参数资料
型号: L64781
厂商: LSI CORP
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PQFP100
封装: PLASTIC, QFP-100
文件页数: 90/164页
文件大小: 2003K
代理商: L64781
Fast Fourier Transform (FFT)
2-11
2.8 Fast Fourier Transform (FFT)
The fast Fourier transform (FFT) block converts from the temporal to the
frequency domain representation. It contains all the necessary data and
coefcient storage elements to operate in either 2-K mode (2048
complex points) or 8-K mode (8192 complex points). All numbers in the
FFT block are in two’s complement and xed-point representation.
Equation 2.8 demonstrates the forward FFT operation:
Equation 2.8
2.9 Frequency Synchronization
The frequency synchronization block corrects for tolerance, or adjusts,
the frequency of the local oscillator in the tuner. The shift, or adjustment,
must be accurate to within a small fraction of the carrier spacing to keep
intercarrier interference to an acceptably low level and to ensure that the
tracking ability of the channel estimation is not absorbed in correcting for
the error in the frequency of the local oscillator.
The L64781 lets you choose either analog or digital frequency
synchronization. Which method to choose depends upon the detailed
design of the analog tuner.
2.9.1 Analog Frequency Synchronization
The analog frequency synchronization block adjusts the frequency of the
local oscillator in the tuner so that the center frequency of the low IF is
equal to its nominal value of fLIF. The block takes the sequence of
complex numbers from the output of the FFT block and produces a
control signal for the local oscillator. The control signal is delivered as a
single-wire sigma-delta (
Σ/) signal.
Xk
()
xn
()e
j 2
π
kn
N
------
n
0
=
N
1
=
l64781.book Page 11 Friday, January 19, 2001 1:28 PM
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