[sdiy] square to sine

Neil Johnson neil.johnson97 at ntlworld.com
Thu Oct 11 04:38:46 CEST 2012


cheater cheater wrote:
> Dave, I'm going out on a limb here, but this reminds me of a technique
> normally used for asynchronous sample rate conversion, which is
> "flywheel sync".

"flywheel synchronisation" was an early term for the then-new
technique of PLL as used in British TV sets:


and later used for the 4.something MHz colour burst.

A blast from the past: BBC R&D report from 1969 talks about flywheel


The diagram on page 2 of the report is a PLL.

> Basically, you have a model of a flywheel - with
> torque and friction - and each rotation of it is one output wave
> cycle. As clocks come in, you give the flywheel a "push" or "jolt". If
> the jolts stop coming in, the flywheel stops eventually. If they come
> in at a lower frequency, the flywheel spins slower. If you rapidly
> lower the frequency, you can add some friction (for example, friction
> gets -df/dt added to it). It is normally used to prevent jitter, but
> can also be used for syncing two different waveforms together.

You're talking about the characteristics of the various components of
the PLL (vco, phase detector, loop filter, etc).

Modules and more: http://www.cesyg.com
Homepage: http://www.njohnson.co.uk

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