AD766:  16-Bit Current-Steering DAC with Voltage Reference

The AD766 16-bit DSP DACPORT provides a direct, three-wire interface to the serial ports of popular DSP processors, including the ADSP-2101, TMS320CXX, and DSP56001. No additional "glue logic" is required. The AD766 is also complete, offering on-chip serial-to-parallel input format conversion, a 16-bit current-steering DAC, voltage reference, and a voltage output op amp. The AD766 is fabricated in Analog Devices' BiMOS II mixed-signal process which provides bipolar transistors, MOS transistors, and thin-film resistors for precision analog circuits in addition to CMOS devices for logic.

The design and layout of the AD766 have been optimized for ac performance and are responsible for its guaranteed and tested 94 dB signal-to-noise ratio to 20 kHz and 79 dB SNR to 250 kHz. Laser-trimming the AD766's silicon chromium thin-film resistors reduces total harmonic distortion below -81 dB (at 1 kHz), a specification also production tested. An optional linearity trim pin allows elimination of midscale differential linearity error for even lower THD with small signals.

The AD766's output amplifier provides a ±3 V signal with a high slew rate, small glitch, and fast settling. The output amplifier is short circuit protected and can withstand indefinite shorts to ground.

The serial interface consists of bit clock, data, and latch enable inputs. The twos-complement data word is clocked MSB first on falling clock edges into the serial-to-parallel converter, consistent with the serial protocols of popular DSP processors. The input clock can support data transfers up to 12.5 MHz. The falling edge of latch enable updates the internal DAC input register at the sample rate with the sixteen bits most recently clocked into the serial input register.

The AD766 operates over a ±5 V to ±12 V power supply range. The digital supplies, +V_L and -V_L, can be separated from the analog signal supplies, +V_S and -V_S, for reduced digital crosstalk. Separate analog and digital ground pins are also provided. An internal bandgap reference provides a precision voltage source to the output amp that is stable over temperature and time.

Power dissipation is typically 120 mW with ±5 V supplies and 300 mW with ±12 V. The AD766 is available in commercial (0°C to +70°C), industrial (-40°C to +85°C), and military (-55°C to +125°C) grades. Commercial and industrial grade parts are available in a 16-pin plastic DIP; military parts processed to MIL-STD-883B are packaged in a 16-pin ceramic DIP. See Analog Devices' Military Products Databook or current military data sheet for specifications for the military version.

APPLICATIONS

• Digital Signal Processing
• Noise Cancellation
• Radar Jamming
• Automatic Test Equipment
• Precision Industrial Equipment
• Waveform Generation