ADF4206 datasheet(21/24 Pages) AD

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ADF4206/ADF4208

Rev. A | Page 21 of 24

LOCAL OSCILLATOR FOR WCDMA RECEIVER

Figure 33 shows the ADF4208 used to generate the local

oscillator frequencies for a wideband CDMA (WCDMA)

system.

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

VCO190-1750T meets this requirement. Channel spacing is

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

32 MHz/V. A charge pump current of 4.375 mA is used and the

desired phase margin for the loop is 45°.

When 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 are chosen to be the same as the RF side.

OSCOUT

MUXOUT

ADF4208

VP2

VDD2 VDD1VP1

CPRF1

RF2IN

RF1IN

OSCIN

CLK

DATA

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

THE ADF4208, AND ON VCC OF THE VCOs HAVE BEEN

OMITTED FROM THE DIAGRAM TO AID CLARITY.

VCO190-200T

VCC

CPRF2

VCC

100pF

18Ω

100pF

IFOUT

100pF

51Ω

30pF

10MHz

18kΩ

1.3nF

13nF

2.7k

620pF

3.3kΩ

VDD

100pF

18Ω

RFOUT

100pF 18Ω

18Ω

100pF

51Ω

LOCK DETECT

30pF

VCO190-1750T

Figure 33. Local Oscillator for WCDMA Receiver Using the ADF4208

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