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WSJ 27th September 2012 09:05 PM

Discrete Opamp test circuits
 
9 Attachment(s)
I started working at Fairchild in 1966 when the μA709 was in production, they sold for $50 each. Gas was 25 cents a gallon and I drove my motor cycle from San Mateo to 313 Farichild Dr. in Mountain View. I still have some μA709 functional rejects. All the rejected devices fill hundreds of 55 gallon drums, which were used as fill in the parking lot asphalt. Sence then I was involved in the design and testing of several Opamps, both IC and discrete. At Siliconix, I developed the UNIVERASAL OPERATIONAL TEST FIXTURE, which was used in the development and characterization of the L144 Opamp.

The following test circuits were used for both IC and discrete Opamp development, characterization and discrete production testing. Each test circuit is mounted on a 3-wafer switch and the fixture has switchable resistors and capacitors to load the output.

Opamp pictured: Xf, 10MHz; THD at 20kHz, .005%; Ib, 10 pA; 100 nV p-p input voltage noise, 0.1 Hz to 10 Hz; 18 V/μs slew rate

dchisholm 28th September 2012 02:38 PM

I used one of those uA709's in a project while I was in High School, circa 1968!

The project was a galvanic skin resistance meter, plugged as a "Lie Detector" on the cover of a Popular Electronics issue. I think I got the '709 from "Poly Paks", and paid around $4.00 or $5.00 for what was probably a sub-prime part. The GSR meter got used as a novelty item at a few parties - on one occasion in particular, it was quite a hit as an impromptu "Kiss Meter".

I recall trying to learn what all that "compensation" stuff was about with the '709, but before I got it figured out the uA741 was available at affordable prices, so it became a moot point. And may be why the '741 is the best selling analog IC ever created, and the '709 is the subject of idle stories by gray-haired old guys.

Dale

RNMarsh 30th September 2012 06:01 PM

It sure would be nice to have them all in a small box to do the various tests. Did anyone ever make, commercially, something like this?

john curl 30th September 2012 09:39 PM

Interesting, WSJ, I got my first uA709's in 1966, as well, from a girlfriend who worked on the line with Bob Widler. Need any? '-)

john curl 30th September 2012 09:42 PM

So that's were we got the pattern for the Levinson JC-2, and the LMP-2 circuits, WSJ

WSJ 30th September 2012 11:26 PM

2 Attachment(s)
I have not seen a commercial Opamp test fixture similar to this design.

The test fixture is based on a 3 wafer rotary switch that switches the Opamp + input, - input and output pins to each component. All components could be on a PCB with one socket for a discrete Opamp. Adapter boards for each Opamp pin configuration could be plugged into the socket. The adapter boards could use another rotary switch to accommodate multiple Opamps.

flg 1st October 2012 12:03 AM

Back in about 81-86 I was Motorola Device Eng for OpAmps. We were just geting the JFET input stuff running good enough back then. I had about 1/2 of the tests available upstairs at my bench, running the HP Semicundutor Parameter Analyzer (SPA) through a box like that. But much less complex. I was doing on it microprobers with wafers though.

WSJ 1st October 2012 12:14 AM

Quote:

Originally Posted by flg (Post 3185483)
Back in about 81-86 I was Motorola Device Eng for OpAmps. We were just geting the JFET input stuff running good enough back then. I had about 1/2 of the tests available upstairs at my bench, running the HP Semicundutor Parameter Analyzer (SPA) through a box like that. But much less complex. I was doing on it microprobers with wafers though.

How did you measure FET input bias current in the range of 10 pA?

john curl 1st October 2012 12:25 AM

WSJ, did you ever know about or use the Fairchild IC tester? I supervised the building of one at Friden in 1966, following Fairchild's instructions. Used it to characterize uA709's.

flg 1st October 2012 01:29 AM

Quote:

Originally Posted by WSJ (Post 3185487)
How did you measure FET input bias current in the range of 10 pA?

Notice I said about half. That certainly would not be one of 'em. Nor the 108 208 308 SuperBeta inputs. The SPA was basically a wammy-bammy curve tracer with 4 VIs, 4standard supplies and several measurement only channels.
Also "most" of the tests could be coorelated to PC data parameters which were only sampled from the lot. I could put a wafer with poor yield on the prober and do the OpAmp tests, the PC Die tests near the poor yield areas or the metal layer test die which brought out actual circuit components individually for measurement.


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