Description
The microcontroller-controlled telephone circuit U4090B-P is a linear integrated circuit for use in feature phones, answering machines and fax machines. It contains the speech circuit, tone ringer interface with DC/DC converter, sidetone equivalent and ear protection rectifiers. The circuit is line powered and contains all components necessary for amplification of signals and adaptation to the line.

FEATUREs
• DC Characteristic Adjustable
• Transmit and Receive Gain Adjustable
• Symmetrical Input of Microphone Amplifier
• Anti-clipping in Transmit Direction
• Automatic Line-loss Compensation
• Symmetrical Output of Earpiece Amplifier
• Built-in Ear Protection
• DTMF and MUTE Input
• Adjustable Sidetone Suppression Independent of Sending
   and Receiving Amplification
• Speech Circuit with Two Sidetone Networks
• Built-in Line Detection Circuit
• Integrated Amplifier for Loud-hearing Operation
• Anti-clipping for Loudspeaker Amplifier
• Improved Acoustical Feedback Suppression
• Power Down
• Voice Switch
• Tone Ringer Interface with DC/DC Converter
• Zero Crossing Detection
• Common Speaker for Loud-hearing and Tone Ringer
• Supply Voltages for all Functional Blocks of a Subscriber Set
• Integrated Transistor for Short-circuiting the Line Voltage
• Answering Machine Interface
• Operation Possible from 10 mA Line Currents
• Filters against EMI on Critical I/O

APPLICATIONs
• Feature Phone
• Answering Machine
• Fax Machine
• Speaker Phone