ADF4158 datasheet(11/36 Pages) AD

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ADF4158

Rev. 0 | Page 11 of 36

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 18 shows a simplified sche-

matic of the PFD. 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.

CLR2

DOWN

HIGH

–IN

+IN

CHARGE

PUMP

DELAY

CLR1

Figure 18. PFD Simplified Schematic

MUXOUT AND LOCK DETECT

The output multiplexer on the ADF4158 allows the user

to access various internal points on the chip. The state of

MUXOUT is controlled by the M4, M3, M2, and M1 bits

(see Figure 22). Figure 19 shows the MUXOUT section in

block diagram form.

MUXOUT

DVDD

THREE-STATE OUTPUT

N-DIVIDER OUTPUT

DVDD

DGND

R-DIVIDER OUTPUT

DIGITAL LOCK DETECT

SERIAL DATA OUTPUT

CLK DIVIDER OUTPUT

R-DIVIDER/2

N-DIVIDER/2

CONTROL

MUX

Figure 19. MUXOUT Schematic

INPUT SHIFT REGISTERS

The ADF4158 digital section includes a 5-bit RF R-counter,

a 12-bit RF N-counter, and a 25-bit FRAC counter. Data is

clocked into the 32-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 eight latches on the rising edge

of LE. The destination latch is determined by the state of the

three control bits (C3, C2, and C1) in the shift register. These

are the three LSBs—DB2, DB1, and DB0—as shown in Figure 2.

The truth table for these bits is shown in Table 6. Figure 20 and

Figure 21 show a summary of how the latches are programmed.

PROGRAM MODES

Table 6 and Figure 22 through Figure 29 show how to set up

the program modes in the ADF4158.

Several settings in the ADF4158 are double buffered. These

include the LSB fractional value, R-counter value, reference

doubler, current setting, and RDIV2. This means that two

events must occur before the part uses a new value for any

of the double-buffered settings. First, the new value is latched

into the device by writing to the appropriate register. Second,

a new write must be performed on Register R0.

For example, updating the fractional value can involve a write

to the 13 LSB bits in R1 and the 12 MSB bits in R0. R1 should

be written to first, followed by the write to R0. The frequency

change begins after the write to R0. Double buffering ensures

that the bits written to in R1 do not take effect until after

the write to R0.

Table 6. C3, C2, and C1 Truth Table

Control Bits

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