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RMS to DC Converter is Accurate and Stable: 09/14/95 EDN-Design Ideas /
(added 11/05) Combining the well-known true RMS-to-dc circuit with a simple S/H circuit eliminates offset errors, which increases accuracy and temperature stability. The circuit in Fig 1 uses a low-cost analog multiplier, IC1; an integrator, IC3A, R5, and C1; and an analog inverter, IC2, R3, R4, and
D1 to convert the analog VIN into a true-RMS dc VOUT. The input signal can be ac, dc, or a combination. With an input-signal range of 0 to 2V, the circuit can handle ac signals with crest factors up to 5. Unfortunately, offsets in IC1 and IC3A contribute significant error to the circuit. Moreover,
these offsets drift with temperature. To remove these offset errors, the circuit performs self-calibration with the help.... |