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Problem of differential amplifer as a comparator

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Jing

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I designed a very simple comparator, actually it is just a CMOS differential amplifier. I put a single comparator on the chip. The measurement showed that the offset is about 10mV and it can detect at least 15mVpp of 10kHz signal.

I used this comparator in one system. But this comparator cannot detect 80mVpp of 10kHz signal. In the system, the comparator input is not ideal square wave, but seriously distorted. However, the peak to peak amplitude is more than 80mV. I really don't understand why the comparator in the system cannot work as it is separated. Is it because the surrounding of the comparator has lots of other CMOS when it is in the system. The surrounding is not symmetrical, so it increases the mismatch and offset of the comparator?

Could anyone give me some suggestions? Thanks a lot
 

payam.hs

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Did u check input impedance of ur system and output impedance of last system? may be it cause some distortions on signal and it becomes less than 15mV.
 

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