ADS1256IDBR

The ADS1256IDBR is a high-performance 24-bit delta-sigma analog-to-digital converter from Texas Instruments, designed for the most demanding precision measurement applications. With its combination of ultra-low noise (27 nV input-referred), exceptional linearity (±0.0010% FSR maximum), and up to 23 bits of noise-free resolution, the ADS1256 sets the benchmark for integrated delta-sigma ADC performance. The device features an 8-channel input multiplexer that can be configured as four differential inputs or eight single-ended inputs, along with integrated sensor detection current sources for detecting open or shorted sensor connections. A chopper-stabilized input buffer provides very high input impedance, enabling direct connection to high-impedance sensors without signal attenuation. The programmable gain amplifier offers gains from 1 to 64, allowing the device to handle both volt-level signals and microvolt-level sensor outputs with high resolution. The fourth-order delta-sigma modulator is followed by a programmable sinc digital filter that provides data rates from 2.5 SPS to 30 kSPS. A key advantage is single-cycle settling: after switching channels or changing gain, the next output sample already has full accuracy, eliminating the need to discard multiple settling samples in multiplexed applications. The ADS1256 includes comprehensive calibration capabilities including self-calibration (offset and gain) and system calibration to remove errors from the entire signal chain. The device operates from a 5V analog supply and 1.8V to 3.6V digital supply, with separate digital I/O that is 5V tolerant for easy interfacing to 3.3V or 5V microcontrollers. Communication is through a 4-wire SPI-compatible serial interface. The ADS1256IDBR is packaged in a 28-lead SSOP (shrink small-outline package) with tape and reel packaging, and is specified over the industrial temperature range of -40C to +85C. For single-channel applications, the pin-compatible ADS1255 offers the same performance in a smaller 20-pin package.

The ADS1256 uses a fourth-order delta-sigma modulator architecture to achieve its exceptional 24-bit resolution and noise performance. The analog input signal passes through an input multiplexer that selects one of eight analog inputs, which can be configured as either single-ended (referenced to AGND) or differential (pairs of inputs). The selected signal then passes through an optional chopper-stabilized input buffer, which provides very high input impedance while minimizing input bias current and offset voltage drift through chopper stabilization techniques. After the buffer, the signal is amplified by the programmable gain amplifier, which can be set to gains of 1, 2, 4, 8, 16, 32, or 64. The PGA is designed for very low noise, contributing only 27 nV of input-referred noise at the highest gain setting. The amplified signal is then fed to the fourth-order delta-sigma modulator, which samples the input at a very high rate (determined by the 7.68 MHz external clock divided down) and produces a high-speed bitstream. The fourth-order modulator provides aggressive noise shaping, pushing most of the quantization noise to frequencies far above the signal band. Following the modulator is a programmable digital decimation filter (sinc filter) that converts the high-rate bitstream into 24-bit output samples at the programmed data rate. The filter order and decimation ratio determine the data rate and noise performance: lower data rates provide more filtering and therefore better noise resolution, while higher rates allow faster measurements. The filter is designed so that full accuracy is achieved on the very first sample after a channel or gain change (single-cycle settling), which is critical for multiplexed systems. The device includes self-calibration circuitry that can automatically measure and correct for offset and gain errors. System calibration allows the user to calibrate out errors from the entire signal chain (including external components). Sensor detect current sources can be enabled to verify that sensors are properly connected by sourcing or sinking small currents and checking the resulting voltage. An internal temperature sensor provides die temperature monitoring for compensation purposes.

• High-precision weigh scales and load cell measurement
• Scientific and laboratory instrumentation requiring nanovolt sensitivity
• Industrial process control and high-accuracy PLC analog modules
• Medical diagnostic equipment and patient monitoring
• Test and measurement: precision multimeters, source measure units
• Strain gauge, force, and pressure measurement
• Flow measurement and mass flow controllers
• High-resolution data acquisition systems
• Seismic monitoring and geophysical exploration equipment
• Precision temperature measurement with platinum RTDs