Am 29.03.2016 um 16:53 schrieb Charles Steinmetz:
(10) Phase_detector_with_low_flicker_noise_BARNES_etal_NIST_2011:
Describes a DIY double-balanced mixer phase detector using
diode-connected 2N2222 transistors. [Note that only the flicker noise
is improved -- the white noise floor is actually significantly higher
than with DBMs using diodes. NB: There are much better transistors
than the 2N2222 for this application.]
.. and they are NOT really used as diodes. They are used as switching
transistors with most current flow C-E, saturation enforced.
That turns faster on than the diode exp-law.
Somewhere they also say that they use 50 Ohm load.
I really wonder where all that ring mixer noise is to come from. The
diodes are just switches, the transformers
have close to no loss and behave properly in power dividers, and even
when the diodes are resistors for a moment,
their noise is only half-thermal.
I find it easy to believe that high power mixers produce more noise. In
that app note by Watkins-Johnson that everybody copies,
there it is clearly shown that they may use resistors to generate bias
voltages.
If I use two 1:4 Wilkinsons, 4 low power ring mixers and put the outputs
in series, will it also turn worse? I don't think so.
Are there anywhere musings about the equivalent noise resistance of a
ring mixer IF output?
If it is really something like 500 Ohms, even a single AD797 may be
excessively over-optimized
for voltage, and not current noise.
regards, Gerhard
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