Electronic Design

More-Integrated ADCs Work On Less Power

ELECTRONIC DESIGN (ED): Is there a clear direction for power supplies for converters?

Osgood: Analog functions are having to address the different voltage standards, dropping from 5 to 3 V and lower. People using DSP and other high-speed digital functions are moving to below 2 V to try to keep the number of supplies low. Everyone is moving down in supply voltage. For the high-speed converters, when people can use the parts at a lower voltage, they will. It's hard to get full accuracy (and your money's worth of bits) when the converter works on less than 1-V swing. At the same time, many systems use multiple supplies--one for the analog and one for the digital parts. The precision parts are going off of the digital board. However, some of the industrial controls still use ±15-V supplies for everything.

ED: Do you expect to see more converter variations?

Osgood: Certainly, the increase of other functions will be integrated with the converter. For example, adding the amplifiers and buffers to make the complete analog-signal-processing chain makes it easier for the end users to configure the system, and it reduces some of the data processing in the DSP. We're going for targeted applications that address specific signal and data requirements at the high end. At the same time, precision converters are mostly standard catalog items. People just look up their speed and precision requirements and buy something to meet them. When they look at spinning variations, it is in vertical equipment markets. The focus on the end equipment leads to higher levels of integration.

ED: Is there a practical upper limit on analog and mixed-signal circuit integration?

Osgood: Not really. Higher levels of integration provide multiple benefits, including higher reliability, lower total cost, higher performance, and shorter time-to-design completion. The design is finished sooner because the analog signal chain is no longer a lot of discrete components, but a single part. For example, they have a 24-bit analog-to-digital converter (ADC) with a microcontroller and a 16-bit DAC in a single package. Another highly integrated function is a multichannel ADC and digital-to-analog converter (DAC) on one chip, with both types of converter in the same package. The increased level of integration is just a grouping of standard building blocks used in fairly standard configurations.

ED: What do you expect to see in processes than other standard CMOS?

Osgood: ADCs are process-limited. The analog and digital resolution is a function of the device characteristics. A fast 14-bit ADC needs a sample-and-hold with precision capacitor ratios and values. The larger the cap, the better the accuracy (up to a point). But the high-value capacitors slow the response. So the only way to get a higher resolution is to get faster parts to charge the capacitors quicker. If the latest CMOS process cannot provide the necessary speed, we will move to other processes to achieve higher speeds and accuracies in our converters.

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