AD637SD

The AD637SD by Analog Devices Inc. is a complete, high-accuracy, RMS-to-DC converter designed to compute the true RMS value of any complex waveform. It offers performance comparable to discrete and modular techniques in accuracy, bandwidth, and dynamic range.

Key features include a maximum nonlinearity of 0.02% for inputs from 0 V to 2 V rms and a wide bandwidth of up to 8 MHz at 2 V rms input, or 600 kHz at 100 mV rms. The device can compute the true root mean square, mean square, or absolute value of AC or AC plus DC input waveforms, providing an equivalent DC output voltage. Superior crest factor compensation allows measurements of signals with crest factors up to 10 with less than 1% additional error.

A direct dB output with a 60 dB range is available on a separate pin. The AD637SD also features a chip select/power-down function that reduces quiescent current from 2.2 mA to 350 µA, making it suitable for low-power applications. When powered down, the output enters a high impedance state, enabling multiple AD637SDs to be connected for wideband true RMS multiplexer applications.

This converter is laser wafer trimmed for rated performance without external trimming, requiring only an external capacitor to set the averaging period. The on-chip buffer amplifier can be used as an input buffer or in an active filter configuration to reduce ripple and increase accuracy.