Vizio VX37L HDTV10A Service Manual page 45

2. 8-VSB and Clear-QAM Reception
MT5112BD contains a 10-bit A/D converter, an 8-VSB/QAM demodulator, followed by a
trellis-code de-modulation (TCM) decoder and a Reed-Solomon forward error correction
(FEC) decoder. Moreover, an embedded 8-bit microprocessor intelligently handles the
acquisition and tracking to ensure the best receiving performance under various channel
conditions. The microprocessor communicates with the external host controller via an
I2C-compatible interface, and also provides direct control to the RF tuner via another
I2C-compatible interface.
MT5112BD accepts the tuner IF output centered at 44MHz or 43.75MHz, or the low IF
signals from a down-converter. With good adjacent channel immunity, additional IF SAW
filters for adjacent channel rejection can be saved. An on-chip programmable
gain-controlled amplifier (PGA) is designed to provide extra signal gain when the tuner
output level is low. The amplified IF signal is then sample and digitized for further
demodulation process.
MT5112BD keeps A/D input power level at a desired level so as to maximize the received
SNR. It measures the power level of the digitized samples and provide two signals (both
sigma-delta encoded; one delayed and one non-delayed) for front-end gain control
purpose. The signals is low-pass filtered before connected to tuner or IF gain stages.
For the 8-VSB reception, the carrier frequency offset is estimated and compensated by a
fully digital synchronizer. It also controls the rate conversion in the digital re-sampling
device by estimating the sampling frequency offset; hence no external VCXO is required.
The digital synchronizer simultaneously offers very wide frequency acquisition range and
stable tracking capability. This makes MT5112BD robust work under severe impairment
conditions.
The MT5112BD is equipped with a powerful equalizer for mitigating the multi-path effects
due to terrestrial propagation of 8-VSB signals. The delicate equalizer design makes the
MT5112BD boast its ability for strong echo cancellation. With this powerful equalizer, the
MT5112BD can not only easily pass the tests of A74 equalization mask, ATTC channel
ensembles, CRC channel ensembles, but also provide superior capability of live signal
receptions.
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File No. SG-0209