ADF4351BCPZ AD [Analog Devices], ADF4351BCPZ Datasheet - Page 25

• Manufacturer Part Number: ADF4351BCPZ
• Description: Wideband Synthesizer
• Manufacturer: AD [Analog Devices]

Data Sheet
APPLICATIONS INFORMATION
DIRECT CONVERSION MODULATOR
Direct conversion architectures are increasingly being used
to implement base station transmitters. Figure 34 shows how
Analog Devices, Inc., parts can be used to implement such a
system.
Figure 34 shows the
The use of dual integrated DACs, such as the
specified ±2% FSR and ±0.001% FSR gain and offset character-
istics, 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.
f
REFIN
4.7kΩ
1nF
1nF
51Ω
29
22
1
2
3
MODULATED
DIGITAL
DATA
AD9788
16
REF
CLK
DATA
LE
R
CP
V
SET
V
VCO
8
VCO
GND
IN
17
SD
DV
28
GND
31
TxDAC® used with the ADL5375.
DD
AV
AGND
10
DD
9
V
CE
4
11 18 21
DD
ADF4351
A
GNDVCO
PDB
AD9788
TxDAC
26
RF
V
10pF
6
P
DGND
AD9788
27
SDV
OUT1_P
OUT1_N
OUT2_P
OUT2_N
32
DD
TEMP V
19
MUXOUT
0.1µF 10pF
DETECT
LOCK
Figure 34. Direct Conversion Modulator
30
with its
COM
51Ω
51Ω
23
RF
RF
RF
RF
LD
CP
25
OUT
OUT
OUT
OUT
V
V
TUNE
OUT
REF
SW
24
B+
A+
Rev. 0 | Page 25 of 28
B–
A–
51Ω
51Ω
14
15
12
13
20
0.1µF 10pF
5
7
3.9nH
LOW-PASS
LOW-PASS
2700pF
FILTER
FILTER
3.9nH
The LO ports of the
the complementary RF
provides 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
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 it must be
ac-coupled, as shown in Figure 34. If the I and Q inputs are
driven in quadrature by 2 V p-p signals, the resulting output
power from the
V
0.1µF
360Ω
VCO
680Ω
39nF
1nF
1nF
ADL5375
LPF
LPF
1200pF
accepts LO drive levels from −6 dBm to +6 dBm.
ADL5375
QBBP
QBBN
IBBP
IBBN
LOIN
LOIP
ADL5375
OUT
A± outputs of the ADF4351. This setup
modulator is approximately 2 dBm.
QUADRATURE
SPLITTER
can be driven differentially from
PHASE
ADL5375
ADF4351
RFOUT
DSOP