Humans are easily guided by vision, so it is not surprising that there is a high-resolution plasma TV market. Although the price of these 40-inch flat behemoths is 10 times that of cathode ray tube (CRT) display devices, consumers are still willing to pay for the improvement in resolution and contrast brought about by the new technology.
Similarly, consumer expectations for video and displays in handheld devices are gradually increasing. Mobile phones, PDAs, and even MP3 players like iPods can provide clear images like the large-scale display devices of a few years ago. Today's portable devices are equipped with brighter, more gorgeous, and better-operated displays, but they are susceptible to noise, which reduces the quality of the video signal.
As the overall quality of the video output signal steadily improves, display errors caused by noise and electrical interference become more apparent. At the same time, as mobile phones, microwave ovens, and wireless networks become more and more widely used, potential sources of interference also become more powerful and widespread. The convenience conditions that make mobile phones so popular also work for other wireless devices.
These trends have brought great challenges to designers who want to integrate high-quality video into portable devices. Consumers ’high expectations, compatibility with multiple formats, limited battery life, unreasonable user operations and multiple external signal interferences all mean that today ’s video drivers must have multiple features and counteract multiple interferences Source capacity.
The trend of single-chip integration makes handheld devices smaller and more reliable, and has multiple functions. The size of the current video driver is already less than 1mm3, but it can still provide a high-quality video output signal without obvious interference. In addition to advances in semiconductor manufacturing technology, the popularity of small-size chips and surface-mount chips also means that more high-tech components can be made to a minimum size. Surface-mount chips have more advantages than through-hole models, such as the ability to use pick-and-place machines for simple automatic assembly, and provide more flexibility in space-saving double-sided circuit board design.
The use of fewer components is another trend that saves space and energy. It enables portable devices to become smaller while extending battery life. The on-chip fully integrated system means that external resistors, capacitors and inductors have no help for the system. For example, the integrated filter can save a dozen external components, and a third-order filter can save 14 components. In addition, compatibility with multiple video signals means that multiple filters must coexist, and they must maintain their own operating mode. In addition, the tolerance of the integrated filter is half that of discrete devices, making operation more reliable and stable.
These filters need to be switched in such a way that the switching process is transparent or trace-free to the user. The conversion from 8MHz standard resolution output to 15MHz progressive scan or 32MHz high resolution output means that the video signal is suddenly placed in a completely different bandwidth interface, so the filter must be compensated accordingly. A 3-channel signal like RGB and a 2-channel signal like Y / C require different filters. There are so many different signal formats on the market, and the current question is whether the chip can support all these formats required by the customer, will there be any problems in the switching process.
AC coupled video signal output method
DC-coupled video signal output method
Due to the large number of options that need to be supported, some uncommon functions in the product also consume some energy, whether it is a filter or an external coaxial cable driver. Coupled with product features, product features, and consumer demand, it has far exceeded the pace of development of battery technology, so efficiency is a key factor for any handheld device. The current lithium-ion battery technology is considerably improved compared to the past nickel-metal hydride and nickel-cadmium battery technology, but who will spend a lot of time discussing how much power is left on the mobile phone? Users must be sure that those who cannot continue within the specified time The phenomenon of having to recharge the power supply is not satisfactory.
For a system designer, he may be powerless in choosing the battery capacity, but he can choose more efficient components. Obviously, when the chip is working, it needs to pay attention to its power consumption, but the power consumption of these devices in the standby state is also important. Many devices have standby power consumption. Even if the standby power consumption of a single device is small, the standby power consumption of the entire system will make the battery life greatly reduced. Fortunately, the current standby power consumption of video drivers on the market is very low, and the current is only 250μA when not working.
Compared with other portable devices, mobile phones pose additional challenges to their design due to physical structural problems. Although more and more new features make mobile phones more practical and more expensive, people will not hesitate to use mobile phones in harsh environments where MP3 players and digital cameras cannot be used. This puts a higher demand on robustness than before.
The robustness of electronic products is indeed more important. Compared with before, current portable products have higher chip density, lower power consumption, and smaller size, but they are also more susceptible to damage by electric shock. A person can generate a few kilowatts of electric charge just by walking on the carpet, and these charges can easily be transferred to the mobile device he holds. Although the spark current may be very low, its extremely high voltage is extremely dangerous to small equipment. Therefore, for components such as video driver chips that are connected to the outside world, it is necessary to have integrated protection functions or additional protection circuits. Equipment with high-quality protection must be able to withstand a high voltage of at least 12kV.
Despite such high requirements for video drivers, all efforts will be wasted if the final video signal fails to meet consumer expectations. In order to maintain the highest possible video output quality, the video driver needs to complete the function of the reconfigurable filter. Only when the noise drops below -20dB (visual level) can it be made undetectable, which can be achieved by the 3rd to 6th order filters.
The types of noise include artificial high-frequency external electromagnetic interference and sideband swing caused by low-frequency oscillation. The external EMI may originate from any wireless devices nearby, even microwave ovens. The space around us is full of radio signals, so the design of the system must be able to adapt to the harshest environment. Signal crosstalk inside the device is also a problem, especially for devices such as mobile phones and GPS receivers that also include transmitting and receiving signals. They need to provide high-quality video displays. Since the human eye is very sensitive to the effects of these noises, the filter requirements are very demanding in all video applications.
End users may never understand how difficult it is to meet their requirements for more features, longer battery life, better compatibility, and clearer audio and video. Fortunately, device manufacturers and chip designers continue to work hard to provide system designers with more cost-effective components.
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