A V-band high linearity two-stage subharmonically pumped mixer

The “gain expansion” of a subharmonically pumped mixer (SHM) is utilized for the first time, to compensate for the “gain compression” of the cascaded amplifier. Consequently, a linear two-stage SHM is obtained. A proof-of-concept circuit is designed and manufactured in a 0.25 μm InP DHBT process, which down-converts a V-band RF signal to an IF signal, driven by a LO signal whose frequency is a half of that for a fundamental mixer (2×SHM). In RF range from 55 GHz to 67 GHz, the SHM has 6 to 9 dB conversion gain when LO power is 5 dBm. Simultaneously, it achieves a high third-order output intercept point (OIP₃) from 10 dBm to 16 dBm. The measured input and output 1-dB compression points (P_1dB and OP_1dB) at RF frequency of 61 GHz are -2 dBm and 3 dBm, respectively. Obtained OP_1dB and OIP₃, to the best of authors' knowledge, is the best among the published 2×SHMs. Furthermore, this SHM is measured as the LO frequency is one-third (3×SHM) and a quarter (4×SHM) of that for a fundamental mixer, which has conversion gains of 3 dB and -1 dB, respectively.