28-GHz CMOS Up-Conversion Mixer With Improved LO Second-Harmonic Leakage Signal Suppression for 5G Applications

A CMOS up-conversion mixer with an intermediate frequency (IF) amplifier and local oscillator (LO) buffer is presented for mobile 28-GHz-band 5G dual-conversion transceivers. A balun transformer with improved common-mode rejection ratio characteristics is proposed to improve the LO second-harmonic signal suppression, which is a problem in the up-conversion mixer of the 5G dual-conversion architecture. By applying the proposed balun transformer instead of the conventional one, a common-mode rejection ratio greater than 10 dB can be achieved at the frequencies of the LO second-harmonic leakage signal. An up-conversion mixer with an IF amplifier and LO buffer incorporating the proposed balun transformer was implemented in a 65-nm CMOS process, and it draws a current of 31.4 mA from a 1-V supply voltage. It provides a gain larger than 22.2 dB, a noise figure less than 4.1 dB, a third-order output intercept point higher than 4.6 dBm, and an LO second-harmonic leakage signal lower than -55.5 dBm in frequencies ranging from 26.5 GHz to 29.5 GHz. It also exhibits a suppression improvement of the LO second-harmonic leakage signal of approximately 14 dB with respect to an up-conversion mixer with IF amplifier and LO buffer using the conventional balun transformer. The proposed up-mixer with IF amplifier and LO buffer is the first one reported that addresses the 2LO leakage issue and the first demonstration of 2LO leakage signal suppression improvement for a 5G mmWave dual-conversion single-quadrature transmitter.