The IL34118 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.

Futures
• Improved Attenuator Gain Range: 52 dB Between Transmit and Receive
• Low Voltage Operation for Line-Powered Applications (3.0-6.5 V)
• 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
• On Board Filter Pinned-Out for User Defined Function
• Dial Tone Detector to Inhibit Receive Idle Mode During Dial Tone Presence