L64733C LSI Logic Corporation, L64733C Datasheet - Page 4

• Manufacturer Part Number: L64733C
• Description: Tuner And Satellite Receiver Chipset Data Sheet 2/01
• Manufacturer: LSI Logic Corporation

The RF signal is sent to a variable gain stage controlled by the L64734
AGC1 signal. The L64734 adjusts AGC1 in conjunction with AGC2 to
maximize the SNR of the RF In signal while maintaining proper levels at
the baseband outputs (IOUT and QOUT). The signal then is fed to two
mixers in the quadrature demodulator. The mixers are fed with local
oscillator signals that are offset by 90 degrees from one another. The
quadrature demodulator converts the frequency of the RF In signal
directly to baseband while splitting the signal into quadrature I and Q
signal paths.
The baseband signals pass through a pair of variable gain amplifiers,
controlled through the AGC2 pin by the L64734. The signals then pass
through a pair of seventh-order filters for antialiasing. The filter shape is
seventh-order Butterworth, followed by a single-pole delay equalizer. The
L64734 FLCLK signal controls the filter cutoff frequency, which is related
to the baud rate. The filtered baseband output signals are fed to
differential output stages at IOUTp, IOUTn, QOUTp, and QOUTn.
The baseband outputs of the L64733C are sent to the L64734 to be
digitized by the analog-to-digital converter (ADC). Then, they are sent to
a BPSK/QPSK demodulator, filtered, and sent to the L64734 forward
error correction (FEC) decoder pipeline, which outputs an MPEG-2
transport stream.
The frequency synthesizer functionality is split between the L64733C and
L64734. The Synthesizer Control Module resides on the L64734 and
generates control signals for the L64733C Tuner IC frequency
synthesizer. The Synthesizer Control Module also contains
programmable counters for the synthesizer feedback loop.
The L64733C provides analog functions for the frequency synthesizer,
the RF local oscillator, and the crystal reference oscillator. Tuning
oscillator signals are generated for the mixers in the 925–2175 MHz
range, with a 0.625 MHz step size when using a 5 MHz crystal reference.
The on-chip VCO tuning frequency is 543–1088 MHz. To tune channels
from 925–1086 MHz, the L64734 disables the frequency doubler (X2
block) on the L64733C. To tune channels from 1086–2175 MHz, the
L64734 enables the frequency doubler.
The L64733C can improve half-harmonic rejection. It requires special
programming of the frequency doubler control pin (FDOUB), which now
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L64733C/L64734 Tuner and Satellite Receiver Chipset