LT op-amps models

[John]

Does anyone know where to fine documentation on the newer LT op-amp
models available at the LTC web site (ie LT6202, LT1630)? There is an
application note by Jung from about 1990 that discusses their older
models but I can't find any documentation at all about the newer ones.
What is modeled? How good is the representation of noise? In
particular, does the current noise vary realisitically with common
mode voltage?
Thanks,
John

 

[Mike Engelhardt]

John,

Does anyone know where to fine documentation on the
newer LT op-amp models available at the LTC web site
(ie LT6202, LT1630)? There is an application note by
Jung from about 1990 that discusses their older
models but I can't find any documentation at all about
the newer ones. What is modeled? How good is the
representation of noise? In particular, does the
current noise vary realisitically with common mode
voltage?

The newer LT opamp models use an internally
developed model that allows current and voltage
noise and corner frequencies to be modeled. These
are generic SPICE models, not LTspice specific.
But noise verses common mode voltage isn't modeled.

I'll separately e-mail you contact information
for the guy who is making those models and the
app engineer that should help you with the
noise verses common node voltage.

--Mike

 

[Fred Bartoli]

"Mike Engelhardt" <nospam@spam.org> a écrit dans le message de
news:a2n%c.17160$wZ2.17027@newssvr29.news.prodigy.com...

But noise verses common mode voltage isn't modeled.

Mike,
Any info, pointer on this, and how/why this happens ?

I've seen you make mention of this in a recent thread about shot noise.
Very little info (read no info) on the subject exists in datasheets and I
have to use a LT1128 in a very critical wrt to noise application.


--
Thanks,
Fred.

 

[Mike Engelhardt]

Fred,

But noise verses common mode voltage isn't modeled.

Any info, pointer on this, and how/why this happens ?

I've seen you make mention of this in a recent thread
about shot noise. Very little info (read no info) on
the subject exists in datasheets and I have to use a
LT1128 in a very critical wrt to noise application.

The noise can be dependent on common mode input voltage,
particularly in something like a rail-to-rail input JFET
opamps. It's not an issue in a bipolar design like the
LT1128.

If you want, e-mail me at the address on LTspice's
Help=>About box(I don't put the address anywhere else
for spam reasons) and I'll give you the contact
information for the apps engineer that can help you
with noise on any LT opamp.

--Mike

 

[Kevin Aylward]

Fred Bartoli wrote:

"Mike Engelhardt" <nospam@spam.org> a écrit dans le message de
news:a2n%c.17160$wZ2.17027@newssvr29.news.prodigy.com...

But noise verses common mode voltage isn't modeled.


Mike,
Any info, pointer on this, and how/why this happens ?

The lack of a model you mean?

If so, probably because it doesn't change much to bother about. Offhand,
about the only real mechanism that might change the noise is bias
base/collector current noise. If the bias current changes with common
mode voltage it will effect the noise a bit. I don't see this happening
much though, certainly not for bipolar. Bias currents are usually pretty
much independent of the CM voltage, they are set by a current source.
For jfets bias current might vary quite a bit more, but then gate noise
is often not significant for many sources.

There is an effect that can potentially reduce 1/f noise when Vce < 0,
but this aint gonna happen in an opamp unless its designed to do this,
or your at the rails.

I've seen you make mention of this in a recent thread about shot
noise. Very little info (read no info) on the subject exists in
datasheets and I have to use a LT1128 in a very critical wrt to noise
application.

I would just ignore noise with CM voltage if it were me. Just make sure
you have a set of models that have a reasonable estimate of max and min
noise over process variations at a spot CM voltage. These will be way
more than that due to CM voltage variations.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.