MC34018

The MC34018 has the following features including (1)All necessary level detection and attenuation controls for a hands-free telephone in a single integrated circuit;(2)Background noise level monitoring with long time constant;(3)Wide operating dynamic range through signal compression;(4)On-chip supply and reference voltage regulation;(5)Typical 100 mW output power (into 25 Ohms) with peak limiting to minimize distortion;(6)Linear Volume Control Function.

The MC34018 Speakerphone integrated circuit incorporates the necessary amplifiers, attenuators, and control functions to produce a high quality hands-free speakerphone system. Included are a microphone amplifier, a power audio amplifier for the speaker, transmit and receive attenuators, a monitoring system for background sound level, and an attenuation control system which responds to the relative transmit and receive levels as well as the background level. Also included are all necessary regulated voltages for both internal and external circuitry, allowing line-powered operation (no additional power supplies required). A Chip Select pin allows the chip to be powered down when not in use. A volume control function may be implemented with an external potentiometer. MC34018 applications include speaker-phones for household and business use, intercom systems, automotive telephones, and others.

The MC34018 Speakerphone IC is designed to provide the functions additionally required when a speaker-phone is added to a standard telephone. The IC provides the necessary relative level detection and comparison of the speech signals provided by the talkers at the speakerphone (near end speaker) and at the distant telephone (far end speaker).The MC34018 is designed for use with an electret type microphone, a 25 ohm speaker, and has an output power capability of (typically)100 mW. All external com-ponents surrounding this device are passive, however,this IC does require additional circuitry to interface to the Tip and Ring telephone lines.Two suggested circuits are shown in this data sheet.All of the above mentioned times will change significantly by varying the amplitude of the input signals, as well as by varying the external components.