amplifierdc-offsetoperational-amplifier
I have 4 op-amps in cascade with a gain of 10 each to give a total gain of 10000. I noticed the circuit produces a DC offset which then gets amplified causing the amplified signal to clip asymmetrically.
I know op-amps have an offset pin but I have never used it before and I am looking for the simplest solution. I thought I might simply add a capacitor after each op-amp but I don't know how large it should be or if it would help. The signal I am amplifying is 40 kHz.
What is my best option?
Do not cascade them it will be extremely noisy and you lose a lot of dynamic range, instead use a splitter and combiner and use them in parallel to get higher gain. Try using a wilkinson divider for that purpose.
You are close to having a working solution.
I attempted to edit your schematic but I don't see a edit link below the schematic in the preview window. So I'll draw a new one here.
simulate this circuit – Schematic created using CircuitLab
R5 & C2 filter noise from your 5V rail. You may need to increase the value of C2 if you are getting excessive noise.
R1 & R2 set the gain. Gain is set to 11 with the values shown.
R1 & C1 set the low-frequency response of the amplifier. Increase C2 if you need a lower break-point.
C3 & the parallel resistance of R4 & R3 also set the low frequency break point of the amp. Note that R5 doesn't affect the low frequency response because C2 keeps the node of R5, R4, C2 at AC ground potential.
Best Answer
Of course you can try to compensate for the DC offset but why not eliminate the influence of DC offset in the first place ? You can do this if you do not need 10000 times gain at DC. You mention that your signal is 40 kHz, I conclude from that the DC value is irrelevant to you. Then I would just make amplifiers that have 10 x gain at 40 kHz but 1 x gain at DC !
Here's an example of how I would do that:
simulate this circuit – Schematic created using CircuitLab