce a variation in current thus introducing a measurement error. If the temperature of resistor  335  can be maintained constant, the resistance will remain constant and this problem may be avoided. To accomplish this, complementary power is applied to the combination of resistor  340 , resistor  380  . . . resistor  385  in a manner such that the total power dissipated in the combination plus resistor  335  is a constant. If the total power dissipated is constant, and if thermal linking agent  310  is utilized, the operational temperature of each resistor will be constant and equal. If the temperature of any resistor is maintained constant its resistance will remain constant. As an example, assume that resistor  335  operates between 1 watt and 10 watts power dissipation. A constant power dissipation for the overall device will occur if the combination resistor  340 , resistor  380  . . . resistor  385  is caused to dissipate between 9 watts and 0 watts in a manner such that the total power is always 10 watts. In other words, Pdiss(comb)=10−Pdiss335 and the total power dissipated will always be 10 watts. A value larger than the maximum dissipation of resistor  335  may also be chosen, such as Pdiss(comb)=35−Pdiss335 wherein the resistor combination would dissipate between 34 watts and 25 watts depending on the value of dissipation in resistor  335 , and the total power dissipated would be constant at 35 watts, and the temperature for all resistors would remain constant. Note that ambient temperature variations are not corrected. The minimum power can optionally be used to improve overall device efficiency since that power is always present and does not need to be supplied at the power ports.  
         [0026]     Refer to  FIG. 4 , which is an exemplary waveform diagram of a thermally stabilized device with up to N signal ports and up to M power ports, in accordance with certain embodiments of the present invention. Resistor  485  receives power from signal port  418 . This power may be AC, DC, or a combination thereof. Resistor  490  receives power from signal port  423 . This power may be AC, DC, or a combination thereof. Resistor  495  receives power from signal port  428 . This power may be AC, DC, or a combination thereof. Signal port  418  consists of high signal line  415  and low signal line  420 , and the signal applied to the port is the difference between these two lines. Signal port  423  consists of high signal line  425  and low signal line  430 , and the signal applied to the port is the difference between these two lines. Signal port  428  consists of high signal line  435  and low signal line  440 , and the signal applied to the port is the difference between these two lines. There may be any number of signal power resistors, designated by resistor  485 , resistor  490  . . . . resistor  495 , and is shown as R 1 , R 2  . . . Rn in the figure for clarity. The power that signal port  418  delivers to resistor  485  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry. The power signal port  423  delivers to resistor  490  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry. The power signal port  428  delivers to resistor  495  is known or measured. The power may be known versus time due to system design characteristics, or it may be measured at desired points in time using established techniques available in the industry. Similar descriptions apply to intermediate resistors and signal ports.  
         [0027]     Resistor  403  receives power from power port  433 . This power may be AC, DC, or a combination thereof. Power port  433  consists of high power line  445  and low power line  450 , and the signal applied to the port is the difference between these two lines. The power that power port  433  will deliver to resistor  403  is known or calculated, as will be explained later. Resistor  408  receives power from power port  438 . This power may be AC, DC, or a combination thereof. Power port  438  consists of high power line  465  and low power line  470 , and the signal applied to the port is the difference between these two lines. The power that power port  438  will deliver to resistor  408  is known or calculated, as will be explained later. Resistor  413  receives power from power port  453 . This power may be AC, DC, or a combination thereof. Power port  453  consists of high power line  475  and low power line  480 , and the signal applied to the port is the difference between these two lines. The power that power port  453  will deliver to resistor  413  is known or calculated, as will be explained later. Similar descriptions apply to intermediate resistors and power ports.  
         [0028]     Thermally stabilized device  405  contains resistor  485 , resistor  490 , resistor  495 , resistor  403 , resistor  408 , resistor  413 , all intermediate resistors, and thermal linking agent  410 . The purpose of thermal linking agent  410  is to provide low thermal resistance between all resistors. This may be accomplished in a number of ways, such as thermal compound, a common substrate, a common heat sink, physical contact between resistors, or any combination of these. There are many thermal management techniques available in the industry. Physical co-location of resistors is not required given adequate thermal linking.  
         [0029]     The maximum and minimum power to be dissipated in the signal resistor combination resistor  485 , resistor  490  . . . resistor  495  must be known, measured, or assumed. These powers may be known from system design characteristics, or may be measured under maximum and minimum power conditions using techniques known to the industry. In operation as maximum and minimum power dissipations occur in the signal resistor combination the temperature of its constituent resistors varies. This variation of temperature will cause the resistors to change resistance and possibly affect loading on signal ports  418 ,  423  . . .  428  which in turn may introduce errors. For example, if the current through resistor  485  is to be measured, any variation of resistance will produce a variation in current thus introducing a measurement error. If the temperature of resistor  485  can be maintained constant, the resistance will remain constant and this problem may be avoided. To accomplish this, complementary power is applied to the power resistor combination resistor  403 , resistor  408  . . . resistor  413  in a manner such that the total power dissipated in the signal resistor combination plus the power resistor combination is a constant. If the total power dissipated is constant, and if thermal linking agent  110  is utilized, the operational temperature of each resistor will be constant and equal. If the temperature of resistor is maintained constant its resistance will remain constant. As an example, assume that signal resistor combination operates between 1 watt and 10 watts power dissipation. A constant power dissipation for the overall device will occur if the power resistor combination is caused to dissipate between 9 watts and 0 watts in a manner such that the total power is always 10 watts. In other words, Pdiss(power)=10−Pdiss(signal) and the total power dissipated will always be 10 watts. A value larger than the maximum dissipation of the signal resistor combination may also be chosen, such as Pdiss(power)=35−Pdiss(signal) wherein the power resistor combination would dissipate between 34 watts and 25 watts depending on the value of dissipation in the signal resistor combination, and the total power dissipated would be constant at 35 watts, and the temperature for all resistors would remain constant. Note that ambient temperature variations are not corrected. The minimum power can optionally be used to improve overall device efficiency since that power is always present and does not need to be supplied at the power port.  
         [0030]     The merit of a plurality of signal resistors is that multiple signal ports may be simultaneously loaded in a stable manner. Another advantage of accommodating multiple signal resistors is that it may be desirable to use more than one resistor because of component power specification limitations.  
         [0031]     The merit of a plurality of power resistors is that using multiple resistors to dissipate power would allow the usage of lower power rating devices. Another advantage would be if different sources, such as AC and DC, were to be utilized simultaneously to provide signals to the power resistors.  
         [0032]     A test network was constructed on a ceramic substrate approximately 0.9 inch long×0.3 inch wide×0.02 inch thick. All resistors were thin film deposited on the ceramic surface. The input signal resistor in this case consisted of 2 resistors, a 9.9 megohm and a 100 k ohm to function as a 100:1 voltage divider. The maximum voltage level of measurement for this network was 1000 volts. Without utilizing the present invention, the temperature change of the network was 6 degrees C. when 1000 volts was applied to the network. This temperature rise caused an unacceptable change in output voltage of the 100:1 divider. When the present invention was utilized by adding a power feedback resistor, the temperature change was reduced to approximately 0.6 degree C. The network was then designed for use in a precision digital voltmeter. The present invention could have wide-ranging application whenever self-heating from variable input power causes an unacceptable change in resistance.  
         [0033]     Those skilled in the art will appreciate that many other circuit and system configurations can be readily devised to accomplish the desired end without departing from the spirit of the present invention.  
         [0034]     While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. By way of example, other resistors and electronic components may be added to the thermally stabilized device even though they do not participate in thermal control (as described above). In so doing these devices will gain the advantage of operation at a constant temperature increment above ambient. It is assumed of course that their power dissipation is negligible as regards the thermal control described above. Many other variations are also possible. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.