300-GHz Band 160-Gb/s InP-HEMT Differential Front End With High LO Leakage Rejection

This article presents a 300-GHz band transmitter (TX) and receiver (RX) wireless front end (FE) with a differential architecture based on our in-house InP-based high electron mobility transistor (InP-HEMT) technology. To resolve the issue of the signal-to-noise-and-distortion ratio (SNDR) deterioration caused by the local oscillator (LO) leakage (LOL) in the integrated FE, we quantitatively investigated the effect of the LOL on SNDR by means of link budget calculation and derived the necessary power/phase imbalances in differential architectures to sufficiently reject the LOL. To achieve a sufficiently high LOL rejection, we propose the use of a 300-GHz band LO power amplifier (PA) with a high common-mode rejection ratio (CMRR). The target value of the LO PA’s CMRR (>15 dB) is also derived by the analysis to clarify the relationship between the power/phase imbalances and the CMRR. The unit amplifier in the LO PA achieves the simulated CMRR of more than 15 dB over the full range of the WR3.4 band (220–330 GHz) thanks to utilizing a common-mode rejection circuit (CMRC) based on passive components. By using the integrated circuit of LO PA and a mixer, we experimentally confirmed that the LOL of the TX is less than −33 dBm with the LO frequency range of 224–330 GHz and LO power of 0 dBm. The fabricated 300-GHz band TX and RX achieve a high conversion gain (CG) of above 5 dB over wide bandwidths of 35 and 56 GHz, respectively. We successfully demonstrated 16QAM 160-Gb/s over-the-air (OTA) data transmission using the fabricated FE with the link distance of 43 m. To the extent of the authors’ knowledge, this is the highest reported data rate achieved with a 300-GHz band FE.