A K(a)-band gallium arsenide HBT direct-conversion QPSK demodulator

In this thesis a novel broadband direct conversion QPSK demodulator operating at the K_a-band will be investigated. The demodulator is based on two wide-band double-balanced direct downconversion mixers connected in phase quadrature. The mixer integrates several passive and active components. First, a novel wideband monolithic passive balun used to provide the differential RF and LO signals required at the mixer inputs has been developed. The balun is implemented using coplanar and microstrip lines and demonstrates a wide bandwidth from 15 to 45 GHz. Then, a modified double-balanced Gilbert cell multiplier is used to obtain the mixing action required while achieving conversion gain and intrinsic port-to-port isolation together with an excellent intermodulation distortion suppression. The down converted signal will be further amplified through a direct-coupled baseband differential amplifier integrated at the mixer output. The mixer is implemented using NORTEL GaAs HBT process.; Finally, the K_a-band direct conversion QPSK demodulator will be presented. (Abstract shortened by UMI.)...