EVAL-ADF4151EB1Z AD [Analog Devices], EVAL-ADF4151EB1Z Datasheet - Page 18

• Manufacturer Part Number: EVAL-ADF4151EB1Z
• Description: Fractional-N/Integer-N PLL Synthesizer
• Manufacturer: AD [Analog Devices]

ADF4151
MUXOUT
The on-chip multiplexer is controlled by Bits[DB28:DB26] (see
Figure 21).
Reference Doubler
Setting DB25 to 0 feeds the REF
R counter, disabling the doubler. Setting this bit to 1 multiplies
the REF
10-bit R counter. When the doubler is disabled, the REF
falling edge is the active edge at the PFD input to the fractional
synthesizer. When the doubler is enabled, both the rising and
falling edges of REF
When the doubler is enabled and the lowest spur mode is
chosen, the in-band phase noise performance is sensitive to the
REF
as 5 dB for the REF
The phase noise is insensitive to the REFIN duty cycle in the
lowest noise mode. The phase noise is insensitive to the REF
duty cycle when the doubler is disabled.
When the doubler is enabled, the maximum allowable REF
frequency is 30 MHz.
RDIV2
Setting the DB24 bit to 1 inserts a divide-by-2 toggle flip-flop
between the R counter and PFD, which extends the maximum
REFIN input rate. This function allows a 50% duty cycle signal
to appear at the PFD input, which is necessary for cycle slip
reduction.
10-Bit R Counter
The 10-bit R counter allows the input reference frequency
(REF
the PFD. Division ratios from 1 to 1023 are allowed.
Current Setting
Bits[DB12:DB9] set the charge pump current setting. This
should be set to the charge pump current that the loop filter
is designed with (see Figure 21).
LDF
Setting DB8 to 1 enables integer-N digital lock detect, when
the FRAC part of the divider is zero; setting DB8 to 0 enables
fractional-N digital lock detect.
IN
IN
duty cycle. The phase noise degradation can be as much
) to be divided down to produce the reference clock to
IN
frequency by a factor of 2 before feeding into the
IN
IN
duty cycles outside a 45% to 55% range.
become active edges at the PFD input.
IN
signal directly to the 10-bit
IN
IN
IN
Rev. B | Page 18 of 28
Lock Detect Precision (LDP)
When DB7 is set to 0, the fractional-N digital lock detect is
activated. In this case after setting DB7 to 0, 40 consecutive PFD
cycles of 10 ns must occur before digital lock detect is set. When
DB7 is programmed to 1, 40 consecutive reference cycles of 6 ns
must occur before digital lock detect goes high. Setting DB8
(LDF) to 1 causes the activation of the integer-N digital lock
detect. In this case, after setting DB7 (LDP) to 0, five
consecutive cycles of 10 ns must occur before digital lock detect
is set. When DB7 is set to 1, five consecutive cycles of 6 ns must
occur. Recommended settings of both the LDP and LDF bits are
shown in Table 6.
Table 6. Recommended LDF/LDP Bit Settings
Mode
Integer-N
Fractional-N Low Noise Mode
Fractional-N Low Spur Mode
Phase Detector Polarity
DB6 sets the phase detector polarity. When a passive loop filter
or noninverting active loop filter is used, set this bit to 1. If an
active filter with an inverting characteristic is used, this bit
should be set to 0.
Power-Down (PD)
DB5 provides the programmable power-down mode. Setting this
bit to 1 performs a power-down. Setting this bit to 0 returns the
synthesizer to normal operation. When in software power-down
mode, the part retains all information in its registers. Only if the
supply voltages are removed are the register contents lost.
When a power-down is activated, the following events occur:
•
•
•
•
•
Charge Pump (CP) Three-State
DB4 puts the charge pump into three-state mode when
programmed to 1. It should be set to 0 for normal operation.
Counter Reset
DB3 is the R counter and N counter reset bit for the ADF4151.
When this bit is 1, the RF synthesizer N counter and R counter
are held in reset. For normal operation, this bit should be set to 0.
The synthesizer counters are forced to their load state
conditions.
The charge pump is forced into three-state mode.
The digital lock detect circuitry is reset.
The RF
The input register remains active and capable of loading
and latching data.
OUT
buffers are disabled.
Data Sheet
DB8
(LDF)
1
0
0
DB7
(LDP)
1
1
0