Humans are easily guided by vision, so it is not surprising that there is a high-resolution plasma TV market. Although these 40-inch flat behemoths are 10 times more expensive than cathode ray tube (CRT) display devices, consumers are still willing to pay for the increased resolution and contrast that new technologies bring.
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Similarly, consumer expectations for video and displays in handheld devices are gradually increasing. Mobile phones, PDAs, and even MP3 players like the iPod can provide clear images like the large-format display devices of a few years ago. Today's portable devices are equipped with brighter, more gorgeous, better-operated displays, but they are susceptible to noise, which reduces the quality of the video signal.
When the overall quality of the video output signal is steadily increasing, display errors caused by noise and electronic interference are becoming more apparent. At the same time, as mobile phones, microwave ovens, and wireless networks become more widely used, the potential sources of interference are becoming more powerful and widespread. The convenience conditions that make mobile phones so popular also work for other wireless devices.
These trends pose significant challenges for designers who want to integrate high-quality video into portable devices. Consumers' high expectations, multiple formats of compatibility, limited battery life, user unreasonable operation and a variety of external signal interference mean that today's video drivers must have multiple features and combat multiple interferences. The ability of the source.
The trend toward single-chip integration has made handheld devices small, reliable, and versatile. Today's video drivers are already smaller than 1mm3, but still provide high quality, no noticeable video output signals. In addition to advances in semiconductor manufacturing technology, the popularity of small-sized chips and surface-mount chips also means that more high-tech components can be made to the smallest size. Surface mount chips offer more advantages than via-type models, such as simple automated assembly with pick and place machines, providing more flexibility in space-saving double-sided board design.
The use of fewer components is another space-saving and energy trend that can make portable devices smaller and extend battery life. An on-chip fully integrated system means that external resistors, capacitors, and inductors have not helped the system. For example, an 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 maintain their own mode of operation. 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 as transparent or traceless to the user. Conversion from a standard resolution of 8MHz to a 15MHz progressive or 32MHz high resolution output means that the video signal is suddenly placed on a completely different bandwidth interface, so the filter must be compensated accordingly. A 3-channel signal such as RGB is different from a filter required for a 2-channel signal such as Y/C. There are so many different signal formats on the market. The question now is whether the chip can support all of the formats that customers need, and there will be no problems in the switching process.
　　
AC-coupled video signal output method
　　
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DC-coupled video signal output method
Because there are a number of options that need to be supported, some of the less common features in the product also consume a portion of the energy, whether it is a filter or an external coaxial cable driver. Coupled with product features, product features, and consumer demand that far exceed the speed of battery technology, efficiency is a key factor for any handheld device. Today's lithium-ion battery technology has improved considerably over the past nickel-metal hydride and nickel-cadmium battery technology, but who will spend a lot of time discussing how much power is left in the phone? Users must be sure that they cannot continue at the specified time interval. The phenomenon of having to recharge the power supply is not satisfactory.
For a system designer, he may not be able to choose the battery capacity, but he can choose more efficient components. Obviously, the chip needs to pay attention to its power consumption when it is working, but the power consumption of these devices in standby mode is also important. The standby power consumption of many devices, even if the standby power consumption of a single device is small, but the standby power consumption of the entire system will greatly reduce the battery life. Fortunately, the video driver standby power consumption on the market is very low, and the current is only 250μA when not working.
Compared to 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 them in harsh environments where MP3 players and digital cameras cannot be used. This puts a higher requirement for robustness than before.
The robustness of electronic products is indeed more important. Compared to the past, portable products have higher density, lower power consumption, and smaller size, but are also more susceptible to electric shock. A person who walks through the carpet can generate several kilowatts of charge, which can easily be transferred to the mobile device he is holding. Although the spark current that can be generated is very low, its extremely high voltage is extremely dangerous for small equipment. Therefore, it is necessary to have an integrated protection function or an external protection circuit for components connected to the outside such as a video driver chip. Devices with high quality protection must be able to withstand at least 12kV.
Despite such high demands on video drivers, if the final video signal fails to meet consumer expectations, all efforts are in vain. In order to maintain the highest possible video output quality, the video driver needs to perform the function of a reconfigurable filter. The noise can only be detected below the -20dB (visible level), which can be achieved by a 3-6th order filter.
The types of noise include artificial high-frequency external electromagnetic interference and sideband oscillation caused by low-frequency oscillation. External EMI may originate from any nearby wireless device, or even a microwave oven. The space around us is full of radio signals, so the system must be designed to adapt to the harshest environments. Signal crosstalk within the device is also a problem, especially for devices that transmit and receive signals, such as cell phones and GPS receivers, which require high quality video display. Because 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 strive to provide system designers with more cost-effective components.
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