DTV Demodulator
Cable, satellite, and terrestrial video service providers use digital television (DTV) demodulators to receive video programs over broadcast mediums such as coaxial cables or air and transform the data back into digital video, audio, and ancillary data. Demodulators transmit data as a transport stream (TS) via the digital video broadcasting (DVB) asynchronous serial interface (ASI) at 270 Mbps. The transport stream includes audio, video, and ancillary data inputs which have been encoded with compression schemes such as the Moving Picture Experts Group (MPEG)-2 or MPEG-4 scheme.
DTV demodulators perform forward error correction (FEC) decoding and map the modulated data back into a binary bit stream. The modulation schemes used for DTV vary by global geography and broadcast medium. Examples of modulation schemes used for DTV broadcasting are quadrature amplitude modulation (QAM), quadrature phase shift keying (QPSK), coded orthogonal frequency division multiplexing (COFDM), and vestigial sideband (VSB) modulation. Figure 1 shows a typical Altera® programmable logic solution for a DTV demodulator.
Figure 1. Altera Usage Example for DTV Demodulators
Notes:
- ADC = Analog-to-digital converter
- AGC = Automatic gain control
- FFT = Fast Fourier transform
Altera has partnered with intellectual property (IP) developers who are experts in DTV modulation/demodulation technologies and offer solutions for video broadcast. Altera also offers the video and image processing library which includes a number of functions required for modulation and demodulation. Examples of Altera IP from the IP MegaStore™ website used in DTV demodulators are:
- Reed-Solomon decoder
- Viterbi decoder
- De-interleaver
- Numerically controlled oscillator (NCO)
- Finite impulse response (FIR) filter
- 8b/10b encoder
A Feature-Rich Programmable Solution for DTV Demodulators
The feature-rich architecture of Altera's Stratix® III and the low-cost Cyclone® III devices provide excellent solutions for the DTV demodulators. These device families use high-performance architectures that accelerate block-based designs for maximum system performance. Stratix III devices include 768 high-performance digital signal processing (DSP) blocks, up to 14 Mbits of embedded TriMatrix memory, 338K equivalent logic elements (LEs), and flexible I/O standards. The low-cost Cyclone III FPGA also provides up to 288, 18 x 18 multipliers and 3.8 Mbits of embedded memory with flexible I/O support. Their feature sets provide an ideal solution for implementing FEC decoding, data de-interleaving, modulation scheme demapping, and DVB-ASI output processing. Stratix III devices give you flexibility, performance, integration, and design resources that are not available in any other solution.
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