Patent ID: 7365588

Claim:
An automatic time constant adjustment circuit comprising: an error detection circuit including an error reference resistor and an error reference capacitor formed, each by an IC process, on a single semiconductor substrate, the error detection circuit passing a current inversely proportional to a resistance of the error reference resistor through the error reference capacitor for a predetermined period and comparing a voltage appearing as a result across the error reference capacitor with a predetermined reference voltage so as to detect a resistance/capacitance error, which corresponds to a value obtained by subtracting from a product of the resistance of the error reference resistor and a capacitance of the error reference capacitance a product of a design resistance of the error reference resistor and a design capacitance of the error reference capacitor, by finding in which of n steps (where n is a natural number equal to or greater than 2) the resistance/capacitance error lies, the error detection circuit then outputting a control signal corresponding to the step in which the resistance/capacitance error is found to lie; and a variable time constant circuit including a resistance portion, a capacitance portion, and a switch portion, the resistance portion being formed with one or more resistors formed by an IC process on the semiconductor substrate, the capacitance portion being formed with one or more capacitors formed by an IC process on the semiconductor substrate, the switch portion being connected between the resistor portion and the capacitor portion, the switch portion setting a time constant of the variable time constant circuit according to the resistance/capacitance error by connecting together one of the resistors of the resistor portion and one of the capacitors of the capacitor portion according to the control signal, wherein at least either a number of resistors provided as the resistors or a number of capacitors provided as the capacitors is two or more.