The BL34118 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 functions. A chip Disable pin permits powering down the entire circuit to conserve power on long loops where loop current is at a minimum.

• Improved Attenuator Gain Range: 52 dB Between Transmit and Receive
• Low Voltage Operation for Line-Powered Applications (3.0 – 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
• On Board Filter Pinned-Out for User Defined Function
• Dial Tone Detector to Inhibit Receive Idle Mode During Dial Tone Presence
• Standard 28-Pin Plastic DIP Package and SOIC Package Available
• Compatible with BL34119 Speaker Amplifier