[time-nuts] Count up/down DAC circuit

[SAIDJACK at aol.com]

Hi Steve,
 
I played with such a circuit a long time ago.
 
The slope is limited to the clocking of your circuit (one LSB digit per  
clock typ), which can present an issue if you cannot follow the OCXO's EFC  
changes fast enough. You could be chasing the OCXO voltage and this may lead to  
instability.
 
Even if it is "locked", the circuit will constantly be "chasing" the OCXO,  
unless you implement a dead-zone where the circuit stops counting up/down when  
you are close enough to your target frequency.
 
This chasing may cause the frequency to modulate up and down, and could  lead 
to large-scale oscillations.
 
Tough to get this to work properly, but with circuitry to add a deadzone,  
and to dampen the lock, and maybe to introduce gain (jump more than one LSB when 
 far off etc) it may work. Then again implementing a standard PI controller 
(in a  micro etc), and calculating it's stability etc is much easier than 
getting this  to work properly.
 
bye,
Said
 
 
In a message dated 12/29/2008 21:30:54 Pacific Standard Time,  
sar10538 at gmail.com writes:

As part  of the current idea I have with the hockey-pucks, I'm thinking
about  feeding the D1 and U1 phase difference pulses out of an MC4044
out to some  circuit that could clock up and down an analog output
which would  ultimately go to the EFC of a ocxo, IE D1 pulses when the
phase of one  input signal is advanced and visa versa for the U1 pin.
Anyone seen a  circuit like that please?

Thanks & 73, Steve
-- 
Steve Rooke  - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis  imminet

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