[time-nuts] Micro phase stepper

David Forbes dforbes at dakotacom.net
Mon Jul 18 11:40:19 EDT 2005

Ulrich Bangert wrote:
> Hi Folks,
> can someone please explain to me how a micro phase stepper works? Is it
> a pure digital device or does it make use of analog delay line
> techniques? What is the maximum delay and what is the delay step size?
> Thanks in advance for your help
> Ulrich Bangert, DF6JB

The common way to make a finely adjustable delay is to generate a fast 
ramp with an integrator (which must be a very low impedance device at 
nanosecond speeds) and trigger a comparator using a reference voltage 
generated by a high-resolution DAC. The comparator output is the 
digital output of this analog system.

The range of adjustment is the time of the ramp, and the resolution is 
the ramp time divided by the counts of the DAC (2^nbits). Note that 
the DAC provides a DC voltage, so it doesn't have to be high speed.

Considering that nanosecond rise times and 16 bit DACs are readily 
available these days, it's possible to obtain femtosecond resolution 
in this way.

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