--- In LTspice@..., brian.howie@b... wrote:
Are there any special considerations with using P-spice op-amp
macro
models with LTspice? I'm trying to simulate a circuit that uses a
Burr Brown/TI electrometer op-amp (OPA128 or OPA129) and I'm
getting
incorrect results. I downloaded the models from TI's website.
The
circuit's been built and thoroughly debugged, so I'm confident in
the
design.
When I couldn't get the circuit to operate correctly, I entered a
simple test circuit to verify some of the basic op-amp
characteristics. I found that the input bias current was way to
high
(about 12nA instead of 100fA), and the gain-bandwidth of the
OPA129
was high by about a factor of 10. I suspect that the models are
just
screwed up, but since I'm new to LTspice I'm not completely
confident
with my conclusion. Any help would be greatly appreciated.
I get similar problems with the OP27A, although in my case it is
the noise that
is reported about 2 orders more than the data sheet and hand
calculations
suggest. The bias currents look right. Other vendors opamps seem to
behave.
I ran a test circuit on Accusim II (Eldo SPICE-like kernal) and
the OP27A gave
sensible answers. I ported the netlist back to LTSPICE and although
the AC
analysis ran, the noise analysis gave up . I put the Accusim OP27A
model into
LTSPICE library and it gave the same wrong noise on my test
circuit.
Brian
--
Brian Howie | Tel: 0131 343 5590
BAE SYSTEMS | Fax: 0131 343 5050
Sensor Systems Division | Email brian.howie@b...
Silverknowes | bhowie@i...
Edinburgh EH4 4AD | Web site www.baesystems.com
***
This email and any attachments are confidential to the intended
recipient and may also be privileged. If you are not the intended
recipient please delete it from your system and notify the sender.
You should not copy it or use it for any purpose nor disclose or
distribute its contents to any other person.
***
Brain,
On one hand, I'm frustrated to learn there are so many issues with
vendor supplied models. This sort of problem can send you down a rat
hole for quite some time, and leave you worrying about the soundness
of your design. On the other hand, I know that I'm going to only use
simulation to validate my initial design and analysis, and not use it
as a substitute for other analytical methods. This experience only
supports my convictions and helps keep me honest.
- John
