The Ripple Cancellation Technique Applied to a Synchronous Buck Converter to Achieve a Very High Bandwidth and Very High Efficiency Envelope Amplifier

This paper presents a single-stage converter for a high-bandwidth and high-efficiency envelope amplifier. In the proposed application, due to the high peak-to-average-power ratio, high bandwidth, and the power level requirements, the envelope amplifier has low efficiency. Therefore, many efforts have been made to increase the efficiency of the envelope amplifier. To achieve this improvement, the current ripple cancellation technique is applied in this paper to a synchronous buck converter to cancel the output current ripple and to decrease the switching frequency without a reduction in the large signal bandwidth, for open-loop operation and for the envelope elimination and restoration technique. The advantages of the proposed design are presented and validated experimentally. The transfer function of the output filter of the buck converter with a ripple cancellation circuit has been modeled and compared to measurements, showing a good correspondence. Experimental validation is provided at 4 MHz of switching frequency, for dc and for variable output voltage, applying a sinusoidal reference and a 64-QAM signal. Experimental validation of the efficiency improvement is provided, compared to the equivalent design of the conventional buck converter in terms of the output voltage ripple rejection ratio and large signal bandwidth.