Patent ID: 7269098

Claim:
An ultrasonic transmitter comprising: a transducer on which a plurality of vibrating elements are arranged; and a transmitting beamformer for forming an ultrasonic transmitting beam by activating vibrating elements by feeding driving pulse signals thereinto so that the individual vibrating elements output ultrasonic signals at a specific transmitting frequency fs and at varying amplitudes, the transmitting beamformer including half-bridge circuits each of which includes a pair of series-connected switching devices and generates the driving pulse signal by alternately switching the two switching devices at a specific switching frequency fa; wherein each of the half-bridge circuits generates the driving pulse signal by matching the switching frequency fa to the transmitting frequency fs and matching the sum of ON periods of the switching devices to the sum of OFF periods of the switching devices within each switching cycle of the switching devices when the ultrasonic signals are transmitted at maximum output power; and each of the half-bridge circuits generates the driving pulse signal based on multiple patterns of ON periods and OFF periods of the switching devices contained in each switching cycle of the switching devices by making the switching frequency fa higher than the transmitting frequency fs and controlling an ON/OFF pattern determined by a combination of the ON periods and the OFF periods of the switching devices when the ultrasonic signals are transmitted at reduced output power.