[time-nuts] Phase Noise Measurement

[Pluess, Tobias]

Dear all,

for a long time I had this project on my todo list. I recently started with
building my own phase noise measurement equipment.
I have a batch of brand new UCT 108663 Oscillators (new old stock
possibly?) and had the possibility to measure them a while ago on a
Keysight E5052B analyser. I now want to make my own PLL + LNA to measure
the oscillators on my own spectrum analyser.
For this, I built the circuit shown in the image. A SRA-1 mixer is used as
phase detector. Since I want to avoid a negative voltage rail, I connected
the IF centre tap to a reference voltage, such that the IF output signal
swings around VCC/2 and not around ground.
The amplifier and integrator are configured in the same way. So far, the
PLL works very nicely. By changing the resistor R3 in the feedback path of
the first amplifier, I can easily adjust the loop bandwidth. Oscillators
stay nicely in quadrature. OK, so far this works.
Now comes the interesting part. The LNA. I would like to use AD797 or
similar (ADA4897 maybe?). I wonder whether it is, from a low noise
viewpoint, possible to use the schematic as shown? I have decoupled VCC/2
with several different capacitors and in theory, this configuration of the
amplifier should work. But will it in practice yield an acceptable result?

I would like to avoid a negative voltage rail if possible, because the
tuning voltage output will need to be positive anyways, and I would like to
avoid any switching converters.

thanks for any hints,
best
Tobias


[image: image.png]
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