Reverse Intermodulation Distortion in Current Mode and Bridge Class D RF Power Amplifiers

Abstract

This article is a continuation of the topic consideration of reverse intermodulation distortions (RIMD) analysis begun by the authors in [1] for class D RF power amplifiers (PA) with a resistive load in the voltage switching mode (Voltage Mode Class D - VMCD). In this article, a theoretical analysis of RIMD in class D RF PA with a resistive load in current switching (CMCD) and bridge (BMCD) modes was carried out. A comparison of the various circuits parameters requirements in order to achieve a given RIMD level not exceeding minus 70 dB showed that: - the VMCD circuit imposes the most stringent requirements for all influencing parameters: the switches saturation resistance variation should not exceed 20%, and the total switches saturation time deviation in any combination should not exceed 0.01, which is 2% from half a period; - the CMCD circuit allows a similar switches saturation time deviation, but the distortion in it does not depend on the difference in switches saturation resistance; - the BMCD circuit allows a 70% difference in the switches saturation resistance. The permissible total switches saturation time deviation depends on the operation mode and is 2.4% for overlapping and 18% for undercovering. The choice of the class D RF PA configuration used in a particular application is based on a large number of factors - efficiency, power level, the ability to work with collector (drain) modulation in a wide frequency range, resistance to load mismatch, element base, etc. The conducted research allows developers to take into account one more parameter - resistance to induced electromagnetic radiation.