ADF4360-3 Analog Devices, ADF4360-3 Datasheet - Page 18

• Manufacturer Part Number: ADF4360-3
• Description: Integrated Synthesizer and VCO
• Manufacturer: Analog Devices

ADF4360-3
APPLICATIONS
DIRECT CONVERSION MODULATOR
Direct conversion architectures are increasingly being used to
implement base station transmitters. Figure 16 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.
FREF
MODULATED
DIGITAL
DATA
1nF
IN
10 µ F
4.7k Ω
1nF
1nF
51 Ω
2kΩ
REFIO
FSADJ
14
16
17
18
19
12
13
CPGND
C
REF
CLK
DATA
LE
C
R
1
V
V
N
C
SET
VCO
VCO
6
IN
3
AD9761
TxDAC
DV
8
21
DD
AGND
9
ADF4360-3
AV
V
DD
10
2
DD
QOUTA
QOUTB
IOUTA
IOUTB
11 22
CE MUXOUT
23
DETECT
LOCK
DGND RF
15
20
RF
V
OUT
OUT
TUNE
CP
A
B
Figure 16. Direct Conversion Modulator
24
7
4
5
V
LOW-PASS
LOW-PASS
VCO
47nH
470pF
FILTER
FILTER
Rev. 0 | Page 18 of 24
6.8k Ω
15k Ω
6.8nF
47nH
2.7pF
2.7pF
220pF
The LO ports of the AD8349 can be driven differentially from
the complementary RF
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 16. 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
4.3nH
4.3nH
QBBP
QBBN
IBBP
IBBN
LOIN
LOIP
OUT
SPLITTER
A and RF
PHASE
VPS1
AD8349
OUT
VPS2
B outputs of the
TO RF PA
100pF