The telephone circuit U4089B-M is a linear integrated circuit for use in feature phones, answering machines and fax machines. It contains the speech circuit, side tone equivalent and ear protection rectifiers. The circuit is line-powered and contains all components necessary for the amplification of signals and adaptation to the line. An integrated voice switch with a loudspeaker amplifier enables loud-hearing or hands-free operation. With an anti-feedback function, acoustical feedback during loudhearing can be reduced significantly. The generated supply voltage is suitable for a wide range of peripheral circuits. Figure 1. Simple Block Diagram Speech