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This paper describes a 32kbit/s adaptive delta modulation (ADM) CODEC which can be applied to digital portable telephones. This ADM CODEC employs a new adaptation algorithm and parameters adjusted for speech signals. The encoding algorithm makes it possible to achieve higher quality with the 32 kbit/s ADM CODEC than with 6 bit µ-law PCM coding. The developed ADM CODEC including a coder, a decoder and switched-capacitor filters on a chip can operate on a single power supply(3.6∼ 5V). The power dissipation is only 30 mW during normal operation and less than 10 mW in the power-down mode. The CMOS chip is an a 16-pin package, 7 × 4.3mm.