Method and circuit for producing control signal for impedance matching

摘要

A method for producing a stable control signal for impedance matching is provided which is capable of suppressing variation in impedance matching data by adding a shift voltage to a voltage to be compared. A comparator (13) compares the voltage to be compared with a reference voltage and an up-down counter (14) performs a counting operation according to a result from the comparison. A code converting circuit (15) converts a count value output from the up-down counter (14) to a thermometer code used for changing an impedance of an impedance varying circuit (11). A change in the impedance is made in a manner that, even when the voltage to be compared gets closest to the reference voltage, a shift voltage for the comparator (13) to make an exact comparison is fed to the voltage to be compared. An averaging circuit (16) averages a count value and the code converting circuit (17) converts a resulting average value to the thermometer code.