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How to provide input dc bias for a opamp with capacitor feedback

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As shown in the figure below, it has a capacitor feedback loop so that the dc voltage from input and output will be blocked at same time, so how can I supply dc bias to the input node of opamp?
Thanks!

Unnamed.jpg
 

Hi
That circuit won't work , fine . you'll need biasing resistor .
Best Wishes
Goldsmith

- - - Updated - - -

( a resistor in parallel with capacitor in feedback path required because of two reason :
1- biasing
2- decreasing open loop DC gain .)
 

If the circuit is used as a boxcar (switched reset) integrator then the circuit will work as shown as long as the integrate time is not too long. During the integrate time the input bias current is supplied by the capacitors and will cause a small offset, depending upon the bias current, cap sizes and integrate time. When the cap is reset to 0V the bias charge is dumped and the bias current will travel through the switch as long as it is closed.

If you need to supply DC from the input source, then just add a resistor in parallel with Cin.
 

hi goldsmith,
Thanks for your answer. If I need to add a res in parallel with cap, how to determine the resistance of it?
 

hi goldsmith,
Thanks for your answer. If I need to add a res in parallel with cap, how to determine the resistance of it?
Click to expand...
Hi again
There is a rule of thumb available which tells , that resistor , should have a resistance a around 10 or 12 time larger than XC instead of frequency of operation .
Good luck
Goldsmith
 

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