Here it is:
http://www.radiolab.com.au/DesignFile/dn003.pdf
The "PLL Widget" they describe here:
http://www.radiolab.com.au/DesignFile/dn002.pdf
They claim this widget can be replaced with a simple resistor
that is higher impedance than the output of the loop filter.
But it seems to me that the loop is still closed in this case,
unless the resistor is extremely high.
It appears they keep the VCO in lock (closed loop),
and add a perturbation between loop filter and VCO, and
measure the amplitude and phase shift.
All the literature i have seen refers to the Open loop bode
response, typically G(s)H(s), in terms of calculating
the phase margin.
On the other hand, it seems like keeping the VCO in lock
is the only practical way to do this.
Slick
http://www.radiolab.com.au/DesignFile/dn003.pdf
The "PLL Widget" they describe here:
http://www.radiolab.com.au/DesignFile/dn002.pdf
They claim this widget can be replaced with a simple resistor
that is higher impedance than the output of the loop filter.
But it seems to me that the loop is still closed in this case,
unless the resistor is extremely high.
It appears they keep the VCO in lock (closed loop),
and add a perturbation between loop filter and VCO, and
measure the amplitude and phase shift.
All the literature i have seen refers to the Open loop bode
response, typically G(s)H(s), in terms of calculating
the phase margin.
On the other hand, it seems like keeping the VCO in lock
is the only practical way to do this.
Slick