adf4351 Analog Devices, Inc., adf4351 Datasheet - Page 25

• Manufacturer Part Number: adf4351
• Description: Wideband Synthesizer With Integrated Vco Preliminary Technical Data Adf4351
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
APPLICATIONS INFORMATION
DIRECT CONVERSION MODULATOR
Direct conversion architectures are increasingly being used to
implement base station transmitters. Figure shows how Analog
Devices, Inc., parts can be used to implement such a system.
Figure 34 shows the AD9761 TxDAC® being used with the
ADL5375. The use of dual integrated DACs, such as the
AD9788 with its specified ±0.02 dB and ±0.001 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 ADF4351.
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
29
22
1
2
3
MODULATED
DIGITAL
DATA
16
REF
CLK
DATA
LE
R
CP
V
SET
V
VCO
8
VCO
GND
IN
17
SD
DV
28
GND
31
DD
2kΩ
REFIO
AV
FSADJ
AGND
10
DD
9
V
CE
4
11 18 21
DD
ADF4351
A
GNDVCO
PDB
AD9761
TxDAC
26
RF
V
10pF
6
P
D
GND
27
SDV
QOUTB
QOUTA
32
IOUTA
IOUTB
DD
TEMP VCOM V
19
MUXOUT
0.1µF 10pF
DETECT
LOCK
30
Figure 34. Direct Conversion Modulator
23
51Ω
51Ω
RF
RF
RF
RF
LD
CP
25
OUT
OUT
OUT
OUT
V
TUNE
OUT
REF
SW
24
B+
B–
A+
A–
Rev. PrC | Page 25 of 28
51Ω
51Ω
14
15
0.1µF 10pF
12
13
20
7
5
3.9nH
LOW-PASS
LOW-PASS
2700pF
FILTER
FILTER
3.9nH
0.1µF
The LO ports of the ADL5375 can be driven differentially from
the complementary RF
This gives 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 input for the
ADL5375. The typical rms phase noise (100 Hz to 5 MHz)
of the LO in this configuration is 0.61°rms.
The AD8349 accepts LO drive levels from −10 dBm to 0 dBm.
The optimum LO power can be software programmed on the
ADF4351, 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 . 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.
360Ω
V
680Ω
39nF
1nF
1nF
VCO
LPF
LPF
1200pF
QBBP
QBBN
IBBN
LOIP
LOIN
IBBP
OUT
A and RF
QUADRATURE
SPLITTER
PHASE
OUT
B outputs of the ADF4351.
ADL5375
ADF4351
RFO
DSOP