DAC cuts power by 70 percent

These fourth generation high-speed Tx D/A converters (DACs) feature a small footprint (32-lead FLCSP), low power consumption (190mW to 135mW), and increased functionality.

Despite the small size and low power consumption features, all four DACs maintain high performance levels, according to Chuck Millet, business manager of Analog Devices Inc.'s High Speed DACs. "SFDR stays the same, but power consumption is dramatically lowered," he said.

While, ADI's 10-year-old, third-generation TxDAC family offered strong AC (80dBc) and DNL (±0.5LSBs typical) specs at a clock frequency of 10MHz, these latest devices boast virtually equivalent AC and DNL specs (80dBc and DNL of ±0.7LSBs). The third-generation 14-bit version devices were so popular that they were second sourced by two competitors, Millet said.

Comparing the previous-generation 14-bit DAC (AD9744) to the latest generation 14-bit device (AD9707), power consumption is 200mW at 3.3V, 20mA for the AD9744, compared to 55mW at 3.3V, 2mA for the older device. Even though the AD9744 has about five to six times the power consumption, the performance level is basically equivalent, Millet said.

In addition, the supply range has been extended from 2.7V to 3.6V for the AD9744 to 1.8V to 3.6V for the AD9707.

ADI was able to accomplish this low power feat by reducing the full scale current to a 1mA to 5mA range instead of 20mA, and by scaling down to finer line geometries. Earlier generation products were made using a .35?m CMOS process while today's devices utilize a .18?m CMOS process.

ADI has also taken advantage of a high-voltage blend, Millet said. "The new devices have a 3.3V transistor capability, which gives us a higher voltage range and higher analog swing (1.7V to 3.6V range)," he said. Doing this makes it easier to interface with other analog components that are already operating at 3.3V (like mixers, modulators and other logic devices, which are usually RF type components).

In terms of added functionality, the new family includes a common mode shift to assist in interfacing with other components. "The fact that you can move the common mode around is important because it saves level translators, which cost money and consume space," Millet said. "Without it, customers would have to shift the common mode voltage with external level translators," he added.

The company is also offering a data pattern generator, which Millet calls, "a magic box that brings evaluation boards to life," for $5,000. "This tool can be quite valuable to customers because there is no easy way to test out a DAC without it," he said.

Very often customers are running some type of communication standard and they want to see how well the D/A converter can perform using their particular vectors, Millet said. "The data pattern generator enables this and shortens the development times," he said. In addition, the D/A converter software program enables designers to manipulate the vectors and the digital inputs to get visual results.

Down the road, expect to see dual and quad versions of these D/A converters, Millet said.

- Bettyann Liotta