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For my following circuit, the input is sine wave. LA25P is a current sensor having a bandwidth of 200 kHz (-1dB). The R2-C5 low-pass filter is designed at 482 kHz.

However, if I have an input sine wave frequency of more than 40 kHz, I get a distorted sine wave after R3 or after the 2nd stage output of the op-amp. There are two op-amps here with unity gain. The output at the R4-R6 junction is good at or below 45 kHz, however, the final output is only good at <=10 kHz. What's wrong here? I want the final output at TP2 to be undistorted even for 50 kHz input frequency.

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You apply an input which is ground referenced, and put it through a unity gain buffer. Then you appear to be trying to add a small positive DC offset of 0.6V with R4/R6, and putting it through another unity gain buffer, than the output of that stage goes via a 100R resistor to two Schottky diodes which clamp the signal at 0V and +3V.

What you don't tell us is the amplitude of the input - what is the pk to pk, and does it swing evenly around 0V?

I would expect any signal of more than about 0.5V pk-pk to start clipping because of the schottky diodes.

By the way, if you want to apply a DC offset to an AC signal, a better way would be to make the second stage an inverting amp, and apply a DC current to the virtual earth point, so that you are actually summing the AC with the right amount of DC.

Schematic drawing tip : using the industry standard symbol for an op amp makes life easier for everyone (including you).

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