Comparison on mHEMT Q-band sub-harmonic mixers with/without delay compensation

Q-band sub-harmonic mixers (SHMs) with and without delay compensation are demonstrated in this paper using 0.15-μm metamorphic high electron mobility transistor (mHEMT) technology. A conventional stacked-LO sub-harmonic mixing cell consists of two Gilbert cells in cascode with quadrature LO inputs. The proposed compensation core in parallel with the stacked-LO core improves the port-to-port isolation. A Marchand balun is employed at the RF port to generate wideband differential signals. As a result, SHMs w/ and w/o compensation achieve the conversion gain of 1/0.5 dB and noise figure of 23/20 dB when 2f_LO=39/42 GHz. However, the compensation circuit improves the 2LO-to-RF isolation by 12 dB, 2LO-to-IF isolation by 5 dB and RF-to-IF isolation by 5 dB without additional power consumption.