D/A converter cuts power by 70 percent

Norwood, Mass. — Analog Devices, Inc. has developed a lower-power version of its TxDAC transmit digital-to-analog converters (D/A converters) that is said to reduce power dissipation by up to 70 percent over the previous generation.

The AD970x family supports update rates at 175 Megasamples/second — an operating rate four times that of its nearest competitor, said Dave Robertson, product line director of ADI's High-Speed Converter Group. The family consists of four products: the flagship AD9707 14-bit D/A converter; and the AD9706, AD9705 and AD9704, which are 12-, 10-, and 8-bit D/A converters, respectively. The family features spurious-free dynamic range (SFDR) of 86 dBc and intermodulation (IMD) of 70 to 50 MHz.

The AD9707 has a flexible power supply operating range from 1.7 V to 3.6 V. At 3.3 V, the AD970x family dissipates 35 mW of power and at 1.8 V dissipates 12 mW. Its power dissipation can be further reduced by 15 mW by lowering the full-scale current output. Sleep and power down modes reduce dissipation to 5 mW for low-power idle periods.

Designed especially for communications, industrial instrumentation and portable applications, the AD970x family is suited for applications that need to synthesize broadband signals efficiently — from handheld radios to portable instruments.

In addition, the AD970x family integrates an on-chip voltage reference and set and load resistors, lowering component count and bill of materials costs, Robertson said. The devices also feature common mode shift capability, minimizing the need for level-shifting circuitry when interfacing with other analog components. This level of integration, which is the first of its kind for transmit path data converters, simplifies analog design and reduces printed circuit board area for smaller portable designs, he said.

The devices are available in 28-lead TSSOP and 32-lead LFCSP packaging. The devices in the LFCSP packaging include an optional serial peripheral interface (SPI), which provides a higher level of programmability, and an adjustable output common mode feature that enables the TxDAC to easily interface to other components that require common modes greater than 0 V.

The AD9707 is also self-calibrating, allowing it to achieve greater accuracy and true 14-bit integral nonlinearity (INL) and differential nonlinearity (DNL) performance.

The devices are supported by an evaluation board and two development tools: the high-speed D/A converter Pattern Generator (DPG), which provides digital data for ADI’s D/A converter evaluation boards, and VisualDAC , an integrated development and debugging environment.

The AD970x family is sampling now with production quantities planned for October. Pricing for the family ranges from $2.75 to $5.75 in 1,000-unit quantities, depending on resolution. Click here for the AD970x data sheets.

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

Despite the small size and low power consumption features, all four D/A converters maintain high performance levels, according to Chuck Millet, business manager of ADI'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 (80 dBc) and DNL (± 0.5 LSBs typical) specs at a clock frequency of 10 MHz, these latest devices boast virtually equivalent AC and DNL specs (80 dBc and DNL of ± 0.7 LSBs). 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 D/A converter (AD9744) to the latest generation 14-bit device (AD9707), power consumption is 200 mW at 3.3 V, 20 mA for the AD9744, compared to 55 mW at 3.3 V, 2 mA 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.

See related power consumption chart

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

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

ADI has also taken advantage of a high-voltage blend, Millet said. “The new devices have a 3.3-V transistor capability, which gives us a higher voltage range and higher analog swing (1.7 to 3.6 V range),” he said. Doing this makes it easier to interface with other analog components that are already operating at 3.3 V (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 $5,000.00. “This tool can be quite valuable to customers because there is no easy way to test out a D/A converter 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.

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