Description

The AD678 is a complete, multipurpose 12-bit monolithic analog-to-digital converter, consisting of a sample-hold amplifier (SHA), a microprocessor compatible bus interface, a voltage reference and clock generation circuitry.The AD678 is specified for ac (or 'dynamic') parameters such as S/N+D ratio, THD and IMD which are important in signal processing applications. In addition, the AD678K, B and T grades are fully specified for dc parameters which are important in measurement applications.The AD678 offers a choice of digital interface formats; the 12 data bits can be accessed by a 16-bit bus in a single read operation or by an 8-bit bus in two read operations (8+4), with right or left justification. Data format is straight binary for unipolar mode and twos complement binary for bipolar mode. The input has a full-scale range of 10 V with a full power bandwidth of 1 MHz and a full linear bandwidth of 500 kHz. High input impedance (10 MΩ) allows direct connection to unbuffered sources without signal degradation.This product is fabricated on Analog Devices' BiMOS process, combining low power CMOS logic with high precision, low noise bipolar circuits; laser-trimmed thin-film resistors provide high accuracy. The converter utilizes a recursive subranging algorithm which includes error correction and flash converter circuitry to achieve high speed and resolution.The AD678 operates from +5 V and ±12 V supplies and dissipates 560 mW (typ). The AD678 is available in 28-pin plastic DIP, ceramic DIP, and 44 J-leaded ceramic surface mount packages.Screening to MIL-STD-883C Class B is also available.PRODUCT HIGHLIGHTS COMPLETE INTEGRATION: The AD678 minimizes external component requirements by combining a high speed sample-hold amplifier (SHA), ADC, 5 V reference, clock and digital interface on a single chip. This provides a fully specified sampling A/D function unattainable with discrete designs. SPECIFICATIONS: The AD678K, B and T grades provide fully specified and tested ac and dc parameters. The AD678J, A and S grades are specified and tested for ac parameters; dc accuracy specifications are shown as typicals. DC specifications (such as INL, gain and offset) are important in control and measurement applications. AC specifications (such as S/N+D ratio, THD and IMD) are of value in signal processing applications. EASE OF USE: The pinout is designed for easy board lay-out, and the choice of single or two read cycle output provides compatibility with 16- or 8-bit buses. Factory trimming eliminates the need for calibration modes or external trimming to achieve rated performance. RELIABILITY: The AD678 utilizes Analog Devices’ monolithic BiMOS technology. This ensures long-term reliability compared to multichip and hybrid designs. UPGRADE PATH: The AD678 provides the same pinout as the 14-bit, 128 kSPS AD679 ADC. The AD678 is available in versions compliant with MIL-STD-883. Refer to the Analog Devices Military Products Databook or current AD678/883B data sheet for detailed specifications.