alpacinoliu
Member level 3
when pll bandwidth close to reference frequency,
ZOH(Zero order holding ) effect in PFD must be considered, which bring phase drift in the loop transfer function:
1-exp(-S*Tref)
————————
S*Tref
practical calculation reveal that :
when bandwidth >20*reference frequency, phase drift<4deg
when bandwidth <=10*reference frequency, phase drift>10deg
we can use "continued fraction" to curefit
1-exp(-S*Tref)
————————
S*Tref
to tf in zeros and poles,
which is useful in verilogA in cadence.
if you interested, please see "Pade" in matlab
ZOH(Zero order holding ) effect in PFD must be considered, which bring phase drift in the loop transfer function:
1-exp(-S*Tref)
————————
S*Tref
practical calculation reveal that :
when bandwidth >20*reference frequency, phase drift<4deg
when bandwidth <=10*reference frequency, phase drift>10deg
we can use "continued fraction" to curefit
1-exp(-S*Tref)
————————
S*Tref
to tf in zeros and poles,
which is useful in verilogA in cadence.
if you interested, please see "Pade" in matlab