[sdiy] 74HC4046 spec -- Thanks

[Magnus Danielson]

From: "Czech Martin" <Martin.Czech at Micronas.com>
Subject: RE: [sdiy] 74HC4046 spec -- Thanks
Date: Fri, 16 May 2003 09:32:29 +0200

> yes , the zener diode is gone, of course there is no process option
> for this any more.
> Good use of an otherwise nc pin.
> 
> In case that you want to pull a signal out of the noise:
> I guess a multiplier is more suitable as phase comparator
> in this case.

It is. The state-machine phase/frequency detectors handle noise very very
badly. If you use the XOR-gate you should know that noise evens it out towards
a multiplier since overtones of the triangle responce gets more and more
evened out as the signal to noise ratio gets lower and lower. This have prisine
effects such as different hold-range etc. If the signal to noise ratio changes
you have a very bad situation since then that would modulate the properties.
Better to go for a real 4-quadrant multiplier straight away. When you have a
digital output of the VCO, an analog mux and some sort of inverting summer
could work as an approximate if one things it is cheaper.

I would also like to point out that Philips have two further developments of
the 4046 PLL chip, both worthy of consideration. They are 74HC7046 and 74HC9046
and they have improved properties. Even if you go with 4046 or 74HC4046 you
should look the these datasheets to widen your knowledge.

Both the Best and Wolaver books should be good introductionary books on PLLs.

Cheers,
Magnus