R
[email protected]
- Jan 1, 1970
- 0
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
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