AD7703

LC2MOS 20-Bit A/D Converter AD7703 FEATURES Monolithic 16-Bit ADC 0.0015% Linearity Error On-Chip Self-Calibration Circuitry Programmable Low-Pass Filter 0.1 Hz to 10 Hz Corner Frequency 0 V to +2.5 V or ؎2.5 V Analog Input Range 4 kSPS Output Data Rate Flexible Serial Interface Ultralow Power APPLICATIONS Industrial Process Control Weigh Scales Portable Instrumentation Remote Data Acquisition FUNCTIONAL BLOCK DIAGRAM DVDD 15 AVDD 14 AVSS 7 DVSS 6 SC1 4 SC2 17 AD7703 CALIBRATION SRAM CALIBRATION MICROCONTROLLER 13 CAL AIN 9 VREF 10 AGND 8 DGND 5 20-BIT CHARGE BALANCE A/D CONVERTER ANALOG MODULATOR 6-POLE GAUSSIAN LOW-PASS DIGITAL FILTER 12 BP/UP 11 SLEEP CLOCK GENERATOR SERIAL INTERFACE LOGIC 20 SDATA 19 SCLK 3 2 1 16 CLKIN CLKOUT MODE CS 18 DRDY GENERAL DESCRIPTION The AD7703 is a 20-bit ADC that uses a S-D 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...