I'm wondering what method folks here use to measure amplifier output impedance in LTSpice? One method I recall reading about is, IIRC, hanging a resistor off the output and stepping it, looking for the closed loop gain*input voltage*output voltage divider halfway point, but that seems kind of kludgey. Any other methods? Thanks.
(1) Transient load the output (IPULSE) and observe voltage. This will show output "impedance" and exhibit any ringing due to poor compensation.
(2) Do a .AC analysis using an AC current source. You can get the real and imaginary parts. Caution: this is "small-signal" linearized at the operating point.
I tend to do both, plus various loop-gain and forward transient examinations. ...Jim Thompson
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| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
You don't need to measure at the half-way point. You can also drive the output with a source and measure the I/V across a resistor (any value). Doesn't LTSpice have an AC mode?
Thank you, that's much clearer. Suck current, measure voltage. I kept thinking about applying a voltage and measuring current, the way one might do it in circuit analysis, but I don't think that will work properly with SPICE.
Minor problem: The vast majority of participants in NGs no longer has access to news servers that support binaries. Thus no attachments. Slow? C'mon, a bit spoiled? Remember the days when one had to wait for the arrival of the 11:00am flight and the tapes to be unloaded?
Bitrex: The way you describe it is how it's usually done, almost. Sometimes a load or current is modulated to see how things are at higher frequencies. It is also customary to check switch-mode converters for load change behavior via pulsed loads.
Yup. Any and all attachments. I've asked the guys at my (paid) server if they couldn't open 100k for attachments since they allow max 100k in the message body. The answer was a resounding "no way". Wouldn't make much sense anyhow, it doesn't do any good if only 1% of the others can read it.
In Europe we had a really nice system, not sure if still available: We had the schedules of all those Intercity fast trains hanging on an office wall. If something urgent needed to get to Munich we'd sprint to the station, hand it over along with some cash, goes onto train. Called the guy in Munich to be at their station at around 4:00pm. Even with air freight today that's impossible unless you charter a plane.
Nowadays many biz folks actually drive if the destination is within 300 miles. Air travel has lost the advantage over short hauls because of the security wait.
Well, shazam! It sure worked. Beats me why because the folks at the news server said it wouldn't. And in the past it hadn't. Probably the Hobbs coefficient was too low on all the others :-)
No, it provided the attachment. I know for sure that a year ago it didn't because we tried it. Question is, how many other here in this exquisite club of soldering iron wielders are able to read the attachment?
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I only drive such distances when there is no other reasonable connection. Many destinations north of here can be a problem, where you have no real choice other than taking the Interstate.
In the old days, about a year ago, such attachments were visible as such but no contents were transmitted. Now LTSpice has a minor problem running a simulation off of hot air. Although Mike Engelhardt could take an internship with a few politician's offices, they'll show him how that's done :-)
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Once you get to about 300 miles from here it is actually very pretty country. Like this:
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