Future of BSS83? Alternatives?

Joerg · 2006-03-08T00:11:34+00:00

Hello Folks,Looking for a "wimpy" discrete n-channel FET for an adjustable phase shifter. The Philips BSS83 would be the ticket. This is not the Infineon BSS83PE which is p-channel and larger die. Although it hails from the early 90's it's still above 20c (ouch...) and it is on back order at a few places. Digikey still has a few thousand but these can be gone in one big slurp.Do you guys think it might be on the way to lala-land or will it stay? A price that doesn't want to come down to jelly bean level always make me uneasy. Ok, this might be like asking for a weather forecast for May so let me also pose the question about alternatives. Are there some nice FETs in the 50-100ohm RDSon class? Preferable not any hot stuff such as the UHF dual-gate tetrodes and it doesn't have to have a separate pin for the substrate.I used to do this stuff with SD5400 but these have become rather pricey and rare.And Jim: No, I can't roll my own here...Regards, Joerg

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Joerg 20 years ago

Hello Fred,

The series element in my case is an inductor.

A varicap is certainly an option. However, in most practical apps it's tough since these need >10V variation to get some decent range out of them. Most digital modules don't have more than 3.3V these days and no negative rail either. That was so cool in the days of the old RAM chips where you always had a -10V to -15V rail. Tomorrow I am going to try it out with PIN diodes. Should work and they are much less expensive than a BSS83. Plus more suppliers.

Regards, Joerg

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Tim Wescott 20 years ago

Hence my suggestion to look at P-channel JFETs. With the source and drain close to ground potential a ground at the gate turns it on as much is it's going to get (100-ish ohms for a J174 -- right in your ballpark, right?). Bringing the gate positive turns things off.

J174 and xxx5460 are a dime apiece at DigiKey as long as you buy scads of them.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/

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Joerg 20 years ago

Hello Tim,

They are cheap and plentiful but the JFET would have to hang on the signal line with its source. Since this signal swings between VCC and GND it'll become forward biased at times which would not be too cool.

Regards, Joerg

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Jim Thompson 20 years ago

Analog signal or digital?

...Jim Thompson

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Joerg 20 years ago

Hello Jim,

It's a digital clock line, clocking an ADC so it is rather noise sensitive.

Regards, Joerg

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Jim Thompson 20 years ago

Why are you using variable-R? Use current mirrors. I posted a simplistic sample a while back that was designed for heavy noise rejection.

...Jim Thompson

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Joerg 20 years ago

Hello Jim,

Do you remember what the topic was or which month? Then I could search it up, assuming it was on a.b.s.e.

Anyway, this is rather fast stuff and for a publication, not actual work. But the instances in which this needs to be used require high speed. Clocks in the 100MHz range and slopes around a nsec. It's the "actuator" in a larger scheme.

What I want to do is present something that is simple enough and doesn't send the digital guys scurrying. The PIN diode variety is another option but when you start explaining carrier lifetimes that is probably like trying to teach me how to read sheet music (done that, didn't get it, wife said it's hopeless...). And the RF tank circuit stuff I sometimes do would really scare them off.

Regards, Joerg

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Jim Thompson 20 years ago

I'm twiddling here late tonight... "N" is out to Girl Scout Service Team meeting ;-)

What are you trying to do... variable delay?

I did a DLL (delay-locked loop) for the Cray descendants some years ago.

...Jim Thompson

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Joerg 20 years ago

Hello Jim,

That's a good thing to do for our youth.

Yes, but no more than a nanosecond or two.

I did that as well with resonant circuits and varicaps and stuff but I'd like to keep this one simple. It used to work like a champ with SD series arrays but they aren't mainstream items anymore and cost is shooting up.

Regards, Joerg

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