Q-Band pHEMT and mHEMT Subharmonic Gilbert Upconversion Mixers

This letter makes a comparison between Q-band 0.15 mum pseudomorphic high electron mobility transistor (pHEMT) and metamorphic high electron mobility transistor (mHEMT) stacked-LO subharmonic upconversion mixers in terms of gain, isolation and linearity. In general, a 0.15 mum mHEMT device has a higher transconductance and cutoff frequency than a 0.15 mum pHEMT does. Thus, the conversion gain of the mHEMT is higher than that of the pHEMT in the active Gilbert mixer design. The Q-band stacked-LO subharmonic upconversion mixers using the pHEMT and mHEMT technologies have conversion gain of -7.1 dB and -0.2 dB, respectively. The pHEMT upconversion mixer has an OIP₃ of -12 dBm and an OP_{1 dB} of -24 dBm, while the mHEMT one shows a 4 dB improvement on linearity for the difference between the OIP₃ and OP_{1 dB}. Both the chip sizes are the same at 1.3 mm times 0.9 mm.