Op Amps Continue To Flourish Since the introduction of the first monolithic bipolar operational amplifier (op amp) in the mid-sixties by Fairchild Semiconductor (www.fairchildsemi.com), the technology has soared to unbelievable heights, and the number of players in the market has grown steadily. Multiple processes, such as CMOS, biCMOS, complementary-bipolar (CB), and gallium arsenide (GaAs), have joined the traditional bipolar technology to serve the varying needs of myriad applications. Additionally, numerous topologies have evolved to broaden the scope of these devices. The specs just keep getting more stringent as new applications emerge.
From just tens of kilohertz in the early days, today's op amps are boasting hundreds of megahertz in bandwidth. In fact, they're approaching gigahertz performance. Equally impressive are dynamic range, distortion, and noise performance, which are accomplished at very low quiescent current and power consumption. Plus, clever calibration and chopper stabilization techniques, including digital, have evolved over the years to maintain the part's stability and accuracy over a wide bandwidth and temperature range.
Also, supply voltages have dropped dramatically. As CMOS becomes the popular process, supplies have dropped to a single 2.7 V. Meanwhile, CB technology has demonstrated 1-V capability with a gain-bandwidth product as high as 100 MHz. Although 1 V was first achieved in 1978, the op amp at the time, National Semiconductor's (www.national.com) LM10, offered only a 100-kHz gain-bandwidth product.
Likewise, op-amp packaging has evolved. From traditional through-holes, op amps have come to be miniature surface-mountable packages that seem to get smaller and thermally better every day. Now, the trend is clearly toward chip-scale and flip-chip packages
For custom and semicustom applications, op-amp cores have joined the ASIC libraries of semiconductor suppliers and foundry service providers. Some have created intellectual property to enable fabless system-on-a-chip (SoC) design houses to implement proprietary amplifiers in their solutions. Others have crafted custom linear designs that pack nearly 50 precision op amps on one CMOS chip for multichannel sensor applications.
Nothing will stop the development of this ubiquitous component. It will continue to flourish as suppliers keep taking advantage of process enhancements. As suppliers combine these advances with circuit techniques, they will raise the performance bar even higher.
In many applications, data converters are dictating the requirements for amplifiers. They must perform equally well or better to get the best signal into or out of the system. Process improvements are combined with new circuit techniques to improve the bandwidth of the amplifier, while minimizing the distortion and noise performance. Manufacturers are readying parts that will offer much higher bandwidth at half the supply current.
Medium-performance, general purpose op amps have appeared in tiny packages like the SC-70 for last the few years. But recent acceptance has driven them into the mainstream. Now, high-performance parts are coming in these packages, with the aim to provide dual and quad versions. Also, the thermal efficiency of the package is being improved. Future movement is in the direction of chip-scale packages.
While precision is the norm in low-speed amplifiers, efforts are under way to extend that accuracy to high-speed junction FET (JFET) parts to meet the strict demands of optical networking, wireless basestations, medical CT scanners, and automatic test equipment (ATE) applications. Therefore, suppliers are targeting offsets of below 0.1 mV and drift ratings of 0.5 µV/°C and better for high-speed amplifiers. In addition, they're offering very low input voltage and current noise, very low input bias current, and wide bandwidth. For instance, the maximum input bias current for Analog Devices' (www.analog.com) latest precision amplifier is 10 pA, with output settling to 0.01% accuracy in less than 600 ns.
Single-supply operation at voltages below 3 V is gaining momentum. As more players enter this domain, they're exploiting a number of processes to reach their goals. While some CMOS- and biCMOS-based amplifiers have demonstrated performance down to 2.7 V, proponents of the CB process have gone a step further. National Semiconductor has shown that its VIP10 CB process can deliver a high-speed op amp with 1-V minimum supply voltage and a gain-bandwidth product of 100 MHz.
Digital techniques are enabling variable-gain amplifiers to precisely control input and output voltages. For very high-performance bipolar op amps, digital functions are implemented in CMOS to keep the cost down. However, if digital control is simple, existing bipolar transistors will provide the digital control cost-effectively.
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