Analog Circuit Design

38

Instrumentation circuitry using RMS-to-DC convertersRMS converters rectify average results

Jim Williams

Introduction

It is widely acknowledged that RMS (root of the mean of the square) measurement of waveforms furnishes the most accurate amplitude information.¹ Rectify-and-average schemes, usually calibrated to a sine wave, are only accurate for one waveshape. Departures from this waveshape result in pronounced errors. Although accurate, RMS conversion often entails limited bandwidth, restricted range, complexity and difficult to characterize dynamic and static errors. Recent developments address these issues while simultaneously improving accuracy. Figure 38.1 shows the LTC®1966/LTC1967/LTC1968 device family. Low frequency accuracy, including ...