jfet

Looks like a CPH3910 selected for high I_DSS.

Nice part--it's about 1 dB quieter than a BF862 in my typical applications, but doesn't like to run at I_DSS, which complicates some things.

Cheers

Phil Hobbs

"High Breakdown Voltage" ... WRT 5V? Make a JFET with 40V (or more) breakdown, then and only ten that would be meaningful. AFAIK they all are rated at 5V, so "High Breakdown Voltage" is BS.

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It's intended for a +12V supply environment. No BS.

..... Phil

Does it make a good diode?

It's also intended as a first-RF antenna amplifier for an automotive antenna - they claim it has high ESD protection. I don't see how though.

Clifford Heath.

Jfets have impact ionization excess gate current above a few volts on the drain, so it's best to run them at a low voltage. Cascode with a bipolar if needed.

Not especially. Lots of capacitance, lots of series resistance, and probably more leakage than other options.

That makes it easy to bootstrap away C_dg as well. I like to run them at about 2-3V D-S.

Cheers

Phil Hobbs

Idss looks like about 35 mA. Is that a problem?

Does noise figure translate directly to nv/rthz? You never know what sort of tuned circuit they may have used.

The noise bottoms out around 10 mA, increasing gently between there and I_DSS. So ine is constantly running them with V_GS ~ -500 mV. On the plus side, the noise minimum and the zero-TC point aren't that far apart.

Their e_N is about 0.7 nV.

Cheers

Phil Hobbs

Noise figure is usually specified relative to a specified source impedance... dB's relative to the source noise. ...Jim Thompson

That one was introduced a while ago. Did you find them featuring it someplace?

Right, but I didn't see that impedance specified. And sometimes there's a tuned network that optimizes the match.

I was just prowling the "new product" pages of various semi companies. I do that now and then to see what's happening.

The electronics mags are literally disappearing, approaching see-through, so one has to do other things to keep up.

Digikey has a periodic new products mailing that is nice.

Thank you *so* much for that, John. As a lapsed Catholic, I'd simply despaired of this world up until reading your post.

What do you know, the SPICE model includes package parasitics.

It's not clear what they're measuring noise figure on. It's not the AM preamp circuit, that's for sure (which, speaking of, is clearly made with a very poor match: s11 is near 0dB across the band, so could be greatly improved).

Tim

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