ADI AD637JRZ

The AD637 is a high accuracy, complete RMS-to-DC converter capable of computing the true RMS value of any complex waveform. It provides performance previously unattainable in an integrated circuit RMS-to-DC converter, and competes in accuracy, bandwidth, and dynamic range with discrete component and hybrid module approaches. The AD637 can compute the true RMS, mean square, or absolute value of any complex AC (or AC plus DC) input waveform, and gives an equivalent DC output voltage. The true RMS value of a waveform is more useful than the average rectified signal because it is directly related to the power of the signal. Statistically, the RMS value of a signal is related to the standard deviation of the signal.

Superior crest factor compensation allows measurement of signals with crest factors of up to 10 with less than 1% additional error. The AD637's wide bandwidth allows measurement of signals up to 600 kHz at 200 mV RMS input; for input levels above 1 V RMS, signals up to 8 MHz can be measured.

A direct dB output of the RMS value is available at a separate pin, with a 60 dB range. An externally programmable reference current allows the user to select any level between 0.1 V and 2.0 V RMS as the 0 dB reference voltage.

The chip select connection on the AD637 allows the user to reduce supply current from 2.2 mA to 350 μA when the RMS function is not in use. This feature facilitates the inclusion of precision RMS measurement in remote or handheld applications where minimum power consumption is critical. Furthermore, when the AD637 is powered down, the output goes to a high impedance state. This allows multiple AD637s to be connected together to form a wideband true RMS multiplexer.

The AD637's input circuit is protected against overload voltages that exceed the supply rails. If the supply voltage is lost, the input signal will not damage the inputs.

The AD637 is laser wafer trimmed to rated performance without external trimming. The only external component required is a capacitor for setting the averaging period. The value of this capacitor also determines low frequency accuracy, ripple level, and settling time.

The on-chip buffer amplifier can be used either as an input buffer or configured as an active filter. The filter can be used to reduce AC ripple, thereby improving accuracy.