Re: programmable gain opamp

On Fri, 31 Mar 2006 20:25:15 +0200, jutek <utech@xxxxxxxxxxxxxxxxx>
wrote:

Ken Smith wrote:



Here's a 2 gain version:

---/\/\/---+---/\/\/---+---/\/\/-------------
! ! !
! ! SW1 !
! --O !
! <----!-\ !
--------------O ! >--------
!+/

So long as the ratio of the resistors in constant and the op-amp is good
enough, the gain does not drift.

There is no current through SW1 so, within reason, its resistance doesn't
matter. The feedthrough capacitances etc still matter however.

If you can break your gain selections into 2 stages, you can save a lot of
switches.

thanks a lot, but why do you say ther is no current through SW1?

The input to the OpAmp draws no (or insignificant) current.

...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 |

I love to cook with wine. Sometimes I even put it in the food.
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