If one performs a more detailed analysis, a good approximation for the output resistance should be:
(rb2/beta2) + re2 + (1/gm2) + ESR
I don't know the parasitic resistances of the transistor, unfortunately, so I'm forced to guess. But a good RF transistor should not have large base resistances. I'll make up a number, 25 ohms, which is higher than I think is reasonable, partly to compensate for neglecting Q1's contribution to the base resistance of Q2 (a few ohms). For beta2, I'll use the universal guess of 100, so the first term contributes 0.25 ohms. You can substitute your own values in the equation above.
The parasitic emitter resistance should similarly be small; I'll conservatively guess 0.25 ohms for the 2N5109. The actual value is likely half that.
At a current of 84mA, 1/gm2 is around 0.3 ohms.
You measured a capacitor ESR of 0.26 ohms, so adding up all the terms gives us a grand total of an ohm or so. Closer to your measured value, but...
--Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
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On 9/17/2022 00:01, Tom Lee wrote:
And the polarity of the input cap, too, of course...
