A multicarrier GMSK modulator with on-chip D/A converter for base stations

A multicarrier Gaussian minimum shift keying (GMSK) modulator with a 14-bit on-chip digital-to-analog (D/A) converter is presented. The design contains four GMSK modulators, which generate GMSK modulated carriers at the user-defined center frequencies. In wireless base stations, the modulated transmit signals are usually combined at the RF frequency after power amplification. The multicarrier modulator combines four GMSK modulated signals in the digital domain, thereby eliminating the need for an antenna microwave combiner. A new digital ramp generator and output power-level controller performs both the burst ramping and the dynamic power control in the digital domain. The maximum dynamic performance is obtained by multiplexing two D/A converters with output sampling switches. The digital multicarrier GMSK modulator is designed to fulfill the derived spectrum and phase-error specifications of the GSM 900/1800/1900 base stations for pico-, micro-, and macrocells. The die area of the chip is 26.8 mm² in 0.35-μm CMOS (in BiCMOS) technology. Power consumption is 706 mW at 3.3 V with 52 MHz.