[HomeBrew] Pll Idea, needs sanity check

[Matt Burns]

Hi All,

I was helping a friend who was doing some work on a late 70's cb pll circuit
when I came up with an idea for a 1 kHz stepping pll.  I've never designed a
pll before so any suggestions, comments, etc are appreciated.

The pll will use 74hc4017's for the high frequency divisions, cd4017's for
the low frequency divisions, a cd4046 for the phase comparator, and discrete
components for the vco, reference osc, loop filter, divider switching, etc.

The basic concept is the same as any other pll, the only difference is that
I want to use decade counters rather than binary counters.  This will up the
parts count but will make understanding, controlling, and troubleshooting a
lot easier.

So here's the idea: I'll start with a crystal oscillator running at 6 MHz,
divide by 6000 to get 1000 Hz (6M/6/10/10/10=1000) and feed this to one
input of the phase comparator (PC), the output of the PC goes through the
loop filter (I still need to work out values for the loop filter) the output
of the loop filter goes to a well shielded colpitts vco (or a switched array
of vco's for different bands).  The output of the vco goes through a sort of
buffer into a decade divider chain, this divider runs constantly and divides
by 10 for 4 stages (Fvco/10, /100, /1000, /10000).

Connected to the output of the buffer and each divider stage is a decade
counter which can be set to a "count to" value to control the frequency. The
"Count to" output of the counter on the slowest stage (Fvco/10000) will be
used to enable the next counter, this goes on until the fastest counter
(Fvco) reaches it's "count to" value, pulses the other input to the PC, and
resets the counters.

This should divide Fvco by Fout in kHz (the desired frequency/1000) and
yield a 1000 Hz signal to the PC when the vco reaches the frequency in kHz
selected by the "count to" values of each counter.

For adjustments smaller than 1kHz the crystal in the 6 MHz reference osc
could be pulled a little bit in either direction or an additional divider +
counter could be added.

Does this make any sense? Or am I missing something? If it would help I
could draw out the block diagram in mspaint.

Thanks,
Matt Burns
kc8com