NAVWEPS REPORT 76 $0 



TEI-IPERATURE OSCILLATOR 



A transistorized-thermistor controlled Wien-bridge oscillator was 

 developed at this Station (Ref . 2). The circuit diagram as used in the 

 SVTP instrument is shown in Fig. 5- 



Wien Bridge . In the Wien-bridge oscillator, the input is in phase 

 with the output at the balance frequency, f^. However, the output of a 

 balanced bridge is zero at f = t^, and hence p = and Ap = at f = f q 



where 



P = E„/E , the ratio of feedback voltage to output voltage 



f o 



A = E /E., ratio of output voltage to input voltage, or 

 forward voltage gain without feedback 



The Barkhausen criterion for an oscillator requires at AP > 1. 

 Therefore, the bridge must be unbalanced but in such a way that the 

 phase shift remains zero. 



Consider the V7ien bridge in the following diagram: 



E^ and Eg are the input and output voltage respectively of the bridge, 



8 



