227
µ
PD17062
Fig. 18-6 Relationship among f
r
, f
N
, UP, and DW Signals
(1) When f
N
is lagging behind f
r
(2) When f
N
is leading f
r
(3) When f
N
is in phase with f
r
(4) When f
N
is lower than f
r
f
r
f
N
UP
DW
“H”
f
r
f
N
UP
DW
“H”
f
r
f
N
UP
DW
“H”
“H”
f
r
f
N
UP
DW
“H”