Load-Modulation-Based IMD3 Cancellation for Millimeter-Wave Class-B CMOS Power Amplifiers Achieving EVM<1.2%
This paper presents a novel load-modulation-based third-order intermodulation distortion (IMD3) cancellation technique for class-B CMOS power amplifiers (PAs). In a class-B PA, the IMD3 generated by the third-order transconductance (gm3) and the gain compression have opposite signs, and thus, they can cancel each other at specific bias and loading conditions. The proposed Doherty topology allows adjusting the gain compression by modulating the effective loading, facilitating IMD3 cancellation over the entire load modulation region. The proposed approach is verified using a 28GHz 40nm CMOS series-Doherty PA topology. The experimental result demonstrates 10/17dB IMD3 improvement compared to class-B/Doherty PA operation. Without using any DPD, the measured EVM of the proposed technique for a 50MHz 64-QAM OFDM signal with 8.9dBm average output power is -38.7dB (1.2%), which is 5.7/11dB better than a standard class-B or Doherty PA operation.