ADF4153
APPLICATIONS INFORMATION
LOCAL OSCILLATOR FOR A GSM BASE STATION
TRANSMITTER
Figure 20 shows the ADF4153 being used with a VCO to
produce the local oscillator (LO) for a GSM base station
transmitter.
The reference input signal is applied to the circuit at REFIN and,
in this case, is terminated in 50 Ω. A 25 MHz reference is used,
which is fed directly to the PFD. To achieve 200 kHz channel
spacing, a modulus of 125 is necessary. Note that with a modulus
of 125, which is not divisible by 2, 3 or 6, subfractional spurs are
avoided. See the Spur Mechanisms section for more information.
The charge pump output of the ADF4153 drives the loop filter.
The charge pump current is ICP = 5 mA. ADIsimPLL is used to
calculate the loop filter. It is designed for a loop bandwidth of
20 kHz and a phase margin of 45 degrees.
The loop filter output drives the VCO, which in turn is fed back
to the RF input of the PLL synthesizer. It 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.
In a PLL system, it is important to know when the loop is in
lock. This is achieved 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
lock detect signal.
VDD
VP
10µF
100nF
100nF
10µF
10pF 100nF
RFOUT
FREFIN
7 15 16
1000pF
10
1000pF 8
AVDD
SVDD
REFIN
DVDD
VP
CP 2
51Ω
ADF4153
22nF
160Ω
82Ω
270nF
5.1kΩ
CLK
DATA
LE
RSET
34
14 LOCK
MUXOUT
DETECT
6 100pF
RFINA
51Ω
RFINB 5
100pF
9
100pF
14
VCC
2
10 100pF 18Ω
18Ω
VCO190-902T
18Ω
8.2nF
DECOUPLING CAPACITORS SHOULD BE PLACED
AS CLOSE AS POSSIBLE TO THE PINS.
Figure 20. Local Oscillator for a GSM Base Station Transmitter
Rev. D | Page 22 of 24