Quadrature integral noise shaping for generation of modulated RF signals

Abstract

This paper introduces a method to produce a modulated RF signal using a digital pulse signal switching at the carrier frequency. The entire modulation and amplification lineup is implemented in the digital domain. Integral Noise Shaping (INS) is used to create the baseband signals (I, Q) as digital PWM signals which are then mixed with a pair of digital carrier signals. All the edges of the digital pulse modulated signal line up with an edge of a fixed frequency clock signal at twice the carrier frequency. The resulting digital signal has high linearity and low quantization noise. All switching spurs and the quantization noise can be cleaned up with a bandpass filter with reasonable Q factor. Simulation results are presented for an offset tone test signal.