You don't really need to redesign the analog front-end - if I understand your
 observations,
it is a cable problem. You need to use low microphonics or low piezoelectric
 cables. Check on
the Net for low-microphonic-noise cables. The best I have used have a low
 capacitance, low
piezoelectric coefficient insulator and carbon powder shield lubricant. I used
 them for both
medical and seismic geophone transducer designs. I am assuming that you are
 using electrode
gel, of course, to reduce the electrode motion noise and CMRR related 60 Hz
 pickup.

Wayne Foletta
Design Engineer
Data Acquisition Products
SiliconSoft, Inc.
San Jose, CA
http://www.siliconsoft.com

You wrote:
>
>I need an analog expert to redesign a low-noise front end for medical
>purposes (to measure EMG and EEG - signals in the low microvolt range). The
>system we have has a million Megaohm (10^12) input impedance, 130dB CMRR,
>and 12 bit resolution,  but the signal waves around too much if the cables
>are jiggled.
>
>I have seen systems that somehow minimize this effect, and need someone who
>could help redesign such a front end on a contract basis.
>
>Craig Webb
>