Thanks for the comments.

What I meant was that, if the output impedence of the source that drives 7135 input is 1Meg, and if I connect a series resistor between source and 7135, and if there is a resistor (to ground) at other end of the resistor (near 7135 input), then it becomes a voltage divider.

If I avoid 100k resistor at 7135 (to ground), I am not able to get zero reading at all. I have checked with 200k also. Result is fine. If I move this 100 K resistor to other end of the series resistor, then I need to lower the value of the resistor to get zero reading. This should be because, the Thevenin resisance as seen by 7135 input amp, is higher. Without a resitor to ground, I am finding it impossible to zero the reading.

I would love to use the capacitor at the input. But, I am sampling 8 channes using 4051 at the highest possible speed. (As soon as the converon is over, I am switching the channel) Even a small capacitor creates a seepage of one channel into the other. I have no idea as to how to avoid this problem. I can discharge the capacitor using a transistor or mosfet at the end of conversion, but I do not want to complicate things.

Since input impedence of 7135 is very high, I do not understand why they use 100K series resistor in all the test circuits.

Probably, a small value series resistor (1K) at the output of the 4051 and a high value resistor to ground at the other end of 1k ie: 200k (at ie input of 7135)should work for me. Hope this wouldn't cause any problem.

Raj