I built a true RMS-to-DC converter circuit using AD736 chip on breadboard. The schematic is shown below. I'm a little confused with the output that I'm getting though. When I applied a sine wave of 100 mVpeak, the DC level equivalent output that I'm getting is 142 mV instead of 70.7 mV. Is this due to the crest factor of this AD736. The crest factor is 2 (Vpeak/V rms). Hence, I assume that it is giving me the output of 142 mVpeak which is equivalent to 70.7 Vrms. Did I get this correct?
You have possibly made an error reading the data sheet - it needs proper + and - supplies with a much "harder" 0V feeding the common pin. You are using 100 k resistors and these are unacceptably large without decouplers across each: -
Also note what the DS says about minimum supply voltage: -
while operating from the minimum power supply voltage of +2.8 V, –3.2 V
That's a total of 6V minimum (when I went to school) so, your 5V supply is too low. For a symmetrical supply I'd be looking at +/- 3.3V to be on the safe side.
You also have Cav connected to a node with an earth symbol - it's unclear where this fits in with the rest of the circuit.
I'm not ruling out other errors but these seem the obvious.