A Polar Modulator Using Self-Oscillating Amplifiers and an Injection-Locked Upconversion Mixer

• Published in: IEEE journal of solid-state circuits 2008-02, Vol.43 (2), p.460-467
• Main Authors: Laflere, W., Steyaert, M.S.J., Craninckx, J.
• Format: Article
• Language: English
• Subjects: 018 mu{\hbox {m}} CMOS; Amplifiers; Amplitude modulation; Amplitudes; Applied sciences; asynchronous pulsewidth modulation; Circuit properties; Circuits; Design. Technologies. Operation analysis. Testing; digital transmitter; Efficiency; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; injection locking; Injection-locked oscillators; Integrated circuits; Mixers; Modulation; Modulators; Oscillators, resonators, synthetizers; Phase modulation; polar modulation; Power amplifiers; Power generation; Pulse amplifiers; Pulse modulation; Radiofrequency amplifiers; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Signal convertors; Signal generators; SOPA; Space vector pulse width modulation; Switching
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2007.914296

A polar modulator for use with non-constant envelope signals is presented. Techniques for efficient behavior of both the amplitude (AM) and phase (PM) path are introduced. The amplitude modulation technique is based on asynchronous pulse-width modulation of a phase-modulated RF signal. The digital signal generated in this way is suited for amplification using a nonlinear, efficient type of PA, while preserving the AM modulation, since this information is present in the signal. The efficiency of the switching amplifier is less dependent of the output power, compared to class B operation. Using a self-oscillating, asynchronous type of pulse-width modulator, the spurs are concentrated in narrow bands well separated from the signal band. These switching spurs are filtered out by the filters already present in the transmitter. The feasibility of this RF-pulse-width-modulation is proven by measurements with amplitude modulated signals on a prototype in 0.18 mum CMOS. Unmodulated, the circuit is able to deliver a peak output power of 8.26 dBm with a drain efficiency of 35%. In the phase-modulation path of the polar modulator, injection locking of an oscillator is used as a single-stage high-gain amplifier. Avoiding multiple stages and related power loss improves the overall power efficiency.