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Volume 3 (Aug 01, 2003)
Commercialization of orthogonal frequency division multiplexing (OFDM) demodulation LSI chip for digital terrestrial broadcast mobile receivers (2/2)
New trends expected to be generated through digital terrestrial broadcasting
Low consumption and miniaturization of receivers will be possible because only central one-segment data is received, thereby enabling mobile phones, PDAs and other mobile devices to get TV reception.
Japanese digital terrestrial broadcasting employs a system in which the transmitter divides data into 13 segments, combines those segments and then sends them according to each specific service. The receiver then chooses from among the specified services and receives the data. Ordinary home-use TVs are capable of receiving all 13 segments at once.
It is now necessary to place priority on reducting power consumption and realizing stable reception for mobile terminal devices such as mobile phones, PDAs and car mobile receivers. To this end, a partial reception method with which the content of one segment rather than 13 segments is received (Figure 2) must be employed. Moreover, through the use of orthogonal frequency division multiplexing (OFDM), multipaths caused by the reflection of electromagnetic waves off of buildings, and ghosts that generate the flickering phenomenon, can be significantly suppressed.
With advancement in the diffusion of not only home-use TVs, but also mobile devices equipped with TV reception functions, people will be able to view terrestrial digital broadcasting whenever and wherever they like. In addition, since it will become possible to exchange e-mail and access the Internet while at the same time watching TV, it can also be expected that new services integrating both communications and terrestrial digital broadcasting will be established. In this way, it can also be expected that the diffusion of terrestrial digital broadcasting will create a new product market and lead to significant changes in our lifestyles.
NEC Electronics - The first company to commercialize an OFDM demodulation LSI chip
NEC Electronics is the first company in the industry to have commercialized an OFDM demodulation LSI chip for digital terrestrial use. The µPD61530 (Figure 4), which is specialized for use in mobile receivers (Figure 3), is capable of receiving only one out of 13 segments. This product integrates onto just one chip all of the functions necessary for digital terrestrial broadcast receivers, including an OFDM demodulation circuit and error correction circuit among others, all of which are compliant with Japanese digital terrestrial broadcasting standards. In addition, through the development of a unique circuit algorithm, a low consumption rate of 40 mW has been realized. One of the major features of this LSI chip is its small body size of 9 mm x 9 mm, enabling its use in even extremely small packages. This small size enables the development of compact mobile terminals capable of digital terrestrial broadcasting reception over long periods of time. Furthermore, in terms of the AV decode section connected to this product, we are currently developing high-performance DSP and DSP middleware such as video and audio decoders to realize an application chip.
In the future, NEC Electronics will continue to make the most of this type of component technology to offer our customers optimal solutions for digital terrestrial receivers to contribute to the diffusion of digital terrestrial broadcasting and prompt commercialization of digital terrestrial receivers.
Digital terrestrial receivers are composed of three blocks: the tuner, the OFDM demodulator and the AV decoder. The OFDM modulation signal selected in the tuner section first undergoes A/D conversion, OFDM demodulation and error correction through the OFDM demodulation LSI chip and then is input into the A/V decoder as transport output. In the A/V decoder, the signal is separated into an audio signal and a video signal within the TS decoder section and then played back as audio and video signals through the audio decoder and video decoder, respectively.
* The following are definitions of the acronyms used in the figure.
TS decoder: Transport stream decoder
Video decoder: Video signal decoder
Audio decoder: Audio signal decoder
OFDM demodulation LSI chips are composed of an OFDM demodulation section, a time de-interleaver section, an error correction section and a CPU section. The OFDM demodulation section consists of the ADC section, in which the OFDM modulation signal received by the tuner section is converted into a digital signal; the AFC section, in which correction of the carrier frequency and clock frequency errors is carried out; the FFT section, in which discrete Fourier transformation is conducted; the equalizer section, in which waveform equalization is performed; the AGC section, in which the AGC control signal is generated and sent to the tuner section; and the DAC section. In the time de-interleaver section, the symbol data that has been temporarily dispersed is restored, and in the error correction section, Viterbi decoding and transport output packet generation are conducted and the signal is output from the LSI ship. The CPU block performs real-time demodulation control as it monitors the status of each block.
* The following are definitions of the acronyms used in the figure.
AGC: Auto Gain Control
AFC: Auto Frequency Control
FFT: Fast Fourier Transform
EQ: Equalizer
RAM: Random Access Memory
DIL: Deinterleaver
RS Decoder: Reed Solomon Decoder
TS Out: Transport Stream Output
TS Demux: Transport Stream De-multiplex
PLL: Phase Locked Loop
I²C: I²C Interface
ref clk: Reference Clock
