Description
The U3810BM multi-standard feature phone circuit is designed to be used with a microcontroller using a 2-wire serial bus. It performs all speech and line interface functions required in an electronic telephone set: the ringing function with switching regulator and melody generator, the DTMF dialling, the loudhearing with antilarsen and antidistortion systems, a power supply, a clock and a reset for the microcontroller. Transmit, receive and loudhearing gains control / AGC range / DTMF frequencies, pre-emphasis and level / melody generator, and mutes are programmable through the serial bus.

Features
● Slope of DC characteristics adjustable by an external resistor
● Gain of transmit and receive amplifiers automatically adjusted by line length control
● Regulation range adjustable by the serial bus
● Possibility of fixed gain (PABX)
● Sidetone balancing system adjustable with line length or by the serial bus
● Dynamic impedance adjustable by external components
● Stabilized power supply for peripherals
● Confidence level during dialling
● +6 dB possibility on second stage transmit gain
● Transmit and receive gains adjustable by serial bus
● Extra transmit input for handsfree and answering machine purpose
● +6 dB possibility on receive gain
● Receive amplifier for dynamic or piezo-electric earpieces
● Extra receive output for handsfree purpose
● High impedance microphone inputs suitable for dynamic, magnetic, piezo-electric or electret microphone
● Distortion of line signal and sidetone prevented by dynamic range limitation in transmission (anti-clipping)
● Squelch system in transmission prevents “room noise” are being transmitted, and improves anti-larsen efficiency (can be inhibited).
● Loudhearing gain programmable in eight steps of 4 dB, using the serial bus, or linearly adjusted, using a potentiometer
● Anti-larsen system efficiency is increased when inhibiting squelch
● Loudhearing anti-distortion system by automatic gain control versus available current and voltage
● Switching regulator in ringing phase
● Input ringing detection, threshold and impedance adjustable with external resistors
● Ringing zero crossing information for external microprocessor
● Ringing programmable gain in eight steps of 4 dB using the serial bus
● Melody generator, with 30 frequencies in steps of semi tones, driven by serial bus
● Internal speed-up circuit permits a faster charge of VDD and VCC capacitor
● DTMF dialer driven by serial bus, in particular level and pre-emphasis adjustment
● Ability to transmit a confidence tone in speech mode using melody generator frequencies
● Five independent mutes driven by serial bus (two in transmission, two in reception, one for the transmit / receive loop)
● Standard low-cost ceramic 455 kHz / clock output for the microcontroller
● Extra loudhearing input for answering machines, handsfree and base station of phones cordless with loudhearing

Benefits
● Complete system integration of analog signal processing and digital control circuitry
● One IC for various PTT standards, e.g. programmable specification via μC
● Only three low-cost transducers needed (instead of four)

Applications
● Feature phones
● Answering machines
● Fax machines