AD1864

The AD1864 is a complete dual 18-bit DAC offering excellent THD+N, while requiring no external components. Two complete signal channels are included. This results in cophased voltage or current output signals and eliminates the need for output demultiplexing circuitry. The monolithic AD1864 chip includes CMOS logic elements, bipolar and MOS linear elements and laser-trimmed thin-film resistor elements, all fabricated on Analog Devices BiMOS II process.

The DACs on the AD1864 chip employ a partially-segmented architecture. The first four MSBs of each DAC are segmented into 15 elements. The 14 LSBs are produced using standard R-2R techniques. Segment and R-2R resistors are laser-trimmed to provide extremely low total harmonic distortion. This architecture minimizes errors at major code transitions resulting in low output glitch and eliminating the need for an external deglitcher. When used in the current output mode, the AD1864 provides two cophased ±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 output amplifier is short-circuit protected and can withstand indefinite short circuits to ground.

The AD1864 was designed to balance two sets of opposing requirements, channel separation and DAC matching. High channel separation is the result of careful layout techniques. At the same time, both channels of the AD1864 have been designed to ensure matched gain and linearity as well as tracking over time and temperature. This assures optimum performance when used in stereo and multi-DAC per channel applications.

A versatile digital interface allows the AD1864 to be directly connected to standard digital filter chips. This interface employs five signals: Data Left (DL), Data Right (DR), Latch Left (LL), Latch Right (LR) and Clock (CLK). DL and DR are the serial input pins for the left and right DAC input registers. Input data bits are clocked into the input register on the rising edge of CLK. A low going latch edge updates the respective DAC output. For systems using only a single latch signal, LL and LR may be connected together. For systems using only one DATA signal, DR and DL may be connected together.

The AD1864 operates from ±5 V to ±12 V power supplies. The digital supplies, V_L and ­V_L, can be separated from the analog supplies, V_S and ­V_S, for reduced digital feedthrough. Separate analog and digital ground pins are also provided. The AD1864 typically dissipates only 225 mW, with a maximum power dissipation of 265 mW.

The AD1864 is packaged in both a 24-pin plastic DIP and a 28-pin PLCC. Operation is guaranteed over the temperature range of ­25°C to +70°C and over the voltage supply range of ±4.75 V to ±13.2 V.