A SiGe HBT 215-240 GHz DCA IQ TX/RX Chipset With Built-In Test of USB/LSB RF Asymmetry for 100+Gb/s Data Rates

A highly integrated fundamentally operated direct-conversion quadrature (IQ) TX/RX chipset with a tunable carrier of 215-240 GHz for high-speed wireless communication is presented. The TX/RX front-ends are fabricated in the 0.13-mu m SiGe HBT technology and combined with wire-bonded chip-on-board (COB) packaging for high-speed baseband (BB) signaling. For test purposes, the chipset features a dedicated dual-polarization architecture with a suitable on-chip antenna to allow controlled variation in I-to-Q channel leakage resulting from frequency-dependent upper sideband (USB)/lower sideband (LSB) asymmetry in the RF path of the jointly operated TX and RX and the corresponding analysis of its impact on system error vector magnitude (EVM) of the complete link. The analysis is aided by system-level BB-referred problem formulation with similarity to the classical IQ error in the local oscillator (LO) and BB paths. While operated in a loop-back configuration, the front-ends support the LO-dependent BB-referred channel bandwidth (BW) of 16-20 GHz at the board level with the typical free-space-related double sideband (DSB) Psat/OP1 of 7/3.5 dBm and single sideband (SSB) conversion gain (CG)/noise figure (NF) of 7.5/17.5 dB for the TX and RX, respectively. Under regular working conditions, data rates above 80 Gb/s are demonstrated for 16-quadrature amplitude modulation (QAM) modulation in a 0.6-m line-of-sight wireless characterization setup, with the maximum of 100 Gb/s at 225 GHz. The achievable speeds are limited by frequency-dependent USB/LSB asymmetry in the RF path resulting in systematic error vector floor independently of the underlying SNR and IQ error. With elimination of the asymmetry-incurred I-to-Q leakage from the RF path, the potential of increasing the data rates to at least 120-140 Gb/s is shown, indicating the severeness of this RF impairment for wide modulation bandwidth.