# Design of Shadow Filter Using Low-Voltage Multiple-Input Operational Transconductance Amplifiers
## 4 Conclusions  
This paper introduces novel shadow filters based on multiple-input operational transconductance amplifiers (MI-OTAs) and presents two configurations of these shadow filters. In contrast to previous shadow filters, the proposed structure enables independent control of the natural frequency and the quality factor via external amplifiers, without affecting the passband magnitude responses of the filters. The first shadow filter allows the quality factor to be varied without affecting the passband gains, while the second shadow filter enables the natural frequency to be varied without altering the passband gains. In both cases, the passband gains are nearly unity. The proposed shadow filters are implemented using MI-OTAs. The use of multiple inputs in the OTA facilitates the realization of various filter responses both non-inverting and inverting transfer functions and external amplifiers with ease. These multiple inputs are achieved through the multiple-input bulk-driven MOS transistor technique. The simulation results confirm the functionality of the filter, demonstrating its operation under low voltage supply and low power consumption.  
Conceptualization, M.K., F.K. and T.K.; methodology, M.K., F.K. and T.K.; software, M.K. and F.K.; validation, M.K., F.K. and N.W.; formal analysis, M.K. and T.K.; investigation, M.K., F.K. and T.K.; resources, M.K.; data curation, M.K. and F.K.; writing--original draft preparation, M.K., F.K., T.K. and N.W.; writing--review and editing, M.K., F.K., T.K. and N.W.; visualization, M.K. and F.K.; supervision, M.K. and F.K.; project administration, M.K. and F.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.  
Data Availability Statement: Data are contained within the article.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Factor** & **Proposed** & **[8] 2017** & **[18] 2020** & **[25] 2023** & **[27] 2019** & **[29] 2022** \\ \hline Number of offered & & & & & & \\ responses & 3 & 3 & 2 (LPF, HPF) & 4 & 5 & 4 (VM) \\ \hline Tuning \(\omega_{o}\) or \(Q\) & & & & & & \\ without affecting the & Yes & No & No & No & No & No \\ passband magnitude & & & & & & \\ \hline All grounded & & & & & & \\ capacitors & Yes & Yes & Yes & Yes & Yes & Yes \\ \hline Electronic control & Yes & No & Yes & Yes & Yes & Yes \\ \hline Natural frequency & & & & & & \\ (Hz) & 106 & 864 & \(1.43\times 10^{6}\) & \(1.036\times 10^{3}\) & \(1\times 10^{6}\) & \(46.22\times 10^{6}\) \\ \hline Supply voltage (V) & 0.45 & \(\pm 0.5\) & \(\pm 1.5\) & \(\pm 0.5\) & \(\pm 0.9\) & \(\pm 1.2\) \\ \hline Simulated power & & & & & & \\ dissipation (nW) & & & & & & \\ \hline Total harmonic & & & & & & \\ distortion (\%) & 16200 mV\({}_{\rm PP}\) & - & - & 1.146250 mV\({}_{\rm PP}\) & 16200 mV\({}_{\rm PP}\) & \textless{}5@600 mV \\ \hline Dynamic range (dB) & & & & & & \\ \hline Verification of result & Sim & Sim/Exp & Sim & Sim & Sim/Exp & Sim \\ \hline \hline \end{tabular} Note: VDGA = voltage differencing gain amplifier, DDTA = differential difference transconductance amplifier, FD-CCCTA = fully differential current conveyor cascaded transconductance amplifier, MM—mixed-mode.  
\end{table}
Table 2: _Cont._