A 3-V GSM baseband transmitter

A dual-channel baseband transmitter has been designed for global system for mobile communications (GSM) cellular phone application. It has been fabric ated in a 0.35-mu m digital CMOS process as part of a single-chip solution for baseband processing. Each channel consists of a switched-capacitor digi tal-to-analog converter, a switched-capacitor filter, a class-AB buffer, an d an active-RC filter. The lack of on-chip precision capacitors and resisto rs poses a major challenge in designing these analog building blocks. Anoth er key implementation issue is to maintain the performance of these analog circuits in the presence of substantial substrate noise from the digital si gnal-processing core. The current consumption is 8.8 mA, and the total acti ve area is 5.1 mm(2). The channel response meets the Gaussian minimum-shift -keying spectral mask.