Reflectionless Q-enhanced Bandpass Filter with Independently Controllable Bandwidth and Frequency

In this paper, a fourth-order Q-enhanced bandpass filter (BPF) with independently controllable center frequency and bandwidth is proposed. The center frequency can be programmed within the range of 2.40 to 2.88 GHz, and the bandwidth is adjustable from 2.28 to 9.72 MHz, with a passband ripple of less than 0.2 dB. The positive feedback loop is used to enhance the quality factor (Q) in this BPF, which stably increases the Q of the original resonator from 21 to 2500. The measured results agrees well with the theory. This work demonstrates the feasibility of designing on-chip filters with high frequency selectivity to adapt to multi-band communications.