Patent ID: 7417473

Claim:
A signal generator for use in driving current through a load, comprising: a current control element for controlling a current flowing through an electric load, wherein the current control element is disposed between a direct current power supply and the electric load; and a signal forming element for outputting a control signal to the current control element, wherein the signal forming element generates the control signal in such a manner that the current flowing through the electric load has a rising edge and a down edge of a substantially sine waveform, the rising edge of the current is disposed at a timing when the current control element is switched on, and the down edge of the current is disposed at a timing when the current control element is switched off, wherein the signal forming element includes approximate-waveform forming means and a low pass filter, the approximate-waveform forming means generates and outputs the control signal, which has a predetermined waveform of a broken line approximation, the low pass filter filters a low frequency part of the control signal, the approximate-waveform forming means includes a capacitor, the capacitor is charged in a case where the control signal is in a rising edge period so that increase degree of a terminal voltage of the capacitor is switched with a plurality of steps, the capacitor is discharged in a case where the control signal is in a down edge period so that decrease degree of the terminal voltage of the capacitor is switched with a plurality of steps, and the approximate-waveform forming means generates the control signal by switching the increase degree and the decrease degree of the terminal voltage with a plurality of steps.