adf4212l Analog Devices, Inc., adf4212l Datasheet - Page 18

• Manufacturer Part Number: adf4212l
• Description: Dual Low Power Pll Frequency Synthesizer
• Manufacturer: Analog Devices, Inc.

ADF4212L
Wideband PLL
Many of the wireless applications for synthesizers and VCOs in
PLLs are narrow-band in nature. These applications include the
various wireless standards such as GSM, DSC1800, CDMA,
or WCDMA. In each of these cases, the total tuning range for
the local oscillator is less than 100 MHz. However, there are
also wideband applications where the local oscillator could have
up to an octave tuning range. For example, cable television
tuners have a total range of about 400 MHz. Figure 8 shows an
application where the ADF4212L is used to control and program
the Micronetics M3500-1324. The loop filter was designed for an
RF output of 2100 MHz, a loop bandwidth of 40 kHz, a PFD
frequency of 1 MHz, I
SPI COMPATIBLE SERIAL BUS
FREF
IN
1000pF
CP
51
of 10 mA (2.5 mA synthesizer I
1000pF
REF
CLK
DATA
LE
V
DD
V
P
IN
1
ADF4212L
V
DD
2
V
V
DD
P
1
MUXOUT
Figure 8. Wideband PLL Circuit
DECOUPLING CAPACITORS ON V
V
THE IF SECTION OF THE CIRCUIT HAS ALSO BEEN OMITTED TO SIMPLIFY THE SCHEMATIC.
V
CC
CP
R
P
RF
2
SET
RF
OF THE M3500-2250 HAVE BEEN OMITTED FROM THE DIAGRAM TO AID CLARITY.
IN
CP
100pF
2.7k
LOCK
DETECT
3.9nF
–18–
51
multiplied by the gain factor of 4), VCO K
(sensitivity of the M3500-1324 at an output of 2100 MHz), and
a phase margin of 45 degrees.
In narrow-band applications, there is generally a small variation
in output frequency (generally less than 10%) and also a small
variation in VCO sensitivity over the range (typically <10%).
However, in wideband applications both of these parameters have
a much greater variation, which will change the loop bandwidth.
This in turn can affect stability and lock time. By changing the
programmable I
varying loop conditions and to ensure that the loop is always
operating close to optimal conditions.
470
27nF
20k
DD
, V
1k
P
130pF
OF THE ADF4212L, ON V
AD820
CP
20V
, it is possible to get compensation for these
3k
V_TUNE
M3500-1324
CC
OF THE AD820 AND ON
GND
12V
V
CC
OUT
100pF 18
D
100pF
of 80 MHz/V
RF
OUT
18
18
REV. A