LM13600 or LM13700

Yikes, OTA! Blast from the past. What are you going to do with this?

One app on the data sheet shows +-5 supplies.

LT chip? A real LM13600 is fairly cheap.

Nice, linear, low distortion, variable gain (must be linear)

I didn't see that one - I must look harder - I can live with +/- 5v

An OTA is basically just a differential pair front end and four to six current mirrors in a package. (Unless I've miscounted.) AFAICT, very roughly it should be okay down to about 5*V_BE, i.e. 3 to 3.5V, if you don't insist on all the specs being met. But the actual IC designers on the group will be able to give better info.

Cheers

Phil Hobbs

Good guess. You need a minimum of +2*Vbe for the positive rail and

-3*Vbe for the negative rail for all mirrors to be happy.

As for linearity I don't know off the top of my head... Tom Frederiksen and Leroy Long did that chip. ...Jim Thompson

Thanks all!

David, I ran across an AppNote that's essentially the same device...

NNTP-Posting-Date: Sun, 25 Aug 2013 14:04:31 -0500 From: Jim Thompson Newsgroups: alt.binaries.schematics.electronic Subject: LM13600 or LM13700 (From S.E.D) - LM3900_Norton_AppNote.pdf Date: Sun, 25 Aug 2013 12:04:31 -0700 Message-ID: ...Jim Thompson

Wow, the LM3900--there's a blast from the past.

A Norton amp is a weird mutation that I've yet to find a real use for, unlike OTAs. They're really quite distinct: a Norton is a crappy op amp with a weird asymmetrical input structure and a voltage output, whereas an OTA has a symmetrical input and a current output.

Way back in the day, like 1972, the 3900 had a fairly decent speed advantage over most contemporary op amps, maybe all except the LM318. National pushed it (and its equally dubious successor, the LM359) fairly hard as a building block for stuff like tachometers and filters. Every time I thought of using one, though, its crummy input specs and really horrible noise (especially the 359) brought me up short.

Quite a different matter from an OTA.

Various folks, notably VTC, made much faster OTAs, but they never achieved enough market penetration to survive. I still have a few VA713

Cheers

Phil Hobbs

Certainly a blast form the past. That was the first version Tom Frederiksen and Leroy Long came up with... after they departed SPD for National. ...Jim Thompson

And the obvious...Why not just buy a modern VGA amp?

around $4

Kevin Aylward B.Sc.

Assuming it's fast enough for the job. It's a nice chip, but it's pretty much audio only. Even the LM13700 is a 2 MHz chip at higher bias currents, whereas the SSM2018 starts rolling off at a couple of hundred kilohertz (Fig 15).

Sometimes it would be really nice to have some of those 50-100 MHz class OTAs like the VA713.

Cheers

Phil Hobbs

Its around $10 here - the slightly better version is $12. It is nice though. I'd have to check how well it works at +/- 5v. Thanks.

Thanks Jim,

Section 3.6 look right - DC gain control. I've got a bit to work through now.

I think I still have a LM3900 or two (IC's not individual amps). They were the first op amps I used. While still a school boy I bought one - it was a