AD1865*

The AD1865 is a complete, dual 18-bit DAC offering excellentTHD+N and SNR while requiring no external components. Twocomplete signal channels are included. This results in cophasedvoltage or current output signals and eliminates the need foroutput demultiplexing circuitry. The monolithic AD1865 chipincludes CMOS logic elements, bipolar and MOS linear elementsand laser-trimmed thin-film resistor elements, all fabricatedon Analog Devices' ABCMOS process.

The DACs on the AD1865 chip employ a partially segmentedarchitecture. The first four MSBs of each DAC are segmentedinto 15 elements. The 14 LSBs are produced using standard R-2Rtechniques. Segment and R-2R resistors are laser trimmed to provideextremely low total harmonic distortion. This architectureminimizes errors at major code transitions resulting in low outputglitch and eliminating the need for an external deglitcher.When used in the current output mode, the AD1865 providestwo ±1 mA output signals.

Each channel is equipped with a high performance output amplifier.These amplifiers achieve fast settling and high slew rate,producing ±3 V signals at load currents up to 8 mA. Each outputamplifier is short-circuit protected and can withstand indefiniteshort circuits to ground.

The AD1865 was designed to balance two sets of opposing requirements,channel separation and DAC matching. High channelseparation is the result of careful layout. At the same time,both channels of the AD1865 have been designed to ensurematched gain and linearity as well as tracking over time andtemperature. This assures optimum performance when used instereo and multi-DAC per channel applications.