GENERAL DESCRIPTION
The TEA1098 is an analog bipolar circuit dedicated to telephony applications. It includes a line interface, handset (HS) microphone and earpiece amplifiers, handsfree (HF) microphone and loudspeaker amplifiers and a duplex controller with signal and noise monitors on both channels.

FEATURES
Line interface
• Low DC line voltage
• Voltage regulator with adjustable DC voltage
• Symmetrical high impedance inputs (70 kΩ) for dynamic, magnetic or electret microphones
• DTMF input with confidence tone on earphone and/or loudspeaker
• Receive amplifier for dynamic, magnetic or piezo-electric earpieces (with externally adjustable gain)
• Automatic Gain Control (AGC) for true line loss compensation.

Supplies
• Provides a strong 3.35 V regulated supply for microcontrollers or diallers
• Provides filtered power supply, optimized according to line current
• Filtered 2.0 V power supply output for electret microphone
• PD logic input for power-down.

Handsfree
• Asymmetrical high input impedance for electret microphone
• Loudspeaker amplifier with single-ended rail-to-rail output and externally adjustable gain
• Dynamic limiter on loudspeaker amplifier to prevent distortion
• Logarithmic volume control on loudspeaker amplifier via linear potentiometer
• Duplex controller consisting of:
    – Signal and noise envelope monitors for both channels (with adjustable sensitivities and timing)
    – Decision logic (with adjustable switch-over and Idle mode timing)
    – Voice switch control (with adjustable switching range and constant sum of gain during switching).

APPLICATIONS
• Line powered telephone sets.