Q-factor enhanced microwave active resonators and their applications to tunable band pass filters

Abstract

The tunable band pass filters are fabricated in monolithic microwave IC (MMIC) and hybrid microwave IC (HMIC). Quality factor, the most important parameter in filter design, is enhanced by the negative resistance circuit using gate-source resistive feedback scheme. The Q factor of a resonator should be variable according to the frequency. To achieve this purpose, the gate bias resistor is used as the frequency dependent loss compensation circuit. Input admittance of the proposed negative resistance circuit is derived to analytical forms and confirmed by the experimental results. It is dependent on the feedback resistor at gate-source terminal of FETs and bias conditions. The active resonator using this negative resistance circuit shows its Q factor as high as 250 with small DC power consumption. The power characteristics of the active resonator are also investigated, based on the systematic approach of large signal modeling. Even though the 1dB gain compression point of resonators or filters are severely dependent on the Q factor, they show superior performance to the conventional negative resistance circuit using the indcutive feedback at gate or capacitive feedback at source. This study shows the fact that the feedback resistor at gate-source of FETs compresses the nonlinear effects caused by the nonlinear operation of FETs. The loss compensation technique of spiral inductors in MMIC is to insert equal negative resistance to the loss of inductors. However, the proposed active resonator which has negative resistance in itself, is easy to compensate by introducing the normal resistor because the negative resistance of the active resonator is larger than the inductor loss. This can be done by the gate bias resistor. It can cancel out the negative resistance and inductor loss, simultaneously. The input impedance of the active resonator employing this Q factor enhanced circuit shows negative resistance value. As a result, Q factor of the resonator is larger than...