differential opamp questions

Thread Starter

Santa klaus

Joined Nov 16, 2014
32
the circuit below is a simple differential amplifier used for current sensing. I know how it works however i had 2 questions.
-what is the purpose of capacitor C1
-why is there a resistor and capacitor on the output
My guess is the resistor is needed to drive the MCU's ADC pin with a high enough source impedance to have the right ADC conversion rate;
Can someone help me clarify this ?
upload_2017-5-16_16-51-27.png
 

wayneh

Joined Sep 9, 2010
17,152
Both questions relate to filtering out noise. The simulation may not do a good job of simulating noise, but it's definitely a real-world concern. You might try injecting some high-frequency noise onto the inputs, so you can see how the circuit behaves with and without C1, C2 and R7.
 
Last edited:

Sensacell

Joined Jun 19, 2012
2,787
Both RC circuits for low-pass filters.

The input cap is probably to suppress RF interference, the output cap provides additional suppression of high frequency garbage.
 
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