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AS2521B Datasheet(PDF) 4 Page - ams AG |
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AS2521B Datasheet(HTML) 4 Page - ams AG |
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4 / 14 page  Preliminary AS2520/21/20B/21B Rev. 5.1 Page 4 May 1999 Functional Description The AS252x contains all the voice circuits needed in a high feature telephone instrument, i .e.: • line adaptation (ac impedance, dc characteristics, 2/4-wire conversion, power extraction) • handset speech circuit • loudhearing with enhanced anti-Larsen • handsfree with dynamic loop gain control • switching converter The line adaptation includes line driver, ac impedance (return loss), 2 to 4 wire converter, dc mask and power extraction circuit for extracting the maximum dc power from the line to supply the whole device and peripheral circuits. The handset speech circuit consists of a transmit and a receive path with mute, dual soft clipping and line regulation (pin option). A volume control is provided with squelch and loop gain compensation to improve signal-to-noise ratio and to assure acoustic stability. Loudhearing and handsfree functions are also provided. The loudhearing function includes an anti- Larsen circuit to prevent acoustic howling. The handsfree circuit has a novel voice control system which is virtually independent of any background noise and works in a dynamic half duplex mode as close to full duplex as the acoustic loop gain allows. The switching converter is used to extract the available power from the ring signal and provides a 4V supply voltage. This allows the same loudspeaker to be used for loudhearing/handsfree and tone ringing. LINE DRIVER IMPEDANCE SYNTESIZER POWER EXTRACTION DC CONTROL VOICE & POWER CONTROL VDD TX-AGC RX-AGC VDD LE HS TI LO RO AGND RTH M2 M1 CI LI CS LS VDD Vss RI STB AGND MT MT or PD 30 Ω L + ZB AS2520/21/20B/21B MT VPP VPP PD PD LEVEL DETECTOR 300 Ω SS SWITCHING CONVERTER CM VssP LSI VOL LOGIC INTERFACE LLC LEVEL DETECTOR ST-AMP RO-AMP LO-AMP MI-AMP M3 MI-AMP HS M4 A PDM INPUT RING Figure 2: Block Diagramme |
Similar Part No. - AS2521B |
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Similar Description - AS2521B |
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