ADF4154 Analog Devices, ADF4154 Datasheet - Page 10

• Manufacturer Part Number: ADF4154
• Description: Fractional-n Frequency Synthesizer
• Manufacturer: Analog Devices

ADF4154
MUXOUT AND LOCK DETECT
The output multiplexer on the ADF4154 allows the user to
access various internal points on the chip. The state of
MUXOUT is controlled by M3, M2, and M1 (see Table 9).
Figure 21 shows the MUXOUT section in block diagram form.
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, the lock detect is high with
narrow low-going pulses.
ANALOG LOCK DETECT
INPUT SHIFT REGISTERS
The ADF4154 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.
THREE-STATE OUTPUT
DIGITAL LOCK DETECT
FAST-LOCK CONTROL
R-DIVIDER OUTPUT
N-DIVIDER OUTPUT
LOGIC HIGH
LOGIC LOW
Figure 21. MUXOUT Schematic
MUX
CONTROL
DGND
DV
DD
MUXOUT
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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 ADF4154.
The ADF4154 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, when-
ever the modulus value is updated, the N-divider register must
then be written to so that the modulus value is loaded correctly.
Table 5. C2 and C1 Truth Table
Control Bits
C2
0
0
1
1
0
C1
0
1
1
Data Latch
N-divider register
R-divider register
Control register
Noise and spur register