GaAs monolithic active filters

High-precision sampled data switched capacitor filters using GaAs up to at least 100 MHz are feasible using fast-settled op-amps and therefore continuous-time GaAs filters should be feasible at much higher frequencies into the GHz band. In the present paper, the authors present preliminary ideas on two different approaches. The first is based on simulation of inductors in LCR networks using capacitatively terminated gyrators, where the gyrators are realised by a back-to-back connection of two very high performance GaAs transconductors with full tuning capability of both gain and phase; simulations confirm satisfactory operation at 1 GHz. In the other approach, the active filter is realised as a cascade of 2nd order sections (and one first order section in the case of odd order filters); for this approach, the authors present a high performance 2nd order section using an inverting amplifier with measured result for a GaAs implementation realising a Q-factor of 50 at 1 GHz