Programmable auto-zero amplifier simplifies sensor designs
9 February 2005
Analogue, Mixed Signal, LSI
The AD8555 is Analog Devices' highly integrated, digitally-programmable precision amplifier designed to provide a complete signal processing solution from the sensor output to an ADC. Using ADI's low noise auto-zero DigiTrim technology, the chip is able to create an accurate and reliable signal processing solution in a very small footprint. The AD8555 has very low input offset voltage (10 μV max over temperature) and input offset voltage drift (60 nV/°C max over temperature). Gain is digitally-programmable over a wide range of 70 to 1280 through a single-wire interface. Output offset voltage is digitally programmed and ratiometric to the supply voltage. Alternatively, it can be reprogrammed indefinitely in simulation mode.
In 8-lead SOIC and 16-lead 4 x 4 mm LFCSP packages, the amplifier chip also integrates a number of useful functions that help reduce cost and board space in industrial applications. The AD8555 provides open and short wire fault detection, low-pass filtering, and output clamp voltage capability, which are ideal for driving low-voltage ADCs. In addition, it offers a readback function to verify correct programming, and a lockout trim function to ensure field reliability. Integrating these features allows designers to reduce manufacturing costs by easily correcting for gain and offset variations in sensor outputs. Typical applications include pressure sensors in flow measurement, precision weigh scales, hydraulic and process control systems.
Another key advantage of using the AD8555 is its ability to drive large capacitive loads. This is useful when the amplifier is placed close to the sensor and needs to drive long cables. The device remains stable over a wide range of capacitive loads, with overshoot response decreasing with loads greater than 22 nF.
The AD8555 is ideal to interface bipolar signals to single-supply ADCs. The bipolar signal can be mapped into the input range of the ADC by programming the output offset of the AD8555 to a desirable input voltage level.
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