Beta variation cancellation in temperature sensors

Abstract

An apparatus and method for canceling variations in the beta for a bipolar junction transistor so that the diode equation can be employed to accurately measure the temperature of the transistor based at least in part on a ratio of two target collector currents and two measurements of the base-emitter voltage of the transistor. If the determined collector current of the transistor is relatively equivalent to one of the first and second target collector currents, the transistor's base-emitter voltage is measured and stored. An analog feedback circuit can be employed to change the determined collector current to be relatively equivalent to the first and second target collector currents. The analog feedback circuit can include an optional sample and hold component to further reduce power consumption and reduce noise. A digital circuit can be employed to change the determined collector current to be relatively equivalent to the first and second target collector currents. Additionally, the transistor can be remotely located in another integrated circuit.

1 . An apparatus for remotely measuring a temperature of a transistor disposed in a separate integrated circuit, comprising: 
 a first circuit that is arranged to adjust a determination of a collector current of the transistor to be relatively equivalent to a first target collector current and is also arranged to adjust another determination of the collector current to be relatively equivalent to a second target collector current, wherein the determination of the collector current that is relatively equivalent to the first target collector current is based on at least one measurement of a first base current for the transistor, and wherein the other determination of the collector current that is relatively equivalent to the second target collector current is based on at least one measurement of a second base current for the transistor; and    a second circuit that is arranged to measure a first base-emitter voltage for the transistor if the determined collector current of the transistor is relatively equivalent to the first target collector current and is also arranged to measure a second base-emitter voltage for the transistor if the determined collector current of the transistor is relatively equivalent to the second target collector current.    
   
   
       2 . The apparatus of  claim 1 , further comprising circuitry that is arranged to determine the temperature of the transistor based at least in part on the measured first and second base-emitter voltages.  
   
   
       3 . The apparatus of  claim 2 , further comprising circuitry that is arranged to at least reduce an effect on determining the temperature of the transistor caused by at least one resistive element coupled in series with the transistor.  
   
   
       4 . The apparatus of  claim 2 , further comprising circuitry that is arranged to communicate a representation of the determined temperature.  
   
   
       5 . The apparatus of  claim 1 , further comprising circuitry that is arranged to adjust an emitter current provided to the transistor, wherein a first adjustment of the emitter current enables the determined collector current to be relatively equivalent to the first target collector current and wherein a second adjustment of the emitter current enables the determined collector current to be relatively equivalent to the second target collector current.  
   
   
       6 . The apparatus of  claim 1 , further comprising circuitry that is arranged to bias the transistor above a common mode voltage.  
   
   
       7 . The apparatus of  claim 1 , wherein the first circuit that adjusts the determinations of the collector current further comprises at least one digital component that is arranged to iteratively change the determinations for the collector current of the transistor to be relatively equivalent to at least one of the first and second target collector currents.  
   
   
       8 . The apparatus of  claim 1 , wherein the first circuit that adjusts the determinations of the collector current further comprises an analog feed back loop that is arranged to change the determinations of the collector current of the transistor to be relatively equivalent to at least one of the first and second target collector currents.  
   
   
       9 . The apparatus of  claim 1 , further comprising circuitry that is arranged to sample and hold an emitter current for the transistor if the transistor's determined collector current is relatively equivalent to at least one of the first and second target collector currents.  
   
   
       10 . The apparatus of  claim 1 , wherein a value for the first target collector current is at least a magnitude greater than another value for the second target collector current.  
   
   
       11 . The apparatus of  claim 1 , further comprising: 
 a third circuit that is arranged with a first ratio to provide the first target collector current and is also arranged with a second ratio to provide the second target collector current, wherein the first ratio and the first target collector current are respectively greater than the second ratio and the second target collector current; and    a fourth circuit that is arranged to adjust an input of the third circuit employing the first ratio, wherein the adjustment causes a difference of a selected target emitter current and the first target collector current to be relatively equivalent to a third base current of the transistor, and wherein the fourth circuit applies the adjustment to the input of the third circuit if the third circuit is providing the second target collector current.    
   
   
       12 . An apparatus for remotely measuring a temperature of a transistor located within a separate integrated circuit, comprising: 
 a first circuit that is arranged to change an emitter current provided to the transistor to cause a determined collector current of the transistor to be relatively equivalent to a first target collector current and is also arranged to change the emitter current provided to the transistor to cause the determined collector current of the transistor to be relatively equivalent to a second target collector current;    a second circuit that is arranged to measure a first base-emitter voltage for the transistor if the determined collector current of the transistor is relatively equivalent to the first target collector current and is also arranged to measure a second base-emitter voltage for the transistor if the determined collector current of the transistor is relatively equivalent to the second target collector current; and    a third circuit that is arranged to determine the temperature of the transistor based at least in part on the measured first and second base-emitter voltages.    
   
   
       13 . The apparatus of  claim 12 , further comprising circuitry that is arranged to measure a first base current for the transistor to enable the determination of the collector current to be relatively equivalent to the first target collector current, and is also arranged to measure a second base current for the transistor to enable the determination of the collector current to be relatively equivalent to the second target collector current.  
   
   
       14 . The apparatus of  claim 12 , wherein the first circuit that changes the emitter current further comprises at least one digital component that is arranged to iteratively adjust the emitter current for changing the determined collector current of the transistor to be relatively equivalent to at least one of the first and second target collector currents.  
   
   
       15 . The apparatus of  claim 12 , wherein the first circuit that changes the emitter current further comprises an analog feed back loop that is arranged to adjust the emitter current to change the determined collector current of the transistor to be relatively equivalent to at least one of the first and second target collector currents.  
   
   
       16 . The apparatus of  claim 12 , further comprising circuitry that is arranged to sample and hold the emitter current if the transistor's determined collector current is relatively equivalent to at least one of the first and second target collector currents.  
   
   
       17 . The apparatus of  claim 12 , further comprising: 
 a fourth circuit that is arranged with a first ratio to provide the first target collector current and is also arranged with a second ratio to provide the second target collector current, wherein the first ratio and the first target collector current are respectively greater than the second ratio and the second target collector current; and    a fifth circuit that is arranged to adjust an input of the fourth circuit employing the first ratio, wherein the adjustment causes a difference of a selected target emitter current and the first target collector current to be relatively equivalent to a base current of the transistor, and wherein the fifth circuit applies the adjustment to the input of the fourth circuit if the fourth circuit is providing the second target collector current.    
   
   
       18 . A method for remotely measuring a temperature of a transistor that is located within a separate integrated circuit, comprising: 
 enabling a determination of the collector current of the transistor to be relatively equivalent to a first target collector current;    if the determined collector current of the transistor is relatively equivalent to the first target collector current, measuring a first base-emitter voltage for the transistor;    enabling the determined collector current of the transistor to be relatively equivalent to a second target collector current; and    if the determined collector current of the transistor is relatively equivalent to the second target collector current, measuring a second base-emitter voltage for the transistor, wherein the temperature of the transistor is determined based at least in part on the measured first and second base-emitter voltages.    
   
   
       19 . The method of  claim 18 , further comprising: 
 changing an emitter current of the transistor to cause the determined collector current of the transistor to be relatively equivalent to the first target collector current; and    changing the emitter current of the transistor to cause the determined collector current of the transistor to be relatively equivalent to the second target collector current.    
   
   
       20 . The method of  claim 18 , further comprising: 
 changing a base current of the transistor to cause the determined collector current of the transistor to be relatively equivalent to the first target collector current; and    changing the base current of the transistor to cause the determined collector current of the transistor to be relatively equivalent to the second target collector current.