LCD high-definition digital TV is becoming a hot application in the field of TV technology. Compared with traditional analog CRT TV, LCD high-definition digital TV has higher requirements in terms of system integration, signal processing complexity and multi-function, so its design It is more difficult and more challenging. This article will discuss the technical development of LCD high-definition digital TV and analyze mainstream solutions.
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Digital TV has increasingly become a driving force in the development of consumer electronics and the entire electronics field. The maturity of tablet technology has added wings to the development of digital TV. Flat paneling and digitization are the two engines that drive the development of today's TV. Digital TV is gradually becoming a true home multimedia entertainment center.
Digital TV refers to a TV receiver that fully digitizes reception (SD/HD), demodulation, digital signal processing and display. At present, digital TV technology standards include ATSC (8VSB) represented by the United States, DVB-T represented by Europe, ISBD-T of Japan, DMB-T or ADTB-T of China (to be determined), and digital television DVB- C and satellite digital television DVB-S.
A flat panel television is a television receiver that uses a flat panel display as a television image display. The display screen can be divided into: liquid crystal (LCD), plasma (PDP), digital light source processing (DLP) and liquid crystal on silicon (LCOS) rear projection. Among them, the LCD display has the fastest development and is the flat panel display with the highest market share. LCD high-definition digital TV has become a hot application in the development of television technology.
With the development of liquid crystal technology and the use of the seventh-generation LCD screen production line in recent years, the LCD screen has broken through the development bottleneck of viewing angle, response speed, contrast level, color vividness and large screen price, combined with unique high resolution. With its low power consumption and long life, LCD TVs are the fastest growing TV category with its perfect image quality and acceptable price. The US Federal Communications Commission (FCC) issued a document on June 9, 2005, deciding to implement the Powell Plan, which is mandatory for digital TV tuners in TV sets, to fully integrate DTV tuning from 25-inch to 36-inch TVs. The requirements for the device were advanced to March 1, 2006. This decision of the FCC further accelerates the pace of development of digital television worldwide.
Figure 1: Composition of a liquid crystal high-definition digital television system.
Technology trends and design challenges
Under the general trend of flat panel TV and digitalization, LCD high-definition digital TV technology is developing towards high integration, high performance and multi-function. In the system single chip integration, the main CPU, transmission code stream (TS) demultiplexing, MPEG decoding, analog color demodulation, video signal processing, image display processing and other functions can be integrated into a chip, and even digital TV signals can be Demodulation and decoding, analog TV signal demodulation, HDMI reception, analog component video signal (YPrPb) / RGB reception, audio signal decoding are also integrated into a single chip, and the chip process can reach 90 nanometers, or even 65 nanometer technology level. High performance is mainly characterized by faster signal processing speed, more advanced image sound processing technology, and higher definition display (1080P). In addition to basic digital TV functions, LCD HDTV will be integrated into more functional interfaces such as USB, SMART Card, 1394/iLINK, hard drive, network interface and H.264/VC1 decoding. The future of the home multimedia entertainment center.
Figure 2: LCD high-definition digital TV reception embedded (Add-on) solution.
Compared with traditional analog CRT TVs, LCD high-definition digital TVs are much higher in terms of system integration, signal processing complexity and versatility, which makes LCD HD digital TVs more difficult to design and more challenging. In terms of chip design, high-performance CPU cores, high integration, high-performance signal processing planning, and high-end chip process technology (90 nm, 65 nm technology) are the main problems faced by designers. In terms of system design, the hardware design will face the design of multiple low-voltage (down to 1V) high-current power systems, high-speed (up to 250MHz) circuit board design, and overall system planning and design challenges.
In addition, the increasingly complex software system design has become the biggest challenge. The hierarchical functional modular design method and the application of advanced software development tools accelerate the software development progress and improve the software quality, and also improve the flexible reusability of the software, making it easier for secondary development. In the final product design phase, since only the top user control interface layer (UCI) needs to be easily designed and changed according to customer requirements, this speeds up the development of software development and even the whole machine, ensuring that the increasingly stringent time-to-market requirements are met. .
LCD high-definition digital TV structure principle
LCD high-definition digital TV usually consists of digital TV receiving channel, analog TV receiving channel, audio signal processing amplification channel, video signal input processing and display output channel, micro control system and power system.
The digital television receiving channel receives the digital television signal by the tuner, outputs the digital intermediate frequency signal to the digital television signal demodulating unit, demodulates the digital signal, and undergoes error correction (FEC), decryption (DES), and demultiplexing (Demux). , MPEG-2 decoding, one output of the decompressed standard digital video component signal to the video signal processing and display output channel, and the other output of the decompressed digital audio signal (I2S) to the audio signal processing amplification channel. The digital TV receiving channel determines the main performance indicators of digital TV reception, such as receiving sensitivity, bit error rate (BER vs. C/N), interference suppression, echo suppression, I/Q imbalance, etc. In the design, special attention should be paid to the ADC, filter, amplifier, and clock circuit.
The analog TV receiving channel receives the analog TV signal from the tuner, outputs the analog intermediate frequency signal to the analog TV signal demodulating unit, and demodulates and outputs the composite video signal through video demodulation to output the standard digital component signal to the video signal input processing and display. The output channel, the other demodulated output audio signal or the accompanying second intermediate frequency signal to the audio signal processing amplification channel. The application of PAL/SECAM/NTSC 3D bright color separation technology enables complete bright color separation.
The audio signal processing amplification channel is composed of an audio signal processing and an audio signal amplifying unit, and is responsible for television sound demodulation, I2S digital sound conversion, surround sound processing, audio control, and amplification output. SRS, Dolby Surround, Auto Volume Adjustment (AVL), multi-band equalization, audio delay, I2S signal (from HDMI and digital TV audio) reception are all common audio processing technologies for LCD digital TV.
The video signal input processing and display output channel are composed of YPrPb/VGA input, HDMI input, video signal processing, image display processing, LVDS output and LCD screen. It undertakes input conversion, image processing and quality improvement of standard component signals, and image display format conversion. Control and LVDS modulation output tasks. Image noise detection and automatic 3D image denoising technology, de-interlacer with motion prediction and compensation and image quality improvement techniques (LTI, CTI, contrast enhancement, sharpness enhancement, multi-dimensional color correction, GAMMA correction) The application also ensures that the perfect image is displayed on the LCD screen.
At present, LCD high-definition digital TV solutions can be divided into digital TV receiving add-on solutions and single-chip solutions. Among them, the embedded solution is to add digital TV receiving function on the basis of the existing analog LCD TV. The digital TV receiving channel is output and component video signal (YPrPb) after being decoded and encoded by MPEG-2, and then input to the analog LCD TV unit. Form a complete digital HD LCD TV. Today's digital TV receiving embedded solutions have high maturity and short development cycle, but the overall cost is high, and the system design and image processing display performance are not optimized.
The single-chip solution is mainly composed of a single chip including MPEG decoding, composite video signal decoding, video signal processing, image display processing, and micro control unit. This solution has a high-performance processing system such as 3D comb filter and image enhancement, which has the advantages of high integration and low cost, but the development technology is difficult, the development cycle is long, and the maturity needs to be improved. However, with the increasing integration and maturity, the single-chip solution will become the leading solution for LCD high-definition digital TV in the future.
ST's LCD HD digital TV solution
STMicroelectronics' LCD high-definition digital TV solutions include digital TV receiver embedded solutions and single-chip solutions.
It can be seen from the block diagram of the digital TV receiving embedded solution shown in FIG. 2 that the digital integrated tuner includes two parts of digital radio frequency tuning and channel decoding, and demodulates the output standard MPEG transmission code from the received digital television radio frequency signal. Stream signal. The MPEG code stream without special encryption is directly input into the ST digital TV signal decoding chip for processing; for the specially encrypted MPEG code stream, first input to the CI card loop for decryption, and then the code stream is directly input into the ST digital TV signal decoding system chip. Process it. Through the MPEG decoding and signal encoding of the ST digital TV signal decoding system chip, the AD conversion outputs analog YPRPB and stereo audio signals, and displays the digital television image to the existing analog television system, thereby forming a complete liquid crystal high definition digital television.
The following are the main functions and features of the ST digital TV signal processing decoder chip:
High performance 200MHz 32-bit CPU core;
2 serial or parallel code stream input, 1 way bidirectional code stream interface, total 3 code stream interfaces;
Programmable Transmission Interface (PTI): suitable for DVB, ATSC, OpenCable, DIRECTV transmission code stream demultiplexing, integrated DES and DVB descrambling;
All the way MPEG-2 HD decoding;
Analog RGB or YPRPB output, 1080I, 720P, 480P, 480I;
Analog PAL/NTSC composite video signal (CVBS) and bright color (YC) signal output;
Built-in bitmap-based character (OSD) generator;
One-way digital audio decoding, which can realize MPEG-1, MPEG-2, MP3, AAC and AC3 decoding;
5.1 channel digital audio conversion to two channel output;
Two 24-bit DACs output analog audio signals, one S/PDIF digital audio output.
Figure 3: LCD high-definition digital TV single-chip solution.
Figure 3 is a block diagram of a liquid crystal high-definition digital TV single-chip solution. ST digital TV single chip system chip and attached FLASH/DDR SDRAM memory, peripheral digital-analog integrated tuner, analog switch chip, HDMI/YPrPb/VGA input processing chip, LCD screen, sound processing chip, audio amplifier circuit, speaker , CI card circuit, and keyboard / remote control reception, together form a liquid crystal high-definition digital TV receiving system.
This digital TV single-chip solution facilitates the reception of all current digital/analog standard signals (of course, different receiving front-ends should be used for different receiving standards in the region), as well as HDMI, HD YPrPb and VGA signals. Receive processing. In terms of image processing display, the scheme has a 3D NTSC/PAL/SECAM bright color separation unit, enhanced edge-finished motion-compensated deinterlacing processing, and high-performance video using 3D noise reduction, contrast enhancement, and color space correction. Processing technology, can support the highest standard 1080P display, can easily achieve PIP, PAP, POP display. In terms of audio processing, the scheme implements digital audio decoding of MPEG1, MPEG2, AC3, and MP3, and analog audio decoding such as AM-FM MONO, NICAM, BTSC, and Zweiton, and can adjust a wide range of sound delays to ensure audio and image synchronization. Dolby, SRS, ST surround sound processing and five-band equalization processing.
The following are the main functions and features of ST LCD HD digital TV single chip:
High-performance 32-bit CPU (266MHz, 480MIPS), DDR333 memory interface, running real-time operating system;
Two NTSC/PAL/SECAM digital color decoders with 3D comb filters;
Two-way high-definition video image processing unit: 12-bit video processing, 3D luminance/chrominity motion-compensated noise reduction processing, interlaced to progressive conversion with dynamic edge compensation with enhanced edge refinement, flexible horizontal/vertical direction Scaling processing, high-performance image quality improvement processing;
HD PIP, PAP and POP;
Two transmission code streams demultiplexed with DES, DVB and MULTI2 descrambling;
Two DVB-CI and CableCARD interfaces;
Two road sign clear (SD) or one way HD (HD) MPEG2 decoding;
Two 24-bit audio processing DSPs for MPEG1, MPEG2, AC3, and MP3 decoding;
Bitmap based OSD;
Rich DTV movement control interface: I2C, GPIOs, ADC, PWM, etc.;
Display output up to 1080P;
90 nanometer chip technology to achieve low power consumption and high reliability.
With the rapid development of digital TV, there will be high, medium and low-end digital TV chip solutions that meet the different needs of the market. A low-cost digital TV chip solution with higher integration, more optimized performance, higher cost performance, and a high-integration, high-performance, high-end digital TV chip solution with digital home entertainment center function will become a liquid crystal high-definition digital TV system chip. Two major development directions.
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