Disclosed is a completely digital solution for a new type of root-mean-square to direct current conversion (RMS-to-DC) apparatus. The design is based on delta-sigma modulation (Δ-ΣM) and the direct nonlinear processing of the Δ-Σ modulated pulse stream. The only external component of the integrated circuit (IC) is capacitor C. The disclosed apparatus consists of low power consuming components which are simple, reliable and inexpensive.