A 325 GHz Quadrature Voltage Controlled

Abstract— We present a 325 GHz quadrature voltage controlledoscillator (QVCO) using 0.25 InP HBT technology and su-perharmoniccouplingoftwodifferentialColpittsVCOs.Theindi-vidual VCOs exhibit about single-ended output powerand 10 GHz frequency tuning range. The quadrature oscillation issuccessfullydemonstratedwithdcpowerconsumptionof92.4mWand phase imbalance less than at around 325 GHz. Index Terms— InP HBT MMIC, quadrature voltage controlledoscillator (QVCO), 300 GHz, THz wireless communication. I. I NTRODUCTION T HE recent emergence of wireless technologies using mil-limeter waves reflects the huge need for high-speed wire-less systems with higher carrier frequencies [1], [2]. In partic-ular,terahertz(THz)wavesabove275GHzhavereceivedmuchattention for the next generation of wireless communicationswith over 10-Gbit/s data capacity [2]. Although the RF circuitblocksforthetransceiverhavebeenchallenginginthe300GHzband, recent semiconductor processes enable high-speed elec-tronic devices operating at up to the 1-THz region with basicfunctionalblocks[3],[4].Forthesignalsource,fundamentalos-cillators operating around the 300 GHz band have been demon-strated with a single transistor configuration using InP HEMTs[5]. Differential voltage controlled oscillators (VCO) with InPHBTs have also been reported [6], [7].The quadrature VCO (QVCO) is another RF circuit blockwidely used in many applications, such as wireless transceiversand radar equipment. Especially in the THz-wave band, thehuge loss of passive structures for quadrature signal generationreveals the advantage of the QVCO. In general, QVCOs in thefew-gigahertz band have been realized with LC VCOs by usingfundamentalinjectionviacouplingtransistors[8].Recently,thepush-pushsuperharmoniccouplingtechniquewithoutactivede-vices or a transformer has enabled the development of a high-frequency QVCO operating at around 100 GHz [9], [10].In thispaper, we presenta QVCO operating around 325GHzusing InP heterojunction bipolar transistor (HBT) technology.The QVCO is composed of two differential VCOs which are