Datasheet
ADF4360-3 Data Sheet
Rev. D | Page 20 of 24
APPLICATIONS
DIRECT CONVERSION MODULATOR
Direct conversion architectures are increasingly being used to
implement base station transmitters. Figure 17 shows how ADI
parts can be used to implement such a system.
The circuit block diagram shows the AD9761 TxDAC® being
used with the AD8349. The use of dual integrated DACs, such
as the AD9761 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 is implemented using the ADF4360-3. The
low-pass filter was designed using ADIsimPLL for a channel
spacing of 100 kHz and an open-loop bandwidth of 10 kHz.
The frequency range of the ADF4360-3 (1.6 GHz to 1.95 GHz)
makes it ideally suited for implementation of a W-CDMA
transceiver.
The LO ports of the AD8349 can be driven differentially from
the complementary RF
OUT
A and RF
OUT
B outputs of the
ADF4360-3. This gives a better performance than a single-
ended LO driver and eliminates the often necessary use of a
balun to convert from a single-ended LO input to the more
desirable differential LO inputs for the AD8349. The typical
rms phase noise (100 Hz to 100 kHz) of the LO in this
configuration is 1.17°.
The AD8349 accepts LO drive levels from −10 dBm to 0 dBm.
The optimum LO power can be software programmed on the
ADF4360-3, which allows levels from −12 dBm to −3 dBm from
each output.
The RF output is designed to drive a 50 Ω load but must be ac-
coupled, as shown in Figure 17. If the I and Q inputs are driven
in quadrature by 2 V p-p signals, the resulting output power
from the modulator will be approximately 2 dBm
AD9761
TxDAC
AD8349
REFIO
FSADJ
MODULATED
DIGITAL
DATA
QOUTB
IOUTA
IOUTB
QOUTA
2kΩ
LOW-PASS
FILTER
LOW-PASS
FILTER
SPI COMPATIBLE SERIAL BUS
ADF4360-3
V
VCO
V
VCO
V
VCO
CPGND AGND DGND
RF
OUT
B
RF
OUT
A
CP
1nF
470pF 220pF
6.8nF
47nH 47nH
2.7pF
2.7pF
100pF
TO RF PA
4.3nH
4.3nH
1nF1nF
4.7kΩ
15kΩ
6.8kΩ
R
SET
C
C
LE
DATA
CLK
REF
IN
FREF
IN
C
N
V
TUNE
DV
DD
AV
DD
CE MUXOUT
VPS1
IBBP
IBBN
QBBP
QBBN
LOIP
LOIN
VPS2
5
4
24
7
2023221
6
14
16
17
18
19
13
1 3 8 9 10 11 22 15
12
V
DD
LOCK
DETECT
PHASE
SPLITTER
04437-021
51Ω
10µF
Figure 17. Direct Conversion Modulator