Description

The AD7703 is a 20-bit ADC that uses a Σ-Δ conversion technique. The analog input is continuously sampled by an analog modulator whose mean output duty cycle is proportional to the input signal. The modulator output is processed by an on-chip digital filter with a six-pole Gaussian response, which updates the output data register with 16-bit binary words at word rates up to 4 kHz. The sampling rate, filter corner frequency, and output word rate are set by a master clock input that may be supplied externally, or by a crystal controlled on-chip clock oscillator. The inherent linearity of the ADC is excellent and endpoint accuracy is ensured by self-calibration of zero and full scale, which may be initiated at any time. The self-calibration scheme can also be extended to null system offset and gain errors in the input channel.The output data is accessed through a flexible serial port, which has an asynchronous mode compatible with UARTs and two synchronous modes suitable for interfacing to shift registers or the serial ports of industry-standard microcontrollers.CMOS construction ensures low power dissipation, and a power-down mode reduces the idle power consumption to only 10 µW.PRODUCT HIGHLIGHTS The AD7703 offers 20-bit resolution coupled with outstanding 0.0003% accuracy. No missing codes ensures true, usable, 20-bit dynamic range, removing the need for programmable gain and level-setting circuitry. The effects of temperature drift are eliminated by on-chip self-calibration, which removes zero and gain error. External circuits can also be included in the calibration loop to remove system offsets and gain errors. Flexible synchronous/asynchronous interface allows the AD7703 to interface directly to the serial ports of industry-standard microcontrollers and DSP processors. Low operating power consumption and an ultralow power standby mode make the AD7703 ideal for loop-powered remote sensing applications, or battery-powered portable instruments.APPLICATIONS Industrial Process Control Weigh Scales Portable Instrumentation Remote Data Acquisition