Precision temperature sensor

Abstract

A temperature sensor circuit in accordance with an embodiment of the present invention includes a temperature sensing element operable to provide a temperature voltage that is linearly related to the absolute temperature of the circuit. The temperature sensing element includes a first bi-polar junction transistor and a second bipolar junction transistor connected between a supply voltage and a common ground, wherein the base of first bipolar junction transistor is connected to the base of the second bipolar junction transistor, a first resistor connected between an emitter of the first bipolar junction transistor and the common ground and a second resistor connected between the common ground and a first node, wherein the temperature voltage is provided to the first node across the second resistor. The temperature sensor circuit also includes a current supply element operable to supply a common current to a collector of the first bipolar junction transistor, the second bipolar junction transistor and to the second resistor, respectively, an early voltage element operable to compensate for variations in voltage, a base current element operable to provide a steady base current to the bases of the first and second bipolar junction transistors, a channel modulation element operable to compensate for channel modulation and a leakage element operable to compensate for epi-substrate leakage between the circuit and a substrate on which it is formed.

1 . A temperature sensor circuit comprising: 
 a temperature sensing element operable to provide a temperature voltage that is linearly related to the absolute temperature of the circuit, the temperature sensing element comprising: 
 a first bi-polar junction transistor and a second bipolar junction transistor connected between a supply voltage and a common ground, wherein the base of first bipolar junction transistor is connected to the base of the second bipolar junction transistor each bipolar junction transistor;  
 a first resistor connected between an emitter of the first bipolar junction transistor and the common ground; and  
 a second resistor connected between the common ground and a first node, wherein the temperature voltage is provided to the first node across the second resistor;  
   a current supply element operable to supply a common current to a collector of the first bipolar junction transistor, the second bipolar junction transistor and the second resistor, respectively;    an early voltage element operable to compensate for variations in voltage;    a base current element operable to provide a steady base current to the bases of the first and second bipolar junction transistors;    a channel modulation element operable to compensate for channel modulation; and    a leakage element operable to compensate for epi-substrate leakage between the circuit and a substrate on which it is formed.    
   
   
       2 . The temperature sensor circuit of  claim 1 , further comprising a start up circuit operable to ensure that the common current is stable at start up and that is disengaged after a predetermine period of time.  
   
   
       3 . The temperature sensor circuit of  claim 2 , wherein the current supply element further comprises a frequency compensation element operable to compensate for frequency changes in the current supply element such that the common current remains stable.  
   
   
       4 . The temperature sensor circuit of  claim 3 , further comprising: 
 a voltage regulator, connected to the temperature sensor circuit and operable to provide a steady supply voltage to the temperature sensor circuit.    
   
   
       5 . The temperature sensor circuit of  claim 4 , wherein the current supply element further comprises: 
 a positive feedback gain loop operable to provide the common current to the first bipolar junction transistor; and    a negative feedback gain loop operable to provide the common current to the second bipolar junction transistor    
   
   
       6 . The temperature sensor circuit of  claim 5 , wherein the leakage element further comprises: 
 a first epi diode connected across the second bipolar junction transistor; and    a second epi diode connected across the second resistor, such that the additional epi-substrate junctions provided in the first and second epi diodes reduces the affect of epi-substrate leakage.    
   
   
       7 . The temperature sensor circuit of  claim 6 , wherein the temperature sensor circuit is implemented in an integrated circuit.