MC33218A Voice Switched Speakerphone Circuit
incorporates the necessary amplifiers, attenuators, level detectors, and
control algorithm to form the heart of a high quality hands–free
speakerphone system. Included are a microphone amplifier with mute,
transmit and receive attenuators, a background monitoring system for both
the transmit and receive paths, and level detectors for each path. An AGC
system reduces the receive gain on long lines where loop current and power
are in short supply. A dial tone detector prevents fading of dial tone. A Chip
Disable pin permits conserving power when the circuit is not in use.
Additionally, the MC33218A has a serial data port which permits
microprocessor control of the receive volume level, microphone mute,
attenuator range, and selection of transmit, receive, idle or normal modes.
The data port can be operated at up to 1.0 MHz.
The MC33218A can be operated from a power supply, or from the
telephone line, requiring typically 4.6 mA. It can be used in conjunction with a
variety of speech networks. Applications include not only speakerphones,
but intercoms and other voice switched devices.
Archived content is no longer updated and is made available for historical reference only.