Reconfigurable GaAs Bandpass Filters Using Cascading of Lowpass and Highpass Filters

Designs of on-chip reconfigurable band-pass filters are proposed based on GaAs process. The filters are constructed by cascading elliptic low- and high-pass filters, and reconfigurable center frequency and bandwidth are achieved by controlling the cut-off frequencies of the low- and high-pass filters. Varactors and switched capacitor arrays formed by the pHEMT transistors are used as tuning element to achieve the tunability. By introducing series LC tank resonator in the low- and high-pass filters, transmission zeros are formed outside the passband to improve the selectivity of the filer. One on-chip bandpass filter with tunable center frequency and one bandpass filter with controllable bandwidth are designed, fabricated and tested using the 0.15um GaAs pHEMT process. The filters realize a frequency tuning range of 1.9~2.53GHz, and a bandwidth tuning range of 330~750MHz, respectively, with bandstop suppression larger than 30dB.