adf4153 Analog Devices, Inc., adf4153 Datasheet - Page 9

• Manufacturer Part Number: adf4153
• Description: Fractional-n Frequency Synthesizer
• Manufacturer: Analog Devices, Inc.

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 14 is a simplified schematic of
the phase frequency detector. The PFD includes a fixed delay
element that sets the width of the antibacklash pulse, which is
typically 3 ns. This pulse ensures that there is no dead zone in the
PFD transfer function, and gives a consistent reference spur level.
MUXOUT AND LOCK DETECT
The output multiplexer on the ADF4153 allows the user to
access various internal points on the chip. The state of
MUXOUT is controlled by M3, M2, and M1 (see Table 8).
Figure 15 shows the MUXOUT section in block diagram form.
ANALOG LOCK DETECT
THREE-STATE OUTPUT
DIGITAL LOCK DETECT
R COUNTER OUTPUT
N COUNTER OUTPUT
+IN
–IN
HI
HI
LOGIC HIGH
LOGIC LOW
D2
D1
CLR1
CLR2
U1
U2
Figure 14. PFD Simplified Schematic
Q1
Q2
Figure 15. MUXOUT Schematic
UP
DOWN
DELAY
MUX
U3
CONTROL
CHARGE
PUMP
DGND
DV
DD
MUXOUT
CP
Rev. B | Page 9 of 24
INPUT SHIFT REGISTERS
The ADF4153 digital section includes a 4-bit RF R counter, a
9-bit RF N counter, a 12-bit FRAC counter, and a 12-bit
modulus counter. Data is clocked into the 24-bit shift register
on each rising edge of CLK. The data is clocked in MSB first.
Data is transferred from the shift register to one of four latches
on the rising edge of LE. The destination latch is determined by
the state of the two control bits (C2 and C1) in the shift register.
These are the 2 LSBs, DB1 and DB0, as shown in Figure 2. The
truth table for these bits is shown in Table 5. Table 6 shows a
summary of how the latches are programmed.
PROGRAM MODES
Table 5 through Table 10 show how to set up the program
modes in the ADF4153.
The ADF4153 programmable modulus is double buffered. This
means that two events have to occur before the part uses a new
modulus value. First, the new modulus value is latched into the
device by writing to the R divider register. Second, a new write
must be performed on the N divider register. Therefore, any
time that the modulus value is updated, the N divider register
must be written to after this, to ensure that the modulus value is
loaded correctly.
Table 5. C2 and C1 Truth Table
C2
0
0
1
1
Control Bits
C1
0
1
0
1
Register
N Divider Register
R Divider Register
Control Register
Noise and Spur Register
ADF4153