Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

The gain of Track-and-Hold circuit

Status
Not open for further replies.

fightshan

Junior Member level 3
Joined
Jul 30, 2013
Messages
28
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Location
China
Activity points
260
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!
 

erikl

Super Moderator
Staff member
Joined
Sep 9, 2008
Messages
8,112
Helped
2,689
Reputation
5,358
Reaction score
2,291
Trophy points
1,393
Location
Germany
Activity points
44,156
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.

What is the influence to ADC of the gain loss?
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.
 

Warpspeed

Advanced Member level 5
Joined
May 23, 2015
Messages
2,213
Helped
754
Reputation
1,510
Reaction score
734
Trophy points
113
Location
Melbourne, Australia
Activity points
17,766
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.
 

fightshan

Junior Member level 3
Joined
Jul 30, 2013
Messages
28
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Location
China
Activity points
260
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.

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.

- - - Updated - - -

- - - Updated - - -

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.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top