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參數(shù)資料
| 型號： | IX1949PA |
| 廠商： | Sharp Corporation |
| 英文描述： | Phase-Locked-Loop Integrated Circuit(鎖相環(huán)集成電路) |
| 中文描述： | 鎖相環(huán)回路集成電路（鎖相環(huán)集成電路） |
| 文件頁數(shù)： | 1/6頁 |
| 文件大小： | 43K |
| 代理商： | IX1949PA |
RF Application Note
Page 1
IX1949PA/IX2083PA-Series
Phase-Locked-Loop Integrated Circuit
RF Application Note
The IX1949PA/IX2083PA-series Phase-Locked-
Loop (PLL) Integrated Circuit (IC) is used in a variety of
Sharp tuners. Applications for this device include satel-
lite and cable television tuner modules. The devices in
this series are IX1949PA and IIX2083PA. These PLLs
cover different frequency ranges and are programmed
in a like manner. The frequency range of the applica-
tion determines which IC and crystal reference fre-
quency is used. In some cases, any one of the PLLs
may meet requirements and be used in the same
model tuner.
The two ICs are not footprint compatible, however,
this is not a problem. These devices were developed
for internal Sharp use, and are not intended for external
sale. The information contained in this Application Note
is for use in developing software to control tuners in a
variety of applications.
The basic control algorithm for the PLL as follows:
(1)
F
VCO
= [(M × N) + A] × F
OSC
÷ R, with A < N
Where:
F
VCO
is the Local Oscillator frequency.
M is the 64 or 256 prescaler divide ratio.
N is the 11-bit divide counter value, 16 to
2,047.
A is the Swallow counter value, 0 to 255.
F
OSC
is the reference crystal, i.e. 4 MHz.
R is the 12-bit programmable reference divide
counter value 8 to 4,095.
The IX2083PA-series of PLLs uses two setup regis-
ters to control operation of the PLL. The Reference
Counter is configured to set the internal reference fre-
quency by dividing the external crystal frequency by a
specific value.
For example, with an external crystal of 4 MHz, set-
ting the R register to a value of 16 provides a step size
of 250 kHz.
This step reduces the expression (1) to:
(2)
F
VCO
= [(M × N) + A] × Step Size
In all cases, the tuner step size is determined by
dividing the crystal reference frequency by R.
In our applications, the internal prescaler is set to a
value of 64. Thus M = 64 and the expression becomes:
(3)
F
VCO
= [(64 × N) + A] × Step Size
The Local Oscillator (LO) in the tuner is positioned
above the channel of interest by a value equal to the
Intermediate Frequency (IF) of the tuner. For example,
in a double-conversion tuner the first IF is at 954 MHz
and the second (output) IF is positioned so the signal
carrier is at 44 MHz for digital applications. The signal
center frequency is positioned to be centered in the
channel filters.
For analog applications the first video IF is at 955.75
MHz and the output IF the video carrier is positioned at
45.75 MHz.
To correctly set up the tuner for the proper conver-
sions, the first and second LOs must be positioned to
the correct frequencies. For example, to convert an
analog input signal with the video carrier at 55.25 MHz,
the first LO is positioned so that the input channel plus
the first IF equals the LO, as shown:
Input + IF = LO.
For the example of 55.25 MHz, using the analog
first IF frequency:
55.25 MHz + 955.75 MHz = 1,011 MHz.
The LO must be positioned at 1,011 MHz in order
to place the correct mixer conversion product in the
first IF filter.
To finish the conversion to the second, or output IF,
the tuner specification will provide the correct pro-
gramming frequency. In the example that we are
using, it is 910 MHz. When the signal in the first IF fil-
ter is mixed with the second LO at 910 MHz, the dif-
ference output is positioned at 45.75 MHz, providing
a standard TV IF signal.
When digitally modulated signals are tuned, a chan-
nel centered at 57 MHz will be converted up the first IF
at 954 MHz. The same expression applies in this case:
57 MHz + 954 MHz = 1,011 MHz.
16
4 MHz
250 kHz
=
SHARP IX1949PA/IX2083PA-Series Tuner Programming
Robert Stuart, RF Applications Engineer
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