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problem simulating AD736 in ADIsimPE

Question asked by suryadeopa on Mar 21, 2017
Latest reply on Mar 21, 2017 by jstaley

simulating AD736.

I was trying to simulate AD736 rms to DC converter for 200mV input for fastest settling time. I have attached the circuit below. I might have made mistakes in selecting the Cav and Cf capacitors. 

When the input was a 1k sine wave the circuit was working properly. But when i increased the input frequency to 4k , the output started oscillating between +- Vcc. At first it seemed the output was settling to the correct rms value but then it started oscillating. I increased the input frequency to 32k, the oscillation started happening even earlier.

I am not able to understand why this is happening. Is it due to the capacitor values?

The requirements of my circuit is to find the rms value of a 32.786 kHz sine wave as fast as possible.

i have used ADIsimPE SIMetrix

the red curve is for 1kHz wave ,green is for 4kHz wave

 

thanks in advance

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