The programmable telephone audio processor U4091BM-N is a linear integrated circuit for use in feature phones, answering machines and fax machines. It contains the speech circuit, tone-ringer interface with DC/DC converter, sidetone equivalent and ear-protection rectifiers. The circuit is line-powered and contains all components necessary for signal amplification and adaptation to the line. The U4091BM-N can also be supplied via an external power supply. An integrated voice switch with loudspeaker amplifier enables hands-free or loudhearing operation. With an anti-feedback function, acoustic feedback during loudhearing can be reduced significantly. The generated supply voltage is suitable for a wide range of peripheral circuits.