ADF4112BCPZ datasheet(22/28 Pages) AD

22 / 28 page

ADF4110/ADF4111/ADF4112/ADF4113

Data Sheet

Rev. F | Page 22 of 28

APPLICATIONS

LOCAL OSCILLATOR FOR GSM BASE STATION TRANSMITTER

Figure 33 shows the ADF4111/ADF4112/ADF4113 being used

with a VCO to produce the LO for a GSM base station

transmitter.

The reference input signal is applied to the circuit at FREFIN

and, in this case, is terminated in 50 Ω. A typical GSM system

would have a 13 MHz TCXO driving the reference input with-

out any 50 Ω termination. In order to have channel spacing of

200 kHz (GSM standard), the reference input must be divided

by 65, using the on-chip reference divider of the ADF4111/

ADF4112/ADF4113.

The charge pump output of the ADF4111/ADF4112/ADF4113

(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 degrees. Other PLL

system specifications are

KD = 5 mA

KV = 12 MHz/V

Loop Bandwidth = 20 kHz

FREF = 200 kHz

N = 4500

Extra Reference Spur Attenuation = 10 dB

All of these specifications are needed and used to come up with

the loop filter component values shown in Figure 33.

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 out-

put 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 system is in

lock. In Figure 33, this is accomplished by using the MUXOUT

signal from the synthesizer. The MUXOUT pin can be pro-

grammed to monitor various internal signals in the synthesizer.

One of these is the LD or lock-detect signal.

ADF4111

ADF4112

ADF4113

CLK

DATA

1000pF

REFIN

100pF

MUXOUT

1nF

8.2nF

620pF

100pF

Ω1

3.3k

Ω

5.6k

Ω

100pF

Ω

1TO BE USED WHEN GENERATOR SOURCE IMPEDANCE IS 50

Ω.

2OPTIONAL MATCHING RESISTOR DEPENDING ON RFOUT FREQUENCY.

DECOUPLING CAPACITORS ON AVDD, DVDD, AND VP OF THE ADF411x

AND ON THE POSITIVE SUPPLY OF THE VCO190-902T HAVE BEEN

OMITTED FROM THE DIAGRAM TO INCREASE CLARITY.

RSET

RFINA

RFINB

AVDD DVDD VP

FREFIN

VDD

LOCK

DETECT

VCC

VCO190-902T

Ω

100pF

RFOUT

4.7k

Ω

Ω2

Figure 33. Local Oscillator for GSM Base Station

ADF4112BCPZ датащи(PDF) 22 Page - Analog Devices

ADF4112BCPZ датащи(HTML) 22 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL