ADF4360-3
Data Sheet
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 LO ports of the AD8349 can be driven differentially from
the complementary RFOUTA and RFOUTB 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 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 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 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 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
REFIO
IOUTA
LOW-PASS
FILTER
IOUTB
MODULATED
DIGITAL
DATA
AD9761
TxDAC
QOUTA
QOUTB
LOW-PASS
FILTER
FSADJ
2kΩ
LOCK
V
V
DETECT
VCO
DD
VPS1
VPS2
IBBP
IBBN
6
21
2
23
20
10μF
V
CE MUXOUT
DD
7
TUNE
CP
V
DV
AV
VCO
DD
15k
6.8nF
6.8k
Ω
14
16
C
100pF
N
24
1nF 1nF
51
FREF
REF
IN
IN
470pF
220pF
Ω
TO RF PA
AD8349
Ω
17 CLK
QBBP
QBBN
ADF4360-3
18
19
12
DATA
LE
V
VCO
C
C
47nH
47nH
2.7pF
2.7pF
4.3nH
4.3nH
13
R
LOIP
LOIN
SET
1nF
RF
A
B
4
5
OUT
PHASE
SPLITTER
4.7kΩ
CPGND
1
AGND
DGND
RF
OUT
3
8
9
10 11 22 15
Figure 17. Direct Conversion Modulator
Rev. C | Page 20 of 24
ADI [ ADI ]
