Central frequency tuning considerations for Gm-C resonators in GaAs technology

The ability of adjustment of the central frequency of a Gm-C resonator in GaAs technology is discussed. First, it is shown that whatever the technology, the desired quality factor can be reached through an appropriate sizing of the transconductance values, by adding an external feedback capacitor in the transconductance amplifiers. Then, it is demonstrated that the adjustment of the central frequency must be made preferentially by a specific transconductance. Finally, because in GaAs technologies varying the transconductance values leads to current offsets which could be detrimental to the performances, the maximal allowed current offsets are determined. To illustrate these considerations, transistor-level simulation of a proposed structure in GaAs P-HEMT 0.2 mum with integrated feedback capacitors is presented and demonstrates a tunable central frequency from 750 to 810 MHz.