An implementation of a complete modulator/demodulator (modem) for use in portable and mobile cellular telephones implementing code-division multiple-access (CDMA) digital technology is described. Key features are high circuit density and complexity, a short design cycle, flexibility, testability, and low power consumption. A universal microprocessor interface allows for efficient control, data transfer, and testability of the ASIC. The chip is fabricated in double-metal 0.8 mu m CMOS technology and implements a mixture of custom and synthesized design approaches. The power consumption is less than 350 mW at 5 V.< >