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VOICE SWITCHED SPEAKERPHONE CIRCUIT
FEATURES
  - Improved Attenuator Gain Range: 52dB Between Transmit and Receive
- Low Voltage Operation for Line-Powered Application (3.0V to 6.5V)
- 4-Point Signal Sensing for Improved Sensitivity
- Background Noise Monitors for Both Transmit and Receive Paths
- Microphone Amplifier Gain Set by External Resistors - Mute Function Included
- Chip Disable for Active/Standby Operation
- Dial Ton Detector to Inhibit Receive Idle Mode During Dial Tone Presence
- Standard 28-Pin Plastic DIP Package and SOP Package Available
- Compatible with MC34119 Speaker Amplifier
DESCRIPTION
  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 60Hz 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 5.0mA. 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.
MC34118
SOP28
 
DIP28
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