Anders wrote:
I'm looking for a solution for galvanic isolation of a 1PPS signal-input to
a distribution amplifier.
* * *
Does anyone have experience with a circuit with good rise-time and low
jitter?
Sometimes the simplest solutions can be best. In this case, capacitive
coupling of the source into the load may be appropriate (see attached
diagram).
If the two chassis can be connected safely, all you need is to
cap-couple the signal line (upper diagram). While there may still be a
ground loop between the two chassis, it will not affect the PPS signal
because the small capacitor used to couple the signal line (probably
around 100pF, depending on the load impedance and the PPS pulse width)
will not carry any significant current at line and line harmonic
frequencies.
If the two chassis cannot be connected safely, then cap-couple the
common line as well (lower diagram). The common cap must be rated for
the maximum possible voltage between the two chassis. The two caps
should have approximately the same value.
The capacitive isolation can be at either end (source or load). I
prefer putting the AC coupling at the source end, so the interconnect
cable is shielded at all frequencies to the load.
This scheme will only work if the PPS output is robust enough to drive
the load impedance without further buffering. Also, there is no DC
reference at the load end. This may not be a problem if the PPS pulse
is short (tens of uS). Just make sure there is a DC path to ground on
the signal line (input termination resistor). Otherwise, you would need
to use a clamp to DC-restore the PPS signal.
Best regards,
Charles
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