Introduction and application of smart integration technology in flat-screen TV design

Flat-panel televisions are rapidly taking over the consumer electronics market, with sales growth rates for these "premium" TVs reminiscent of the early days of personal computers (PCs). The concept of "premium TV" now refers to liquid crystal televisions (LCD TVs), plasma televisions (PDP TVs), microdisplay rear-projection TVs (including liquid crystal displays (LCD), digital light processors (DLP) and liquid crystal on silicon (LCoS)), front-projection projectors and flat-panel cathode ray tube (CRT) TVs.

To remain competitive in a rapidly growing market, manufacturers cannot stand still. They must work tirelessly to improve their products by reducing costs, improving image quality, enhancing reliability, and adding new user features. Most importantly, manufacturers must improve the manufacturability of their products, making them easier to produce and less expensive. A key issue in achieving all of these design goals is how to use "smart integration" technology in the display interface.

Integrating discrete functions onto a single chip can reduce the number of components and manufacturing costs, a strategy that has proven successful for PC manufacturers over the past decade. But displays require "smart integration" because there are significant technical challenges to overcome when combining various display interface functions. If high-performance analog circuits and high-speed digital circuits are to be integrated into a single solution, experience in specialized mixed-signal design techniques is required. An integrated interface requires products that meet the requirements of low cost and small package size without sacrificing image quality and production capabilities.

1 Typical LCD TV

A typical LCD TV offers several options for system integration (see Figure 1), including:

Analog and digital interfaces are combined to provide "legacy compatibility" with most current DVD players and set-top boxes, and "digital readiness" for the future;

·Interfaces are combined with graphics controller functions and major image-related circuits in LCD TVs;

Reduce the number of internal connections and simplify printed circuit board (PCB) routing to reduce signal distortion that affects image quality;

Provides CD-quality audio and PC compatibility at a minimal additional cost.

Figure 1. A typical advanced TV system block diagram provides multiple options for system integration.

1.1 Integrated analog interface

Although interest in emerging digital flat-panel display interfaces continues to grow, component analog video interfaces remain the primary high-quality interface of choice for advanced TVs currently on the market. Many advanced TVs also include an analog video graphics adapter (VGA) interface for compatibility with PC applications. Integrated component analog interfaces, such as the AD9883A from Analog Devices (ADI), have integrated all the traditional analog functions required for a display interface on a single chip (see Figure 2). This first step in display interface integration has helped reduce costs, improve image quality, and simplify PCB routing.

Mixed-signal complementary metal oxide semiconductor (CMOS) or BiCMOS wafer manufacturing processes can be used to mass produce such integrated analog interface chips and meet the requirements of flat panel display interface applications, namely, high-speed (greater than 100 MHz) analog-to-digital converters (ADCs) with typical linearity errors [integral linearity error (INL) and differential linearity error (DNL)] of 0.5 LSB and input bandwidths greater than 200 MHz. However, standard digital CMOS wafer manufacturing processes cannot provide the mixed-signal characteristics required to achieve high-performance analog signal processing and ADCs.

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Figure 2: Analog Devices’ AD9833A integrated analog interface integrates all the traditional analog functions required for display interfaces on a single chip.

1.2 Add digital interface

The next step in display interface integration is to integrate both analog and digital interfaces on a single chip. This makes it easy to provide legacy compatible displays while also preparing for the digital future. Most new advanced TVs support component analog signal inputs for direct connection to existing DVD players and set-top box tuners. This ensures that users can use their new TVs correctly.

High-Definition Multimedia Interface (HDMI) is designed specifically for advanced TV applications. The HDMI interface can provide a digital interface for high-quality video (1080p resolution at 1920×1080 pixels) and audio with CD quality (192kHz) and 7.1-channel surround sound. In addition, the HDMI interface also supports the High-bandwidth Digital Content Protection protocol (HDCP), which Hollywood filmmakers will need to use to protect their newly shot high-definition DVD movies from being illegally copied. Advanced TVs that include an analog interface for receiving component analog signals and an HDMI digital interface will give users a long service life because of the improvement of their display interface.

1.3 AD9880 Integrated Interface

The AD9887 is the world's first integrated dual interface for advanced televisions (see Figure 3). The analog interface is based on the AD9883A analog interface design, with an operating bandwidth of up to 150MHz for 1080p and SXGA display resolutions. The digital interface uses HDMI to provide image resolutions up to 1080p and SXGA (150 Mbps). The two interfaces share the same output signal, thus saving 48 pins compared to a dual-chip analog and digital interface design. The chip also provides automatic detection of the interface connected to a display, as well as the option of allowing users to connect the interface on a serial data line.

This chip is available in two grades: one is AD9800-100 for 720p/1080i and XGA displays; the other is AD9800-150 for 1080p and SXGA displays. These two grades allow TV design engineers to choose the most cost-effective solution for their displays. AD9880 is now available with samples, complete technical data and evaluation boards to support display design engineers.

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Figure 3 The world's first integrated dual-interface (analog and HDMI) AD9887 for advanced TVs supports resolutions up to 1080p or SXGA format at both analog and HDMI inputs.

1.4 Reduce internal connections

The image quality of a premium TV depends largely on the design and layout of the display interface circuit board. One of the benefits of increasing the integration of display circuits is that the wiring between devices is reduced, thereby improving image quality. For display manufacturers, it has been a great challenge to place "noisy" digital circuits close to noise-sensitive phase-locked loops (PLLs) and ADCs and still produce an interface circuit board with satisfactory image quality. Some display manufacturing companies have spent considerable money, time, PCBs and energy trying to produce an analog interface that is not hand-made, but no company has succeeded. Increasing the integration of interface circuits can simplify PCB design and produce better image quality than the discrete component PCB design of the past.

1.5 Relationship between image quality and integration level

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The trend in LCD desktop monitors for PC applications is to integrate analog interfaces and digital image scaling into a single chip. These integrated solutions usually provide good enough image quality in smaller (15" to 17") monitors used to display basic PC applications such as e-mail, web surfing or spreadsheets. However, for advanced TV applications with display screens in sizes ranging from 30" to 80", the requirements for image quality are much higher.

To provide the exquisite picture quality that customers demand for advanced TVs, consumer electronics manufacturers are currently designing TVs with separate interfaces and scaler chips. In many cases, industry-leading TV manufacturers are designing their own custom scaler chips to meet system requirements. Other manufacturers are choosing to use commercially available scaler chips developed specifically for advanced TVs. These digital scaler chips are sometimes integrated with a built-in microcontroller and EEPROM to store the display's microcode. These digital chips can be manufactured using the latest digital circuit processes (0.13 μm or 0.18 μm CMOS) to provide lower costs and higher performance.

2. Questions about complexity

Most of the die area consists of digital logic gates, so this integration approach requires the use of 0.13μm or 0.18μm digital CMOS manufacturing processes to reduce costs. In some cases, embedded dynamic random access memory (DRAM) manufacturing processes are used to integrate frame buffer memory into the same chip as the graphics controller, but these chips are not well suited for implementing high-performance analog functions.

In order to adapt to high-performance analog circuits and reduce costs, a mixed-signal CMOS manufacturing process is needed. Because mixed-signal manufacturing processes have not been widely adopted, and there are still few design engineers with high-performance mixed-signal experience, its analog performance is difficult to meet the requirements. As people have seen, the image quality of its early integrated products has declined, not as good as separate analog interface and digital interface products.

Although the HDMI interface is generally considered a digital interface, its design requires considerable mixed-signal circuitry. In fact, the number of high-speed comparators in each color channel of the HDMI interface is greater than that of the ADC used in analog interfaces. The HDMI standard specifies an input frequency of up to 1.6Gbps, so achieving the appropriate performance requirements still requires a lot of money to complete mixed-signal design.

Using today's advanced CMOS manufacturing processes helps integrate mixed-signal circuits (analog interface and HDMI digital interface) into a monolithic "interface" chip. Mixed-signal CMOS manufacturing processes are generally the next generation of manufacturing processes that follow the latest digital CMOS manufacturing processes. The latest advanced CMOS manufacturing processes can be used by simply placing the high-speed digital circuits on the scaler chip. This clearly illustrates the concept of "smart integration" - a two-chip solution can provide high performance, which accelerates time to market and reduces total cost compared to integrated single-chip solutions.

3 Product Qualification Test

Integrated interface and scaler products are true mixed-signal devices that require 100% high-speed mixed-signal electrical performance testing to ensure high-quality performance. Today's mixed-signal test solutions for ADCs are almost as complex as the chip design itself.

Digital circuit engineers are familiar with the development of digital test programs, which are usually used to input test vectors into automatic test pattern generator (ATPG) software to generate a digital test pattern. Joint Test Action Group (JTAG) standard boundary scan and internal scan techniques can also be used to detect at least 98% failure rate in digital circuits. Existing digital logic test protocols are often used when testing these digital circuits.

However, high-performance mixed-signal circuits require "high-speed" testing to verify their electrical performance. Testing high-speed analog circuits requires test code and unique test hardware provided by test development engineers to ensure accurate measurement of ADC signal jitter, signal-to-noise ratio (SNR), and linearity errors. High-performance mixed-signal test platforms have the ability to test high-performance analog circuits and high-speed, multi-pin digital circuits in the same integrated device. Integrated interface products that have not been rigorously tested by high-performance mixed-signal test platforms may have large deviations in performance that follow the normal distribution of wafer manufacturing processes.

Defective parts can cause serious problems for advanced TV manufacturers who are constrained by production time and their resources. For example, consider an interface product that has consistent deviations in key parameters from batch to batch (with a defect rate of only 10%). If the supplier of the interface product cannot screen out all of these defective products, the TV manufacturer using this product must test 100% of its displays, thereby increasing the cost of its final product. Careful design engineers are now further discovering how to test integrated interface products to ensure only the highest quality products.

4. Take it to a whole new level

Smart integration is the key to increasing the yield of advanced TV and other high-quality display products. Reducing the number of components can improve image quality, reduce costs, and reduce size, making the product easier to manufacture. However, the result of reducing components is increased complexity of integrated circuit design. Unless the integrated circuit is designed properly and can be adequately tested, the idea of ​​increasing integration can only bring disappointing results. Therefore, design engineers must seek components that exceed product design specifications to ensure that they can get reliable components that meet the requirements of new advanced TVs.