ADF4116 datasheet(10/20 Pages) AD

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ADF4116/ADF4117/ADF4118

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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 24 is a simpliﬁed schematic.

The PFD includes a ﬁxed delay element which sets the width of

the antibacklash pulse. This 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.

DELAY

CLR1

DOWN

CLR2

N DIVIDER

R DIVIDER

CHARGE

PUMP

CP GND

R DIVIDER

CP OUTPUT

N DIVIDER

Figure 24. PFD Simpliﬁed Schematic and Timing (In Lock)

MUXOUT AND LOCK DETECT

The output multiplexer on the ADF4116 family allows the

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

MUXOUT is controlled by M3, M2 and M1 in the function

latch. Table VI shows the full truth table. Figure 25 shows the

MUXOUT section in block diagram form.

CONTROL

MUX

DVDD

MUXOUT

DGND

ANALOG LOCK DETECT

DIGITAL LOCK DETECT

R COUNTER OUTPUT

N COUNTER OUTPUT

SDOUT

Figure 25. MUXOUT Circuit

Lock Detect

MUXOUT can be programmed for two types of lock detect:

Digital Lock Detect and Analog Lock Detect.

Digital Lock Detect is active high. It is set high when the phase

error on three consecutive phase detector cycles is less than 15 ns.

It will stay set high until a phase error of greater than 25 ns is

detected on any subsequent PD cycle.

The N-channel open-drain analog lock detect should be oper-

ated with an external pull-up resistor of 10 k

Ω nominal. When

lock has been detected it is high with narrow low-going pulses.

INPUT SHIFT REGISTER

The ADF4116 family digital section includes a 21-bit input shift

a 5-bit A counter and a 13-bit B counter. Data is clocked into

the 21-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, C1)

in the shift register. These are the two LSBs DB1, DB0 as

shown in the timing diagram of Figure 1. The truth table for

these bits is shown in Table VII. Table II shows a summary

of how the latches are programmed.

Table II. C2, C1 Truth Table

Control Bits

Data Latch

R Counter

N Counter (A and B)

Function Latch

Initialization Latch

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