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ADF4350BCPZ-RL View Datasheet(PDF) - Analog Devices

Part Name
Description
Manufacturer
ADF4350BCPZ-RL
ADI
Analog Devices ADI
ADF4350BCPZ-RL Datasheet PDF : 28 Pages
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CIRCUIT DESCRIPTION
REFERENCE INPUT SECTION
The reference input stage is shown in Figure 16. SW1 and SW2
are normally closed switches. SW3 is normally open. When
power-down is initiated, SW3 is closed, and SW1 and SW2 are
opened. This ensures that there is no loading of the REFIN pin
during power-down.
POWER-DOWN
CONTROL
NC 100k
REFIN NC
SW2
SW1
SW3
NO
TO R COUNTER
BUFFER
Figure 16. Reference Input Stage
RF N DIVIDER
The RF N divider allows a division ratio in the PLL feedback
path. The division ratio is determined by INT, FRAC and MOD
values, which build up this divider.
INT, FRAC, MOD, AND R COUNTER RELATIONSHIP
The INT, FRAC, and MOD values, in conjunction with the
R counter, make it possible to generate output frequencies
that are spaced by fractions of the PFD frequency. See the RF
Synthesizer—A Worked Example section for more information.
The RF VCO frequency (RFOUT) equation is
RFOUT = fPFD × (INT + (FRAC/MOD))
(1)
where RFOUT is the output frequency of external voltage
controlled oscillator (VCO).
INT is the preset divide ratio of the binary 16-bit counter
(23 to 65535 for 4/5 prescaler, 75 to 65,535 for 8/9 prescaler).
MOD is the preset fractional modulus (2 to 4095).
FRAC is the numerator of the fractional division (0 to MOD − 1).
fPFD = REFIN × [(1 + D)/(R × (1 + T))]
(2)
where:
REFIN is the reference input frequency.
D is the REFIN doubler bit.
T is the REFIN divide-by-2 bit (0 or 1).
R is the preset divide ratio of the binary 10-bit programmable
reference counter (1 to 1023).
ADF4350
FROM
VCO OUTPUT/
OUTPUT DIVIDERS
RF N DIVIDER
N COUNTER
INT
REG
N = INT + FRAC/MOD
TO PFD
THIRD-ORDER
FRACTIONAL
INTERPOLATOR
MOD
REG
FRAC
VALUE
Figure 17. RF INT Divider
INT N MODE
If the FRAC = 0 and DB8 in Register 2 (LDF) is set to 1, the
synthesizer operates in integer-N mode. The DB8 in Register 2
(LDF) should be set to 1 to get integer-N digital lock detect.
R COUNTER
The 10–bit R counter allows the input reference frequency
(REFIN) to be divided down to produce the reference clock
to the PFD. Division ratios from 1 to 1023 are allowed.
PHASE FREQUENCY DETECTOR (PFD) AND
CHARGE PUMP
The phase frequency detector (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
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
there is no dead zone in the PFD transfer function, and gives a
consistent reference spur level.
HIGH
+IN
UP
D1 Q1
U1
CLR1
DELAY
U3
CHARGE
PUMP
CP
HIGH
–IN
CLR2 DOWN
D2 Q2
U2
Figure 18. PFD Simplified Schematic
Rev. 0 | Page 11 of 28
 

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