ADF4207 datasheet(18/20 Pages) AD

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APPLICATIONS SECTION

Local Oscillator for GSM Handset Receiver

Figure 7 shows the ADF4207 being used in a classic superhet-

erodyne receiver to provide the required LOs (Local Oscillators).

In this circuit, the reference input signal is applied to the circuit

at OSCIN and is being generated by a 10 MHz Crystal Oscillator.

This is a low-cost solution and for better performance over tem-

perature, a TCXO (Temperature Controlled Crystal Oscillator)

may be used instead.

In order to have a channel spacing of 200 kHz (the GSM stan-

dard), the reference input must be divided by 50, using the

on-chip reference counter.

The RF output frequency range is 1050 MHz to 1086 MHz. Loop

ﬁlter component values are chosen so that the loop bandwidth is

20 kHz. The synthesizer is set up for a charge pump current of

4.375 mA and the VCO sensitivity is 15.6 MHz/V.

OSC

OUT

MUXOUT

ADF4208

DD2 VDD1VP1

RF1

RF2IN

RF1IN

OSC

CLK

DATA

DECOUPLING CAPACITORS (22 F/10pF) ON VDD, VP OF

THE ADF4208, AND ON VCC OF THE VCOs HAVE BEEN

OMITTED FROM THE DIAGRAM TO AID CLARITY.

VCO190-200T

RF2

100pF

OUT

100pF

30pF

10MHz

18k

1.3nF

13nF

2.7k

620pF

3.3k

100pF

OUT

100pF 18

100pF

LOCK DETECT

30pF

VCO190-1750T

Figure 8. Local Oscillator for WCDMA Receiver Using the ADF4208

The IF output is ﬁxed at 125 MHz. The IF loop bandwidth is

chosen to be 20 kHz with a channel spacing of 200 kHz. Loop

ﬁlter component values are chosen accordingly.

Local Oscillator for WCDMA Receiver

Figure 8 shows the ADF4208 being used to generate the local

oscillator frequencies for a Wideband CDMA (WCDMA) system.

The RF output range needed is 1720 MHz to 1780 MHz. The

VCO190–1750T will accomplish this. Channel spacing is

200 kHz with a 20 kHz loop bandwidth. VCO sensitivity is

32 MHz/V. Charge pump current of 4.375 mA is used and

the desired phase margin for the loop is 45

°.

The IF output is ﬁxed at 200 MHz. The VCO190–200T is used.

It has a sensitivity of 10 MHz/V. Channel spacing and loop

bandwidth is chosen to be the same as the RF side.

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