| 摘要 |
A volume control circuit for an audio transducer comprises a driver circuit driven by a first pulse rate signal to excite the audio transducer and render an audio signal at a desired volume and audio frequency corresponding to the first pulse rate signal, and a control circuit selectively activated to pulse modulate the excitation of the audio transducer during its pulsed excitation periods to alter the volume of the audio signal rendered by the audio transducer. In one embodiment, the control circuit includes a logical AND gate having as one input the first pulse rate signal and as another input a selected signal of either a second pulse rate signal or a signal representative of a logical one, the AND gate selectively activated to pulse rate modulate the first pulse rate signal with the second pulse rate signal which is preferably ultrasonic. In another embodiment, the AND gate may be coupled to a variable pulse rate signal to pulse rate modulate the first pulse rate signal to render the audio signal at a volume commensurate with the varied pulse rate. Various other alternate embodiments of the present invention are described all including the foregoing described volume control circuit.
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