Electronic Design

Op Amps Play Major Role In New Digital Technology

The advent of the worldwide Web and expansive, new video displays that significantly magnify artifacts, smearing, and color imbalance has created a daunting challenge for amplifier developers. They must achieve near-zero signal degradation during the transmission, reception, and digitization of the analog video signal. In video, this is extremely important because of the direct sensory impact on the end user.

It can be done. The processes, designers, and technology now exist to make 0.1-dB bandwidths up to 300 MHz feasible (approximately 1.5 GHz, −3-dB bandwidth) and slew rates that can enable black/white transition within 1 ns, thus supporting the most demanding resolution of video. In keeping with the macro trends of the IC industry, these devices are more cost-effective than their predecessors, and more importantly, they consume less power.

Despite their increased importance, it seems that amplifier selection is one of the last decisions made during the system design process. The component selection process still in effect seems to emanate from the DSP/microprocessor/controller at the center, to the data-converters, and finally to the amplifier crouching at the edge of the board. This is a function of the relevant cost magnitudes of the silicon, which, to be fair, is tied to the richness of features that can be marketed.

However, this model could be more efficient. Experienced designers now know that the amplifier and data-converter combine to determine the quality of the mixed-signal board. It is nearly impossible to rectify all analog degradation through digital methods, so why not use good analog design from the outset as a way to save downstream processor MIPS?

Specifications such as distortion, slew rate, and overshoot all significantly affect the integrity of the video signal. After all, silicon is cheaper than MIPS. Plus, the extra value invested in high-performance analog components usually amounts to only a fraction of the added digital processing costs required if analog performance is neglected.

The technology investment and innovation arising from the transition to digital video opens many other markets for analog ICs as well. High-end video serves as a spearhead in terms of exacting requirements and has spurred a lot of innovation in the amplifier arena. Primarily due to this impetus, we now have voltage-feedback amplifiers with slew rates of as fast as 90% of the current-feedback amplifiers that ease system design.

As a result, current-feedback amplifiers continue to scale up bandwidth and slew rate to keep pace with the finer resolutions that are demanded of displays every year. Distortion levels on these amplifiers have dropped precipitously to enable 14- and 16-bit digital video that creates unprecedented color depth. Programmable gamma buffers adjust the pictures continuously to compensate for the nonlinearity of the human eye, making the pictures more lifelike. All of these innovations typically do not cost the system designer much more in terms of power budget or total cost.

As a result, a walk through any major electronics retailer is a feast for the eyes, in terms of the quality of the displays. With this transition, the time has come to give the high-speed amplifier its due. Without it, we would have no Internet, no mobile phones, and no digital television. One way to do so is to factor analog design into the selection process as early as possible.

In your search for amplifiers to meet your system requirements, you will find many choices but also many tradeoffs. One way to narrow down the field is to look at the ratio of ac performance, measured by bandwidth and slew rate, to power consumption. The higher, the better. Focusing on this ratio will narrow the list of amplifier choices, as this parameter is an excellent proxy for an op amp's quality and behavior.

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