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A delta-sigma (ΔΣ) digitised polar RF transmitter with a CMOS switching power amplifier is presented. The proposed power amplifier consists of a class-E amplifier with a modulating current source which allows high efficiency and high linearity. A current source is introduced in the proposed power amplifier to achieve ΔΣ digitised amplitude modulation. The current mode amplitude modulation is suitable for a high speed modulated signal such as an oversampled ΔΣ signal.