Differential Switched Mode RF Power Amplifiers

Overview & Synopsis

The digitization of the analog radio frequency (RF) domain, carried out to realize flexible, low-cost software-defined radio transmitters, has reached the power amplifier (PA). Switched mode operation is used to implement a digital input interface and optimize the efficiency of RF amplifiers by minimizing the current-voltage overlap at the transistor. Differential (push-pull) operation is used to enhance the bandwidth of an amplifier by taking advantage of the symmetry to match even harmonics. This work discusses differential switched mode operation to design simultaneously efficient and wideband PAs. Using the example of the current mode class-D (CMCD) amplifier, the required harmonic output impedances in differential and common mode are derived from the ideal waveforms. In order to implement the output impedances with a large bandwidth, this thesis presents optimized designs of wideband output filters and planar baluns. The book concludes with several examples of differential switched mode RF PAs. Furthermore, the integration of antennas as differential loads for differential PAs is examined and an implementation of a so-called "amplitenna" is presented.