AoE x-Chapters, High-Speed op-amps section, DRAFT

Distortion is "so much". The output stage is class B so exhibits crossover distortion unless you bias it. Among other quirks that some are suspiciously quick to forget... :-)

I'm partial to TLV2372 myself.

Tim

What's needed is a circuit to provide the demonstration. I asked for something like that pertaining to some other phenomenon, but even if it's more appropriate for the lab book it should be somewhere, especially in a case where, as you say, people need proof.

You get a lot. Offset, noise, crossover distortion, amplifier interaction, thermal self-destruction, and really interesting behavior if any input is pulled a few tenths of a volt below ground.

ESD tolerance is spec'd at 250 volts!

I've seen visible crossover distortion amplifying a 60 Hz sine wave.

For me, the fascination is why they thought a sub-nV/rtHz opamp would be marketable with a 1/f noise corner so high.

Perhaps I misunderstood the intended application.

Allan

Now there's an impractically broad question :)

NT

NT

It's not hard to avoid distortion. Quirks must be remembered with every IC or circuit.

NT

The main thing you get is cheap. ALL opamps have offset & noise. Other low cost opamps aren't significantly different to the 324 in that respect. FWIW its prime limitation is slew rate. There's no end of applications that don't run into any problems with it - that's why it's so common in consumer equipment. You of course are in a different market.

NT

Why only with opamps? Do you also get that effect in some transistor amps?

I design almost exclusively with single SOT23 or SO8 amps. The PCB layouts are much nicer than with duals or quads.

What would that transistor do?

Seems easier to buy a decent opamp than to kluge a bad one.

I thought it was in AoE-III, but it was one of the "advanced" things that got moved to the x-Chapters, when we thought they were still going to be part of the main book. Sorry. Here's a link:

That extra transistor isn't a kludge, and I'll bet it's actually in most modern op-amps, etc.

Here's an EMI fix for the front end of a diffamp, 16x on a VME module.

The customer was seeing EMI from an adjacent CPU module that was causing 10 or so LSB offsets in a 16-bit ADC. The adapter allows an emi hard amp, ADA4522, to go into the weird footprint of an LT1124. The 1124 is a great RF detector.

The customer wanted to pay us to fix our EMI problem.

This is incidentally pretty much the circuit in AoE3 p 361.

I like to put it this way: it's noticeable even in a control loop.

Tim

That is truly *beautiful* - wonderfully elegant.

Thanks Win, not seen that before.

piglet

Yes, it's simple and obvious once you see it. It's hopefully in most ICs with shared mirrors, although simplified schematics may not show it.

You should be happy to pay extra for integrated deadband.

Actually, it's professional malpractice to use an LM324 in a control loop.

=0

Sorry, I thought you meant to add an external transistor somehow.

Transistors are so cheap in an IC, why share current mirrors between opamp sections?

LM324 is ancient, full of hazards.