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CHAPTER 13 PLL FREQUENCY SYNTHESIZER
User’s Manual U15104EJ2V0UD
Figure 13-7. Configuration of Reference Frequency Generator
(3) Operation of phase comparator (
φ
-DET)
Figure 13-8 shows the configuration of the phase comparator (
φ
-DET), charge pump, and unlock F/F.
The phase comparator (
φ
-DET) compares the phase of the divided frequency f
N
of the programmable divider
with that of the reference frequency f
r
of the reference frequency generator, and outputs an up request signal,
UP, or a down request signal, DW.
If the divided frequency f
N
is lower than the reference frequency f
r
, the up request signal is output. If f
N
is higher
than f
r
, the down request signal is output.
Figure 13-9 shows the relation among reference frequency f
r
, divided frequency f
N
, up request signal UP, and
down request signal DW.
When the PLL is disabled, neither the up nor the down request signal is output.
The up and down request signals are input to the charge pump and unlock F/F.
Figure 13-8. Configuration of Phase Comparator, Charge Pump, and Unlock F/F
PLLRF3 to PLLRF0
4-16 decoder
Divider
4.5 MHz
MUX
1 kHz
3 kHz
9 kHz
25 kHz
50 kHz
PLL disable signal
f
r
To -DET
φ
f
N
EO1
PLLUL
Unlock F/F
Charge pump
EO0
PLL disable signal
f
r
UP
Reference frequency
generator
Programmable
divider
DW
Phase
comparator
( -DET)
φ