This paper presents an innovative CMOS structure for Differential Difference Transconductance Amplifiers (DDTA). While the circuit operates under extremely low voltage supply 0.5 V, the circuit's performance is improved thanks to using the multiple-input MOS transistor (MI-MOST), the bulk-driven, self-cascode and partial positive feedback (PPF) techniques. As a result, the DDTA structure is less complex, with high gain of 93 dB, wide input voltage range nearly rail-to-rail, and wide transconductance tunability. As an example of application, a second-order voltage-mode universal filter using three DDTAs and two 6 pF integrated capacitors is presented. The filter is designed such that no matching conditions are required for the input and passive components, and the input signals need not be inverted. The natural frequency and the quality factor can be set orthogonally while the natural frequency can be electronically controlled. The circuit was designed and simulated in Cadence environment using 0.18 µm TSMC technology. The simulation results including intensive Monte-Carlo (MC) and process, temperature, voltage (PVT) analysis confirm the stability and the robustness of the design to process, mismatch variation and PVT corners.

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This paper presents a 0.5 V fifth-order Butterworth low-pass filter based on multiple-input operational transconductance amplifiers (OTA). The filter is designed for electrocardiogram (ECG) acquisition systems and operates in the subthreshold region with nano-watt power consumption. The used multiple-input technique simplifies the overall structure of the OTA and reduces the number of active elements needed to realize the filter. The filter was designed and simulated in the Cadence environment using a 0.18 µm Complementary Metal Oxide Semiconductor (CMOS) process from Taiwan Semiconductor Manufacturing Company (TSMC). Simulation results show that the filter has a bandwidth of 250 Hz, a power consumption of 34.65 nW, a dynamic range of 63.24 dB, attaining a figure-of-merit of 0.0191 pJ. The corner (process, voltage, temperature: PVT) and Monte Carlo (MC) analyses are included to prove the robustness of the filter.

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