A 5-V front-end chip for a universal voice-band modem

A circuit that, combined with one or two commercially available digital signal processing (DSP) chips, may implement all voice-band modem standards from 300 b/s to 14.4 kb/s, in full or half duplex operation including echo-cancelling standards, is presented. All analog functions and all non-DSP digital functions are performed by the circuit. Good dynamic range with low distortion in the analog circuitry is maintained while designing for a high-density digital process with high-quality capacitors. Such a process can be used to achieve an area-efficient circuit. The circuit has been implemented in a 1.2- mu m CMOS double-poly, double-metal process, operates off a single 5-V supply, and measures only 63 kmil/sup 2/ (40.7 mm/sup 2/).<
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