A Study on Flying Capacitor Linear Amplifier Configured by Only N-channel MOSFETs

Abstract

This paper presents a flying capacitor linear amplifier (FCLA) without p-channel MOSFETs. The FCLA is an advanced topology for the conventional class-B linear amplifier to enhance the conversion efficiency. It maintains multiple voltages by flying capacitors in the circuit and reduces the linear operation losses generated in the MOSFETs as the number of the series connected MOSFETs increases. As the result, the FCLA with a high number of series devices can achieve a noiseless and no-harmonic output voltage maintaining high efficiency. The conventional FCLA typically utilizes complementary operation between n-channel and p-channel MOSFETs. However, p-channel MOSFETs have worse characteristics than those of n-channel MOSFETs in general. It causes a limitation of the efficiency improvement of the whole circuit. In particular, when the number of series devices increases, the total series on-state resistance of the current path increases more by that of the p-channel MOSFETs. Therefore, it is desirable to use only n-channel MOSFETs for all the power devices. In this study, a circuit configuration of the FCLA using individual linear gate circuits for each MOSFET. It does not only achieve capacitor voltage balance, but also makes it possible to use only n-channel MOSFETs. It is verified that the proposed circuit configuration with only using n-channel MOSFETs realizes higher efficiency than that of the conventional FCLA.