VOICE SWITCHED SPEAKER-PHONE CIRCUIT

DESCRIPTION

As a voice switched speaker-phone integrated circuit, the UTC

MC34118A includes the necessary amplifiers, attenuators, level

detectors and control algorithm.

To form the UTC MC34118A’s internal circuit, there is an internal

microphone amplifier with adjustable gain and mute control, internal

transmit and Receive attenuators (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.

The dial tone can be pretended from being attenuated by the

receive background noise monitor circuit by a dial tone detector.

There are also 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 for other filtering functions, and especially

to filter out 60Hz noise in the receive channel.

The UTC MC34118A which requiring typically 5mA may be

operated from a power supply, or it can be powered from the

telephone line.

FEATURES

* Attenuator gain range: 52dB (between Transmit and Receive)

* For line-powered applications : 3~6.0V low voltage operation

* For improved sensitivity :4-point signal sensing

* For Transmit and Receive paths: background noise monitors

* External resistors set microphone amplifier gain

* Mute function included

* Chip disable: active or standby operation

* During dial tone presence: dial tone detector to inhibit receive idle mode