ABSOLUTE VALUE CIRCUIT, MEAN VALUE CIRCUIT AND EFFECTIVE VALUE/DC VOLTAGE CONVERSION CIRCUIT

PROBLEM TO BE SOLVED: To convert an input signal to a DC voltage corresponding to the approximate absolute value thereof by inverting the polarity of an input signal alternately in synchronism with a pulse signal of constant frequency and subjecting the output to full- wave rectification thereby converting the input signal into a DC voltage corresponding to the approximate absolute value thereof. SOLUTION: An oscillation circuit 5 oscillates a pulse signal of constant frequency at a duty ratio of 0.5, for example. A switch control circuit 6 switches the movable contact of switch 11a, 11b in a polarity inversion circuit 7 between the inverting side and the noninverting side depending on the fact whether the pulse signal has H level or L level. Consequently, an operational amplifier 12 performs inverted amplification or non-inverted amplification of the input signal and a full-wave rectification circuit 8 performs fall-wave rectification of the output to output a DC voltage corresponding to the approximate absolute value of the input signal. Subsequently, a smoothing circuit 3 smooths the output from the full-wave rectification circuit 8 and a correction circuit 4 amplifies the smoothed output such that an error due to the reverse error voltage of the full-wave rectification circuit 8 is compensated to output a DC signal having voltage value equal to the true means voltage of the input signal.