Poojan A. Wagh

Quadrature integral noise shaping for generation of modulated RF signals

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.

An all-digital universal RF transmitter [CMOS RF modulator and PA]

This paper presents a CMOS class-D PA with on-chip all-digital RF modulator. The IC is fabricated in a 0.18 /spl mu/m digital CMOS process with MIM capacitors. The die size is a square 2.5 mm on each side. The active area used for the modulator (excluding the pads and bypass capacitance) is 0.315 mm/sup 2/. The class D PA shows 75 dB IM, -50 dB feedthrough, and puts out 19.6 dBm at >69% drain efficiency from a 1.8 V supply. The modulator operates in the IQ domain, without the use of bias control nor envelope modulation.

Distortionless RF pulse width modulation

A method is presented to synthesize a switching signal which linearly encodes a complex-modulated RF signal to an RF carrier frequency. The switching distortion associated with this method is limited to high-pass components out of band. Consequently, the switching signal may be filtered after high efficiency amplification to produce the linear RF modulation. The method requires a switching frequency slightly higher than the highest frequency in the band of interest.