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A fully digital up-converter for wireless transmission in the GHz range is presented. The system consists of a polar modulator which uses PWM for the amplitude modulator (AM). Phase modulation (PM) is implemented by shifting the carrier in time. Both the PWM and the PM are implemented using asynchronous delay lines which allow time resolutions down to 10 ps without the need for high-frequent clock signals. The system is designed to drive two class-E power amplifiers with a power combiner. It supports a continuous range of carrier frequencies starting at 946 MHz and limited upwards only by the desired resolution. The modulator has been implemented in 65-nm CMOS. Results show error vector magnitude (EVM) values between 1.24% (-38.1 dB) at 946 MHz and 3.98% (-28.0 dB) at 2.4 GHz for 64-QAM OFDM signals.

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Conventional RF transmitters with power amplifiers in e.g. Class-AB operation provide only moderate electrical efficiencies for complex modulated signals. To increase the overall efficiency considerably, we can employ switched-mode power amplifiers (SMPA) with an appropriate baseband signal processing. Such efficient SMPAs generate a lot of spectral out-of-band components, which has to be attenuated by a bandpass filter before the signal is fed to the transmit antenna. Unfortunately, this impacts the electrical efficiency because these unwanted signal components are usually dissipated within the transmitter. A measure for the electrical efficiency degradation for complex modulated signals in a switched-mode operation is the coding efficiency. In this paper we develop different switched-mode transmitter architectures based on baseband PWM coding and analyze the coding efficiencies for different signal statistics.

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Abstract-This paper introduces a novel method for bandpass cancellation of the quantization noise occurring in high efficiency, envelope pulsed transmitter architectures -or carrier bursting. An equivalent complex baseband model of the proposed system, including the ΣΔ-modulator and cancellation signal generation, is developed. Analysis of the baseband model is performed, leading to analytical expressions of the power amplifier drain efficiency, assuming the use of an ideal class B power amplifier. These expressions are further used to study the impact of key system parameters, i.e. the compensation signal variance and clipping probability, on the class B power amplifier drain efficiency and signal-to-noise ratio.The paper concludes with simulations followed by practical measurements in order to validate the functionality of the method and to evaluate the performance-trend predictions made by the theoretical framework in terms of efficiency and spectral purity.