FULLY DIGITAL TRANSMITTER INCLUDING A DIGITAL BAND-PASS SIGMA-DELTA MODULATOR

摘要

A digital transmitter (20) that may be advantageously used in a high-frequency transceiver, such as a wireless telephone handset, is disclosed. The transmitter (20) includes digital upconverter functions (361, 36Q) that operate in combination with a digital band-pass sigma-delta modulator (40) to generate modulated digital signals at a sample frequency that is a multiple of the transmit frequency. The digital band-pass sigma-delta modulator (40) applies a noise transfer function in a feedback filter in which the center of the pass band corresponds to the transmit frequency, and in which notches in the characteristic can be symmetrically or asymmetrically selected to correspond to specific frequencies, such as the receive band frequency, in which transmit noise is to be minimized. A combined FIR digital filter (42) and MOS power switch array (44) is also disclosed, in which a cascode arrangement of drain-extended MOS power transistors and switching transistors provide the output RF signal, with a coarse gain control applied.