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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: 1kHz sinewave -153 dB
Date: Sat, 10 May 2025 00:35:23 -0400
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In case anyone is interested (and I know most people aren't but at least it's on topic) this circuit has the following features.

1. Almost constant output level from startup. It does take time to fully stabilize (about 40 seconds) but during that time the peak 
output level only changes by 60mV.

2. An FFT on the last 6 seconds with Blackman-Harris window shows 2kHz at -153 dB

Performance can probably be improved further with fine adjustment of some component values.
Any suggestions for further improvement (whether for lower cost or better performance) are welcome.

JM mentioned some time ago that adding buffers for the rectifier phases would improve performance. He wasn't wrong but the ones used 
here may be overkill. If you know of a cheaper buffer which will do the same job please let me know.

It won't be cheap to build, if it's ever built. I'd expect test equipment to cost a lot more, assuming equipment exists which can 
measure at 153 dB down.

LTSpice 24.1.8 with all component updates (9th May 2025) was used for this simulation.

This circuit only exists in an LTSpice simulation. Reality may be different.

If you want to simulate the full 60 seconds then you probably want to run it overnight.

My next move will be to move this circuit to QSpice. I'll have to use generic op amps but it will be interesting to get familiar 
with QSpice. Does anyone know of any suitable op amp and/or buffer models I can import into QSpice?

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