U4055B

` An electronic circuit replaces the microphone hybrid transformer
` Symmetrical input for dynamic or piezo microphone
`High performance through the use of dynamic transducers as the earphone (non-linear distortion 2%)
` Automatic line loss compensation
` DTMF interface with muting
` Supply voltage for dialer
` High range of line feeding current
` Input resistance independent of line current and sidetone suppression circuit.
` Built-in ear protection by earphone voltage limiter
` Operation possible from 8 mA

The U4055B electronic speech circuit is a linear integrated circuit for use in telephone and other line fed terminal equipment. It replaces the common speech circuit with carbon microphone, hybrid transformer, sidetone equivalent and ear protection rectifiers. A low-cost electrodynamic transducer is used as the earphone. U4055B contains all components necessary for amplification of signals and adaption to the line.