[time-nuts] DAC resistors

Neville Michie namichie at gmail.com
Tue Oct 6 22:19:25 UTC 2009


Hi,
I am constructing a phase meter to monitor the phase creep of clocks.
It consists of a BCD counter counting say microseconds that has its
count strobed into a latch by a pulse from the clock.
The Latch drives a DAC which drives a pen recorder and an analogue  
data logger.
Now I am familiar with R - 2R networks, and that method is used on  
each decade
but the resistors that combine the decades in a 10:1 ratio are the  
problem.
I have an approximate value, and I will probably have to trim them to  
eliminate
digital errors later.
But I can not find a reference anywhere to how to calculate the correct
resistors or even a working example except for an old Analog Devices
data sheet which seems to use a different structure, by reducing the
supply voltage of each decade.
Can anyone Help?

Cheers, Neville Michie



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