Amplifiers and mixed-signal data converters have come a long way since their humble beginnings in the first rudimentary monolithic operational amplifier designed by Robert Widlar in 1965. Little did the engineering genius realize at the time that this marvel would soon become a workhorse of the analog world, and that it would spawn a multitude of other single-chip functions as well. Nor could he foresee that it would spark a revolution whose impact would soon be felt in every nook and corner of this world.
In essence, Widlar's first op-amp IC containing a few transistors on a silicon chip broke the ground for an industry that has mushroomed into a more than $35 billion business worldwide and continues to grow. Meanwhile, the dramatic progress in process technology over 36 years has allowed designers to build analog and mixed-signal chips with millions of transistors on a single die.
While the older bipolar process has evolved into the complementary-bipolar (CB) form to maintain its performance lead, the majority of analog and data-converter designers have migrated to popular CMOS and biCMOS processes, whose benefits include low power, high density, and low cost. The major thrust now is to narrow the decades-old technology gap between analog and digital CMOS ICs. Obviously, the designers are racing to build analog ICs on the same mainstream CMOS processes used for digital ICs.
Meanwhile, exotic materials like gallium arsenide (GaAs) have also surfaced to deliver amplifiers and data converters for niche applications. Although substantial gains have been made in the last decade, many challenges remain on the road to a true system-on-a-chip (SoC)—that is, an IC on which high-performance analog functions and high-density digital circuits reside side by side and use the same power supply.
Nevertheless, analog and mixed-signal ICs continue to make strides on all fronts. Continual improvements in process technology and circuit techniques are motivating designers to adopt 0.25-µm and finer CMOS design rules, with a migration path to even smaller geometries. At their current pace, I'm sure they will take full advantage of nanometer gate lengths, sub-2.0-V supply voltages, higher speeds, and lower power consumption in the next few years. The result will be SoC solutions that combine high-performance wideband amplifiers, signal conditioning circuitry, and faster high-resolution analog-to-digital and digital-to-analog converters (ADCs and DACs) with microprocessors, DSPs, and dense logic for a plethora of applications.
Even as CMOS continues to permeate the analog/mixed-signal domain, many applications will still demand the performance of CB transistors, especially those built with silicon-on-insulator (SOI) processes. Silicon germanium (SiGe) will also boost the performance of CB transistors. This will permit designers to develop amplifiers and other linear ICs with much lower noise and higher speed, while reducing power consumption, die size, and supply voltage. Concurrently, designers will focus on miniaturizing packages. In fact, packaging will play a key role in meeting the demands of future applications.
As digital circuits drop below 1-V operation, pressure is mounting to make analog ICs perform well at less than 2 V. Consequently, developers will combine advances in process technologies with circuit techniques to achieve amplifiers with wide bandwidths and faster slew rates at a 1.5-V supply, with pressure to go even below 1 V.
While the density of op-amp arrays on a single CMOS die will continue to rise to serve the needs of multichannel data-acquisition systems, current-feedback amplifiers will set new standards in high-speed amplifier design. And, digitally controlled variable-gain amplifiers will offer a new level of flexibility to designers of analog and mixed-signal circuits.
As for data-converter architectures, the delta-sigma (Ä-Ó) topology pervaded the scene, making precision data converters possible on a 5-V CMOS process without thin-film resistors or laser trimming. Today,Ä-Ó exploits the latest advances in CMOS to realize faster, monolithic high-resolution ADCs and DACs with high dynamic range and lower noise. This opens the door to commercially feasible software-defined radios for wireless communications, including digital audio broadcasting. Innovative techniques are also propelling pipelined and successive-approximation-register ADCs to break speed barriers and set new standards,
Meanwhile, wideband high-resolution DACs are enabling multicarrier, multimode transmission in cellular basestations. Additionally, advances in CMOS process technology will let designers integrate high-performance data converters with powerful digital signal processing cores to create integrated solutions for a variety of audio, industrial control, and communications applications. Finally, highly integrated analog front ends optimized for a specific task will gain momentum, as developers seek fewer analog and mixed-signal ICs to solve their respective problems.
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