An Externally Linear-Internally Nonlinear RMS-to-DC Converter

The article presents a root mean square (RMS) to direct current (dc) converter based on an externally linear-internally nonlinear (ELIN) filter. The converter contains an averaging filter and two nonlinear blocks. The principle of operation of an ELIN circuit using an example of the ELIN integrator was presented. Three converters were developed and simulated each using four multiplier/divider integrated circuits. Preliminary tests of the input dynamic range of the three circuits were made by SPICE simulations. The prototype of the RMS-to-dc converter with a third-degree ELIN filter shows an improved dynamic range in comparison to classic “implicit square-rooting” converters as its error is reduced at lower amplitudes of the input voltage. The measured bandwidth of the ELIN converter prototype is wider in comparison to the “implicit square-rooting” converter prototype, built from nominally the same nonlinear components. The converter based on the presented circuit can be used in applications, where a wide voltage range and wide bandwidth are needed.