[time-nuts] Micro phase stepper
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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