LPNF Research Fair Poster
Transcript of LPNF Research Fair Poster
Digitally Tunable Lowpass-Notch Filter Design for Analog Front-Ends in Brain Signal Measurement Applications Undergraduate Student: Kaidi Du (BSEE) Advisor: Prof. Marvin Onabajo
Analog & Mixed-Signal Integrated Circuit (AMSIC) Research Laboratory, Northeastern University, Boston, MA
OverviewA digitally tunable Transconductance-
Capacitor Low-pass Notch Filter (LPNF) for
Electroencephalography (EEG) application is
presented. EEG signals fall into four basic
frequency bands, δ (1-4Hz), θ (4-8Hz), α (8-
13Hz), and β (13-40Hz), but the power line
interference at 60Hz negatively affects the
EEG signal measurement. For this reason, a
combination of a notch filter and a high-order
low-pass filter are employed in this work.
Digitally-assisted tuning methods are
becoming increasingly popular in integrated
circuit (IC) implementations [1]. In this
project, a LPNF was assembled on a
prototype board to perform measurements to
investigate the feasibility of digital tuning.
Tunable Filter DesignIn order to suppress power line interference,
it is necessary to have a lowpass filter with
the following characteristics:
1. A steep roll-off outside of the passband
2. High attenuation at the notch frequency
3. The size of the filter has to be small for
implementation on chips
Schematic of the fifth-order single-ended
low-pass notch filter [2]
Equations for the Null Frequencies
LPNF Diagram
Simulation Results
Transfer Function of LPNF
Measurement Results
Summary of Simulation Results
Screenshot from the Oscilloscope for Point 1
Input Signal Waveform and FFT at Point 1
Output Signal Waveform and FFT at Point 1
Screenshot from the Oscilloscope for Point 2
Input Signal Waveform and FFT at Point 2
Output Signal Waveform and FFT at Point 2
Conclusion A digitally tunable fifth-order Transconductance-Capacitor (Gm-C) Low-pass Notch Filter for EEG applications has been
presented. This design allows to digitally tune the notch frequency to be at 60Hz so that the power line interference signal can be
filtered out. Since the values of the grounded programmable capacitors are distributed in a binary manner, changing the gate
voltage of each NMOS transistor switch (i.e., changing the binary switch code) leads to tuning of the notch frequency.
References[1] S. A. Zahrai, L. Xu, C.-H. Chang, K. Wang, I. Farah, and M. Onabajo, “On-chip digital calibration for automatic input
impedance boosting during biopotential measurements”, in Proc. IEEE Intl. Midwest Symp. on Circuits and Systems (MWSCAS),
Aug. 2015.
[2] X. Qian, Y. P. Xu, and X. Li, “A CMOS continuous-time low-pass notch filter for EEG system,” Analog Integrated Circuits
Signal Processing, vol. 44, no. 3, pp. 231-238, Sep. 2005.
Department of Electrical & Computer Engineering
In Support of College Honors in Electrical Engineering