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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)： | 5/6頁 |
| 文件大?。?/td> | 43K |
| 代理商： | IX1949PA |
SHARP IX1949PA/IX2083PA-Series . . .
IX1949PA/IX2083PA-Series
RF Application Note
5
Satellite Tuner
In our satellite tuners, the first IF is at 479.5 MHz. All
of the input frequencies for these tuners is above the IF.
In this type of application, the input frequencies in the
band of 950 - 2050 MHz (depending on tuner type) is
converted down to the first IF at 479.5 MHz. This signal
is then either passed out as an IF signal, or further con-
verted down to a secondary IF at 70 MHz, for example.
For the first conversion, an input signal at 950 MHz
must be converted to the IF at 479.5 MHz. To do this,
the LO must be positioned 479.5 MHz above the chan-
nel frequency of interest. For this example:
950 MHz + 479.5 MHz = 1,429.5 MHz
In a tuner with a 10 MHz reference crystal and a
250 kHz step, the calculation for R is:
If the crystal reference is 14.58 MHz with a
364.5 kHz step size:
The Phase Noise of the LO is affected by the value
of R, N and A, so we try to keep R as low as reasonably
possible at the first LO.
Using the 1,429.5 MHz LO above:
1,429.5 MHz = (64N + A) × 250 kHz
For this frequency,
For the value of 5718, N = 89, A = 22
This process will provide accurate number for most
standard frequencies. The value of R can be changed
by a few increments to create offsets in tuning, how-
ever large changes are not recommended unless you
have a thorough grasp on the effects of your changes.
In the double-conversion satellite tuners, the second
LO is controlled by an analog input voltage. The oscil-
lator is preset to the center frequency for the conver-
sion to the correct center frequency of the second IF for
each model.
250 kHz
10 MHz
40
=
364.5 kHz
14.58 MHz
40
=
250 kHz
1,429.5 MHz
(64N + A) = 5,718
=
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