AW: more frequency tracking..

Haible Juergen Juergen.Haible at nbgm.siemens.de
Thu Jul 2 11:23:22 CEST 1998


	>The idea of using PLL to have a VCO track along isn't new, the Moog
921
	>oscillators have a PLL mode.

Great surprise for me. Guess I have to look at these schemos again ...

	>A first degree is pretty useless for most applications, it has no
loop
	>filter and will make abrupt jumps and has no memory what so
	>ever. Whenever there is a phase difference it will cause a jump on
the
	>output, not very neat.

I have to disagree with "pretty useless", because I worked with
the first degree PLL in my diploma thesis (I hope this is the right
word), and this PLL made a hell of a good demodulator for
FM radio. BTW, it can be shown that the schmitt trigger / integrator
triangle / square oscillator that is widely used in LFOs will
act as 1st order zero crossing PLL when you add one more resistor
to the integrator input summing node and use this to feed in your
signal. The ratio between the two resistors will then set the
hold range of the PLL. I mention this, because I remember seeing
a similar circuit in Buchla's famous noise and random module,
but I may be wrong here. (Have to look again.)
As for no memory: If there is a pole, there must be some memory,
and while there is no capacitor in the (nonexisting) loop filter, there
is surely one in the VCO.

So I couldn't resist to comment here. Great post, nevertheless!

JH.




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