L64780 LSI Logic Corporation, L64780 Datasheet - Page 26

• Manufacturer Part Number: L64780
• Description: Dvb-t Cofdm Demodulator Technical Manual 2/00
• Manufacturer: LSI Logic Corporation

2.5 Fast Fourier Transform (FFT) Block
2.6 Time Synchronization
2.6.1 Timing Loop Gain
2-8
The FFT block converts from the temporal to the frequency domain
representation. It has the following modes of operation:
This block finds the optimum timing for the start of the FFT window, and
synchronizes the frequency of the clock, f
The options for the duration of the symbol and the duration of the guard
interval are given in paragraph 4.4 of the DVB-T/ETSI Specification.
The block takes the sequence of complex numbers from the real-to-
complex conversion block and, to synchronize the clock, produces a
control signal for the voltage-controlled oscillator. The control voltage of
the VCXO is converted into a Sigma-Delta (
output as a single wire signal. This signal requires external low-pass
filtering to extract its mean value, which represents the control voltage of
the oscillator.
The transmitter repeats a segment of the signal during the guard interval.
This block detects the repeated portion of the signal. The signal
processing resists impairment from high levels of echoes or interference.
In 2 k mode, the optimal IIRGAIN is 0b01, or
This leads to K
Equation 2.8
In 8 k mode, the optimal IIRGAIN is 0b11, or
Architectural Overview
FFT and Inverse FFT
2 k (2048 points) and 8 k (8192 points) mode
I
K
and K
I
------------------
K
P
1.69
VCXO
values of:
CLK18
K
P
, to the received signal
) Modulated signal and
512 K
3.125 10
7.8 10
I
–
3
–
.
2
.