Jacki
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Thank you for your advices, loose-electron and raj. I try different types of continuous time buffer, the simulation results are not good, when the amplitude is below 300mV (600mV full swing), the distortion is OK. But when the amplitude is 500mV, then the distortion is too high (0.18um CMOS). Because the previous stage in front of the buffer is a SC-amplifier, I don't want to use any resistive feedback based on an opamp to be the buffer, then the load for the previous stage will change a lot. Now I will consider to use the SC buffer with the capacitor feedback (based on an opamp, the last stage could be source follower which can give enough driving ability), I guess it could work with the large dynamic range. Also it could be easier for the fully differential architecture. At the beginning, I thought maybe I didn't need pay too much attention on the buffer design since it only drove the output signal for the measurement. But now I think I have to change my mind.
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