Opamps - everything

You're talking applications (and buzzwords ;-)... I was talking the basics of OpAmps themselves.

Of course, it was probably presumptuous of me to assume that the reader is actually a circuit design engineer >:-} ...Jim Thompson

Cost?

More than that assumption... hardly six months goes by that I don't design another variation of an OpAmp to fit the needs of a specific

...Jim Thompson

Very important, a practical matter that costs me tons of time: Specifications: - what opamps have what specs, tradeoffs in specs, implications of certain specs. And very useful, what's going on inside the opamp to achieve the specs.

Also important: Circuit tricks to avoid degrading said specs.

Yes, I think there's enough for a book. One of the useful topics in Dostal's book, how to measure opamp specs. There's 40 pages in one section, many more in other sections.

I daresay that would go out of date quite quickly. It also varies around the world in that in some areas many opamps are hard to get.

NT

I have in mind more something good for the beginner, and also good for them to come back to and learn more years later. Something to get them as good as possible in minimum page space.

NT

There's always this old favorite from TI:

Add a section: weird opamps.

What OpAmps would you consider weird?

Those with three stages of gain ?>:-} ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

I'm looking for work... see my website.

Thinking outside the box... producing elegant solutions.

Bad opamps, (got an email from a HV opamp maker, wanting to visit.. no thanks.)

Oh I would add opamp output impedance to the list. I talked (email) with a burr-brown tech guy answering questions.. output impedance is complex and the basic test circuit measures the total impedance, I wanted the resistive part. (I ended up measuring by just loading it down.)

George H.

C-load, advertised or not

High voltage

Low voltage

High current

Clamp-amps

Outrageous bandwidth, 1 GHz or so

fA bias current

Low noise

High noise

Especially buggy

I don't think I could do those topics justice. I mainly see opamps as black boxes. Well, maybe not in that I understand the 2 or 3 stages in them, but how the variants relate to differing specs/issues I only have partial knowledge of.

NT

LM324--class B plus weirdness due to bias generator shared between all sections;

LT1028--nice and quiet but with a weird gigantic noise peak near 300 kHz, plus squirrelly compensation due to 3 gain stages;

Chopamps and their *ahem* unexpected current noise peaks;

ADSL drivers like the one John has been posting about;

TCA0372--dual 1.4 A op amps in an SO-14 package with no power pad;

MC33078/9: super cheap, quiet, single-supply, but with 300 nA input bias current;

Those TI CMOS things with the noisy internal bootstrap that have super low input capacitance but horrible current noise;

All the FET amps whose datasheets quote the current noise as being the shot noise of the typical input bias current.

There are lots more.

Cheers

Phil Hobbs

Apex?

Open-loop Zout can be interesting.

Open-loop behavior of opamps can be interesting in general.

Plus, fun things happen all over the chip if one pin is pulled slightly below ground.

I suppose THS3062 can work as an ADSL line driver, but don't use it for anything else!

But lots of pins to heat sink!

I've got a tray of expensive noisy HV opamps. Apex doesn't want them back. now replaced by LT(6090?) at ~$10 or so.

George H.

My HV amplifier designs have input stages that run on +/-12V or 15V, and good performance.

In Apex designs, input stage common-mode works over the whole HV range. They use special parts to achieve this, and many are noisy. APEX amps are easy to use (although very expensive). They can do the low-noise accurate job, when paired with a low-voltage op-amp. We're talking about simple composite op-amps, two stages, where the quiet low-offset input stage runs from low-voltage supplies and the HV op-amp runs the output stage. Often the input op-amp can be in a SOT-23 package, taking little space.

Are there any op-amps with say a 800V/uS slew rate but a GBWP of like 1kHz?

Apex has a company culture of delivering very strange, buggy, noisy opamps. It's their niche.