# 0.5-V High-Order Universal Filter for Bio-Signal Processing Applications
## 4 Conclusions  
This paper presents a novel low-voltage, ultra-low-power, multiple-input operational transconductance amplifier based on a bulk-driven MOS transistor with a multiple-input technique. In order to express the advantage of the multiple-input OTA, it was used to realize a high-order multiple-input voltage-mode universal filter. It is worth pointing out that the non-inverting and inverting transfer functions of the variant responses of the low-pass, high-pass, band-pass, band-stop, and all-pass filters can be obtained from the same configuration with appropriate arrangement of the input signals. These filter functions were achieved without additional buffering circuits and any inverted input signals because the filter has multiple plus/minus inputs and high input impedance. The natural frequency can be controlled electronically. The proposed MI-OTA and high-order universal filter were designed and verified using a 0.18 \(\upmu\)m CMOS process. The MI-OTA can operate with a supply voltage of 0.5 V and consumes 937 pW of power at a current setting of 625 pA. The simulation results of the second-order universal filter confirmed its suitability for processing biological signals of extremely low frequencies.  
Conceptualization, F.K., M.K. and T.K.; methodology, F.K., M.K. and T.K.; software, F.K. and M.K.; validation, F.K., M.K. and S.L.; formal analysis, T.K. and M.K.; investigation, F.K., M.K. and T.K.; resources, M.K.; data curation, F.K. and M.K.; writing--original draft preparation, F.K., M.K., T.K. and S.L.; writing--review and editing, F.K., M.K., T.K. and S.L.; visualization, F.K. and M.K.; supervision, F.K. and M.K.; project administration, F.K. and M.K.; funding acquisition, M.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported in part by the University of Defence within the Organization Development Project VAROPS.  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Factor** & **Proposed** & [12] **2024** & [13] **2024** & [32] **2022** & [38] **2023** \\ \hline Type of filter & MISO & MISO & MISO & MISO & MISO \\ \hline Operation mode & VM & VM & MM & VM & MM \\ \hline Number of offered responses & 10 & 2 (LPF) & \
\begin{tabular}{c} 5 (VM) \\ 20 (MM) \\ \end{tabular} & 5 &
\begin{tabular}{c} 5 (VM) \\ 20 (MM) \\ \end{tabular} \\ \hline Electronic control of \(\omega_{o}\) & Yes & Yes & Yes & No & Yes \\ \hline No need for inverted input signal & Yes & Yes & No & No \\ \hline Natural frequency (Hz) & 11 & 250 & 462 & \(158.7\times 10^{3}\) & \(14\times 10^{3}\) \\ \hline Voltage supply (V) & 0.5 & 0.4 & 0.5 & \(\pm\)0.9 & \(\pm\)0.5 \\ \hline Power dissipation (nW) & 2.81 & 20.5 & 32 & \(143\times 10^{3}\) & 429 \\ \hline THD (\%) & 2@200 mV\({}_{\text{PP}}\) & - & \textless{}2@40 mV\({}_{\text{PP}}\) & - & 1@200 mV\({}_{\text{PP}}\) \\ \hline Dynamic range (dB) & 54.4 & 41.5 & 43.59 & - & 63.18 \\ \hline \(\text{FOM}=P_{diss}/(f_{o}\times N\times DR)\) & 2.3 \(\times\)\(10^{-12}\) & 3.45 \(\times\)\(10^{-13}\) & 0.229 \(\times\)\(10^{-12}\) & - & 0.01 \(\times\)\(10^{-12}\) \\ \hline Verification of result & Sim & Post-sim & Sim & Sim & Post-sim \\ \hline \end{tabular} Note: MM = Mixed-Mode, VM = Voltage-Mode.  
\end{table}
Table 5: _Cont._