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參數(shù)資料
| 型號： | ADF4219L |
| 英文描述： | ADF4217L/18L/19L: Dual Low Power Frequency Synthesizers Data Sheet (Rev. B. 7/02) |
| 中文描述： | ADF4217L/18L/19L：雙低功耗頻率合成器數(shù)據(jù)手冊（啟示二7月2日） |
| 文件頁數(shù)： | 18/20頁 |
| 文件大小： | 400K |
| 代理商： | ADF4219L |
REV. A
–18–
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
CP
of 10 mA (2.5 mA synthesizer I
CP
multiplied by the gain factor of 4), VCO K
D
of 80 MHz/V
(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
CP
, it is possible to get compensation for these
varying loop conditions and to ensure that the loop is always
operating close to optimal conditions.
REF
IN
D
R
A
R
D
I
A
I
RF
IN
MUXOUT
R
SET
V
P
1
V
P
2
V
DD
2
V
DD
1
ADF4212L
SPI COMPATIBLE SERIAL BUS
CLK
DATA
LE
1000pF
1000pF
51
FREF
IN
V
DD
V
P
2.7k
LOCK
DETECT
100pF
51
CP
RF
AD820
20k
3.9nF
27nF
470
130pF
1k
20V
3k
V_TUNE
M3500-1324
GND
V
CC
OUT
100pF18
18
18
100pF
RF
OUT
DECOUPLING CAPACITORS ON V
, V
OF THE ADF4212L, ON V
OF THE AD820 AND ON
V
OF THE M3500-2250 HAVE BEEN OMITTED FROM THE DIAGRAM TO AID CLARITY.
THE IF SECTION OF THE CIRCUIT HAS ALSO BEEN OMITTED TO SIMPLIFY THE SCHEMATIC.
12V
Figure 8. Wideband PLL Circuit
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