Integrated measurement techniques for RF-power amplifiers

The introduction of the internet of things (IoT) resulted in a significant increase in the demand for low-cost battery powered wireless transceivers. To decrease the cost of wireless transceivers, a full implementation on a single die or package, in a modern CMOS technology is preferred. However, with newer CMOS technologies both the maximum supply voltage and the breakdown voltage decrease, reducing the maximum achievable output power that the RF-PA can achieve from the nominal power-supply for a fixed load impedance.

Switched mode class-E PAs are promising candidates for battery powered wireless devices, since they can ideally achieve 100% power efficiency and can be integrated in modern CMOS technologies. The performance and reliability of class-E PAs strongly depends on the load impedance, where load variations can reduce the performance and even permanently damage the RF-PA. To enable tuning and improving the performance and reliability of RF-PAs accurate information about its current operating conditions are required, which can be acquired from the internal nodes of the RF-PA.

The focus of this work is on integrated measurement techniques, reliability improvements and linearisation for RF-PAs to enable efficient, robust and high-performance RF-PAs for use in modern wireless transceivers. A sampling technique to measure relevant internal RF-waveforms is presented. The acquired waveform information is later used to improve reliability and performance of a class-E PA.

To improve the reliability of class-E PAs, a technique to self-protect the class-E PA by decreasing the PAs sensitivity to load variations is introduced. An on-chip switched-capacitor bank is used to tune the relative-resonance frequency of the switch-LC tank, minimizing the stress on the switch transistor over load variations, improving the reliability.

A polar class-E PA with adaptive digital pre-distortion (ADPD) is presented, resulting in a reduction of the effect of load variations on the polar modulated class-E PA. The on-chip waveform characterizer is used to measure the internal drain voltage of the PA, after which the measured waveform is used to adaptively tune the DPD coefficients such that the RF-PA can maintain its performance over an VSWR up to 9:1.