ADF4351BCPZ AD [Analog Devices], ADF4351BCPZ Datasheet - Page 27

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

Data Sheet
OUTPUT MATCHING
For optimum operation, the output of the
matched in a number of ways; the most basic method is to con-
nect a 50 Ω resistor to V
connected in series, as shown in Figure 37. Because the resistor
is not frequency dependent, this method provides a good broad-
band match. When connected to a 50 Ω load, this circuit typically
gives a differential output power equal to the value selected by
Bits[DB4:DB3] in Register 4 (R4).
A better solution is to use a shunt inductor (acting as an RF choke)
to V
output power.
Experiments have shown that the circuit shown in Figure 38
provides an excellent match to 50 Ω for the W-CDMA UMTS
Band 1 (2110 MHz to 2170 MHz). The maximum output power
in this case is approximately 5 dBm. Both single-ended archi-
tectures can be examined using the EVAL-ADF4351EB1Z
evaluation board.
Table 8. LC Balun Components
Frequency
Range (MHz)
137 to 300
300 to 460
400 to 600
600 to 900
860 to 1240
1200 to 1600
1600 to 3600
2800 to 3800
VCO
. This solution gives a better match and, therefore, more
RF
V
Figure 37. Simple Output Stage
VCO
OUT
VCO
Inductor L1 (nH)
100
51
30
18
12
5.6
3.3
2.2
. A dc bypass capacitor of 100 pF is
50Ω
100pF
50Ω
ADF4351
Capacitor C1 (pF)
10
5.6
5.6
4
2.2
1.2
0.7
0.5
can be
Rev. 0 | Page 27 of 28
RF Choke
Inductor L2 (nH)
390
180
120
68
39
15
10
10
If differential outputs are not needed, the unused output can be
terminated, or both outputs can be combined using a balun.
A balun using discrete inductors and capacitors can be imple-
mented with the architecture shown in Figure 39. The LC balun
comprises Component L1 and Component C1. L2 provides a dc
path for RF
OUT
A−, and Capacitor C2 is used for dc blocking.
RF
RF
OUT
OUT
Figure 39. LC Balun for the
RF
V
Figure 38. Optimum Output Stage
V
VCO
VCO
OUT
A+
A–
DC Blocking
Capacitor C2 (pF)
1000
120
120
120
10
10
10
10
3.9nF
L2
1nF
L1
C1
L1
C1
C2
ADF4351
50Ω
Measured Output
Power (dBm)
9
10
10
10
9
9
8
8
50Ω
ADF4351