Hi,
Ok, so i've simulated my loop filter (active Op-amp, integrator) in ADS, complete with split input resistors for improved transient suppression, and i got a phase shift of
+163 degrees at a unity gain frequency of 10Hz. So I add the +90 degrees from the 1/s integration of the VCO, and i get +253 degrees of phase shift open loop, which gives me a phase margin of 73 degrees, if i'm not mistaken. Supposedly 45 degrees is optimum, but higher phase margins are more stable.Which got me to wondering, if the closed loop system instability is dependent on the Barkhausen criteria, and the characteristic equation of the closed loop is of the form: (1+G(s)H(s)), then because of the "+", the Phase Detector must have a 180 degree phase shift.
Do all phase detectors, whether XOR or phase/frequency, have this
180 degree phase shift inherently built-in?Thanks in advance!
Slick