Digital Compensation of DC-DC Converter Voltage Ripple for Switched-Capacitor Power Amplifiers

This paper presents a novel method to digitally compensate the voltage ripple of a DC-DC switching converter supplying a Switched-Capacitor Power Amplifier (SCPA). Switched DC-DC converters are highly efficient, but their output voltage exhibits a small switching ripple. These unwanted variations on the supply of the SCPA mix with the input code and create unwanted harmonics in the output signal. This effect decreases the linearity of the SCPA, and potentially causes violations of the spectral mask. Currently, additional circuitry is used to block the DC-DC voltage ripple and provide a stable power supply for the SCPA. Such circuits decrease the efficiency of the system and need additional active and passive components on and off-chip. This work proposes a digital compensation of the distortions of the DC-DC voltage ripple in the SCPA to omit additional circuitry in the SCPA supply. Furthermore, a proper solution to eliminate timing mismatches of the modulated input code and the true ripple at the SCPA is presented. The concept has been validated with MATLAB/Simulink and shows a significant suppression of the distortions created by the DC-DC voltage ripple.