Your analysis is spot on (well done for an FPGA designer!); it's the same as that in my first post, although I used 100 for beta of both transistors. In any case, the intrinsic output impedance is very low. The actual output impedance will be dominated by parasitic resistances. For the 2N5109, I would guess emitter resistances of a few hundred milliohms. That would be in series with whatever ESR the output cap possesses. Overall, I would expect something under an ohm. Measurements much greater than that would lead me to check the capacitor, wiring parasitics, and VNA cal.
--Tom
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Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
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On 9/16/2022 22:04, John Kolb wrote:
Googling Output resistance of an emitter follower, I find it's input resistance divided by (Beta + 1) plus some other factors, internal emitter resistance of Q2, etc, that I as a FPGA designer couldn't understand. Beta of a darling configuration is the beta of Q1 times beta of Q2. 50 ohm Rin (R1, R2, R3 in parallel) /(100 (beta of Q1) * 30 (beta of Q2)) would be 0.018 ohms.? Beta numbers are SWAG.? Would a real analog engineer speak up here?? At any rate, the output resistance would seem to be much lower than R5, 220 ohms, or 75 ohms, R1 of transformer.
Would really like to read the complete manual for the 4342A.
