FETを用いたミリ波帯MMICスイッチの広帯域化・小型化に関する研究

摘要

The aim of this study is to reduce the monolithic microwave integrated circuit (MMIC) chip size and to obtain the broadband characteristics for the millimeter-wave MMIC switches.To find out the techniques for the size reduction and to obtain the broadband characteristics, the novel two-port small signal and large signal equivalent circuits for the switch circuits are proposed.The newly developed ohmic electrodes sharing technology (OEST) has successfully minimized the size of the series-shunt configuration MMIC switches with the broadband characteristics. By applying the OEST, an ohmic electrode can be shared by two drains or sources of field effect transistors (FETs), which are connected with the same voltage potential. Four FETs, which composed the seriesshunt SPDT MMIC switch, are integrated into a lumped small area of approximately 0.018 mm2. From dc to 60 GHz, a single pole single throw (SPST) MMIC switch achieves the insertion loss and the isolation of better than 1.64 and 20.6 dB, respectively. Because the OEST neglects the parasitic capacitance, the broadband characteristics up to 60 GHz can be obtained with the smaller MMIC size. The developed MMIC switches have a high power handling capability with low insertion loss and high isolation at 40 GHz. The insertion loss is increased by 1 dB at the input power of 21 dBm.The novel switch circuit named as the traveling wave switch (TWSW) using the fully distributed FET (FD-FET) is proposed. It is a long one-finger FET with more than 1/16 of the propagation wavelength finger with in/out ports at each end of its drain electrode. From the theoretical investigation, the TWSW using FD-FET has the feature of having the extremely broadband characteristics and having no cutoff frequency because it is the same equivalent circuit as the complete transmissionline. Then, the frequency response of the group delay shows the constant value. Circuit analytical results based on a lossy transmission-line model for small-signal performance and circuit simulation results using the two-terminal nonlinear FET model for large-signal operation successfully showed good agreement with the experimental results. The circuit design considerations for the TWSW single-pole multi-throw (SPnT) MMIC utilizing a FD-FET are also presented. The normalized length of the impedance transformer for a SPnT TWSW using the FD-FET is found to be less than a quarter-wavelength at the operating frequency.The developed SPST TWSW MMIC using FD-FET indicates the broadband characteristics over measured frequency from dc to 110 GHz. With a 400-μm-gate finger FET, the switch indicates an insertion loss of less than 2.55 dB and an isolation of better than 22.2 dB from dc to 110 GHz. It has no degradation of an insertion loss up to an input power of 26.5 dBm at 40 GHz. The newly developed SPDT TWSW MMIC using the 400-μm-gate finger FD-FET delivers broadband characteristics over more than an octave frequency range with highly reliable MMIC technology. It shows low insertion loss of less than 2.1 dB and high isolation of over 25.5 dB from 38 to 80 GHz, coupled with the benefit of very small size.In the future, the millimeter-wave system would be minimized and show the broadband characteristics easily by the contribution of this study.