Electronic Design

Instrumentation Amplifier Provides Industry-Best CMR In Half The Space

The AD8295 precision instrumentation-amplifier front end from Analog Devices uses 50% less board space than competing amplifier solutions for industrial process controls, precision data acquisition systems, medical instrumentation equipment, and Wheatstone bridge measurement applications, according to the company. The 4- by 4-mm, 16-lead lead-frame chip-scale package (LFCSP) includes the instrumentation amplifier, two uncommitted operation amplifiers, and two precision-trimmed matched resistors.

As part of a complete signal chain, the AD8295 works well with a range of ADI’s analog-to-digital converters (ADCs), including the AD7656, AD7763, and AD7690, and multiplexers like the ADG1209. It also delivers the highest common-mode rejection (CMR) over frequency in its class, ADI says. While the CMR of competing devices typically falls off at 200 Hz, the AD8295 maintains a minimum CMR of 80 dB to 8 kHz for all grades at G = 1. High CMR over frequency enables the device to reject wideband interference and line harmonics, greatly simplifying filter design.

The gain-programmable instrumentation amplifier uses a single resistor to set the gain from 1 to 1000, delivering 1-ppm/°C maximum gain drift (B grade), 8-nV/√Hz maximum input voltage noise at 1 kHz, and 0.25-µV p-p input noise (0.1 Hz to 10 Hz). The AD8295 operates on single and dual supplies and is well suited for applications where ±10-V input voltages are encountered. The entire chip only uses 2 mA of total current, allowing for more channel density and lower-cost designs.

The AD8295’s components are arranged so typical application circuits such as a differential ADC driver or an instrumentation amplifier with output filtering have short routes and few vias. Unlike most chip-scale packages, the chip doesn’t have an exposed metal pad on its back, freeing additional space for routing and vias. Operating temperature ranges from –40°C to 85°C. Available now, the AD8295 costs $2.89 each in quantities of 1000.

Analog Devices


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