CMOS compatible transformer power combiner

Introduction: Power amplifiers are a key building block in any radio transceiver, usually necessitating a multi-chip module solution owing to the requirement of a specialised process with high voltage breakdown and low-loss passive components. Several researches have demonstrated that CMOS technology is a viable option for implementation of the power amplifier. Fully integrated transformer based power combining has been demonstrated by [1], utilising so-called ‘slab’ inductors to realise highly efficient on-chip magnetic coupling structures called the DAT. In this Letter we propose a classic transformer based power combiner, shown in Fig. 1. Each pair of windings are realised with ring based transformer structures that are simple to design and scale with frequency. Since each stage is DC isolated, each amplifier runs on a low supply voltage, allowing low breakdown transistors to be employed. An additional benefit of the ring based structure is simple power control. Since each stage operates independently, we can turn off amplifier stages to back-off power without dramatically altering the efficiency of the power combiner [2].