Single Supply Dual 18-Bit Audio DAC

The AD1868 is a complete dual 18-bit DAC offering excellent performance while requiring a single +5 V power supply. It is fabricated on Analog Devices' ABCMOS wafer fabrication process. The monolithic chip includes CMOS Logic elements, bipolar and MOS linear elements, and laser-trimmed thin-film resistor elements. Careful design and layout techniques have resulted in low distortion, low noise, high channel separation, and low power dissipation.
The DACs on the AD1868 chip employ a partially segmented architecture. The first three MSBs of each DAC are segmented into seven elements. The 15 LSBs are produced using standard R-2R techniques. The segments and R-2R resistors are laser trimmed to provide extremely low total harmonic distortion. The AD1868 requires no deglitcher or trimming circuitry. Low noise is achieved through the use of two noise-reduction capacitors.
Each DAC is equipped with a high performance output Amplifier These Amplifiers achieve fast settling and high slew rate, producing 1 V signals at load currents up to 1 mA. The buffered output signal range is 1.5 V to 3.5 V. Reference voltages of 2.5 V are provided, eliminating the need for "False Ground" networks.
A versatile digital Interface allows the AD1868 to be directly connected to all digital Filter chips. Fast CMOS Logic elements allow for an input Clock rate of up to 13.5 MHz. This allows for operation at 2x, 4x, 8x, or 16x the sampling frequency for each channel. The digital input pins of the AD1868 are TTL and +5 V CMOS compatible.
The AD1868 operates on +5 V power supplies. The digital supply, VL, CAN be separated from the Analog supply, VS, for reduced digital feedthrough. Separate Analog and digital ground pins are also provided. In systems employing a single +5 volt power supply, VL and VS should be connected together. In battery operated systems, operation will continue even with reduced supply voltage. Typically, the AD1868 dissipates 50 mW.
The AD1868 is packaged in either a 16-pin plastic DIP or a 16- pin plastic SOIC package. Operation is guaranteed over the temperature range of -35C to +85C and over the voltage supply range of 4.75 V to 5.25 V.
By Analog Devices, Inc.