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SEMICONDUCTOR TECHNICAL DATA
ARCHIVED - 6/2010
Silicon Monolithic Integrated Circuit
The MC34118 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 adjustable gain and MUTE control, Transmit and
Receive attenuators which operate in a complementary manner, level detectors
at both input and output of both attenuators, and background noise monitors for
both the transmit and receive channels. A Dial Tone Detector prevents the dial
tone from being attenuated by the Receive background noise monitor circuit.
Also included are two line driver amplifiers which can be used to form a hybrid
network in conjunction with an external coupling transformer. A high--pass filter
can be used to filter out 60 Hz noise in the receive channel, or for other filtering
functions. A Chip Disable pin permits powering down the entire circuit to
conserve power on long loops where loop current is at a minimum.
The MC34118 may be operated from a power supply, or it can be powered
from the telephone line, requiring typically 5.0 mA. The MC34118 can be
interfaced directly to Tip and Ring (through a coupling transformer) for
stand--alone operation, or it can be used in conjunction with a handset speech
network and/or other features of a featurephone.