A Fully Integrated Controllable Bandpass Filter with a Constant Q-Factor for Ultrasonic Applications

In this paper, a tuneable low-power active bandpass filter (BPF) is designed for channel selection in TSMC’s 65-nm CMOS technology. The proposed filter consists of two identical BPFs which are based on a gm-C topology, and can be controlled with a constant quality factor. The center frequency of this design can be changed to acquire a specific passband channel from 60 kHz to 2.5 MHz by adjusting the bias voltage in discrete increments, with an almost constant quality factor equal to 7.2. To validate the design, the integrated circuit and a test board are fabricated. Five passband channels are measured from the proposed design with a low power consumption equal to 68 ‘W. The measured dynamic range is equal to 51.6 dB when the total harmonic distortion (THD) is equal to 1%. Hence, the proposed controllable channel selection filter shows an excellent performance as compared to existing work and offers a great potential for use applications with heterogeneous sensor nodes.