ADF4150 AD [Analog Devices], ADF4150 Datasheet - Page 25

• Manufacturer Part Number: ADF4150
• Description: Fractional-N/Integer-N PLL Synthesizer
• Manufacturer: AD [Analog Devices]

APPLICATIONS INFORMATION
DIRECT CONVERSION MODULATOR
Direct conversion architectures are increasingly being used to
implement base station transmitters. Figure 30 shows how Analog
Devices, Inc., parts can be used to implement such a system.
The circuit block diagram shows the
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 local oscillator (LO) is implemented using the ADF4150.
The low-pass filter was designed using ADIsimPLL™ for a channel
spacing of 200 kHz and a closed-loop bandwidth of 35 kHz.
FREF
IN
4.7kΩ
1nF
1nF
51Ω
19
24
1
2
3
MODULATED
DIGITAL
DATA
AV
REF
CLK
DATA
LE
R
SET
9
DD
IN
DV
18
DD
AV
2kΩ
16
CP
REFIO
DD
FSADJ
8
GND
V
CE
4
DD
A
PDB
GND
12
ADF4150
17
AD9788
RF
TxDAC
A
AD9788
GND
13
VP
6
SDV
SD
22
23
GND
DD
QOUTA
QOUTB
IOUTA
IOUTB
TxDAC® being
MUXOUT
21
51Ω
51Ω
Figure 30. Direct Conversion Modulator
DETECT
RF
RF
LOCK
RF
LD
RF
20
OUT
OUT
SW
CP
IN
IN
+
–
+
–
51Ω
51Ω
15
14
10
11
5
7
Rev. 0 | Page 25 of 28
100pF
100pF
LOW-PASS
LOW-PASS
V
VCO
2700pF
FILTER
FILTER
3.9nH
3.9nH
VCO
V
360Ω
V
39nF
VCO
680Ω
CC
The LO ports of the ADL5375 can be driven differentially from
the RF
better performance than a single-ended LO driver and
eliminates the use of a balun to convert from a single-ended LO
input to the more desirable differential LO inputs for the
ADL5375. The typical rms phase noise (100 Hz to 5 MHz) of
the LO in this configuration is 0.61°rms.
The ADL5375 accepts LO drive levels from −10 dBm to 0 dBm.
The optimum LO power can be software programmed on the
ADF4150, which allows levels from −4 dBm to +5 dBm from
each output.
The RF output is designed to drive a 50 Ω load but must be
ac-coupled, as shown in Figure 30. 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.
OUT
V
TUNE
VCO
1200pF
1nF
1nF
OUT
+ and RF
QBBP
QBBN
IBBN
IBBP
LOIP
LOIN
OUT
− outputs of the ADF4150. This gives
QUADRATURE
SPLITTER
PHASE
ADL5375
ADF4150
RFOUT
DSOP