Millimeter-wave CMOS Power Amplifiers for 5G Applications
The race to deploy fifth generation (5G) wireless services by 2020 is ongoing, and mm-Wave technology will play a key role in meeting the demand for broadband data traffic. Recent advances make the 28 GHz band particularly interesting for 5G mobile standardization. To counter heavy propagation losses, directive antenna arrays need to be integrated into base station and user equipment (UE) form factors in commercial grade technologies. Besides wave propagation, battery power efficiency for low-cost UE devices is another critical 5G challenge, limited by integrated power amplifiers (PAs). Maximizing data rate implies =100 MHz RF bandwidth, and spectrally efficient signaling. The large peak-to-average power ratios (PAPRs) of these signals force the PA to operate in 8–10 dB power back-off and drastically lower its efficiency. Also, low cost and a high level of integration for UE phased arrays make CMOS the technology of choice. Limitations from substrate conductivity and silicon breakdown field degrade power efficiency in CMOS relative to, e.g., GaAs. Furthermore, in a high-volume production setting, cost and complexity preclude the use of calibration, e.g., using digital pre-distortion, due to differing nonlinear behavior among PAs in an integrated array. Thus, 5G UE radios require efficient CMOS mm-Wave PAs having inherent circuit-level linearity.
This talk begins with a link budget analysis of phased array transmitter power consumption versus carrier frequency. From a 5G standardization viewpoint, this helps to make a more informed choice of carrier band while incorporating the impact of UE power consumption. Subsequently, PA circuit requirements based on this detailed analysis are derived. From this point, detailed circuit implementation of a narrowband and a broadband linear and efficient CMOS PAs will be presented and the experimental results are discussed in terms of the derived 5G requirements.