Datasheet
REV. B–12–
ADF4252
Phase Frequency Detector (PFD) and Charge Pump
The PFD takes inputs from the R counter and N counter and
produces an output proportional to the phase and frequency
difference between them. Figure 6 is a simplified schematic. The
antibacklash pulse. This pulse ensures that there is no dead zone
in the PFD transfer function and minimizes phase noise and
reference spurs.
+IN
D1
Q1
CLR1
U1
U3
DELAY
ELEMENT
HI
UP
D2
Q2
CLR2
U2
HI
DOWN
CHARGE
PUMP
CP
–IN
Figure 6. PFD Simplified Schematic
MUXOUT and Lock Detect
The output multiplexer on the ADF4252 allows the user to
access various internal points on the chip. The state of MUXOUT
is controlled by M4, M3, M2, and M1 in the master register.
Table I shows the full truth table. Figure 7 shows the MUXOUT
section in block diagram format.
LOGIC LOW
IF ANALOG LOCK DETECT
IF R DIVIDER OUTPUT
IF N DIVIDER OUTPUT
RF ANALOG LOCK DETECT
IF/RF ANALOG LOCK DETECT
IF DIGITAL LOCK DETECT
LOGIC HIGH
RF R DIVIDER OUTPUT
RF N DIVIDER OUTPUT
THREE STATE OUTPUT
RF DIGITAL LOCK DETECT
RF/IF DIGITAL LOCK DETECT
LOGIC HIGH
LOGIC LOW
MUX CONTROL
MUXOUT
DV
DD
D
GND
Figure 7. MUXOUT Circuit
Lock Detect
MUXOUT can be programmed for two types of lock detect: digital
and analog. Digital is active high. The N-channel open-drain
analog lock detect should be operated with an external pull-up
resistor of 10 kΩ nominal. When lock has been detected, this
output will be high with narrow low going pulses.
Input Shift Register
Data is clocked in on each rising edge of CLK. The data is
clocked in MSB first. Data is transferred from the input register
to one of seven latches on the rising edge of LE. The destination
latch is determined by the state of the three control bits (C2, C1,
and C0) in the shift register. These are the three LSBs: DB2,
DB1, and DB0, as shown in Figure 1. The truth table for these
bits is shown in Table I. Table II summarizes how the registers
are programmed.
Table I. Control Bit Truth Table
C2 C1 C0 Data Latch
000 RF N Divider Reg
001 RF R Divider Reg
010 RF Control Reg
011 Master Reg
100 IF N Divider Reg
101 IF R Divider Reg
110 IF Control Reg