Two-electrode Voltage Clamp Amplifier Circuits

nikNjegovan at nikNjegovan at
Mon Mar 14 21:33:37 EST 2005

Good Day all,

I am a bioengineering and electrical engineering undergrad from the
University of the Pacific and am building a voltage clamp circuit for a
senior project.

I noticed a post from quite awhile ago on building voltage clamp
amplifiers to which no one replied. I'm not sure if anyone has
experience in builing these puppies out of discrete components but I
was wondering if I might discuss it with an experienced mentor. I'm
currently trying to mimick the OC-725C clamp from Warner Instruments.
I.E. come up with a black box that matches their specs.

I was wondering about the preamp headstages for the current injection
and voltage channels and some of the problems that I'm running into
with the bath headstage.

First, with the current channel, I will be using a NPN/PNP pull up/down
network to get the necessary voltage through the high impedance
(10Mohm) electrode but I know that the only way to know if the
electrode has pierced the cell to begin with is to also have a voltage
capture mode associated with the current channel headstage. Is this
normally a mirror image of the circuitry that is available in the
voltage channel preamp headstage?

Concerning the preamp headstage, what type of instrumentation
amplifiers are used with typical headstages? I found one produced by TI
(INA326), would this be a good option for low noise and precision
capture of that weak signal?

Third, I was also wondering about the virtual ground in the bath
headstage. I want this to be an option but I'm still wondering what
devices to use. Any guidance in any of these matters would be much

Also if anyone happens to know the patent number for the OC-725C, it
would be useful.

Thanks for your time,

Nik Njegovan
University of the Pacific
Stockton, CA 95211

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