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Op amps claim near-zero drift and input noise

Posted: 26 Jan 2007 ?? ?Print Version ?Bookmark and Share

Keywords:op amps? operational amplifier? sensors? instrumentation? ADI?

The AD8231 from Analog Devices Inc. (ADI) gets close to the theoretical ideal instrumentation amplifier (in amp). These specialized op amps, vital to extract tiny signals from industrial and instrumentation sensors, despite high common-mode voltages, play a critical role in defining ultimate system performance. The AD8231 also features programmable binary gains from x1 to x128, which is software settable using a three-pin interface, or hardware-settable via pin strapping, and an uncommitted high-performance op amp which can implement auxiliary functions, all in a 16-lead LFCSP housing.

Unlike some components whose ultimate performance is largely designed by software or other ICs, an in-amp's performance is fully defined by its own max/min specifications. The single-supply AD8231 (3.3-5V) uses a classic three op amp architecture and provides maximum voltage offset of 50nV/C across its operating temperature range, and maximum gain-coefficient drift of 10ppm/C. Instead of being specified over the conventional industrial temperature range of -40C to 85C, this part is specified to 125C.

Noise level is 32nV/rt-Hz, which ADI documents as being just 1/5 the value of competing "zero-drift" instrumentation amplifiers, while bandwidth is 1MHz, five times the nearest competitor. The rail-to-rail output device has input impedance of 10 gigaohms, and its performance does not degrade with the use of high-impedance sensors. Maximum input offset voltage is 25?V, with 100pA maximum input bias current. Common-mode rejection is at least 122dB at gain of 128.

Although there are few free lunches in components, the AD8231 comes close with an uncommitted, on-chip op amp. This amplifier can be used for level shifting, error correction, filtering or providing a differential output to interface with a differential-input ADC. To improve vibration integrity with respect to the PCB (which can affect signal integrity with these miniscule signals), the package includes a center paddle underneath which is soldered to the board along with the package leads.

The AD8231 is priced at $1.69 each in 1,000-piece quantities.

- Bill Schweber
Site Editor, Planet Analog

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Related Datasheets
Part Number Description Category
? AD8231 Zero Drift, Digitally Programmable Instrumentation Amplifier Actives - Sensors and Transducers



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