OSCILLATION DETECTION METHOD AND OSCILLATION SUPPRESSION METHOD FOR MODULATION CIRCUIT

摘要

PROBLEM TO BE SOLVED: To detect an oscillation of a modulation circuit of a switching amplifier 21 in which a semiconductor power amplification device in a constant- voltage switch 29 is made to operate in a saturation region in response to a one-bit signal obtained by modulation, a high voltage from a power supply is switched, and the switched high voltage is amplified with a high efficiency to protect the semiconductor power amplification device from breakdown. SOLUTION: A pulse counting circuit 36 counts the number of pulses which defines a timing of a one-bit signal, and are generated by clock generating circuit 28 to measure a period while the one-bit signal is continuously at a high level or at a low level. If the period exceeds a prescribed threshold, a power supply cut-off circuit 37 is made to operate to cut off a power supply line to a constant-voltage switch 29.