MOTM

> > If you are careful to match the input resistors can't you get
> > good common mode rejection with active balancing?
>
> No, you can't.

Addition: yes you can, but not with that simple one-opamp
circuit. Three opamps is much better, or even better, discrete
symmetrical frontend and then an opamp, as in (now obsolete)
SSM2017.

JH.

This is great information to have coming from someone that knows something
about it.  There is so much information out there, and not all of it good.
I never stopped to think about the difference in impedance of the two
inputs.

Would the 3 op amp solution be an inverting buffer for signal +, a
non-inverting buffer for signal -, and then the third to sum the outputs of
the first two?

Larry

----- Original Message -----
From: <jhaible@...>
To: <motm@yahoogroups.com>
Sent: Sunday, February 04, 2001 1:30 PM
Subject: Re(2): [motm] Re: Balanced/Unbalanced - P.S.


> > If you are careful to match the input resistors can't you get
> > good common mode rejection with active balancing?
>
> No, you can't.

Addition: yes you can, but not with that simple one-opamp
circuit. Three opamps is much better, or even better, discrete
symmetrical frontend and then an opamp, as in (now obsolete)
SSM2017.

JH.

> Would the 3 op amp solution be an inverting buffer for signal +, a
> non-inverting buffer for signal -, and then the third to sum the outputs
of
> the first two?

Charles Stella just posted a hint on 2 other SSM chips.
Take a look at the block diagrams (data sheets at www.analog.com)
Replacing a transformer at the output is even more involved
than on the input, if you really want it "floating" (but still within
the supply voltage bounds).

JH.