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 mm
²
. 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.