OTA-based Circuit Research Articles

High-complex chaotic system based on new nonlinear function and OTA-based circuit realization

This research proposes a chaotic system using a new modified rectangular nonlinear function based on the principle of the third-order jerk concept. The dynamic behaviors can be realized by manipulating only one parameter from periodic, non-periodic, single-scroll, and double-scroll attractors. The proposed chaotic system can achieve relatively high-complexity chaotic behavior, as evident in the comparatively high Kaplan-Yorke dimension (DKY = 2.43) with the existing jerk systems. The performances of the proposed chaotic system are also computed and simulated through the MATLAB numerical analysis, including scenarios of bifurcations branches, Lyapunov exponents, route to chaos, phase portraits, 0–1 test charts, and Poincaré map. The proposed system analyzes the coexistence of asymmetric or symmetric attractors confirmed with basins of attraction to highlight the presence of multiple attractors, which influence initial conditions. In addition, the system's offset boosting and amplitude control are included. Furthermore, a double-scroll attractor and a four-scroll attractor can also be achieved by placing nonlinear functions at different positions in the third-order system., The circuits of the proposed chaotic systems can be conveniently realized using commercially available operational transconductance amplifiers (OTAs) and capacitors. The performances of the circuit are also proven through the experimental results compared with the numerical results. The experimental results exhibit the ease of construction based on the new nonlinear function and are suitable for applying in the data encryptions.

Versatile Voltage-Mode Biquadratic Filter and Quadrature Oscillator Using Four OTAs and Two Grounded Capacitors

This article presents a versatile voltage-mode (VM) biquad filter with independently electronic tunability. The proposed structure using one dual-output operational transconductance amplifier, three single-output operational transconductance amplifiers (OTAs) and two grounded capacitors was explored to derive a new VM quadrature oscillator with the independent control of the oscillation frequency and the oscillation condition. The proposed versatile VM biquad filter achieves nearly all of the main advantages: (i) simultaneous realizations of band-reject, band-pass, and low-pass from the same architecture, (ii) multiple-input and multiple-output functions, (iii) independent electronic adjustability of quality factor and resonant angular frequency, (iv) no resistor needed, (v) all input terminals with cascade functions, (vi) no additional inverting amplifier for input signals, (vii) using only grounded capacitors, and (viii) easy to implement a VM quadrature oscillator with independent electronically controlled oscillation frequency and oscillation condition. The proposed versatile VM biquad filter employs only four OTAs and two grounded capacitors. The active components of the proposed VM biquad filter are one less than that of recent reports. The proposed circuit also brings versatility and simplicity to the design of VM biquad filters and VM quadrature oscillators. Filters and oscillators with less active and passive components have the advantages of low cost, low power dissipation, low circuit complexity, and low noise. Commercially available integrated circuit LT1228 and discrete components can be used to implement the proposed OTA-based circuits. The simulation and experiment results validated the theoretical analysis.

Low-Voltage OTA-C Filter With an Area- and Power-Efficient OTA for Biosignal Sensor Applications.

This paper presents a systematic method for decreasing the amount of transconductors used by an operational transconductance amplifier-capacitor (OTA-C) filter to decrease the power consumption and the active area. An OTA with a local-feedback linearized technique and a transconductance booster is proposed based on the presented method. The proposed OTA combines current division with source degeneration to enhance linearity and implement low transconductance. This topology enables the proposed OTA to drive multiple integration capacitors without an additional output stage. The OTA-based circuit realizes low power consumption by operating under a weak inversion at a supply voltage of 1 V. Thus, a fifth-order ladder-type low-pass Butterworth OTA-C filter is implemented for the acquisition of electrocardiograph signals. The proposed method is validated using a prototype fabricated through a 1P6M 0.18-μm CMOS process. Results show that in ECG signal acquisition, the proposed filter has a signal bandwidth located within 250Hz, a dynamic range of 61.2dB, and a power consumption of 41nW to achieve a figure-of-merit of 5.4 × 10-13. The active area of the filter is 0.24mm2.

A novel OTA-based circuit model corroborated by an experimental semiconductor memristor

A semiconductor memristor device based on a 300-nm ZnO thin film was fabricated by direct-current reactive sputter. The memristive behavior of this device was confirmed by time dependent current–voltage (I-V-t) measurements, and the distinctive pinched hysteresis I-V loops of the memristor were observed. Structural analysis of the ZnO memristor was carried out using both X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). After physical implementation of the memristor, an operational transconductance amplifier (OTA) based memristor circuit was designed to emulate the ZnO-based semiconductor memristor for use in memristor-based circuit applications. All simulations were in good agreement with experimental results. In addition, a comparison of the proposed circuit with other memristor emulators was presented.

An Improved Describing Function With Applications for OTA-Based Circuits

Electronic systems make extensive use of operational transconductance amplifiers (OTAs) to build filters and oscillators. Studying the effects of the saturation nonlinearity on these OTA-based circuits is difficult and often requires lengthy simulations to check the system’s performance under large-signal operation. The describing function (DF) theory allows to circumvent these simulations by deriving a signal-dependent linearized gain, which predicts the effects of the nonlinearity. However, its use is limited since the state-of-the-art DFs deviate significantly from the real saturating behavior of OTAs. This paper proposes an improved DF, which can be directly derived from the static nonlinear characteristic of the transconductance amplifier. The performance of the proposed methodology is demonstrated for both an OTA-based filter and oscillator. It is shown that the proposed DF has a better nonlinear prediction capability than the state-of-the-art solutions.

An OTA-C filter for ECG acquisition systems with highly linear range and less passband attenuation**Project supported by the National Natural Science Foundation of China (Nos. 61161003, 61264001, 61166004) and the Guangxi Natural Science Foundation (No. 2013GXNSFAA019333).

A fifth order operational transconductance amplifier-C (OTA-C) Butterworth type low-pass filter with highly linear range and less passband attenuation is presented for wearable bio-telemetry monitoring applications in a UWB wireless body area network. The source degeneration structure applied in typical small transconductance circuit is improved to provide a highly linear range for the OTA-C filter. Moreover, to reduce the passband attenuation of the filter, a cascode structure is employed as the output stage of the OTA. The OTA-based circuit is operated in weak inversion due to strict power limitation in the biomedical chip. The filter is fabricated in a SMIC 0.18-μm CMOS process. The measured results for the filter have shown a passband gain of −6.2 dB, while the −3-dB frequency is around 276 Hz. For the 0.8 VPP sinusoidal input at 100 Hz, a total harmonic distortion (THD) of −56.8 dB is obtained. An electrocardiogram signal with noise interference is fed into this chip to validate the function of the designed filter.

An Ultra-Low Power OTA-C Bandpass Filter Design for ECG Application

An ultra-low power OTA-C bandpass filter is presented in this paper. An 1-150 Hz 4-th order OTC-C bandpass filter is design which is suitable for ECG application. A subthreshold region OTA is designed with current cancellation technology to achieve a very small transconductance. The OTA-C filter is design with TSMC 0.18μm CMOS process. The MIM capacitor is used in this design. The supply of the proposed circuit is 1V. The total power consumption is only 245nW. I. I NTRODUCTION The development of portable heart monitoring system is not only useful in long-term healthcare, but also demanded in an increasing number of researches in the biomedical file (1). Filters is continually a critical block of biopotential acquisition systems for enhancing the signal quality (2). However, for low frequency biomedical applications, realizing filter circuits with large time constant under an acceptable capacitor's value isn't an easy task (3). Switching-capacitor circuit is a popular technique used in implementing filter circuit. Due to the leakage problem of the advanced process, the sample-hold circuits of the switch-based topologies are not suitable for applications requiring large time constant. Compared with the switching-capacitor filters, continuous-time OTA-C filter has their benefits of lower power consumption and freeing the system from switching noise. The cut-off frequency is proportional to the transconductance (g m ) of the OTA; this allows a low-power implementation for low frequency biopotential signals. In OTA-based circuits, OTA will dominate the performance of the filter circuit, while the ratio of the capacitor to the small transconductance determines the time constant of OTA-C integrators. Thus, an OTA in which the transistors are operated in the subthreshold region is needed to save more power and realize a very low transconductance. A 4-order Butterworth bandpass is presented in this paper. The bandwidth of this filter is 1-150Hz. A subthreshold OTA is used to achieve the 1Hz cut-off frequency. The transconductance is below 1nA/V. The performance of the OTA is based on the behavior of MOS devices operating in the subthreshold region. The channel current of subthreshold region is:(3)

Systematic Design and Modeling of a OTA-C Filter for Portable ECG Detection

This study presents a systematic design of the fully differential operational transconductance amplifier-C (OTA-C) filter for a heart activities detection apparatus. Since the linearity and noise of the filter is dependent on the building cell, a precise behavioral model for the real OTA circuit is created. To reduce the influence of coefficient sensitivity and maintain an undistorted biosignal, a fifth-order ladder-type lowpass Butterworth is employed. Based on this topology, a chip fabricated in a 0.18- mum CMOS process is simulated and measured to validate the system estimation. Since the battery life and the integration with the low-voltage digital processor are the most critical requirement for the portable diagnosis device, the OTA-based circuit is operated in the subthreshold region to save power under the supply voltage of 1V. Measurement results show that this low-voltage and low-power filter possesses the HD3 of -48.9 dB, dynamic range (DR) of 50 dB, and power consumption of 453 nW. Therefore, the OTA-C filter can be adopted to eliminate the out-of-band interference of the electrocardiogram (ECG) whose signal bandwidth is located within 250 Hz.

Temperature compensation of translinear currentconveyor and OTA

A simple and integrable temperature compensation scheme for translinear current conveyor-based circuits and OTA-based circuits is introduced. It uses a new bias circuit which has a current that is directly proportional to the absolute temperature, and can also be electronically varied. Performance of the scheme is confirmed through PSPICE simulation results.

Realization of current-mode transfer function using second-generation current conveyors

This paper proposes an entirely new method for performing current-mode analogue signal filtering. Along with adjoint block diagrams, second-generation current conveyor-based (CCII-based) voltage-amplifier filter circuits can be converted to equivalent CCII-based current-amplifier filter circuits with identical sensitivity properties. This new transformation method may also be suitable for some OTA-based circuits.