[Technology Report]
On-Chip Processors Turn Monolithic ADCs Into Data-Acquisition Systems
Suppliers are readying integrated development environments to make it painless for analog engineers to work the new ADCs.
The last few years have seen dramatic improvements in the analog-to-digital converter (ADC) world, changing the landscape of this data-conversion chip beyond recognition. With the migration toward CMOS processes, the number of functions being integrated around the converter are transforming the part into a subsystem solution while maintaining the performance at lower power and smaller die size. As makers adopt finer CMOS geometries, these highly integrated ADCs are beginning to look like complete analog front ends for applications like data acquisition, wireless communications, and audio. They also might find a home in the industrial and instrumentation markets.
While this trend remains popular, efforts continue to increase the level of integration at low supply voltages. Designers are exploring circuits and techniques to bring memory, microcontrollers, and processors like DSPs on board at the digital end. In the RF domain, they're investigating technologies to pack functions like mixers, local oscillators, and amplifiers on chip. Doing so will transform the ADC into a complete radio receiver for mobile communications.
In the last year, several major ADC vendors have demonstrated high-resolution ADCs that include all of the key functions needed to directly link sensors, as well as other such sources of signals, to microprocessors or digital systems. These integrated ADCs have drastically simplified the analog front-end design to enable complete data-acquisition solutions with a minimum number of chips, along with unprecedented levels of accuracy, speed, and resolution. They also keep power consumption within design budgets.
A good example is Cirrus Logic Inc.'s ultra-low-noise data-acquisition IC, the CS553x, which was unveiled late last year (see "Ultra-Low-Noise Data-Acquisition IC Tackles Multiple Sensors," Electronic Design, Oct. 28, 1999, p. 59). Designed for precise measurement of low-level unipolar or bipolar signals, this 24-bit ADC has a lot of on-chip features: a multiplexer, an ultra-low-noise programmable-gain instrumentation amplifier (PGIA), a selectable Sinc filter, calibration, control logic, a clock generator, and a three-wire serial interface for microprocessors and microcontrollers.
In essence, it integrates all of the necessary analog and digital functions to directly and singlehandedly link a variety of sensors to general-purpose microcontrollers. It used to be that two or more chips were required to perform a similar task. A high-performance instrumentation amplifier was needed to achieve ultra-low noise, adding to cost, space, and design time.
To extend the applications range for this line, Cirrus Logic is now in the data-gathering mode. It's exploring a variety of power, speed, and noise combinations to address myriad applications. By readying subgrade members with lower power, the company can meet the requirements of applications like weigh scales, in which battery life takes precedence over high accuracy.
Likewise, higher-speed versions are in preparation for medical equipment and other similar instrumentations. There, conversion speed is an important specification. Meanwhile, Cirrus Logic designers are actively pursuing the challenge of integrating a microcontroller on the same CS553x chip. However, further details were unavailable at the time of this writing.
Also in the microcontroller race is Burr-Brown Corp. This supplier has stepped up its effort to bring a general-purpose microcontroller on board. Toward that end, it has licensed an 8-bit, 8051 synthesizable core from Synopsys Inc. It plans to integrate that core with 20-bit converters, providing data at moderate output rates.
"For the initial introduction, the ubiquitous 8051 processor core was selected for its popularity and its established infrastructure of development and programming tools," states Robert Schreiber, strategic marketing engineer at Burr-Brown. By combining existing development tools with evaluation modules, the company is readying "an integrated development environment that will make it painless for analog engineers to work with these mixed-signal parts," says Schreiber.
The early introductions target smart transmitters, in which size is a constraint and remote processing is desired. "On-chip flash memory will allow it to be programmed in the field or remotely," Schreiber points out. "Plus, it will provide better control of system calibration with added intelligence. In short, it will enable more specialized processing on chip to offload the system microcontroller and relieve it for other tasks."
Under development are two delta-sigma (Δ−Σ) ADC chips for release later on this year. One of them will include an 8051 core (Fig. 1). The other will incorporate an 8-bit RISC core for applications that demand faster on-chip processing. Both devices will offer a variety of memory and I/O configurations.
The 20-bit, 25-kHz ADC with an on-chip 8051 core will provide up to 32 kbytes of program flash memory. In addition, it will have up to 4 kbytes of data flash memory and 1 kbyte of RAM. The chip also is home to a multiplexer with eight single and four differential channels, a low-noise PGA, a clock generator, a Sinc3 filter, serial ports, and an I/O port. It will implement debugging capability.
This integrated converter will be implemented in a 0.6-µm CMOS process to keep power consumption and die size within design budgets. Preliminary specifications indicate that the device will consume less than 10 mW at a 5-V supply and a 4-kHz data rate. Due to the size of the memory on the same die, however, the company says that the user will have to pay a slightly higher premium for an ADC with a microsystem controller on board.
This was just what I needed for reference. It's nice to have a place to look AND FIND what you need.
Kerry Adams -April 13, 2006 (Article Rating: )
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