adf4207 Analog Devices, Inc., adf4207 Datasheet - Page 18

• Manufacturer Part Number: adf4207
• Description: Dual Rf Pll Frequency Synthesizers
• Manufacturer: Analog Devices, Inc.

ADF4206/ADF4207/ADF4208
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 OSC
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.
IN
100pF
and is being generated by a 10 MHz Crystal Oscillator.
18
18
IF
OUT
DECOUPLING CAPACITORS (22 F/10pF) ON V
THE ADF4208, AND ON V
OMITTED FROM THE DIAGRAM TO AID CLARITY.
18
100pF
51
VCO190-200T
100pF
V
CC
CC
1.3nF
OF THE VCOs HAVE BEEN
30pF
30pF
2.7k
3.3k
13nF
DD
10MHz
, V
620pF
18k
P
OF
CP
V
RF2
OSC
OSC
V
P
P
2
RF2
IN
IN
OUT
ADF4208
V
V
DD
DD
2 V
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.
DD
1
MUXOUT
CP
DATA
RF1
CLK
V
V
RF1
LE
P
P
IN
1
LOCK DETECT
V
VCO190-1750T
CC
100pF
100pF 18
51
100pF
RF
OUT
18
18