Power Circuit Board Chips U209B Monolithic Integrated Control Circuitboard
Monolithic Integrated Feature Phone Circuit
Description
The µc controlled telephone circuit U4090B 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. An integrated voice switch with loudspeaker amplifier allows loudhearing or handsfree operation. With an anti-feedback function, acoustical feedback during loudhearing can be reduced significantly. The generated supply voltage is suitable for a wide range of peripheral circuits.
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 loudhearing operation
Anti-clipping for loudspeaker amplifier Improved acoustical feedback suppression
Power down
Benefits
Savings of one piezo electric transducer
Complete system integration of analog signal processing on one chip
Very few external components
Applications
DC line interface and supply voltage generation
The DC line interface consists of an electronic inductance and a dual port output stage, which charges the capacitors at VMPS and VB. The value of the equivalent inductance is given by L = RSENSE CIND (RDC R30) / (RDC + R30)In order to improve the supply during worst case operating conditions two PNP current sources - IBOPT and IMPSOPT - hand an extra amount of current to the supply voltages, when the NPNs in parallel are unable to conduct current.
A flowchart for the control of the current sources (figure 5) shows, how a priority for supply VMPS is achieved.
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