Digital Quadrature Mixing of Lowpass Sigma-Delta Modulators for Switch-mode Power Amplifiers

In this paper a phase compensation technique for the digital upconversion of a quadrature signal for amplification with switch mode power amplifiers is proposed. When a digital signal generator is used to generate the complex envelope signal care must be taken to compensate for the phase skew between the two paths. If phase compensation is not implemented an image caused by up converting the complex envelope of the modulation signal is created. By compensating for phase skew between the I and Q signal paths it is possible to remove this image signal and enable the transmission of multi carrier signals. As a direct result of this technique there is a reduction in the filtering effort at the output of the power amplifier to meet spectral mask requirements

Digital Quadrature Mixing of Lowpass Sigma-Delta Modulators for Switch-mode Power Amplifiers

In this paper a phase compensation technique for the digital upconversion of a quadrature signal for amplification with switch mode power amplifiers is proposed. When a digital signal generator is used to generate the complex envelope signal care must be taken to compensate for the phase skew between the two paths. If phase compensation is not implemented an image caused by up converting the complex envelope of the modulation signal is created. By compensating for phase skew between the I and Q signal paths it is possible to remove this image signal and enable the transmission of multi carrier signals. As a direct result of this technique there is a reduction in the filtering effort at the output of the power amplifier to meet spectral mask requirements

Digital Quadrature Mixing of Lowpass Sigma-Delta Modulators for Switch-mode Power Amplifiers

In this paper a phase compensation technique for the digital upconversion of a quadrature signal for amplification with switch mode power amplifiers is proposed. When a digital signal generator is used to generate the complex envelope signal care must be taken to compensate for the phase skew between the two paths. If phase compensation is not implemented an image caused by up converting the complex envelope of the modulation signal is created. By compensating for phase skew between the I and Q signal paths it is possible to remove this image signal and enable the transmission of multi carrier signals. As a direct result of this technique there is a reduction in the filtering effort at the output of the power amplifier to meet spectral mask requirements

Linear Operation of Switch-Mode Outphasing Power Amplifiers

Radio transceivers are playing an increasingly important role in modern society. The ”connected” lifestyle has been enabled by modern wireless communications. The demand that has been placed on current wireless and cellular infrastructure requires increased spectral efficiency however this has come at the cost of power efficiency. This work investigates methods of improving wireless transceiver efficiency by enabling more efficient power amplifier architectures, specifically examining the role of switch-mode power amplifiers in macro cell scenarios. Our research focuses on the mechanisms within outphasing power amplifiers which prevent linear amplification. From the analysis it was clear that high power non-linear effects are correctable with currently available techniques however non-linear effects around the zero crossing point are not. As a result signal processing techniques for suppressing and avoiding non-linear operation in low power regions are explored. A novel method of digital pre-distortion is presented, and conventional techniques for linearisation are adapted for the particular needs of the outphasing power amplifier. More unconventional signal processing techniques are presented to aid linearisation of the outphasing power amplifier, both zero crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear regions of the amplifiers. In combination with digital pre-distortion the techniques will improve linearisation efforts on outphasing systems with dynamic range and bandwidth constraints respectively. Our collaboration with NXP provided access to a digital outphasing power amplifier, enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural modelling and linearisation efforts. The collaboration resulted in a bench mark for linear wideband operation of a digital outphasing power amplifier. The complimentary linearisation techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in both simulated and practical outphasing test benches. Initial results are promising and indicate that the benefits they provide are not limited to the outphasing amplifier architecture alone. Overall this thesis presents innovative analysis of the distortion mechanisms of the outphasing power amplifier, highlighting the sensitivity of the system to environmental effects. Practical and novel linearisation techniques are presented, with a focus on enabling wide band operation for modern communications standards