| dc.description.abstract | Several microwave and millimeter-wave broadband circuits using Darlington cell are presented in this dissertation for high speed data communications. Design and analysis of the broadband hybrid Darlington cell are completely presented with the experimented results. Four broadband Darlington amplifiers using a GaAs heterojunction bipolar transistor (HBT)- high electron mobility transistor (HEMT) process are reported in Chapter 2. The gain-bandwidth analysis of the Darlington amplifiers using HEMT-HBT, HBT-HEMT, HEMT-HEMT, and HBT-HBT configurations are presented. The bandwidth, gain, input and output impedances are investigated with transistor size, feedback resistances, and series peaking inductance. The design methodology of the broadband Darlington amplifier in HBT-HEMT process is successfully developed, and the direct-coupled technique is also adopted for high speed data communications. Furthermore, the proposed monolithic HEMT-HBT and HEMT-HEMT Darlington amplifiers are achieved from dc to millimeter-wave, and successfully evaluated with 40-Gbps eye diagram. The HEMT-HBT Darlington amplifier exhibits the highest gain-bandwidth product of 115.64 GHz with good input and output return losses among the four configurations.
Two broadband and compact inductorless active power dividers and an active balun using Darlington cell are presented in Chapter 3, since the Darlington cell exhibits broadband performance and compact chip size. For the inductorless active power dividers, the 3-dB bandwidth, small-signal gain, and OP1dB versus device size ratio of the Darlington cell have been investigated. The feedback resistance and device size ratio of the Darlington cell are discussed for both better small-signal gain and input matching. An active load technique is adopted for the compact chip size and broad bandwidth. The proposed 1- and 2-stage inductorless active power dividers exhibit high gain-bandwidth product per chip area of 100.4 and 60.2 GHz/mm2 with an amplitude imbalance of 0.1 dB and a phase imbalance of 2o, respectively. The proposed power dividers exhibit potential for the ultra-high speed data rate transmission due to successful evaluation using OC-192 transmission mask with a data rate of up to 10-Gbps. For the low imbalance active balun, a differential Darlington amplifier is adopted for the 3-dB bandwidth enhancement. A feedback capacitor is designed to compensate the phase imbalance between two output ports at high frequency caused by parasitic effect of the transistors. The proposed active balun achieves a broad bandwidth of 21 GHz, an average small signal gain of 2.5 dB, a maximum amplitude imbalance of 1.2 dB, and a phase imbalance of less than 5o. The measured group delays of the two paths are lower than 30 ps with low variation for the balun. The active balun is also appropriate for high speed data communications due to successful evaluation of an eye diagram up to 12.5-Gbps.
A monolithic Ka-band bidirectional distributed amplifier (BDA) with a quadrature phase shift keying (QPSK) modulator/demodulator is presented in Chapter 4. A modified BDA topology is proposed to improve the isolation between the bidirectional ports. With the proposed circuit topology, the bidirectional transmission can be achieved with modulation/demodulation to further reduce the complexity of the transceiver. The gain cell of the BDA is investigated for the bandwidth enhancement, and a cascode Darlington amplifier is adopted. The proposed BDA exhibits a high gain-bandwidth product of 349.2 GHz for the forward and reverse paths among the previously published works. For the QPSK modulator/demodulator, a design procedure is summarized. The integrated bidirectional building block is further evaluated in the vector signal characterization of the digital modulation/demodulation. An output spectrum of the QPSK modulation signal is measured, and the measured error vector magnitude (EVM) is less than 9.9%. For the demodulation, the measured eye diagram is evaluated up to 2-Gbps.
Finally, the conclusions and future works are addressed in Chapter 5. | en_US |