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A 500-mV, 124.11-nW first-order universal shadow filter based on multiple-input DDTAs
(2026-07-01)
Kumngern, Montree
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Khateb, Fabian
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Kulej, Tomasz
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Thanyaratsakul, Nattapong
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Arbet, Daniel
This paper proposes a novel first-order multifunction filter capable of simultaneously realizing non-inverting and inverting low-pass, high-pass, and all-pass filter responses using multiple-input differential difference transconductance amplifiers (MI-DDTAs). The design leverages the shadow filter technique, enabling electronic tuning of the pole frequency across all filter responses through an external voltage-controlled amplifier. This approach offers enhanced flexibility and reconfigurability, making it highly attractive for adaptive analog signal processing. The MI-DDTA core is implemented using a multiple-input bulk-driven MOS transistor architecture, optimized for ultra-low-voltage and ultra-low-power operation. Designed in Cadence Virtuoso using the 65 nm TSMC CMOS (1P9M) process, the proposed MI-DDTA occupies a compact silicon area of 171 μm × 119 μm. Operating from a 500 mV supply, the shadow filter achieves a dynamic range of 55.9 dB for a 200 mV<inf>pp</inf> input signal, with total harmonic distortion limited to 1%. Owing to its exceptionally low bias currents, the shadow filter exhibits a total power consumption of only 124.11 nW, making it well suited for energy-constrained biomedical and IoT sensor applications, where low-frequency signal processing, compact implementation, and high energy efficiency are essential. To validate the proposed concept, a discrete prototype was also developed using MI-DDTA configurations built with LM13700 operational transconductance amplifiers. The experimental results confirm the expected filter behavior and demonstrate the feasibility of the proposed design in practical scenarios.
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A Novel Low-Power Mixed-Mode Universal Filter Design Using Multiple-Input Operational Transconductance Amplifiers
(2026-06-01)
Khateb, Fabian
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Suksaibul, Pichai
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Kulej, Tomasz
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Kumngern, Montree
This study introduces an innovative mixed-mode universal biquad filter implemented using multiple-input operational transconductance amplifiers (MI-OTAs). Based on the advantage of OTAs, which possess multiple inputs, the proposed mixed-mode universal filter using MI-OTAs can implement both non-inverting and inverting standard filtering functions such as low-pass, high-pass, band-pass, band-stop, and all-pass filters in voltage-mode, transadmittance-mode, current-mode, and transimpedance-mode, which is the maximum capability of mixed-mode universal filters. The natural frequency of all filtering functions can be electronically controlled. Based on the multiple-input bulk-driven MOS transistor (MOST) technique, the OTA can also operate at very low supply voltage and provide wide-input voltage swing. The technique of MOST, operating in the weak inversion region, is used to achieve the low-power consumption of OTA. The MI-OTA circuit and mixed-mode universal filter were designed and simulated using Cadence Virtuoso, utilizing TSMC’s 65-nm CMOS technology. At a 0.5 V supply voltage, the filter demonstrated a simulated power consumption of 450 nW at a natural frequency of 156 Hz. In these ranges of power consumption and natural frequency, it can be expected that the proposed filter can be built as an versatile integrated circuit for low-frequency applications such as bio-signal processing. The design parameters were successfully validated through both post-layout extractions and discrete hardware prototyping utilizing commercially available LM13700N ICs.
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Nano-Power OTA-Based Low-Pass Filter for Ultra-Low-Energy Biomedical Signal Processing
(2026-05-01)
Kulej, Tomasz
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Kumngern, Montree
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Khateb, Fabian
This paper presents a nanowatt-scale operational transconductance amplifier (OTA) and an electronically tunable third-order low-pass filter (LPF) designed for energy-constrained biomedical signal conditioning. The circuits are implemented in a 65 nm CMOS process and verified through comprehensive schematic-level simulations. Biased in the deep subthreshold region at 1 nA, the OTA achieves a 50 dB low-frequency gain, a 225 Hz unity-gain bandwidth at 10 pF load capacitance and an input-referred noise floor of 1.55 μV/√Hz, with a total power consumption of only 1.75 nW. The integrated third-order LPF provides a wide tuning range (37–668 Hz) via bias current modulation, exhibiting excellent linearity with a THD of 0.059% and a 65.3 dB dynamic range. Monte Carlo and PVT corner analyses demonstrate the design’s theoretical robustness against process variations and environmental fluctuations. ECG signal simulations validate the circuit’s effectiveness in suppressing high-frequency artifacts while preserving morphological integrity, providing a proof-of-concept for ultra-low-power wearable healthcare architectures.
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EX-CCCII with Controlled Current Gain and Its Applications
(2026-04-01)
Tooprakai, Siraphop
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Khateb, Fabian
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Kulej, Tomasz
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Nonthaputha, Thanat
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Vavra, Jiri
This paper presents a novel extra-X second-generation current-controlled conveyor (EX-CCCII) with controllable current gain. Unlike the conventional EX-CCCII, the proposed EX-CCCII provides a controllable current gain between the (Formula presented.) - and (Formula presented.) -terminals. To demonstrate the advantages of the EX-CCCII with the controllable current gain, the proposed EX-CCCII is employed to realize a universal current-mode filter and a three-phase current-mode oscillator. The universal filter can realize five standard filtering responses (low-pass, high-pass, band-pass, band-stop, and all-pass) using the same topology. The current gains of these filters can be controlled through the current gain of the EX-CCCII, while the natural frequency of the universal filter can be electronically tuned via the intrinsic resistance at the x-terminal. When the proposed EX-CCCII is used to implement the three-phase oscillator, the condition of oscillation can be adjusted through the current gain of the EX-CCCII, whereas the oscillation frequency can be tuned using the parasitic resistance of the x-terminals. The proposed EX-CCCII and its applications were verified through SPICE simulations using the transistor model parameters NR100N (NPN) and PR100N (PNP) of the bipolar array ALA400-CBIC-R from AT&T to confirm the functionality and feasibility of the proposed topologies. Furthermore, experimental verification of the EX-CCCII and its integration into a three-phase oscillator further substantiates the proposed concept and demonstrates its practical viability.
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An Ultralow-Power 0.5-V MI-OTA-Based Universal Filter for Efficient Low-Frequency Signal Processing
(2026-01-01)
Kulej, Tomasz
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Kumngern, Montree
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Khateb, Fabian
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Lerkvaranyu, Somkiat
This work introduces novel universal filters implemented using multiple-input operational transconductance amplifiers (MI-OTAs). The MI-OTA is specifically designed for a minimal 0.5-V supply, achieving nano-watt level power dissipation, which positions the design as highly viable for demanding ultralow-power systems. The architecture employs a subthreshold, multiple-input, bulk-driven MOS configuration. This design not only extends the operational input voltage range but concurrently ensures minimal voltage and power consumption. The primary filter topology utilizes five MI-OTAs and two grounded capacitors to concurrently deliver all five standard filtering responses—low-pass, high-pass, band-pass, band-stop, and all-pass filter—from a single, fixed circuit structure. By integrating a sixth MI-OTA, the architecture becomes reconfigurable for operation in both voltage-mode (VM) and transimpedance-mode (TIM). This versatility yields both non-inverting and inverting transfer functions for all five fundamental responses, resulting in a total of 20 distinct output functions. This multifunctionality and power efficiency make the proposed designs exceptionally well-suited for low-frequency applications, such as bio-signal processing and sophisticated sensor interfacing circuits. Furthermore, a key feature is that the filter's natural frequency is electronically tunable across all responses. The MI-OTA was designed and simulated in Cadence Virtuoso, utilizing the TSMC 65-nm (1P9M) CMOS process. The device occupies a modest silicon footprint of 125 μm × 92 μm. Simulation results confirm a power dissipation of 150 nW at a 177-Hz cutoff frequency under the 0.5-V supply. Post-layout simulations verified the expected circuit performance. Finally, experimental validation was conducted using a discrete-component MI-OTA-based circuit built with the LM13700, thereby confirming the filter's correct operation.
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MI-OTA Based First Order Filters for Biomedical Applications
(2026-01-01)
Khateb, Fabian
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Kumngern, Montree
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Kulej, Tomasz
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Arbet, Daniel
A low-power, electronically tunable voltage-mode first-order universal filter employing a multiple-input operational transconductance amplifiers (MI-OTAs). It does not require component matching, input matching, or signal inversion, simplifying practical implementation. Designed in 65 nm CMOS at 0.5 V, it consumes 10 nW and achieves a 41.7 dB dynamic range. Experimental results using commercially available LM13600N integrated circuits confirm its practical feasibility and versatility for low-power biomedical applications.
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A 0.5-V MI-OTA-based shadow universal filter with integrated passband gain compensation and low-pass control for low-frequency applications
(2025-12-01)
Kumngern, Montree
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Khateb, Fabian
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Kulej, Tomasz
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Arbet, Daniel
Ultra-low-power active filters have received increasing attention in recent years due to emerging applications such as bio-signal sensing and wearable electronic devices, where they are employed in the analog front-end to eliminate interference noise. This paper presents a novel voltage-mode shadow universal filter based on multiple-input operational transconductance amplifiers (MI-OTAs). The multiple-input functionality of the OTA is implemented using the multiple-input bulk-driven MOS transistor (MIBD-MOST) technique, which enables low supply voltage operation and a wide input voltage swing. Additionally, the use of subthreshold operation contributes to the low-power consumption of the OTA. The proposed shadow filter is implemented using a voltage-mode universal filter, in which the low-pass section is employed to control the natural frequency through an external amplifier. The proposed filter provides both non-inverting and inverting transfer functions of low-pass filter (LPF), high-pass filter (HPF), band-pass filter (BPF), band-stop filter (BSF), and all-pass filter (APF). The circuit was designed and simulated using Cadence Virtuoso, utilizing TSMC’s 65-nm 1P9M CMOS technology. The total silicon area of the MI-OTA measured 148 μm × 89 μm. Operating at a supply voltage of 0.5 V and a cutoff frequency of 31.2 Hz, the filter achieved an overall power consumption of 350 nW. Experimental validation was conducted using a prototype implemented with commercially available LM13700N integrated circuits, confirming the filter’s functionality and effectiveness. The proposed design is well suited for low-voltage, low-power applications, particularly low-frequency bio-signal processing such as EEG and EGG acquisition systems, as well as sensor interface systems.
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Shadow universal filter with independent Q tuning at 0.45 V using MI-OTAs
(2025-09-01)
Kumngern, Montree
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Khateb, Fabian
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Thanyaratsakul, Nattapong
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Kulej, Tomasz
This paper presents a novel shadow universal filter implemented in voltage mode, based on multiple-input operational transconductance amplifiers (MI-OTAs). The proposed shadow universal filter incorporates both non-inverting and inverting transfer functions for low-pass, high-pass, band-pass, band-stop, and all-pass responses within a single topology. The proposed filter is a shadow universal filter that employs low-pass and high-pass filters feedback to the input. It enables independent control of the quality factor for all filtering responses through an external amplifier, without altering the natural frequency. Moreover, during quality factor tuning, any variation in passband gain can be compensated by appropriately adjusting the input signal configuration. These advantages of the proposed shadow universal filter are enabled by the multiple-input capability of the operational transconductance amplifier (OTA), which is implemented using the multiple-input bulk-driven MOS transistor (MIBD-MOST) technique. The MI-OTA operates at an ultra-low supply voltage of 0.45 V and consumes only 270 nW of power. For the low-pass shadow filter configuration, a dynamic range of 48 dB was achieved at 1% total harmonic distortion. Experimental validation was conducted using a prototype implemented with commercially available LM13700N integrated circuits, confirming the filter's functionality and effectiveness.
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A 0.3 V Current Differencing Buffered Amplifier and Its Application in Current-Mode Third-Order Low-Pass Filters
(2025-05-01)
Khateb, Fabian
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Kumngern, Montree
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Kulej, Tomasz
This paper introduces an innovative low-voltage, low-power current differencing buffered amplifier (CDBA). The proposed CDBA utilizes a bulk-driven MOS transistor operating in the subthreshold region, allowing it to function effectively at low supply voltages while minimizing power consumption, making it suitable for sensor and biomedical applications. To demonstrate the performance of the proposed CDBA, it is incorporated into the design of a current-mode, third-order low-pass filter that is specifically tailored for bio-sensing applications. Both the CDBA and the low-pass filter are designed and simulated in Cadence Virtuoso using the TSMC 0.18 µm CMOS process. The CDBA operates at a supply voltage of 0.3 V, consuming 170 nW of power, while the third-order low-pass filter achieves a dynamic range of 57.2 dB with a total harmonic distortion (THD) of 1%.
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A 328 nW, 0.45 V Current Differencing Transconductance Amplifier and Its Application in a Current-Mode Universal Filter
(2025-04-01)
Khateb, Fabian
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Kumngern, Montree
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Kulej, Tomasz
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Vavra, Jiri
This paper presents a low-voltage, low-power current differencing transconductance amplifier (CDTA) utilizing the bulk-driven MOS transistor technique in the subthreshold region for reduced voltage and power consumption. The proposed CDTA includes a z-copy terminal, which enhances its functionality in current-mode circuit applications. Designed in the Cadence Virtuoso environment using 0.18 µm CMOS technology from Taiwan Semiconductor Manufacturing Company (TSMC), the amplifier operates with a supply voltage of 0.45 V and consumes 328 nW of power, with a bias current set to 10 nA. The current bandwidth and offset of the CDTA are 35 kHz and 0.3 nA, respectively. To demonstrate its performance, the CDTA is applied in a current-mode universal filter, which can realize low-pass, band-pass, high-pass, band-stop, and all-pass responses within a single topology. This design eliminates issues related to inverting input signals, input signal matching, or the need for multiple input signals. Additionally, the natural frequency of these filtering functions can be electronically controlled. The low-pass filter achieves a dynamic range of 61 dB, with a total harmonic distortion of 0.8%.

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