An Ultra-Low Power OTA-C Bandpass Filter Design for ECG Application

Abstract

An ultra-low power OTA-C bandpass filter is presented in this paper. An 1-150 Hz 4-th order OTC-C bandpass filter is design which is suitable for ECG application. A subthreshold region OTA is designed with current cancellation technology to achieve a very small transconductance. The OTA-C filter is design with TSMC 0.18μm CMOS process. The MIM capacitor is used in this design. The supply of the proposed circuit is 1V. The total power consumption is only 245nW. I. I NTRODUCTION The development of portable heart monitoring system is not only useful in long-term healthcare, but also demanded in an increasing number of researches in the biomedical file (1). Filters is continually a critical block of biopotential acquisition systems for enhancing the signal quality (2). However, for low frequency biomedical applications, realizing filter circuits with large time constant under an acceptable capacitor's value isn't an easy task (3). Switching-capacitor circuit is a popular technique used in implementing filter circuit. Due to the leakage problem of the advanced process, the sample-hold circuits of the switch-based topologies are not suitable for applications requiring large time constant. Compared with the switching-capacitor filters, continuous-time OTA-C filter has their benefits of lower power consumption and freeing the system from switching noise. The cut-off frequency is proportional to the transconductance (g m ) of the OTA; this allows a low-power implementation for low frequency biopotential signals. In OTA-based circuits, OTA will dominate the performance of the filter circuit, while the ratio of the capacitor to the small transconductance determines the time constant of OTA-C integrators. Thus, an OTA in which the transistors are operated in the subthreshold region is needed to save more power and realize a very low transconductance. A 4-order Butterworth bandpass is presented in this paper. The bandwidth of this filter is 1-150Hz. A subthreshold OTA is used to achieve the 1Hz cut-off frequency. The transconductance is below 1nA/V. The performance of the OTA is based on the behavior of MOS devices operating in the subthreshold region. The channel current of subthreshold region is:(3)