Ghosting issue

[SunilSinha]

Hi,

I have made my own hardware board for acquisition of analog parameters. In that design I am facing ghosting problem. I have a small doubt regarding it:

1) In this document http://digital.ni.com/public.nsf/websearch/CF83426BC3AC514A86256C10005A4771?OpenDocument it talks about putting an OPAMP in unity follower mode before multiplexer. However in my design I have put OPAMP in unity follower mode after multiplexer and it is in between multiplexer and ADC. Can any one tell me that in this case OPAMP will have any role in reducing ghosting.

Sunil

[crossrulz]

No, it won't.  The idea is that the output of the MUX needs a way to drain off the voltage.  The input to an op-amp tends to be of a high impedence.  You therefore are not helping the draining of capacitance on the output of the MUX.  But op-amps tend to have a low output impedence.  So by using op-amps on the signals before the MUX, you are giving the capacitance a path to drain off.