A High-Performance Continuously Tunable MEMS Bandpass Filter at 1 GHz

摘要

This paper reports a continuously tunable lumped bandpass filter implemented in a third-order coupled resonator configuration. The filter is fabricated on a Borosilicate glass substrate using a surface micromachining technology that offers high-$Q$ tunable passive components. Continuous electrostatic tuning is achieved using three tunable capacitor banks, each consisting of one continuously tunable capacitor and three switched capacitors with pull-in voltage of less than 40 V. The center frequency of the filter is tuned from 1 GHz down to 600 MHz while maintaining a 3-dB bandwidth of 13%–14% and insertion loss of less than 4 dB. The maximum group delay is less than 10 ns across the entire tuning range. The temperature stability of the center frequency from ${-}{hbox{50}}^{circ}$ C to 50$^{circ}$ C is better than 2%. The measured tuning speed of the filter is better than 80 $mu{hbox{s}}$ , and the ${rm IIP}_{3}$ is better than 20 dBm, which are in good agreement with simulations. The filter occupies a small size of less than 1.5 cm$,times,$1.1 cm. The implemented filter shows the highest performance amongst the fully integrated microelectromechanical systems filters operating at sub-gigahertz range.