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In Reply to: Output Z of cathode follower... posted by Lew on September 1, 2011 at 20:51:46:
1/gm is another small signal parameter. gm changes when you move the operating point's position from one place to another. Thus the output impedance must change.
The problem is that most want a single number in ohms for the average, not a graph of the output impedance shifting with phase of an inputted sinewave. The same goes for output power. People want the average power outputted over the full cycle, not a plot of instantaneous power. We know it's a number with large signal distortion involved.
The issue here is: can we calculate and then measure the average integrated impedance over the full cycle at every power level, knowing the larger signals are more distorted? Math can calculate almost anything once you get the idea of a good method.
It's really quite a complex effort, and it would need a DC element input for the large signal Rout=Vout/Iout when stopped there, and then add small signal wiggling sinewaves for the small signal zout at that position. Then move around 360 degrees in "DC" steps measuring all small signal output impedances at those positions. Then integrate for a mean value and check the standard deviation while you're at it. This is then the mean Zout with a now known distorted deviation.
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- RE: Output Z of cathode follower... - kurt s 00:42:47 09/02/11 (0)
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