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LT Spice universal opamp

Started by John Larkin December 17, 2018

The LT Spice Universal Opamp 2 is not documented in the 'help'.

It appears to have zero input capacitance, and maybe no parameters to
add any internally. I guess we'll have to add caps externally.

Capacitances would have to be to a rail, I guess.

I see opamp data sheets that specify common-mode and differential
input capacitances, but I'm not sure what that means.





-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

On 2018-12-17, John Larkin <jjlarkin@highland_snip_technology.com> wrote:
> > > The LT Spice Universal Opamp 2 is not documented in the 'help'. > > It appears to have zero input capacitance, and maybe no parameters to > add any internally. I guess we'll have to add caps externally. > > Capacitances would have to be to a rail, I guess. > > I see opamp data sheets that specify common-mode and differential > input capacitances, but I'm not sure what that means.
I would think that common mode capacitance would be to a supply rail (which?) and differential would be between inputs. I am also not sure that this interpretation is correct. -- When I tried casting out nines I made a hash of it.
On Mon, 17 Dec 2018 11:28:12 -0800, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

> > >The LT Spice Universal Opamp 2 is not documented in the 'help'. > >It appears to have zero input capacitance, and maybe no parameters to >add any internally. I guess we'll have to add caps externally. > >Capacitances would have to be to a rail, I guess. > >I see opamp data sheets that specify common-mode and differential >input capacitances, but I'm not sure what that means.
https://e2e.ti.com/blogs_/b/analogwire/archive/2016/03/21/spice-it-up-extracting-the-input-capacitance-of-an-op-amp-part-3 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
>"I see opamp data sheets that specify common-mode and differential input capacitances, but I'm not sure what that means."
The only logical conclusion is that differential means between + and - inputs and common means both to common, like ground or a bypassed rail. I would say having zero capacitance in the device is a good thing. Just add whatever capacitance you think your actual device will have and everything should run fine, the simulation etc. What I would like to see is tubes and potentiometers in the library. And dual pots, tetrodes, pentodes and all that. Might be able to squeak by if they have any dual gate JFETs... It is not a perfect solution and I have had to take to pencil and paper again for some things. But it beats nothing and the LT incarnation of it is free so at least the price is nice.
On Mon, 17 Dec 2018 12:36:00 -0800 (PST), jurb6006@gmail.com wrote:

>>"I see opamp data sheets that specify common-mode and differential input capacitances, but I'm not sure what that means." > >The only logical conclusion is that differential means between + and - inputs and common means both to common, like ground or a bypassed rail. >
It looks like cm capacitance is *each* input to ground, where ground must really be a supply rail.
>I would say having zero capacitance in the device is a good thing. Just add whatever capacitance you think your actual device will have and everything should run fine, the simulation etc. > >What I would like to see is tubes and potentiometers in the library. And dual pots, tetrodes, pentodes and all that. Might be able to squeak by if they have any dual gate JFETs... > >It is not a perfect solution and I have had to take to pencil and paper again for some things. But it beats nothing and the LT incarnation of it is free so at least the price is nice.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com