Auto-zero amp

Analog Devices has unveiled what it claims is the industry’s first digitally programmable, signal-conditioning auto-zero amplifier for strain-bridge and other sensors.

Analog Devices Inc. (ADI) has unveiled what it claims is the industry’s first digitally programmable, signal-conditioning auto-zero amplifier for strain-bridge and other sensors.

Within the new chip, ADI has integrated a full range of amplifier, comparator, resistor, trimpot and buffer functionality into a SOIC or 4 mm by 4 mm chipscale package (CSP), providing a complete path from a sensor to analog-to-digital (A/D) converter.

This allows systems designers to automatically, under software control, eliminate variations between sensors. Sensor outputs can be digitally programmed for gain and output offset voltage. Prior to the ADI solution engineers relied on devices that had lower accuracy and less stability and involved manual adjustments that were difficult, time consuming and expensive.

With flexible controls enabled by a one-wire serial interface, the AD8555 offers designers zero drift, programmable gain, a small footprint and low cost. By using ADI’s patented low-noise auto-zero and DigiTrim technologies, the chip accurately converts differential and single-ended sensor outputs to a well-defined output voltage range, effectively rejecting common mode noise in the process.

The gain and offset adjustment can be simulated in-circuit before being permanently programmed. The chip also offers fault detection (open and short wire and data integrity) to ensure high reliability. In addition, users can easily add a low-pass filter and clamp the maximum output level to protect low voltage A/D converter inputs.

The chip offers integrated low-pass filtering, open and shorted wire fault detection, and output clamp voltage capability – suitable for driving low-voltage analog-to-digital converters. In addition, it has a read-back function to verify correct programming, and a trim lockout function to assure field reliability. By integrating these features, the AD8555 allows users to manage sensor outputs easily and cost effectively.

The device sports 10uV max input offset voltage over temperature, 50-nV/degrees C max input offset drift, and 96-dB common mode rejection, resulting in high dc accuracy. Gain is digitally programmable with high resolution over a wide range from 70 to 1280 through a single-wire interface. Output offset voltage is digitally programmed and ratiometric to the supply voltage.

It allows gain and offset adjustment to be simulated in-circuit before being permanently programmed with reliable poly-fuse trim technology. The amplifier can also drive high capacitive loads.

The AD8555 is currently sampling in 8-lead SOIC or 16-lead LFCSP packaging. The device is priced at $2.80 and $2.90, respectively, per unit in 1,000-piece quantities.

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