A controller and method changing a frequency of a control (or carrier)
signal in accordance with a waveform that periodically changes within a
first frequency range from a frequency fc1 to a frequency fc2, where the
frequency fc1 is smaller than the frequency fc2, and a second frequency
range from a frequency fc3 to a frequency fc4, where the frequency fc3 is
smaller than the frequency fc4. The frequencies fc1 and fc4 satisfy the
inequalities (n-1)fc4.ltoreq.nfc2 and nfc3.ltoreq.(n+1)fc1 and/or satisfy
an approximate expression nfc4.apprxeq.(n+1)fc1 where n is an integer.
The frequencies fc2 and fc3 satisfy the inequalities
nfc2.ltoreq.fs-.DELTA.fs and fs+.DELTA.fs.ltoreq.nfc3 where
fs.+-..DELTA.fs represents a predetermined frequency band.