A pair of instrumentation amplifiers from Analog Devices, Inc. shows that precise, high-performance analog functions still play a critical role in instrumentation and data-acquisition applications. Such in-amps provide signal conditioning and amplification over large input voltage ranges, with well-defined dc accuracy and gain settings.
The AD8250, with digitally (or pin-strapped) settable gain of 1, 2, 5, and 10, and the similar AD8251 with gain of 1, 2, 4, and 8, operate on signals up to ±10V range, with a 12 MHz 3-dB bandwidth (at gain of 1), to accommodate fast-slewing signals. Common-mode rejection ratio is at least 80 dB to 10 kHz, also at unity gain, and 100 dB at gain of 10. The 30 V/μsec slew rate, and 0.5 μsec settling time to 0.01%, illustrate ac performance.
But a good in-amp is also defined by its dc specs. These devices promise input-referred noise below 15 nV per √Hz at gain of 10, gain drift better than 10 ppm/° C, input offset below 100 μV, coupled with maximum input offset drift of 1 μV/° C.
The in-amps operate from ±5 to ±12V supplies, and consume less than 4 mA. Housed in 10-lead MSOP packages (3.1×3.1mm body size), which the vendor claims is 90% smaller than competitive 16-lead SOIC devices, the in-amps are $4.95 (1000).–Bill Schweber.