A 270 kbit/s 35 mW modulator IC for GSM cellular radio hand-held terminals

The modulator IC has been designed to integrate all analog baseband processing components of the European Groupe Special Mobile (GSM) digital cellular radio terminals onto a single component. The IC is located at the interface of the analog 900-MHz radio-frequency part and the baseband digital signal processing part of the mobile terminal. The modulator part time-multiplexes the receive and transmit operations and combines low-noise receive circuitry with a digital modulator. The device uses digital waveform generation and a balanced quadrature representation for both modulation and demodulation of the Gaussian minimum-shift-keying (GMSK) signal. To enhance testability of the high-density printed-circuit boards, advanced test features have also been implemented in the modulator IC. In the transmit direction, the modulator IC converts digitally encoded speech or data at an instantaneous rate of 270 kb/s to the I (in-phase) and Q (quadrature) analog signals which are used to modulate a 900-MHz carrier.<>