Imput impedance of common emitter amplifier at RF frequencies

Jfets are terrible diodes. Lots of series resistance, lots of capacitance, a relative lot of reverse leakage. The c-b junction of a cheap RF transistor is a vastly better diode.

That's nice, 24 volts and 10 GHz. The pinout is bizarre.

The RF PNP situation remains grim.

"That's the joke"

They make OK zener didoes in a pinch

Some people don't get the joke:

That's ah spicy-ah meat-ah ball!

$13 is a lot to pay for a forward voltage spec of: ah, it's, eh. whatever

I'm doing a front end for a tiled MPPC (silicon PMT) that needs 40 MHz bandwidth and has a capacitance of 700 pF. I'm going to use a SAV-551+ bootstrap, but Mini Circuits doesn't have a SPICE model for it, so I used the one for the ATF38143 of fond memory.

I can calculate the noise easily, but just for grins I did a SPICE .noise run. The pHEMT, running at 10 mA from a 4V supply, allegedly will produce 74.2 kV RMS noise. I'm rich!

Cheers

Phil Hobbs

Is LTSpice able to run monte carlos yet? I haven't had cause to use it for about 2 years now.

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NT

Free energy. Make a Youtube video.

Look at "MonteCarlo.asc" in the Educational folder.

My guys run MC sims in LT Spice. I don't think it can frob the parameters internal to a device model, like Idss. Can it?

Looks like these are not discontinued but they'll make them for you if you order a bunch:

Yes. You go .model myfet ako:BF862 Idss=5mA

or .model myfet ako:BF862 Idss={Id_at_zero_bias} .step param Id_at_zero_bias list 8m 12m 17m

Cheers

Phil Hobbs

Yes, I have tried the simple formula S11 = (Zin - Z0)/(Zin + Z0), assuming a standard RF Z0=50.0 Ohm, for listed S parameter freqeuncies. for non-listed frequencies, the small signal S parameters can be obtained via SPICE .AC analysis.

For new breed of RF transistors as HFA3134, small signal S parameters are not provided, and only the detailed SPICE model is available.

So true. I have spent hours and hours digging out SPICE models for RF transistors, online.