A 6th-Order Current-Mirror-Based Gm-C Bandpass Filter with the Binary Searching Calibration Scheme for Capacitor Sensing Applications

Abstract

This paper presents the current-mirror-based Gm-C bandpass filter with a digitally binary searching calibration scheme. The current-mirror-based circuit technique can be a highly regular structure, which drives the proposed filter to implement the conceptions of the modularized unit and repeatable layout. Furthermore, it employs a tunable bias current circuit and a successively counting logic to implement the binary searching calibration scheme to reduce the mass test timing budget and to obtain the correct frequency response. Thus, the proposed 6th-order current-mirror-based Gm-C bandpass filter can overcome the PVT variations with this automatically tunable bias scheme. Accordingly, a Gm-C LC oscillator, which forms the same unit cell as the filter, generates the oscillated clock for this digital successively counting calibration scheme. This work is designed and implemented in the 0.18μm CMOS process with a supply voltage of 1.8V. The specifications include the center frequency of 200kHz and bandwidth of 100kHz for capacitor sensing applications. The measured power dissipations of the filter and calibrating scheme are 0.65mW and 0.56mW, respectively. After calibrating, the mean offset and standard deviation ratios to the calibrated clock frequency are only 2.1% and 1.66%, respectively.