Summing Amplifier with non-ideal op-amp

[Jim Thompson]

On 10 Mar 2005 12:58:41 -0600, <rp0000003356@127.0.0.1:7501> wrote:

Jim Thompson <thegreatone@example.com> wrote:

Which reminds me... sometimes bypassing the summing node to ground can
improve system noise problems.

...Jim Thompson

When you "improve a problem" do you make it better or worse?

Jim

Depends ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

 

[John Woodgate]

I read in sci.electronics.design that rp0000003356@127.0.0.1 wrote (in
<423098e1$1_1@127.0.0.1&gt about 'Summing Amplifier with non-ideal op-
amp', on Thu, 10 Mar 2005:

Jim Thompson <thegreatone@example.com> wrote:

Which reminds me... sometimes bypassing the summing node to ground can
improve system noise problems.

...Jim Thompson

When you "improve a problem" do you make it better or worse?

Neither; the words are orthogonal.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Larkin]

On Thu, 10 Mar 2005 19:23:55 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that rp0000003356@127.0.0.1 wrote (in
423098e1$1_1@127.0.0.1&gt about 'Summing Amplifier with non-ideal op-
amp', on Thu, 10 Mar 2005:

Jim Thompson <thegreatone@example.com> wrote:

Which reminds me... sometimes bypassing the summing node to ground can
improve system noise problems.

...Jim Thompson

When you "improve a problem" do you make it better or worse?

Neither; the words are orthogonal.

p
i m p r o v e
o
b
l
e
m


Holy Moley, he's right!

John

 

[Larry Brasfield]

"Fred Bloggs" <nospam@nospam.com> wrote in
message news:422FF0B7.7030305@nospam.com...

Larry Brasfield wrote:
"Fred Bloggs" <nospam@nospam.com> wrote in
message news:422EC4E8.9000108@nospam.com...

Larry Brasfield wrote:

(Responding to the question: "If an OP-77 connected as simple
inverting summing op-amp stage has N inputs, how could you
estimate the practical limit for N ?")

In addition to the issues mentioned by Mr. Grise and Mr. Shoppa,
as N approaches the open loop gain of the op-amp divided by
the hoped-for realized gain from each input, the loop gain will
approach something near 1, leading to limited accuracy of the
actual closed loop gain and increased distortion.

Oh yeah- people are running that check all the time in their
calculations. Why don't you review OpAmps 101 before you post your
irrelevant pedantic drivel........

[Cut a load of non-electronics related ad hominum crap.]

Do you deny that loop gain imposes a practical
limit on how many inputs a summing op-amp
circuit can have? If so, you are the one that
needs remedial training in op-amp theory.

If you are merely suggesting that the limit I have
stated is never applicable, why have you not
given some hint as to what the real limit on N is?
My bet is that you cannot.

[Cut a load of non-electronics related ad hominum crap.]

I note that you have well developed name-calling skills,
but are unable to answer the challenge I posed. I take
this to mean that your "review OpAmps 101" suggestion
is nothing but empty pretense.

You can take this as my response to your other two
content-free posts.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.