Dual Fractional-N/Integer-N
Frequency Synthesizer
ADF4251
FEATURES
GENERAL DESCRIPTION
3.0 GHz Fractional-N/1.2 GHz Integer-N
2.7 V to 3.3 V Power Supply
Separate VP Allows Extended Tuning Voltage to 5 V
Programmable Dual Modulus Prescaler
RF: 4/5, 8/9
IF: 8/9, 16/17, 32/33, 64/65
Programmable Charge Pump Currents
3-Wire Serial Interface
Digital Lock Detect
Power-Down Mode
Programmable Modulus on Fractional-N Synthesizer
Trade-Off Noise versus Spurious Performance
Software and Hardware Power-Down
The ADF4251 is a dual fractional-N/integer-N frequency
synthesizer that can be used to implement local oscillators
(LO) in the upconversion and downconversion sections of
wireless receivers and transmitters. Both the RF and IF syn-
thesizers consist of a low noise digital PFD (phase frequency
detector), a precision charge pump, and a programmable refer-
ence divider. The RF synthesizer has a ⌺-⌬ based fractional
interpolator that allows programmable fractional-N division.
The IF synthesizer has programmable integer-N counters. A
complete PLL (phase-locked loop) can be implemented if the
synthesizer is used with an external loop filter and VCO (volt-
age controlled oscillator).
Control of all the on-chip registers is via a simple 3-wire inter-
face. The devices operate with a power supply ranging from
2.7 V to 3.3 V and can be powered down when not in use.
APPLICATIONS
Base Stations for Mobile Radio (GSM, PCS, DCS,
CDMA, WCDMA)
Wireless Handsets (GSM, PCS, DCS, CDMA, WCDMA,
PHS)
Wireless LANs
Communications Test Equipment
CATV Equipment
FUNCTIONAL BLOCK DIAGRAM
V
1
V
2
V
3
DV
V 1
V 2
R
SET
DD
DD
DD
DD
P
P
CE
CP
ADF4251
REFERENCE
4-BIT R
ꢀ2
COUNTER
REF
PHASE
IN
DOUBLER
CHARGE
PUMP
FREQUENCY
DETECTOR
RF
LOCK
OUTPUT
MUXOUT
DETECT
MUX
RF
RF
A
IN
FRACTIONAL N
RF DIVIDER
B
IN
CLK
DATA
LE
24-BIT
DATA
REGISTER
INTEGER N
IF DIVIDER
IF
IF
B
IN
FROM
REFIN
A
IN
PHASE
CHARGE
PUMP
CP
FREQUENCY
DETECTOR
IF
ꢀ2
15-BIT R
DOUBLER
COUNTER
A
1
A
2
D
CP
1
CP
2
GND
GND
GND
GND
GND
REV. 0
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