A 100 MHz IF amplifier quadrature demodulator for GSM cellular radio mobile terminals

A circuit including a 100-MHz IF amplifier with a digitally controlled gain of 0-to-45 dB, a quadrature phase-shifter, balanced mixers, and active/sleep mode capability is described. The measured gain and quadrature phase variation was less than 1 dB and 1°, respectively. The 92-mW circuit was fabricated using a 4.0 GHz complementary bipolar process. A complementary bipolar integrated circuit with a digitally controlled-gain 100-MHz IF (intermediate frequency) and GMSK (Gaussian minimum shift keying) quadrature demodulator is described. The digital selection of IF amplifier gains from 0 to 45 dB in 3-dB steps with a gain error of less than ±1 dB has been achieved. In addition, a phase error variation of less than ±1° in the quadrature demodulator has been demonstrated. The circuit has applications for use in digital cellular telephony with specifications suited for mobile cellular terminals that comply with the GSM (Groupe Special Mobile) digital cellular standard