描述 Description

The AT76C651B is a DVB-compliant Quadrature Amplitude Modulation (QAM) demodulation circuit, which can be used in DVB and other applications using Quadrature Phase Shift Keying (QPSK) or QAM transmission systems. The signal, after output from tuner and adjacent channels rejection filter, is sampled at Intermediate Frequency (IF).

The signal is converted to digital format and goes through several processing steps required for demodulation: automatic gain control, baseband down conversion, timing recovery with anti-aliasing filtering, square root raised-cosine receive filtering, carrier recovery and digital gain control and equalization (linear and decision feedback dual structure). The output from demodulation then goes through forward error decoding:DVB/DAVIC de-mapping, frame synchronization, de-interleaving, Reed-Solomon decoding and spectrum de-randomization. The output before decoding may also be output directly for use with post-processing devices in applications other than DVB.An additional block situated in the back-end may be used to filter out programmable PIDs, providing additional flexibility in interactive solutions or DVB data-broadcast PC receive cards.

It is especially designed for modem implementations with a 24-bit mask on one PID (medium access control) and can be used for return channel implementation.

特性 Features

? DAVIC/DVB/ETS300.429/ITU-T J.83 Annex A, C Fully Compliant
? Direct IF Sampling (No Second IF Down Conversion Required) or Baseband Input
? Internal 10-bit A/D Converter or Possibility to Use External A/D
? 1024, 512, 256, 128, 64, 32, 16 QAM And QPSK Demodulation
? Roll-off Factor Adapted to Raised-cosine Filtered Signal (0.11 to 0.4)
? Fully Digital Timing Recovery
? Variable Symbol Rate Recovery
? Anti-aliasing Continuously Variable Digital Filtering with Symbol Rate Adaptive Bandwidth (1 to 18.75M Baud at the Same Sampling Frequency)
? Fully Digital Carrier Recovery (Coherent or Differential For QPSK)
? Robust Equalizer Acquisition
? Selectable Transversal or Decision Feedback Equalizer
? Dual Phase/Frequency Offset Recovery Up To 12% of the Symbol Rate with no Degradation
? MPEG2 Frame Synchronization
? Reed-Solomon Decoder (204, 188, 8)
? De-interleaving (I = 12 and I = 17)
? Energy Dispersal Descrambling
? 2-wire Serial Interface (2WSI) Switch for Separate Bi-directional 2WSI Bus-to-tuner To Avoid Phase Noise Problems Due to 2WSI
? Integrated Clock Reference for Tuner, Especially Designed For NIU in CAN
? Two AGCs: Analog and Digital Gains
? Three Program Identifiers (PIDS) Filtering
? IRQ Interrupt Request Generation to Simplify Monitoring
? Bit Error Rate and Packet Error Rate Monitoring
? Signal-to-noise Ratio Estimation, Residual Phase Noise Estimation
? Automatic Spectrum Inversion
? JTAG Support
? 0.35μ CMOS Technology, 3.3V Operation
? Available in a 144-lead LQFP Package