The gain of Track-and-Hold circuit

I designed a open loop track and hold circuit in a folding and interpolating ADC, the source follower buffer is used in the circuit. As we all know , source follower has a gain<1, so the simulation results show that the output voltage is not equal to input signal.
What is the influence to ADC of the gain loss? if this is a problem , what should I do to compensate it？
thank you!

You should either
- compensate the gain loss somewhere in the whole analog chain by amplifying the signal with an appropriate gain>1
not ideal, as your source follower buffer's gain may be not constant over signal voltage and temperature.
A correction at the digital output would need a microprocessor action.
or
- change your buffer amp for gain=1. I'd think this is the much better - and simpler - solution.

fightshan said:

What is the influence to ADC of the gain loss?

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I don't quite understand this question. It's clear that the ADC part gets a lower input voltage from your simple source follower buffer. You could compensate for that before or within the proper ADC part - still in the analog chain of course.

Your best bet is to toss the source follower into the dumpster, and use a proper op amp follower where there will be no gain loss.

Warpspeed said:

Your best bet is to toss the source follower into the dumpster, and use a proper op amp follower where there will be no gain loss.

Click to expand...

Thank you for your suggestion, actually a closed loop op-amp with unit gain feedback is nice for the track and hold circuit, because its gain can be controled accurately. But the ADC we designed is a high speed ADC , the signal bandwidth is >800MHz, it is difficult to use closed loop op-amp.
I have to use open loop topology in the analog chain, but the precision of TH become hard to control.

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Thank you for your reply.

"What is the influence to ADC of the gain loss?"
I mean if I don`t compensate the gain loss of TH circuit, how the output of ADC wil be influenced ?

"as your source follower buffer's gain may be not constant over signal voltage and temperature."
The temperature wil influence the gain, of course, all the PVT variation will make the gain slightly deviating from the designed value; the gain should be constant over signal voltage, this is about distortion issure，the linearity of source follower I designed is enough for the resolution of TH circuit and the whole ADC.