Much better! I believe those numbers a lot more than the previous ones.
And a low-MHz corner frequency (where the inductive component of the output impedance equals the resistive one) is about where it's expected, too.
A tip of the hat to you for your persistence, Steve.
-- Cheers,
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 11:50, Steve Ratzlaff wrote:
I finally have much better results! The Q1 input transistor makes all the difference. I've been trying various Q1's and have found several that work very well. Low end input impedance is now under one ohm. The same 2N5109 Q2 is used; I haven't tried changing it (Central Semi, DC beta 110). I've been looking at the 1 MHz point for my Q1 comparisons. Best is 1.05 ohms with an obsolete Motorola 2N4401; a metal can BC108B gives 1.07 ohms; a metal can 2N3947 gives 1.10 ohms; an obsolete Motorola PN2222A gives 1.11 ohms.
50 kHz 0.86 ohms input impedance
1 MHz 1.05 ohms
10 MHz 2.93 ohms
20 MHz 5.33 ohms
30 MHz 7.79 ohms
Steve
On 9/17/2022 2:58 AM, Tom Lee wrote:
If one performs a more detailed analysis, a good approximation for the output resistance should be:
(rb2/beta2) + re2 + (1/gm2) + ESR
a grand total of an ohm or so. Closer to your measured value, but...
--Tom
