Re: Differential amplifier design with input-side biasing??

On 20 Feb 2006 10:17:47 -0800, chessaurus@xxxxxxxxx wrote:

I need to design an amplifier that takes in a differential signal (call
these inputs A and B), adds a bias C (where this signal is referenced
to amplifier's ground), and applies a high gain (G ~= 100). In other
words:

Output = ((A-B) + C) * G

I need this operation performed for two channels, and I want to
minimize the number of ICs and components required. High CMRR is a
plus. In an earlier generation of this design, I was performing this
operation using an instrumentation amplifier (where bias signal C was
added after the gain, i.e.):

Output = (A-B)*G + C

But I've realized that I definitely need to be biasing before the gain.
Any creative ideas?

Best,
Chess

Perhaps something of this sort...

http://www.analog-innovations.com/SED/InsertCommonMode.pdf

Twisted from EDN-Design Ideas, October 1, 1992 (I save everything I
run across that amuses me ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

It's what you learn, after you know it all, that counts.
.

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