How Do I Choose the Best Amplifier Design?

Video Amplifier (Video Amplifier) is used to amplify the video signal to enhance the brightness, chroma and synchronization signals of the video. When the video transmission distance is relatively long, it is better to use a thicker video cable. At the same time, a video amplifier can be added to the line to enhance the signal strength to achieve the purpose of long-distance transmission. The video amplifier can enhance the video's brightness, chroma and synchronization signals, but the interference signals in the line will also be amplified. In addition, too many video amplifiers cannot be connected in series in the loop, otherwise saturation will occur and cause image distortion.

Video splitter

Video matrix

What is the difference between AC coupling and DC coupling in a video high speed amplifier?

By using input and output capacitors ^[1]

Requirements for lower power consumption, smaller packages, and good matching

In recent years, with the continuous expansion of markets such as mobile phones and LCD TVs, user requirements for video amplifiers ^[2] have changed. Lower power consumption, smaller packages, and good matching performance have become very important. Companies such as Intel, Linear Technology, Texas Instruments, and Fairchild Semiconductor have introduced new amplifiers to meet the driver and buffer needs of video applications.

Linear Technology introduced the LT6553 amplifier for the high-performance video field with a resolution of more than 1600x1200 pixels. The LT6553 is suitable for SXGA and UXGA LCD projectors and monitors, digital displays (presenters), scanners, and car navigation and automotive Internal video systems such as automotive display systems, digital cameras and CCD imaging systems. For simple multiplexing

Video amplifier

With signal routing, the LT6553 has a close / close function that can be activated within 50ns, making it suitable for spread spectrum and portable applications.

In order to meet the requirements of high-resolution display interfaces, Intel Corporation has introduced the new EL536x series of operational amplifiers. The EL536x series of three electrical feedback amplifiers meet the requirements of high bandwidth and low noise. Most importantly, the impulse response is controlled. These new devices consume less power than combining three separate amplifiers, and the monolithic architecture also enables better gain matching. Texas Instruments' OPA693 video driver solution provides good impulse response for emerging high-resolution RGB applications. OPA693 is currently the fastest +/- 5V fixed gain amplifier on the market, with significantly improved DC and AC accuracy. Its advantage lies in the high-pixel pulse fidelity provided by a bandwidth of up to 700MHz and 2500 V / us conversion. And the price is lower than similar products.

Fairchild s FMS6418A is a highly integrated three-output video driver that can be used for high-definition (HD) or standard-resolution (SD) signal filtering, eliminating high-frequency noise before digitizing the signal (antialiasing), Used to eliminate artifacts caused by the encoder (reconstruction filtering) D / A conversion process. This product is targeted at leading video applications such as HDTV displays, cable and satellite set-top boxes, DVD, PVR, video on demand, audio / video receivers, etc., with higher performance and flexibility, reducing the number of components. The FMS6418A has three 6-generation sequential filters, and the frequency can be 30 MHz (HD) or 8 MHz (SD). FMS6418A combines a 2: 1 multiplexer on each filter channel. All three channels have filtering and output amplification functions. Cost and design advantages over discrete solutions.

Different requirements in different application areas

Although manufacturers have introduced such a wide range of products, the performance of amplifier products required by different end products is not the same. The most demanding application area is the field of LCD projectors, which are small, fragile, and have bright, high-resolution displays, while also having good prices. This requires the video amplifier to have higher bandwidth and slew rate, low power, small package size, and good channel separation performance. Soule also pointed out that another challenge was to get the video through very long cables, such as the older CAT5 cable. Linear Technology's new LT6552 is a differential video amplifier that solves this problem and can transmit video over 1,000 feet of twisted pair.

When designing a video system for any application, the performance of the video amplifier is critical. One application is broadband video routers and switches, with bandwidths ranging from 100 to 500 MHz. In order to support such a high bandwidth, the end product needs an internal operational amplifier with extremely high bandwidth, even 10 times the required bandwidth. The bandwidth numbers mentioned in the manufacturer's advertisements can be faked. The important bandwidth numbers to be concerned with are the large signal bandwidth (LSBW) specifications, which are generally considered to be 1 volt peak-to-peak (Vpp) or higher. Many manufacturers' advertisements refer to small signal bandwidth (SSBW), but overall, video signals use large signals (2Vpp). Customers may be tempted by small signal specifications, but products with higher LSBW values are more valuable.

Recognizing the market demand for LSBW, National Semiconductor recently introduced a three-bandwidth, 750 MHz operational amplifier LMH6738 and a three-bandwidth, 750 MHz programmable gain buffer (PGB) LMH6739 with 40

Video amplifier circuit

0 MHz LSBW, 3300 V / us conversion rate, and 0.1dB gain flatness at 200 MHz are superior to similar products in driving high-resolution RGB video signals. An important feature of video amplifiers is the 0.1dB gain flatness. Generally, the higher the gain flatness, the higher the supported video resolution. For example, HDTV systems require a 0.1dB gain flatness of 30 to 50 MHz. On the other hand, when facing high-resolution video signals (such as computer images), the required gain flatness is close to 100 ~ 200MHz 0.1dB.

At the same time, when using a video amplifier for design, there are also some issues that need attention, such as signal distortion and so on. This is important to minimize the distortion of the video signal from the video amplifier. Most customers using professional-grade equipment will consider second- and third-order harmonic distortion, with -80 to -90 dBc @ 5MHz being the minimum requirement for their system. When facing a composite video signal, the differential gain / differential phase (DG / DP) value is very important, and it is generally required to be 0.02% / 0.02, or lower. In composite video, the color information is above the brightness information, so the lowest DF / DP values will produce the sharpest and least distorted image quality.

For portable video equipment such as digital cameras and mobile phones that can play TV, the most important are high integration, low power shutdown, small package size, and embedded video D / A converters that are easy to connect to DSP chips. Good video display is important, but the video requirements of consumer products are not as demanding as those in broadcast and professional video. Voltage feedback is an extremely important configuration for this application. Important features of this type of amplifier include integrated filters to help rebuild the DAC signal, low power shutdown (preferably below 5uA), low voltage (preferably run with a single power supply of 2.8-5V), SAG correction, and ability to perform DC coupling The output does not affect synchronization pulses, and is available in SC70, QFN, or CSP packages.

Future market demand trends

There are many trends in the video field. One of the more important trends is that the resolution is getting higher and higher. As the video resolution of portable products increases from VGA to SXGA and higher, the speed of operational amplifiers will also increase, and operational amplifiers will also need to improve their bandwidth and distortion performance to meet the requirements of high-resolution video. The overall market demand trend is generally the same: For example, the lower voltage requirements of portable products mean that the voltage of video amplifiers is lower, and more rail-to-rail amplifiers are required; smaller packages are used, and more on-chip functions are integrated at the same time , Such as gain resistors, use on-chip feedback paths at higher bandwidths to improve signal integrity and reduce crosstalk and low power consumption; faster speeds to meet higher screen resolutions, such as SXGA, UXGA, and HDTV formats; and finally, Lower power consumption, such as Linear Technology's LT6210 / 1 current feedback amplifier features an 'Rset' resistor, which allows system designers to adjust the bandwidth, which is actually a speed-power knob. This means that the system designer can set the amplifier so that it never consumes too much power at a given signal bandwidth.