Data Sheet

ADF4153A

Rev. A | Page 21 of 24

APPLICATIONS INFORMATION

LOCAL OSCILLATOR FOR A GSM BASE STATION

TRANSMITTER

Figure 25 shows the ADF4153A being used with a VCO to

produce the local oscillator (LO) for a GSM base station

transmitter.

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 ADF4153A drives the loop

filter.

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

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.

ADF4153A

22nF

82Ω

160Ω

270nF

VCO190-902T

18Ω

18Ω

18Ω

100pF

100pF

1000pF

1000pF

51Ω

4.7kΩ

4

1

6

17

16

7

18

5

15

14

10

20

2

MUXOUT

LOCK

DETECT

100pF

100pF

CLK

DATA

LE

DECOUPLING CAPACITORS SHOULD BE PLACED

AS CLOSE AS POSSIBLE TO THE PINS.

CP

8

11

3

9

10

2

8.2nF

100nF

10µF

100nF

10µF

10pF

100nF

51Ω

Figure 25. Local Oscillator for a GSM Base Station Transmitter