Linearity Considerations for Low-EVM, Millimeter-Wave Direct-Conversion Modulators

This paper presents the analysis and implementation of a millimeter-wave (mm-wave) I/Q modulator and determines the impact of I- and Q-channel nonlinearity, PA nonlinearity, and other nonideal circuit implementations on the error vector magnitude (EVM). The modulator is fabricated in 120-nm SiGe BiCMOS process and occupies an area of 5 mm² . For a 64-QAM constellation at a 42-GHz carrier frequency, the EVM is less than 2.5% at 48-Mbps data rate. The on-chip digital-to-analog conversion resolution is capable of employing digital pre-distortion (DPD) and calibration. An external power amplifier is linearized to improve the EVM with DPD. To the best of the authors´ knowledge, this is the lowest EVM reported at these mm-wave frequencies.