An approach to integrated electret electroacoustic transducer. Experimental digital microphone

Most electret electroacoustic transducers are analog condenser microphones, and only a very small percentage are earphones or loudspeakers. The principal reason for this imbalance is the condition required for matching of electronic circuits. Condenser microphones have excellent circuit matching due to FET. On the other hand, matching of condenser earphone/loudspeakers and linear amplifiers is difficult. This problem is solved by a digital system whose electronic circuit consists of a DC power source and gate switches. Some examples of digital earphones, digital to analog converting electroacoustic transducers, are described. Using this electroacoustic DAC, a direct converting digital microphone system which enables speech communication systems to be completely digital is also described. A conceptual digital microphone including an experimental DAC-subtractor transducer having a diaphragm of electret foil, a detecting electrode and divided driving electrodes is developed. A prototype model of the integrated transducer is experimentally fabricated. As the total integration including transducers and electronic circuit for the next generation devices