Re: Current mirror version of the lowish distortion 1kHz sine wave osillator

"Edward Rawde" <invalid@invalid.invalid> wrote in message news:vmmdff$10ii$1@nnrp.usenet.blueworldhosting.com...

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmlpii$364is$7@dont-email.me...

On 15/01/2025 11:33 pm, Bill Sloman wrote:

This just reworks my circuit to use a controllable asymmetric current mirror instead of the FET for gain control. I take the
feedback from the full wave rectifier and switch every half-cycle to reconstruct a variable amplitude sine wave to control the
output amplitude. It does use a lot of components, but it strikes me as fairly comprehensible.
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R30 isn't a real part - it's just there to let me do an FFT on the correction signal.
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The circuit just copes with worst case capacitors - 15.15nF and 14.85nF - at C5 and C6, as it was intended to do. Using a trim
pot to take out component tolerances would let you get away with a smaller correction signal injecting smaller doses of the odd
harmonics.
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The circuit does cry out for monolithic dual transisors.The On-Semi
NST45010MW6T1G pnp and the
NST45011MW6T1G npn parts are cheap and widely available.

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There was a dumb error in the original circuit. The two transistor switch (Q5 and Q6 in the original circuit) that turned the
full wave rectified waveform back into a sine wave was set up with very little headroom. It didn't stop the circuit from working
as intended after it had settled down, but it made start-up a bit tricky.
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Here's the corrected version. It's performance isn't noticeably differ
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Check simulation at 180 ms
raw file is now 32 GB
FFT on a few cycles (approx 1V pk-pk) with blackman harris windows shows 80dB down at 3kHz.
Stop simulation.