Datasheet ADF4151 Datasheet (ANALOG DEVICES)

Fractional-N/Integer-N PLL Synthesizer
ADF4151
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MUXOUT
CP
OUT
LD
SW
REF
IN
CLK
DATA
LE
AV
DD
xSDV
DD
DV
DD
V
P
A
GND
CE CP
GND
SD
GNDDGND
R
SET
RFIN+
RF
IN
PHASE
COMPARATOR
FL
O
SWITCH
CHARGE
PUMP
10-BIT R
COUNTER÷2DIVIDER
×2
DOUBLER
FUNCTION
LATCH
DATA REGISTER
INTEGER
REG
N COUNTER
FRACTION
REG
THIRD-ORDER
FRACTIONAL
INTERPOLATOR
MODULUS
REG
MULTIPLEXER
LOCK
DETECT
ADF4151
10265-001
Data Sheet

FEATURES

Fractional-N synthesizer and integer-N synthesizer RF bandwidth to 3.5 GHz
3.0 V to 3.6 V power supply
1.8 V logic compatibility Separate charge pump supply (V
voltage (up to 5.5 V) in 3 V systems Programmable dual-modulus prescaler of 4/5 or 8/9 Programmable RF output phase 3-wire serial interface Analog and digital lock detect Switched bandwidth fast lock mode Cycle slip reduction

APPLICATIONS

Wireless infrastructure (W-CDMA, TD-SCDMA, WiMax, GSM,
PCS, DCS, DECT) Test equipment Wireless LANs, CATV equipment Clock generation
) allows extended tuning
P

GENERAL DESCRIPTION

The ADF4151 allows implementation of fractional-N or integer-N phase-locked loop (PLL) frequency synthesizers if used with an external voltage controlled oscillator (VCO), loop filter, and external reference frequency.
The ADF4151 is used with external VCO parts and is footprint and software compatible with the ADF4350. The part consists of a low noise digital phase frequency detector (PFD), a precision charge pump, and a programmable reference divider. There is a Σ-Δ based fractional interpolator to allow programmable fractional-N division. The INT, FRAC, and MOD registers define an overall N divider [N = (INT + (FRAC/MOD))]. The RF output phase is programmable for applications that require a particular phase relationship between the output and the reference. The ADF4151 also features cycle slip reduction circuitry, leading to faster lock times without the need for modifications to the loop filter.
Control of all the on-chip registers is through a simple 3-wire interface. The device operates with a power supply ranging from 3.0 V to 3.6 V that can be powered down when not in use.
The ADF4151 is available in a 5 mm × 5 mm package.
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of thi rd parties that may result from its use. Specifications subject to change with out notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

FUNCTIONAL BLOCK DIAGRAM

Figure 1.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700
www.analog.com
ADF4151 Data Sheet

TABLE OF CONTENTS

Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Timing Characteristics ................................................................ 5
Absolute Maximum Ratings ............................................................ 6
Transistor Count ........................................................................... 6
ESD Caution .................................................................................. 6
Pin Configuration and Function Descriptions ............................. 7
Typical Performance Characteristics ............................................. 9
Circuit Description ......................................................................... 11
Reference Input Section ............................................................. 11
RF N Divider ............................................................................... 11
INT, FRAC, MOD, and R Counter Relationship.................... 11
INT N Mode ................................................................................ 11
R Counter .................................................................................... 11
Phase Frequency Detector (PFD) and Charge Pump ............ 11
MUXOUT and Lock Detect ...................................................... 12
Input Shift Registers ................................................................... 12
Program Modes .......................................................................... 12
Register Maps .............................................................................. 13
Register 0 ..................................................................................... 17
Register 1 ..................................................................................... 17
Register 2 ..................................................................................... 17
Register 3 ..................................................................................... 19
Register 4 ..................................................................................... 19
Register 5 ..................................................................................... 19
Initialization Sequence .............................................................. 19
RF Synthesizer—A Worked Example ...................................... 20
Modulus ....................................................................................... 20
Reference Doubler and Reference Divider ............................. 20
12-Bit Programmable Modulus ................................................ 20
Cycle Slip Reduction for Faster Lock Times ........................... 21
Spurious Optimization and Fast lock ...................................... 21
Fast Lock Timer and Register Sequences ................................ 21
Fast Lock—An Example ............................................................ 22
Fast Lock—Loop Filter Topology ............................................. 22
Spur Mechanisms ....................................................................... 22
Spur Consistency and Fractional Spur Optimization ........... 23
Phase Resync ............................................................................... 23
Applications Information .............................................................. 24
Direct Conversion Modulator .................................................. 24
Interfacing ................................................................................... 25
PCB Design Guidelines for Chip Scale Package .................... 25
Outline Dimensions ....................................................................... 26
Ordering Guide .......................................................................... 26

REVISION HISTORY

12/11—Rev. A to Rev. B
Changes to Normalized 1/f Noise Parameter, Table 1 ................. 4
11/11—Rev. 0 to Rev. A
Changes to Figure 28 ...................................................................... 23
10/11—Revision 0: Initial Version
Rev. B | Page 2 of 28
Data Sheet ADF4151
Fractional-N Mode
Input Capacitance, CIN
5.0 pF
Low Power Sleep Mode
1
µA

SPECIFICATIONS

AVDD = DVDD = SD temperature range is −40°C to +85°C.
Table 1.
Parameter
REFIN CHARACTERISTICS
Input Frequency 10 250 MHz For f < 10 MHz, ensure slew rate > 21 V/µs
Input Sensitivity 0.7 AVDD V p-p Biased at AVDD/21
Input Capacitance 10 pF
Input Current ±60 µA
RF INPUT CHARACTERISTICS For lower frequencies, ensure slew rate > 400 V/µs
RF Input Frequency (RFIN) 0.5 3.5 GHz −10 dBm ≤ RF input power ≤ +5 dBm
Prescaler Output Frequency 750 MHz
MAXIMUM PFD FREQUENCY
Low Spur Mode 26 MHz Low Noise Mode 32 MHz
Integer-N Mode 32 MHz
CHARGE PUMP
ICP Sink/Source R
High Value 4.5 mA Low Value 0.281 mA R
Range 2.7 10 kΩ
SET
ICP Leakage 1 nA VCP = VP/2
Sink and Source Matching 2 % 0.5 V ≤ VCP ≤ VP − 0.5 V
ICP vs. VCP 1.5 % 0.5 V ≤ VCP ≤ VP − 0.5 V
ICP vs. Temperature 2 % VCP = VP/2
LOGIC INPUTS
Input High Voltage, V
Input Low Voltage, V
Input Current, I
= 3.3 V ± 10%; VP = AVDD to 5.5 V; A
VDD
GND
= D
= 0 V; TA = T
GND
B Version
Unit Conditions/Comments Min Typ Max
1.5 V
INH
0.6 V
INL
±1 µA
INH/IINL
MIN
to T
, unless otherwise noted. Operating
MAX
= 5.1 kΩ
SET
LOGIC OUTPUTS
Output High Voltage, VOH DVDD − 0.4 V CMOS output chosen
Output High Current, IOH 500 µA
Output Low Voltage, VO 0.4 V IOL = 500 µA
POWER SUPPLIES
AVDD 3.0 3.6 V
DVDD, SD
VP AVDD 5.5 V
DIDD + AI
VPI
DD
AVDD
VDD
2
40 50 mA
DD
2
2 mA VP = 5 V
Rev. B | Page 3 of 28
ADF4151 Data Sheet
B Version
Parameter
NOISE CHARACTERISTICS
Normalized In-Band Phase Noise
Floor (PN
Normalized 1/f Noise (PN
SYNTH
)3
)4 −118 dBc/Hz 10 kHz offset. Normalized to 1 GHz (ABP = 3 ns)
1_f
Normalized In-Band Phase Noise
Floor (PN
Normalized 1/f Noise (PN
Spurious Signals Due to PFD
Frequency
1
AC coupling ensures AVDD/2 bias.
2
TA = 25°C; AVDD = DVDD = 3.6 V; prescaler = 4/5; f
3
The synthesizer phase noise floor is estimated by measuring the in-band phase noise at the output of the VCO and subtracting 20 log N (where N is the N divider
value) and 10 log F
4
The PLL phase noise is composed of 1/f (flicker) noise plus the normalized PLL noise floor. The formula for calculating the 1/f noise contribution at an RF frequency (fRF)
and at a frequ ency offset (f) is given by PN = P
5
Spurious measured on EVAL-ADF4151EB1Z with RF buffer between VCO output and RF input by-passed, using a Rohde & Schwarz FSUP signal source analyzer.
SYNTH
5
)3
)4 −115 dBc/Hz 10 kHz offset; normalized to 1 GHz (ABP = 6 ns);
1_f
. PN
= PN
PFD
SYNTH
– 10 log f
TOT
−221 dBc/Hz PLL loop BW = 500 kHz (ABP = 3 ns)
−220 dBc/Hz PLL loop BW = 500 kHz (ABP = 6 ns);
−107 dBc PFD = 25 MHz
= 130 MHz; f
REFIN
– 20 log N
PFD
+ 10 log(10 kHz/f) + 20 log(fRF/1 GHz). Both the normalized phase noise floor and flicker noise are modeled in ADIsimPLL
1_f
= 26 MHz; fRF = 1.742 GHz.
PFD
Unit Conditions/Comments Min Typ Max
low noise mode
low noise mode
Rev. B | Page 4 of 28
Data Sheet ADF4151
CLK
DATA
LE
LE
DB31 (MSB) DB30
DB1 (LSB)
(CONTROL BIT C2)
DB2 (LSB)
(CONTROL BIT C3)
DB0 (LSB)
(CONTROL BIT C1)
t
1
t
2
t
3
t
7
t
6
t
4
t
5
10265-002

TIMING CHARACTERISTICS

AVDD1, AVDD2 = DVDD = SD Operating temperature range is −40°C to +85°C.
Table 2.
Parameter Limit (B Version) Unit Test Conditions/Comments
t1 20 ns min LE setup time t2 10 ns min DATA to CLK setup time t3 10 ns min DATA to CLK hold time t4 25 ns min CLK high duration t5 25 ns min CLK low duration t6 10 ns min CLK to LE setup time t7 20 ns min LE pulse width
= 3.3 V ± 10%; VP = AVDD to 5 . 5 V; A
VDD
GND
= D
= 0 V; TA = T
GND
MIN
to T
, unless otherwise noted.
MAX
Figure 2. Timing Diagram
Rev. B | Page 5 of 28
ADF4151 Data Sheet
Peak Temperature
260°C

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.
Table 3.
Parameter Rating
AVDD1, AVDD2 to GND1 −0.3 V to +3.9 V AVDD1, AVDD2 to DVDD −0.3 V to +0.3 V VP to AVDD1, AVDD2 −0.3 V to +5.8 V Digital I/O Voltage to GND1 −0.3 V to VDD + 0.3 V Analog I/O Voltage to GND1 −0.3 V to VDD + 0.3 V REFIN to GND1 −0.3 V to VDD + 0.3 V Operating Temperature Range −40°C to +85°C Storage Temperature Range −65°C to +125°C Maximum Junction Temperature 150°C LFCSP θJA Thermal Impedance
(Paddle-Soldered) 27.3°C/W
Reflow Soldering
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

TRANSISTOR COUNT

36685 (CMOS) and 967 (bipolar)

ESD CAUTION

Time at Peak Temperature 40 sec
1
GND = A
GND
= D
GND
= 0 V.
Rev. B | Page 6 of 28
Data Sheet ADF4151
1
CLK
2
DATA
3
LE
4
CE
5
SW
6 7
24 23
NC
22 21 20 19 18 17
8
SDV
DD
ADF4151
TOP VIEW
(Not to Scale)
9
A
GND
10
11
REF
IN
12
D
GND
13
DV
DD
141516
3231302928
SD
GND
27
26
25
PIN 1 INDICATOR
V
P
CP
OUT
CP
GND
MUXOUT
R
SET
NC
RF
IN
+
RF
IN
NC
NC NC
D
GND
LD
A
GND
A
GND
A
GND
NC
AV
DD
2
AV
DD
2
AV
DD
1
NOTES
1. NC = NO CONNE CT. DO NOT CONNECT TO THIS PIN.
2. THE LFCSP HAS AN EXPO S E D P ADDLE THAT MUST BE CONNECTED TO GND.
10265-003
5
SW
Fast Lock Switch. Make a connection to this pin from the loop filter when using the fast lock mode.
8
CP
Charge Pump Ground. This is the ground return pin for CP
.

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 CLK Serial Clock Input. Data is clocked into the 32-bit shift register on the CLK rising edge. This input is a high
impedance CMOS input.
2 D ATA Serial Data Input. The serial data is loaded, MSB first, with the three LSBs as the control bits. This input is a high
impedance CMOS input.
3 LE Load Enable, CMOS Input. When LE goes high, the data stored in the shift register is loaded into the register
that is selected by the three LSBs.
4 CE Chip Enable. A logic low on this pin powers down the device and puts the charge pump into three-state
mode. Taking the pin high powers up the device depending on the status of the power-down bits.
6 VP Charge Pump Power Supply. This pin should be greater than or equal to AVDD. In systems where AVDDx is 3 V, it
can be set to 5.5 V and used to drive a VCO with a tuning range of up to 5.5 V.
7 CP
9, 11, 18,
Charge Pump Output. When enabled, this provides ±ICP to the external loop filter. The output of the loop filter
OUT
GND
A
Analog Ground. This is a ground return pin for AVDD1 and AVDD2.
GND
is connected to V
to drive the external VCO.
TUNE
21 10 AVDD1 Analog Power Supply. This pin ranges from 3.0 V to 3.6 V. Decoupling capacitors to the analog ground plane
12, 13, 19,
are to be placed as close as possible to this pin. AV
NC No connect. Do not connect to this pin.
DD
20, 23, 24 14 RFIN+ Input to the RF Input. This small signal input is ac-coupled to the external VCO. 15 RFIN− Complementary Input to the RF Input. This pin must be decoupled to the ground plane with a small bypass
16, 17 AVDD2 Analog Power Supply. This pin ranges from 3.0 V to 3.6 V. Decoupling capacitors to the analog ground plane
capacitor, typically 100 pF.
are to be placed as close as possible to this pin. AV
Rev. B | Page 7 of 28
DD
OUT
must have the same value as DVDD.
x must have the same value as DVDD.
ADF4151 Data Sheet
SET
CP
R
I
22.95
=
28
DVDD
Digital Power Supply. This pin should be the same voltage as AVDD. Decoupling capacitors to the ground plane
Multiplexer Output. This multiplexer output allows either the lock detect, the scaled RF, or the scaled reference
Pin No. Mnemonic Description
22 R
25 LD Lock Detect Output Pin. This pin outputs a logic high to indicate PLL lock; a logic low output indicates loss of PLL
26, 27 D
29 REFIN Reference Input. This is a CMOS input with a nominal threshold of VDD/2 and a dc equivalent input resistance
30 MUXOUT
31 SD 32 SDVDD Power Supply Pin for the Digital Σ-Δ Modulator. Should be the same voltage as AVDDx. Decoupling capacitors
EP The exposed pad must be connected to GND.
Connecting a resistor between this pin and GND sets the charge pump output current. The nominal voltage
SET
bias at the R
pin is 0.49 V. The relationship between ICP and R
SET
SET
is
where:
R
= 5.1 kΩ.
SET
= 4.5 mA.
I
CP
lock.
Digital Ground. Ground return path for DVDD.
GND
should be placed as close as possible to this pin.
of 100 kΩ. This input can be driven from a TTL or CMOS crystal oscillator, or it can be ac-coupled.
frequency to be accessed externally.
Digital Sigma-Delta (Σ-Δ) Modulator Ground. Ground return path for the Σ-Δ modulator.
GND
to the ground plane are to be placed as close as possible to this pin.
Rev. B | Page 8 of 28
Data Sheet ADF4151
0
–40
–35
–30
–25
–20
–15
–10
–5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
POWER (dBm)
FREQUENCY ( GHz)
–40°C
+25°C
+85°C
10265-004
6.0
–6.0
–5.5
–5.0
–4.5
–4.0
–3.5
–3.0
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 5.04.54.0
I
CP
(mA)
VCP (V)
0.28mA
0.28mA
0.56mA
0.56mA
1.13mA
1.13mA
2.25mA
2.25mA
4.5mA
4.5mA
SOURCE SINK
10265-005
–90
–100
–99
–98
–97
–96
–95
–94
–93
–92
–91
2.60 2.61 2.62 2.63 2.64 2.65 2.66 2.67 2.68 2.702.69
PHASE NOISE (dBc/Hz)
FREQUENCY ( GHz)
LOW NOISE MODE
LOW SP UR M ODE
10265-006
6.0
–6.0
–5.5
–5.0
–4.5
–4.0
–3.5
–3.0
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 5.04.54.0
I
CP
MISMATCH ( %)
V
CP
(V)
ICP = 0.28mA ICP = 0.56mA ICP = 1.13mA ICP = 2.25mA ICP = 4.5mA
10265-007

TYPICAL PERFORMANCE CHARACTERISTICS

Figure 4. RF Input Sensitivity
Figure 5. Charge Pump Output Characteristics, VP = 5 V, Selected ICP Values
Between 0.28 mA (Min) and 4.5 mA (Max), R
= 5.1 kΩ
SET
Figure 6. In-Band Phase Noise Measured at 10 kHz Offset
for Low Noise Mode and Low Spur Mode,
PFD = 25 MHz, PLL Loop Bandwidth = 50 kHz
Figure 7. Charge Pump Output Mismatch vs. VCP , Selected ICP Values Between
0.28 mA (Min) and 4.5 mA (Max), R
= 5.1 kΩ
SET
Rev. B | Page 9 of 28
ADF4151 Data Sheet
–60
–80
–100
–120
–140
–160
–180
1k 10k 100k 1M 10M
PHASE NOISE (dBc/Hz)
FREQUENCY OFFSET (Hz)
10265-008
–60
–80
–100
–120
–140
–160
–180
1k 10k 100k 1M 10M
PHASE NOISE (dBc/Hz)
FREQUENCY OFFSET (Hz)
10265-009
–60
–80
–100
–120
–140
–160
–180
1k 10k 100k 1M 10M
PHASE NOISE (dBc/Hz)
FREQUENCY OFFSET (Hz)
10265-010
–60
–80
–100
–120
–140
–160
–180
1k 10k 100k 1M 10M
PHASE NOISE (dBc/Hz)
FREQUENCY OFFSET (Hz)
10265-011
–60
–80
–100
–120
–140
–160
–180
1k 10k 100k 1M 10M
PHASE NOISE (dBc/Hz)
FREQUENCY OFFSET (Hz)
10265-012
–60
–80
–100
–120
–140
–160
–180
1k 10k 100k 1M 10M
PHASE NOISE (dBc/Hz)
FREQUENCY OFFSET (Hz)
10265-013
Figure 8. Integer-N Phase Noise and Spur Performance;
Low Noise Mode; VCO
= 1750 MHz, REFIN = 100 MHz,
OUT
PFD = 25 MHz, Loop Filter Bandwidth = 50 kHz
Figure 9. Fractional-N Phase Noise and Spur Performance; Low Noise Mode;
VCO
= 1755.2 MHz, REFIN = 100 MHz, PFD = 25 MHz, Loop Filter
OUT
Bandwidth = 50 kHz, Channel Spacing = 200 kHz, FRAC = 26, MOD = 125
Figure 11. Integer-N Phase Noise and Spur Performance;
Low Noise Mode; VCO
= 900 MHz, REFIN = 100 MHz,
OUT
PFD = 25 MHz, Loop Filter Bandwidth = 20 kHz
Figure 12. Fractional-N Phase Noise and Spur Performance; Low Noise Mode;
VCO
= 905.2 MHz, REFIN = 100 MHz, PFD = 25 MHz, Loop Filter
OUT
Bandwidth= 20 kHz, Channel Spacing = 200 kHz, FRAC = 26, MOD = 125
Figure 10. Fractional-N Phase Noise and Spur Performance; Low Spur Mode;
VCO
= 1755.2 MHz, REFIN = 100 MHz, PFD = 25 MHz, Loop Filter
OUT
Bandwidth = 50 kHz, Channel Spacing = 200 kHz, FRAC = 26, MOD = 125
Figure 13. Fractional-N Phase Noise and Spur Performance; Low Spur Mode; VCO
= 905.2 MHz, REFIN = 100 MHz, PFD = 25 MHz, Loop Filter Bandwidth
OUT
= 20 kHz, Channel Spacing = 200 kHz, FRAC = 26, MOD = 125
Rev. B | Page 10 of 28
Data Sheet ADF4151
BUFFER
TO R COUNT E R
REF
IN
100k
NC
SW2
SW3
NO
NC
SW1
POWER-DOWN
CONTROL
10265-014
THIRD-ORDER
FRACTIONAL
INTERPOLATOR
FRAC
VALUE
MOD REG
INT
REG

RF N DIVIDE R

N = INT + F RAC/MOD
FROM
VCO OUTPUT/
OUTPUT DIVIDERS
TO PFD
N COUNTER
10265-015
U3
CLR2
Q2D2
U2
DOWN
UP
HIGH
HIGH
CP
–IN
+IN
CHARGE
PUMP
DELAY
CLR1
Q1D1
U1
10265-016

CIRCUIT DESCRIPTION

REFERENCE INPUT SECTION

The reference input stage is shown in Figure 14. 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 REF on power-down.
IN
pin
Figure 14. Reference Input Stage
RF N DIVIDER
The RF N divider allows a division ratio in the PLL feedback path. Division ratio is determined by the INT, F RAC , 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 (RF
RF
= f
OUT
× (INT + (FRAC/MOD)) (1)
PFD
where:
RF
is the output frequency of the external voltage controlled
OUT
oscillator (VCO). INT is the preset divide ratio of the binary 16-bit counter (23 to 32,767 for 4/5 prescaler, 75 to 65,535 for 8/9 prescaler).
FRAC is the numerator of the fractional division (0 to MOD − 1). MOD is the preset fractional modulus (2 to 4095 for low noise
mode, 50 to 4095 for low spur mode).
f
= REFIN × [(1 + D)/(R × (1 + T))] (2)
PFD
where:
REF
is the reference input frequency.
IN
D is the REF
doubler bit.
IN
R is the preset divide ratio of the binary 10–bit programmable reference counter (1 to 1023). T is the REF
divide-by-2 bit (0 or 1).
IN
) equation is
OUT
Figure 15. 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. Additionally, lower phase noise is possible if the antibacklash pulse width is reduced to 3 ns. This mode is not valid for fractional-N applications.

R COUNTER

The 10-bit R counter allows the input reference frequency (REF
) to be divided down to produce the reference clock
IN
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 16 is a simplified schematic of the phase frequency detector. The PFD includes a programmable delay element that sets the width of the antibacklash pulse, which can be either 6 ns (default, for fractional-N applications) or 3 ns (for integer-N mode). This pulse ensures that there is no dead zone in the PFD transfer function and gives a consistent reference spur level.
Figure 16. PFD Simplified Schematic
Rev. B | Page 11 of 28
ADF4151 Data Sheet
D
GND
DV
DD
CONTROL
MUX
MUXOUT
ANALOG L OCK DETECT
DIGITAL LOCK DETECT
R COUNTER OUTPUT N COUNTER OUTPUT
DGND
RESERVED
THREE-STATE-OUTPUT
DV
DD
R COUNTER INP UT
10265-017

MUXOUT AND LOCK DETECT

The output multiplexer on the ADF4151 allows the user to access various internal points on the chip. The state of MUXOUT is controlled by M3, M2, and M1 (for details, see Figure 21). Figure 17 shows the MUXOUT section in block diagram form.
Figure 17. MUXOUT Schematic

INPUT SHIFT REGISTERS

The ADF4151 digital section includes a 10-bit RF R counter, a 16-bit RF N counter, a 12-bit FRAC counter, and a 12-bit modulus 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 six 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. There are three LSBs: DB2, DB1, and DB0, as shown in Figure 2. The truth table for these bits is shown in Tabl e 5. Figure 18 shows a summary of how the latches are programmed.
Table 5. C3, C2, and C1 Truth Table
Control Bits
C3 C2 C1 Register
0 0 0 Register 0 (R0) 0 0 1 Register 1 (R1) 0 1 0 Register 2 (R2) 0 1 1 Register 3 (R3) 1 0 0 Register 4 (R4) 1 0 1 Register 5 (R5)

PROGRAM MODES

Figure 19 through Figure 24 show how the program modes are to be set up in the ADF4151.
A number of settings in the ADF4151 are double buffered. These include the modulus value, phase value, R counter value, reference doubler, reference divide-by-2, and current setting. This means that two events must occur before the part uses a new value of 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, any time the modulus value is updated, Register R0 must be written to, thus ensuring that the modulus value is loaded correctly.
Rev. B | Page 12 of 28
Data Sheet ADF4151
DB31
DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0
N16 N15 N14 N13 N12 N11 N10 N9
RESERVED
16-BIT INTEGER VALUE ( INT) 12-BIT F RACTIONAL VALUE ( FRAC)
CONTROL
BITS
N8 N7 N6 N5 N4 N3 N2 N1 F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 C3(0) C2(0) C1(0)
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 PH1 PR1 P12 P11 P10 P9
12-BIT PHASE VALUE (PHASE)
12-BIT MODULUS VALUE ( MOD)
CONTROL
BITS
P8 P7 P6 P5 P4 P3 P2 P1 M12 M11 M10 M9 M8 M7 M6 M5 M4 M3 M2 M1 C3(0) C2(0) C1(1)
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 L2 L1 M3 M2 M1 RD2 RD1 R10 R9 R8 R7 R6 R5 R4 R3 R2 R1 0 CP4 CP3 CP2 CP1 U6 U5 U4 U3 U2 U1 C3(0) C2(1) C1(0)
CSR
RDIV2
REFERENCE
DOUBLER
CHARGE
PUMP
CURRENT
SETTING
10-BIT R COUNTER
CONTROL
BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 0 0 F3 F2 0 0 F1 0 C2 C1 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 C3(0) C2(1) C1(1)
CONTROL
BITS
12-BIT CL OCK DIVIDER VALUE
LDP
PD
POLARITY
POWER-DOWN
CP THREE-
STATE
COUNTER
RESET
CLK
DIV
MODE
DBR
1
1
DBR = DOUBLE BUF FERED REGIS TER—BUFFERE D BY THE WRIT E TO REGIS TER 0.
RESERVED
LDF
RESERVED
ABP
CHARGE
CANCEL
RESERVED
REGISTER 4
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C3(1) C2(0) C1(0)
CONTROL
BITS
RESERVED
LD PIN
MODE
REGISTER 0
REGISTER 1
REGISTER 2
REGISTER 3
REGISTER 5
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 0 D15 D14 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C3(1) C2(0) C1(1)
CONTROL
BITS
RESERVED
RESERVED
RESERVED
DBR
1
DBR
1
DBR
1
DBR
1
DBR
1
RESERVED
PRESCALER
LOW NOISE AND LOW SPUR
MODES
MUXOUT
PHASE ADJUST
RESERVED
10265-018

REGISTER MAPS

Figure 18. Register Summary
Rev. B | Page 13 of 28
ADF4151 Data Sheet
N16 N15 ... N5 N4 N3 N2 N1 INTEGER VALUE (I NT )
0 0 ... 0 0 0 0 0 NOT ALLOWED 0 0 ... 0 0 0 0 1 NOT ALLOWED 0 0 ... 0 0 0 1 0 NOT ALLOWED
. . ... . . . . . ...
0 0 ... 1 0 1 1 0 NOT ALLOWED 0 0 ... 1 0 1 1 1 23 0 0 ... 1 1 0 0 0 24
. . ... . . . . . ...
1 1 ... 1 1 1 0 1 65533 1 1 ... 1 1 1 1 0 65534 1 1 ... 1 1 1 1 1 65535
F12 F11 .......... F2 F1 FRACTIONAL VALUE ( FRAC)
0 0 .......... 0 0 0
0 0 .......... 0 1 1
0 0 .......... 1 0 2
0 0 .......... 1 1 3
. . .......... . . .
. . .......... . . .
. . .......... . . .
1 1 .......... 0 0 4092
1 1 .......... 0 1 4093
1 1 .......... 1 0 4094
1 1 ......... 1 1 4095
DB31
DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0
N16 N15 N14 N13 N12 N11 N10 N9
RESERVED
16-BIT INTEGER VALUE ( INT) 12-BIT F RACTIONAL VALUE (F RAC)
CONTROL
BITS
N8 N7 N6 N5 N4 N3 N2 N1 F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 C3(0) C2(0) C1(0)
INTmin = 75 WITH PRES CALER = 8/9
10265-019
P12 P11 .......... P2 P1 PHASE VALUE (PHASE)
0 0 .......... 0 0 0
0 0 .......... 0 1 1 (RE COMMENDED)
0 0 .......... 1 0 2
0 0 .......... 1 1 3
. . .......... . . .
. . .......... . . .
. . .......... . . .
1 1 .......... 0 0 4092
1 1 .......... 0 1 4093
1 1 .......... 1 0 4094
1 1 .......... 1 1 4095
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 PH1 PR1 P12 P11 P10 P9
12-BIT PHASE VALUE (PHASE) 12-BIT MODULUS VALUE (MOD)
CONTROL
BITS
P8 P7 P6 P5 P4 P3 P2 P1 M12 M11 M10 M9 M8 M7 M6 M5 M4 M3 M2 M1 C3(0) C2(0) C1(1)
RESERVED
M12 M11 ..........
..........
..........
..........
..........
..........
..........
..........
..........
..........
M2 M1 INTERPO LAT OR MODULUS ( MOD)
0 0 1 0 2 0 0 1 1 3
. . . . .
. . . . .
. . . . .
1 1 0 0 4092 1 1 0 1 4093 1 1 1 0 4094 1 1 1 1 4095
PRESCALER
PHASE ADJUST
P1 PRESCALER 0 4/5 1 8/9
PH1 PHASE ADJUST 0 OFF 1 ON
DBR DBR
10265-020
Figure 19. Register 0 (R0)
Figure 20. Register 1 (R1)
Rev. B | Page 14 of 28
Data Sheet ADF4151
RD2
REFERENCE
DOUBLER 0 DISABLED 1 ENABLED
RD1 REF ERENCE DIVIDE BY 2 0 DISABLED 1 ENABLED
CP4 CP3 CP2 CP1
ICP (mA)
5.1kΩ
0 0 0 0 0.28 0 0 0 1 0.56 0 0 1 0 0.84 0 0 1 1 1.13 0 1 0 0 1.41 0 1 0 1 1.69 0 1 1 0 1.97 0 1 1 1 2.25 1 0 0 0 2.53 1 0 0 1 2.81 1 0 1 0 3.09 1 0 1 1 3.38 1 1 0 0 3.66 1 1 0 1 3.94 1 1 1 0 4.22 1 1 1 1 4.5
R10 R9 ..........
..........
..........
..........
..........
..........
..........
..........
..........
..........
R2 R1 R DIVIDER (R)
0 0 0 1 1 0 0 1 0 2
. . . . .
. . . . .
. . . . .
1 1 0 0 1020 1 1 0 1 1021 1 1 1 0 1022 1 1 1 1 1023
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 L2 L1 M3 M2 M1 RD2 RD1 R10 R9 R8 R7 R6 R5 R4 R3 R2 R1 0 CP4 CP3 CP2 CP1 U6 U5 U4 U3 U2 U1 C3(0) C2(1) C1(0)
RDIV2 DBR
REFERENCE
DOUBLER DBR
CHARGE
PUMP
CURRENT
SETTING
10-BIT R COUNTER DBR
CONTROL
BITS
LDP
PD
POLARITY
POWER-DOWN
CP THREE-
STATE
COUNTER
RESET
LDF
MUXOUT
RESERVED
U5 LDP 0 10ns 1 6ns
U4 PD POLARIT Y 0 NEGATIVE 1 POSITIVE
U3 POWER-DOWN 0 DISABLED 1 ENABLED
U2
CP
THREE-STATE 0 DISABLED 1 ENABLED
U1
COUNTER
RESET 0 DISABLED 1 ENABLED
U6 LDF 0 FRAC-N 1 INT-N
RESERVED
M3 M2 M1 OUTPUT 0 0 0 THREE-STATE OUTPUT 0 0 1 DV
DD
0 1 0 DGND 0 1 1 R DIVIDER OUTPUT 1 0 0 N DIVIDER OUTPUT 1 0 1 ANALOG LOCK DET ECT 1 1 0 DIGITAL LOCK DETECT 1 1 1 RESERVED
L1 L2 NOISE MODE 0 0 LOW NOISE MODE 0 1 RESERVED 1 0 RESERVED 1 1 LOW SPUR MODE
LOW NOISE AND LOW SPUR
MODES
10265-021
Figure 21. Register 2 (R2)
Rev. B | Page 15 of 28
ADF4151 Data Sheet
C2 C1 CLOCK DIVIDER MODE 0 0 CLOCK DIVI DER OFF 0 1 FAST LOCK ENABLE 1 0 RESYNC ENABLE 1 1 RESERVED
D12 D11 .......... D2 D1 CL OCK DIVIDER VALUE
0 0 .......... 0 0 0
0 0 .......... 0 1 1
0 0 .......... 1 0 2
0 0 .......... 1 1 3
. . .......... . . .
. . .......... . . .
. . .......... . . .
1 1 .......... 0 0 4092
1 1 .......... 0 1 4093
1 1 .......... 1 0 4094
1 1 .......... 1 1 4095
CSR
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 0 0 F1 0 C2 C1 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 C3(0) C2(1) C1(1)
CONTROL
BITS12-BIT CL OCK DIVIDER VALUE
CLK
DIV
MODE
RESERVED
F1
CYCLE SLIP
REDUCTION 0 DISABLED 1 ENABLED
RESERVED
0
0
RESERVED
F3 F2
F2
CHARGE
CANCELLATION 0 DISABLED 1 ENABLED
F3
ANTIBACKLASH
PULSE WIDTH 0 6ns (FRAC-N) 1 3ns (INT_N)
CHARGE
CANCEL
ABP
10265-022
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C3(1) C2(0) C1(0)
CONTROL
BITS
RESERVED
10265-023
LD PIN
MODE
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 0 D15 D14 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C3(1) C2(0) C1(1)
CONTROL
BITSRESERVEDRESERVED
D15 D1 4 LO CK DETECT PIN OPERATION 0 0 LOW 0 1 DIGIT AL L OCK DETECT 1 0 LOW 1 1 HIGH
10265-024
Figure 22. Register 3 (R3)
Figure 23. Register 4 (R4)
Figure 24. Register 5 (R5)
Rev. B | Page 16 of 28
Data Sheet ADF4151

REGISTER 0

Control Bits

With Bits[C3:C1] set to 0, 0, 0, Register 0 is programmed. Figure 19 shows the input data format for programming this register.

16-Bit Integer Value (INT)

These 16 bits set the INT value, which determines the integer part of the feedback division factor. They are used in Equation 1 (see the INT, FRAC, MOD, and R Counter Relationship section). All integer values from 23 to 32,767 are allowed for 4/5 prescaler. For 8/9 prescaler, the minimum integer value is 75, and the maximum value is 65,535.

12-Bit Fractional Value (FRAC)

The 12 FRAC bits set the numerator of the fraction that is input to the Σ-Δ modulator. This, along with INT, specifies the new frequency channel that the synthesizer locks to, as shown in the RF Synthesizer—A Worked Example section. FRAC values from 0 to MOD − 1 cover channels over a frequency range equal to the PFD reference frequency.

REGISTER 1

Control Bits

With Bits[C3:C1] set to 0, 0, 1, Register 1 is programmed. Figure 20 shows the input data format for programming this register.

Phase Adjust

The phase adjust bit, enabled by programming a 1 to DB28, permits adjustments to the output phase of a given output frequency. If enabled, it does not perform a phase resync function on updating R0. If set to 0, the phase resync (if enabled in R3, Bits[DB16:DB15]) occurs on every update of R0.

Prescaler Value

The dual modulus prescaler (P/P + 1), along with the INT, FRAC, and MOD counters, determines the overall division ratio from the VCO output to the PFD input.
Operating at CML levels, it takes the clock from the VCO output and divides it down for the counters. It is based on a synchronous 4/5 core. When set to 4/5, the maximum RF frequency allowed is 3 GHz. Therefore, when operating the
ADF4151 above 3 GHz, this must be set to 8/9. The prescaler
limits the INT value, where:
P = 4/5, N P = 8/9, N
In the ADF4151, PR1 in Register 1 sets the prescaler values.
MIN
MIN
= 23 = 75

12-Bit Phase Value (PHASE)

These bits control what is loaded as the phase word. The word must be less than the MOD value programmed in Register 1. The word is used to program the RF output phase from 0° to 360° with a resolution of 360°/MOD. See the Phase Resync section for more information. In most applications, the phase relationship between the RF signal and the reference is not important. In such applications, the phase value can be used to optimize the fractional and subfractional spur levels. See the Spur Consistency and Fractional Spur Optimization section for more information.
If neither the phase resync nor the spurious optimization functions are being used, it is recommended that the phase word be set to 1.

12-Bit Modulus Value (MOD)

This programmable register sets the fractional modulus. This is the ratio of the PFD frequency to the channel step resolution on the RF output. See the RF Synthesizer—A Worked Example section for more information.

REGISTER 2

Control Bits

With Bits[C3:C1] set to 0, 1, 0, Register 2 is programmed. Figure 21 shows the input data format for programming this register.

Low Noise and Spur Modes

The noise modes on the ADF4151 are controlled by DB30 and DB29 in Register 2 (see Figure 21). The noise modes allow the user to optimize a design either for improved spurious perfor­mance or for improved phase noise performance.
When the lowest spur setting is chosen, dither is enabled. This randomizes the fractional quantization noise so it resembles white noise rather than spurious noise. As a result, the part is optimized for improved spurious performance. This operation would normally be used when the PLL closed-loop bandwidth is wide, for fast locking applications. (Wide-loop bandwidth is seen as a loop bandwidth greater than 1/10 of the RF step resolution (f
)). A wide loop filter does not attenuate the
RES
spurs to the same level as a narrow-loop bandwidth.
For best noise performance, use the lowest noise setting option. As well as disabling the dither, it also ensures that the charge pump is operating in an optimum region for noise performance. This setting is extremely useful where a narrow-loop filter bandwidth is available. The synthesizer ensures extremely low noise, and the filter attenuates the spurs. The typical performance characteristics give the user an idea of the trade-off in a typical W-CDMA setup for the different noise and spur settings.
channel
OUT
Rev. B | Page 17 of 28
ADF4151 Data Sheet
MUXOUT
The on-chip multiplexer is controlled by Bits[DB28:DB26] (see Figure 21).
Reference Doubler
Setting DB25 to 0 feeds the REFIN signal directly to the 10-bit R counter, disabling the doubler. Setting this bit to 1 multiplies the REF 10-bit R counter. When the doubler is disabled, the REF
frequency by a factor of 2 before feeding into the
IN
IN
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
become active edges at the PFD input.
IN
When the doubler is enabled and the lowest spur mode is chosen, the in-band phase noise performance is sensitive to the REF
duty cycle. The phase noise degradation can be as much
IN
as 5 dB for the REF
duty cycles outside a 45% to 55% range.
IN
The phase noise is insensitive to the REFIN duty cycle in the lowest noise mode. The phase noise is insensitive to the REF
IN
duty cycle when the doubler is disabled.
When the doubler is enabled, the maximum allowable REF
IN
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
) to be divided down to produce the reference clock to
IN
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.
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 occ u r. Recommended settings of both the LDP and LDF bits are shown in Tab l e 6.
Table 6. Recommended LDF/LDP Bit Settings
DB8
Mode
Integer-N 1 1 Fractional-N Low Noise Mode 0 1 Fractional-N Low Spur Mode 0 0
(LDF)
DB7 (LDP)
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:
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
buffers are disabled.
OUT
The input register remains active and capable of loading
and latching data.
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.
Rev. B | Page 18 of 28
Data Sheet ADF4151

REGISTER 3

Control Bits

With Bits[C3:C1] set to 0, 1, 1, Register 3 is programmed. Figure 22 shows the input data format for programming this register.

Antibacklash Pulse Width

Setting DB22 to 0 sets the PFD antibacklash pulse width to 6 ns. This is the recommended mode for fractional-N use. By setting this bit to 1, the 3 ns pulse width is used and results in a phase noise and spur improvement in integer-N operation. For fractional-N mode it is not recommended to use this smaller setting.

Charge Cancellation Mode Pulse Width

Setting DB21 to 1 enables charge pump charge cancellation. This has the effect of reducing PFD spurs in integer-N mode. In fractional-N mode, this bit should not be used. This results in a phase noise and fractional spur improvement.

Cycle Slip Reduction (CSR) Enable

Setting DB18 to 1 enables cycle slip reduction. This is a method for improving lock times. Note that the signal at the phase fre­quency detector (PFD) must have a 50% duty cycle for cycle slip reduction to work. The charge pump current setting must also be set to a minimum. See the Cycle Slip Reduction for Faster Lock Times section for more information.

Clock Divider Mode

Bits[DB16:DB15] must be set to 1, 0 to activate phase resync or 0, 1 to activate fast lock. Setting Bits[DB16:DB15] to 0, 0 disables the clock divider. See Figure 22.

12-Bit Clock Divider Value

The 12-bit clock divider value sets the timeout counter for activation of phase resync. See the Phase Resync section for more information. It also sets the timeout counter for fast lock. See the Fast Lock Timer and Register Sequences section for more information.

REGISTER 4

Control Bits

With Bits[C3: C1] set to 1, 0, 0, Register 4 is programmed. Figure 23 shows the input data format for programming this register.
This register is reserved and has to be programmed with the values as shown in Figure 23. Bits[DB31:DB24] and [DB22:DB3] must be programmed to 0, while Bit DB23 must be set to 1.

REGISTER 5

Control Bits

With Bits[C3:C1] set to 1, 0, 1, Register 5 is programmed. Figure 24 shows the input data form for programming this register.

Lock Detect PIN Operation

Bits[DB23:DB22] set the operation of the lock detect pin (see Figure 24).

INITIALIZATION SEQUENCE

The following sequence of registers is the correct sequence for initial power up of the ADF4151 after the correct application of voltages to the supply pins:
1. Register 5
2. Register 4
3. Register 3
4. Register 2
5. Register 1
6. Register 0
Rev. B | Page 19 of 28
ADF4151 Data Sheet
f
PFD
PFD VCO
N
DIVIDER
RF
OUT
10265-025

RF SYNTHESIZER—A WORKED EXAMPLE

The following is an example of how to program the ADF4151 synthesizer:
RF
= [INT + (FRAC/MOD)] × [f
OUT
where:
RF
is the RF frequency output.
OUT
INT is the integer division factor. FRAC is the fractionality. MOD is the modulus. RF Divider is the output divider that divides down the VCO
frequ e nc y.
f
= REFIN × [(1 + D)/(R × (1 + T))] (4)
PFD
where:
REF
is the reference frequency input.
IN
D is the RF REF
doubler bit.
IN
R is the RF reference division factor. T is the reference divide-by-2 bit (0 or 1).
For example, in a UMTS system, where 2112.6 MHz RF frequency output (RF frequency input (REF resolution (f
RESOUT
) is required, a 10 MHz reference
OUT
) is available, and a 200 kHz channel
IN
) is required on the RF output. A 2.1 GHz
VCO is suitable to cover the required fractional frequency of
2112.6 MHz.
Figure 25. Loop Closed Before Output Divider
A channel resolution (f
) of 200 kHz is required at the output
RES
of the VC O.
MOD = REF
IN/fRES
MOD = 10 MHz/200 kHz = 50
From Equation 4
= [10 MHz × (1 + 0)/1] = 10 MHz (5)
f
PFD
2112.6 MHz = 10 MHz × (INT + FRAC/50) (6)
where:
INT = 211 FRAC = 13
]/RF Divider (3)
PFD

MODULUS

The choice of modulus (MOD) depends on the reference signal (REF
) available and the channel resolution (f
IN
the RF output. For example, a GSM system with 13 MHz REF
) required at
RES
IN
sets the modulus to 65. This means that the RF output resolution (f
) is the 200 kHz (13 MHz/65) necessary for GSM. With dither
RES
off, the fractional spur interval depends on the modulus values chosen (see Tabl e 7).

REFERENCE DOUBLER AND REFERENCE DIVIDER

The reference doubler on chip allows the input reference signal to be doubled. This is useful for increasing the PFD comparison frequency. Making the PFD frequency higher improves the noise performance of the system. Doubling the PFD frequency usually improves noise performance by 3 dB. It is important to note that the PFD cannot operate above maximum value (see Tabl e 1) due to a limitation in the speed of the Σ-Δ circuit of the N-divider.
The reference divide-by-2 divides the reference signal by 2, resulting in a 50% duty cycle PFD frequency. This is necessary for the correct operation of the cycle slip reduction (CSR) function. See the Cycle Slip Reduction for Faster Lock Times section for more information.

12-BIT PROGRAMMABLE MODULUS

Unlike most other fractional-N PLLs, the ADF4151 allows the user to program the modulus over a 12-bit range. This means that the user can set up the part in many different configurations for the application, when combined with the reference doubler and the 10-bit R counter.
For example, consider an application that requires 1.75 GHz RF and 200 kHz channel step resolution. The system has a 13 MHz reference signal.
One possible setup is feeding the 13 MHz directly to the PFD and programming the modulus to divide by 65. This results in the required 200 kHz resolution.
Another possible setup is using the reference doubler to create 26 MHz from the 13 MHz input signal. The 26 MHz is then fed into the PFD, programming the modulus to divide by 130. This also results in 200 kHz resolution and offers superior phase noise performance over the previous setup.
The programmable modulus is also very useful for multi­standard applications. If a dual-mode phone requires PDC and GSM 1800 standards, the programmable modulus is a great benefit. PDC requires 25 kHz channel step resolution, whereas GSM 1800 requires 200 kHz channel step resolution.
Rev. B | Page 20 of 28
Data Sheet ADF4151
A 13 MHz reference signal can be fed directly to the PFD, and the modulus can be programmed to 520 when in PDC mode (13 MHz/520 = 25 kHz).
The modulus needs to be reprogrammed to 65 for GSM 1800 operation (13 MHz/65 = 200 kHz).
It is important that the PFD frequency remain constant (13 MHz). This allows the user to design one loop filter for both setups without running into stability issues. It is important to remem­ber that the ratio of the RF frequency to the PFD frequency principally affects the loop filter design, not the actual channel spacing.

CYCLE SLIP REDUCTION FOR FASTER LOCK TIMES

As outlined in the Low Noise and Spur Mode section, the
ADF4151 contains a number of features that allow optimization
for noise performance. However, in fast locking applications, the loop bandwidth generally needs to be wide, and, therefore, the filter does not provide much attenuation of the spurs. If the cycle slip reduction feature is enabled, the narrow-loop bandwidth is maintained for spur attenuation but faster lock times are still possible.

Cycle Slips

Cycle slips occur in integer-N/fractional-N synthesizers when the loop bandwidth is narrow compared to the PFD frequency. The phase error at the PFD inputs accumulates too fast for the PLL to correct, and the charge pump temporarily pumps in the wrong direction. This slows down the lock time dramatically. The ADF4151 contains a cycle slip reduction feature that extends the linear range of the PFD, allowing faster lock times without modifications to the loop filter circuitry.
When the circuitry detects that a cycle slip is about to occur, it turns on an extra charge pump current cell. This outputs a constant current to the loop filter or removes a constant current from the loop filter (depending on whether the VCO tuning voltage needs to increase or decrease to acquire the new frequency). The effect is that the linear range of the PFD is increased. Loop stability is maintained because the current is constant and is not a pulsed current.
If the phase error increases again to a point where another cycle slip is likely, the ADF4151 turns on another charge pump cell. This continues until the ADF4151 detects that the VCO frequency has gone past the desired frequency. The extra charge pump cells are turned off one by one until all the extra charge pump cells have been disabled and the frequency is settled with the original loop filter bandwidth.
Up to seven extra charge pump cells can be turned on. In most applications, it is enough to eliminate cycle slips altogether, giving much faster lock times.
Setting Bit DB18 in the Register 3 to 1 enables cycle slip reduction. Note that the PFD requires a 45% to 55% duty cycle for CSR to operate correctly.

SPURIOUS OPTIMIZATION AND FAST LOCK

Narrow-loop bandwidths can filter unwanted spurious signals, but these usually have a long lock time. A wider loop bandwidth achieves faster lock times, but a wider loop bandwidth may lead to increased spurious signals inside the loop bandwidth.
The fast lock feature can achieve the same fast lock time as the wider bandwidth, but with the advantage of a narrow final loop bandwidth to keep spurs low.

FAST LOCK TIMER AND REGISTER SEQUENCES

If the fast lock mode is used, a timer value must be loaded into the PLL to determine the duration of the wide bandwidth mode.
When Bits[DB16:DB15] in Register 3 are set to 0, 1 (fast lock enable), the timer value is loaded by the 12-bit clock divider value. The following sequence must be programmed to use fast lock:
1. Initialization sequence (see the Initialization Sequence
section); occurs only once after powering up the part.
2. Load Register 3 by setting Bits[DB16:DB15] to 0, 1 and
the chosen fast lock timer value, Bits[DB14:DB3]. Note that the length of time the PLL remains in wide bandwidth is equal to the fast lock timer/f
PFD
.
Rev. B | Page 21 of 28
ADF4151 Data Sheet
ADF4151
CP
OUT
SW
C1
C2
R2
R1
R1A
C3
VCO
10265-026
ADF4151
CP
OUT
SW
C1
C2
R2
R1R1A
C3
VCO
10265-027
If MOD is divisible by 2, but not 3
2 × MOD
Channel step/2
If MOD is divisible by 3, but not 2
3 × MOD
Channel step/3

FAST LOCK—AN EXAMPLE

If a PLL has a reference frequency of 13 MHz, a f and a required lock time of 50 µs, the PLL is set to wide bandwidth for 40 µs. This example assumes a modulus of 65 for channel spacing of 200 kHz.
If the time period set for the wide bandwidth is 40 µs, then
Fast Lock Timer Value = Time In Wide Bandwidth × f
Fast Lock Timer Value = 40 µs × 13 MHz/65 = 8
Therefore, 8 must be loaded into the clock divider value in Register 3 in Step 1 of the sequence described in the Fast Lock Timer and Register Sequences section.
of 13 MHz
PFD
PFD
/MOD

FAST LOCK—LOOP FILTER TOPOLOGY

To use fast lock mode, the damping resistor in the loop filter is reduced to ¼ of its value while in wide bandwidth mode. To achieve the wider loop filter bandwidth, the charge pump current increases by a factor of 16. To maintain loop stability, the damping resistor must be reduced a factor of ¼. To enable fast lock, the SW pin is shorted to the GND pin by setting Bits[DB16:DB15] in Register 3 to values 0, 1. The following two topologies are available:
The damping resistor (R1) is divided into two values (R1
and R1A) that have a ratio of 1:3 (see Figure 26).
An extra resistor (R1A) is connected directly from SW,
as shown in Figure 27. The extra resistor is calculated such that the parallel combination of an extra resistor and the damping resistor (R1) is reduced to ¼ of the original value of R1 (see Figure 27).
Figure 26. Fast Lock Loop Filter Topology—Topology 1

SPUR MECHANISMS

This section describes the three different spur mechanisms that arise with a fractional-N synthesizer and how to minimize them in the ADF4151.

Fractional Spurs

The fractional interpolator in the ADF4151 is a third-order Σ-Δ modulator (SDM) with a modulus (MOD) that is programmable to any integer value from 2 to 4095. In low spur mode (dither enabled), the minimum allowable value of MOD is 50. The SDM is clocked at the PFD reference rate (f output frequencies to be synthesized at a channel step resolution of f
/MOD.
PFD
In low noise mode (dither off ), the quantization noise from the Σ-Δ modulator appears as fractional spurs. The interval between spurs is f
/L, where L is the repeat length of the code sequence
PFD
in the digital Σ-Δ modulator. For the third-order modulator used in the ADF4151, the repeat length depends on the value of MOD, as listed in Table 7.
Table 7. Fractional Spurs with Dither Off
Repeat
Condition (Dither Off)
Length Spur Interval
If MOD is divisible by 6 6 × MOD Channel step/6 Otherwise MOD Channel step
In low spur mode (dither on), the repeat length is extended to
21
2
cycles, regardless of the value of MOD, which makes the quantization error spectrum look like broadband noise. This may degrade the in-band phase noise at the PLL output by as much as 10 dB. For lowest noise, dither off is a better choice, particularly when the final loop bandwidth is low enough to attenuate even the lowest frequency fractional spur.

Integer Boundary Spurs

Another mechanism for fractional spur creation is the interactions between the RF VCO frequency and the reference frequency. When these frequencies are not integer related (the point of a fractional-N synthesizer) spur sidebands appear on the VCO output spectrum at an offset frequency that corresponds to the beat note or difference frequency between an integer multiple of the reference and the VCO frequency. These spurs are attenuated by the loop filter and are more noticeable on channels close to integer multiples of the reference where the difference frequency can be inside the loop bandwidth; therefore, the name integer boundary spurs.
) that allows PLL
PFD
Figure 27. Fast Lock Loop Filter Topology—Topology 2
Rev. B | Page 22 of 28
Data Sheet ADF4151
10265-028
LE
PHASE
FREQUENCY
SYNC
(INTERNAL)
–100 0 100 200 1000
300 400 500 600 700 800 900
TIME (µs)
PLL SETTLES TO CORRECT PHASE
AFTER RESYNC
t
SYNC
LAST CYCLE SLIP
PLL SETTLES TO
INCORRECT PHASE

Reference Spurs

Reference spurs are generally not a problem in fractional-N synthesizers because the reference offset is far outside the loop bandwidth. However, any reference feedthrough mechanism that bypasses the loop can cause a problem. Feedthrough of low levels of on-chip reference switching noise, through the RF
IN
pin back to the VCO, can result in reference spur levels as high as −90 dBc. PCB layout must ensure adequate isolation between VCO traces and the input reference to avoid a possible feedthrough path on the board.

SPUR CONSISTENCY AND FRACTIONAL SPUR OPTIMIZATION

With dither off, the fractional spur pattern due to the quanti­zation noise of the SDM also depends on the particular phase word with which the modulator is seeded.
The phase word can be varied to optimize the fractional and subfractional spur levels on any particular frequency. Thus, a look-up table of phase values corresponding to each frequency can be constructed for use when programming the ADF4151.
If a look-up table is not used, keep the phase word at a constant value to ensure consistent spur levels on any particular frequency.

PHASE RESYNC

The output of a fractional-N PLL can settle to any one of the MOD phase offsets with respect to the input reference, where MOD is the fractional modulus. The phase resync feature in the
ADF4151 produces a consistent output phase offset with respect
to the input reference. This is necessary in applications where the output phase and frequency are important, such as digital beam forming. See the Phase Programmability section for how to program a specific RF output phase when using phase resync.
Phase resync is enabled by setting Bit DB16, Bit DB15 in Register 3 to 1, 0. When phase resync is enabled, an internal timer generates sync signals at intervals of t
given by the
SYNC
following formula:
t
= CLK_DIV_VALUE × MOD × t
SYNC
PFD
where: CLK_DIV_VALUE is the decimal value programmed in Bits[DB14:DB3] of Register 3 and can be any integer in the range of 1 to 4095. MOD is the modulus value programmed in Bits[DB14:DB3] of Register 1 (R1).
t
is the PFD reference period.
PFD
When a new frequency is programmed, the second sync pulse after the LE rising edge is used to resynchronize the output phase to the reference. The t
time must be programmed to
SYNC
a value that is at least as long as the worst-case lock time. This guarantees that the phase resync occurs after the last cycle slip in the PLL settling transient.
In the example shown in Figure 28, the PFD reference is 25 MHz and MOD is 125 for a 200 kHz channel spacing. t
SYNC
is set to 400 µs by programming the clock divider value, CLK_DIV_VALUE, to 80.
Figure 28. Phase Resync Example

Phase Programmability

The phase word in Register 1 controls the RF output phase. As this word is swept from 0 to MOD, the RF output phase sweeps over a 360° range in steps of 360°/MOD.
Rev. B | Page 23 of 28
ADF4151 Data Sheet
10265-029
AD9788
TxDAC
REFIO
FSADJ
OUT2_N
OUT1_P
OUT1_N
OUT2_P
2kΩ
LOW-PASS
FILTER
LOW-PASS
FILTER
2700pF 1200pF
39nF
680
360
IBBP
IBBN
QBBP
QBBN
LOIP
LOIN
SPI-CO M P ATIBLE SERIAL BUS
ADF4151
CP
GND
A
GND
A
GND
SD
GND
1nF1nF
4.7kΩ
R
SET
LE
DATA
CLK
REF
IN
FREF
IN
CP
OUT
AV
DD
2 AV
DD
2 CE MUXOUT
V
CC
VCO
OUT
VCO
V
TUNE
1716
AV
DD
1
10
29
1 2
3
22
8 11 18 31
V
DD
LOCK
DETECT
51Ω
51Ω51Ω
51Ω51Ω
25
30
LD
7
D
VDD
28
32
6
SDV
DD
V
P
5
SW
4
ADL5375
RFOUT
QUADRATURE
PHASE
SPLITTER
DSOP
RF
IN–
RF
IN+
15
14
1nF
1nF
100pF
100pF
V
VCO
18Ω
100pF
18Ω
18Ω
MODULATED DIGITAL DATA
V
P
9
A
GND
A
GND
21
D
GND
27
D
GND
26

APPLICATIONS INFORMATION

DIRECT CONVERSION MODULATOR

Direct conversion architectures are increasingly being used to implement base station transmitters. Figure 29 shows how Analog Devices, Inc., parts can be used to implement such a system.
The circuit block diagram shows the AD9788 TxDAC® being used with the ADL5375. The use of dual integrated DACs, such as the AD9788 with its specified ±0.02 dB and ±0.004 dB gain and offset matching characteristics, ensures minimum error contribution (over temperature) from this portion of the signal chain. The signal for the I channel of the quadrature modulator is taken from the OUT1 differential outputs of the
AD9788, and the OUT2 differential outputs provide the signal
for the Q channel of the quadrature modulator ADL5375.
The local oscillator (LO) is implemented using the ADF4151. The low-pass filter was designed using ADIsimPLL™ for a channel spacing of 200 kHz and a closed-loop bandwidth of 35 kHz.
The LO ports of the ADL5375 can be driven from the VCO output. To ensure that all three RF ports (VCO output, RF
IN
and LOIP) are connected to 50 Ω impedance, the matching network of three 18 Ω resistors must be placed as in Figure 29. AC coupling of the RF signal is implemented by the capacitors connected in serial with the 18 Ω resistors . It is possible, as well, to use a balun to convert from a single-ended LO input to the differential LO inputs for the ADL5375.
If the I and Q inputs are driven in quadrature by 2 V p-p signals, the resulting output power from the modulator is approximately 2 dBm.
Figure 29. Direct Conversion Modulator
Rev. B | Page 24 of 28
Data Sheet ADF4151
ADuC812
ADF4151
CLK DATA
LE CE
MUXOUT (LOCK DET E CT)
SCLOCK
MOSI
I/O PORTS
10265-030
ADSP-BF527
ADF4151
CLK DATA LE CE MUXOUT
(LOCK DET E CT)
SCLK
MOSI GPIO
I/O FLAGS
10265-031

INTERFACING

The ADF4151 has a simple SPI-compatible serial interface for writing to the device. CLK, DATA, and LE control the data transfer. When LE goes high, the 32 bits that have been clocked into the appropriate register on each rising edge of CLK are transferred to the appropriate latch. See Figure 2 for the timing diagram and Table 5 for the register address table.

ADuC812 Interface

Figure 30 shows the interface between the ADF4151 and the
ADuC812 MicroConverter®. Because the ADuC812 is based
on an 8051 core, this interface can be used with any 8051-based microcontroller. The MicroConverter is set up for SPI master mode with CPHA = 0. To initiate the operation, the I/O port driving LE is brought low. Each latch of the ADF4151 needs a 32-bit word, which is accomplished by writing four 8-bit bytes from the MicroConverter to the device. When the fourth byte has been written, the LE input should be brought high to complete the transfer.

Blackfin BF527 Interface

Figure 31 shows the interface between the ADF4151 and the Blackfin ADSP-BF527 digital signal processor (DSP). The
ADF4151 needs a 32-bit serial word for each latch write. The
easiest way to accomplish this using the Blackfin family is to use the autobuffered transmit mode of operation with alternate framing. This provides a means for transmitting an entire block of serial data before an interrupt is generated. Set up the word length for eight bits and use four memory locations for each 32-bit word. To program each 32-bit latch, store the four 8-bit bytes, enable the autobuffered mode, and write to the transmit register of the DSP. This last operation initiates the autobuffer transfer. As in the microcontroller case, just make sure that the clock speeds are within the maximum limits outlined in Table 2.
Figure 30. ADuC812 to ADF4151 Interface
I/O port lines on the ADuC812 are also used to control power­down (CE input) and detect lock (MUXOUT configured as lock detect and polled by the port input). When operating in the described mode, the maximum SCLOCK rate of the ADuC812 is 4 MHz. This means that the maximum rate at which the output frequency can be changed is 125 kHz.
Figure 31. ADSP-BF527 to ADF4151 Interface

PCB DESIGN GUIDELINES FOR CHIP SCALE PACKAGE

The lands on the chip scale package (CP-32-7) are rectangular. The PCB pad for these must be 0.1 mm longer than the package land length and 0.05 mm wider than the package land width. The land is to be centered on the pad. This ensures that the solder joint size is maximized. The bottom of the chip scale package has a central thermal pad.
The thermal pad on the PCB must be at least as large as the exposed pad. On the PCB, there is to be a minimum clearance of 0.25 mm between the thermal pad and the inner edges of the pad pattern. This ensures that shorting is avoided.
Thermal vias can be used on the PCB thermal pad to improve the thermal performance of the package. If vias are used, they are to be incorporated in the thermal pad at 1.2 mm pitch grid. The via diameter must be between 0.3 mm and 0.33 mm, and the via barrel must be plated with one ounce copper to plug the via.
Rev. B | Page 25 of 28
ADF4151 Data Sheet
COMPLIANT TO JE DE C S TANDARDS MO-220- WHHD.
112408-A
1
0.50
BSC
BOTTOM VIEWTOP VIEW
PIN 1
INDICATOR
32
9
16
17
24
25
8
EXPOSED
PAD
PIN 1 INDICATOR
3.25
3.10 SQ
2.95
SEATING
PLANE
0.05 MAX
0.02 NOM
0.20 REF
COPLANARITY
0.08
0.30
0.25
0.18
5.10
5.00 SQ
4.90
0.80
0.75
0.70
FOR PRO P E R CONNECTIO N OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPT IONS SECTION OF THIS DATA SHEET.
0.50
0.40
0.30
0.25 MIN

OUTLINE DIMENSIONS

Figure 32. 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
5 mm × 5 mm Body, Very Thin Quad
(CP-32-7)
Dimensions shown in millimeters

ORDERING GUIDE

Model1 Temperature Range Package Description Package Option
ADF4151BCPZ −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ] CP-32-7 ADF4151BCPZ-RL7 −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ] CP-32-7
EVAL-ADF4151EB1Z Evaluation Board
1
Z = RoHS Compliant Part.
Rev. B | Page 26 of 28
Data Sheet ADF4151
NOTES
Rev. B | Page 27 of 28
ADF4151 Data Sheet
©2011 Analog Devices, Inc. All rights reserved. Trademarks and
NOTES
registered trademarks are the property of their respective owners. D10265-0-12/11(B)
Rev. B | Page 28 of 28
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