FREQUENCY SHIFTER AND OPTICAL DISPLACEMENT MEASURING APPARATUS

摘要

PURPOSE: To drive a frequency shifter using an electro-optical element stably and at a precise waveform. CONSTITUTION: In a frequency shifter, a voltage is applied to an electro-optical element and the phase of a luminous flux which is incident on the electro-optical element is modulated. The frequency shifter is provided with a constant-current circuit 20A by which a circuit applying a driving voltage to the electro-optical element supplies a constant current and with a discharge circuit 20B in which a switching element Q3 is constituted of an FET transistor. The voltage of a switching signal by the switching element Q3 is set nearly at the IQ point of the FET transistor.