opa4350 ,differential iput ,sigle-end out

Antony,

Is the problem only with the op amp circuitry, U7A?

I'm sorry but we do not understand the problem. Please provide a more complete description of the problem. Please provide circuit values for the components connected to U7A. Please provide information on the power supply voltage and V_COM_REF voltage.

Regards, Bruce.

thank you for your response.

this circuit is used to measure AC voltage.the problem is when I input a stable AC signal on the Ua and Un,the result measured by the ADS8365 is not stable.the result center on the expected value,and swing a small aplititude.

I mean the RMS is not stable,it swings a small amplitude,and this make the precision bad.

Antony,

For the resistor values you have indicated, the amplifier differential gain is very low-- 0.000824 V/V. It would require more than 1000V differential input to create a 1V output from the amplifier. Is this what you intended?

Regards, Bruce.

thank you for your response.

yes, I want to measure high voltage.

Antony,

You will need to provide more specific information on the performance you are getting. Describe what you mean by "unstable." What is your input voltage? What output voltage are you getting. Have you looked at the output with an oscilloscope? Can you provide an ocillloscope waveform of the output that defines this behavior?

Sorry, but I can't help without a clear understanding of the problem.

Regards, Bruce.