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Simulated inductor with 100:1 current range

Gosh, didn't think to bring the bling tome to the cabin. Silly me. ;)

Looks fairly easy if I use range switching--two steps per decade let's me d rop between 5 and 15 volts in the drain current generator, and a one-transi stor servo loop to take it back out of the source. (A BFC on the source get s rid of that noise adequately.)

I can run an MC1496 as a lock-in, with a bit of flying-cap magic to do a du al-differential detection to get rid or the offset, and the resulting DC (r epresenting the pilot amplitude) applied to the 1496's tail source as AGC.

A 25-Hz filter and a perfect rectifier gets me a spot noise measurement any where I like. (Perfect rectifiers are easy to make at 25 Hz.)

Fun. I'll compare it to yours when I get home.

Thanks

Phil Hobbs

Reply to
Phil Hobbs
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Fun fact: The engineering units of the TDS694C were originally code named "SCREAMER" That's how they were labeled on the rear of the scope. Their target market (one of them anyway) was Rambus signal integrity testing, IIRC. I bought one about a year and half ago from Ebay seller "chipxs" a surplus seller affiliated with Tektronix. The bad news was that CH3 and CH4 had trigger failures. Since then, I've learned that only two trigger chips are needed, not the four that are on the ACQ board. (from John Miles.)

Weird. Why are there two extra trigger chips? There's an EEVblog thread on that.

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JW

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--
 Thanks, 
    - Win
Reply to
Winfield Hill

Nice... I (also) found 2N4401's to work better than other small transistors (2N3904's) in cap multipliers.

George H.

Reply to
George Herold

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Thanks, Win. I wound up with something sort of similar, except without the manual set-up (it's more complicated than yours, of course).

I have a variable BJT current source that drops 5 to 15 volts, to keep the shot noise contribution down, and an undegenerated tail source that keeps t he DC output voltage still. The tail source of course has full shot noise, but a BFC on the source/emitter of the DUT gets rid of that adequately. A V FO puts a few microvolts of AC on the input, and an MC1496 doubles as a loc k-in and AGC amp. (I may use something fancier, but I tend to trust BJT mo dels much further than fancier ones.)

At that point I just need a full-wave perfect rectifier (one TL082, a diode , and 2 resistors), and I have a spot noise measurement anyplace I like.

If my MF/HF spectrum analyzer were working, I'd probably do it closer to yo ur way. I have in the back of my mind using this as a production test jig a t some near-future date, and since Beautiful Layout Hunchback is still lear ning electronics, simple setup is worth a lot.

Cheers

Phil Hobbs (Back to the salt mines tomorrow)

Reply to
Phil Hobbs

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