Data Sheet
ADF4106
APPLICATIONS
LOCAL OSCILLATOR FOR LMDS BASE STATION
TRANSMITTER
Loop Bandwidth = 50 kHz
FPFD = 1 MHz
Figure 22 shows the ADF4106 being used with a VCO to
produce the LO for an LMDS base station.
N = 5800
Extra Reference Spur Attenuation = 10 dB
The reference input signal is applied to the circuit at FREFIN
and, in this case, is terminated in 50 Ω. A typical base station
system would have either a TCXO or an OCXO driving the
reference input without any 50 Ω termination.
These specifications are needed and used to derive the loop
filter component values shown in Figure 22.
The circuit in Figure 22 shows a typical phase noise
performance of −83.5 dBc/Hz at 1 kHz offset from the carrier.
Spurs are better than −62 dBc.
To achieve a channel spacing of 1 MHz at the output, the
10 MHz reference input must be divided by 10, using the
on-chip reference divider of the ADF4106.
The loop filter output drives the VCO, which in turn is fed
back to the RF input of the PLL synthesizer and also drives the
RF output terminal. A T-circuit configuration provides 50 Ω
matching between the VCO output, the RF output, and the RFIN
terminal of the synthesizer.
The charge pump output of the ADF4106 (Pin 2) drives the
loop filter. In calculating the loop filter component values, a
number of items need to be considered. In this example, the
loop filter was designed so that the overall phase margin for
the system would be 45°.
In a PLL system, it is important to know when the system
is in lock. In Figure 22, this is accomplished by using the
MUXOUT signal from the synthesizer. The MUXOUT pin
can be programmed to monitor various internal signals in the
synthesizer. One of these is the LD or lock-detect signal.
Other PLL system specifications include:
KD = 2.5 mA
KV = 80 MHz/V
V
V
P
DD
RF
OUT
100pF
18Ω
18Ω
16
7
15
100pF
14
18Ω
V
P
CP
AV
DV
6.2kΩ
DD
DD
10
V
CC
1000pF
1000pF
2
2
FREF
8
IN
REF
IN
20pF
100pF
4.3kΩ
51Ω
V956ME03
ADF4106
1, 3, 4, 5, 7, 8,
9, 11, 12, 13
1.5nF
CE
LOCK
DETECT
MUXOUT
14
CLK
DATA
LE
100pF
6
5
RF
RF
A
B
IN
R
1
SET
51Ω
IN
5.1kΩ
100pF
3
4
9
NOTE
DECOUPLING CAPACITORS (0.1
OF THE ADF4106 AND ON V OF THE V956ME03 HAVE
µ
CC
F/10pF) ON AV , DV , AND
DD DD
V
P
BEEN OMITTED FROM THE DIAGRAM TO AID CLARITY.
Figure 22. Local Oscillator for LMDS Base Station
Rev. E | Page 19 of 24
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