A 20–80 MHz Continuously Tunable Gm-C Low-Pass Filter for Ultra-Low Power WBAN Receiver Front-End

Xiaoying Wang,Lingshan Kong,Kaituo Yang,Chirn Chye Boon

doi:10.1109/access.2021.3128154

Xiaoying Wang, Lingshan Kong + Show 2 more

Open Access

https://doi.org/10.1109/access.2021.3128154

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Journal: IEEE Access	Publication Date: Jan 1, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: Nanyang Technological University

Abstract

This paper presents a third-order Butterworth low-pass filter (LPF) with continuously tuning capability to be used in the receiver front-end for Wireless Body Area Network (WBAN). To realize the bandwidth tuning for multi-standard operation in WBAN receivers with ultra-low power consumption and minimized area, a novel transconductor-capacitor (Gm-C) filter is proposed. The proposed transconductor core uses an additional gain stage with regulated cascode structure to control the transconductance ( $G_{m}$ ) by tuning the drain-source voltage $V_{ds}$ of the input transistors operating in linear region. Based on fundamental analysis, $V_{ds}$ should be reduced to attenuate the nonlinear effects caused by higher-order harmonic components. This proposed transconductor circuit enables the $G_{m}$ tuning and widens the tuning range while maintaining good linearity with negligible power and area consumption. This work is then implemented into a third-order Butterworth LPF. Measurements show that with external control voltage varying from 450 mV to 550 mV, the cutoff frequency of the LPF can be continuously adjusted from 20 MHz to 80 MHz. This design is implemented in 40 nm CMOS process with 1.1 V supply voltage. The total power consumption of this work is below 2 mW with an active area of 0.0105 mm 2 . Its low power consumption and good area efficiency makes this LPF suitable for WBAN applications.

Highlights

T HE rapid development in biomedical devices shows the rising public concern towards health topic
Through the tuning of either Gm or the capacitance value, the filter’s cutoff frequency is determined. With such tunable frequency response, we can obtain the prototype of the bandwidth-tunable third-order Butterworth low-pass filter (LPF), where we propose a novel transconductor circuit to meet the wireless body area network (WBAN) network design requirements
Tion, to hold the output common mode level at constant, the common-mode feedback (CMFB) loop is implemented with dual-differential pair (DDP) common-mode detector topology based on current-steering principle, as depicted in Fig. 6 (b)

Summary

INTRODUCTION

T HE rapid development in biomedical devices shows the rising public concern towards health topic. This paper provides a low-pass reconfigurable filtering solution at high frequency while meeting the stringent power and area requirements for short-range WBAN communications. For short-range WBAN devices or corresponding peripherals, power consumption, linearity performance and area efficiency are all important attributes. The third-order Butterworth filter realized by the proposed transconductor occupies small chip area since the Gm tuning scheme with fixed capacitors largely reduces the area as compared to those conventional designs with the capacitor bank. With the common-mode feedback, the complete fully differential third-order low-pass filter is shown with the proposed transconductor cells. The fraction a in this design is set to zero so that the result follows a lowpass frequency response and create a pole in the final transfer function. The subsequent gyrator cell formed by Gm3 and Gm4 together with another capacitor C2 has an equivalent inductance as in (5)

Gm3Gm4

PROPOSED ULTRA-LOW POWER TUNABLE TRANSCONDUCTOR WITH ENHANCED LINEARITY

MEASUREMENT RESULTS AND COMPARISON

CONCLUSION