Analysis and Reduction of Nonlinear Distortion in AC-Coupled CMOS Neural Amplifiers with Tunable Cutoff Frequencies

Integrated CMOS neural amplifiers are key elements of modern large-scale neuroelectronic interfaces. The neural amplifiers are routinely AC-coupled to electrodes to remove the DC voltage. The large resistances required for the AC coupling circuit are usually realized using MOSFETs that are nonlinear. Specifically, designs with tunable cutoff frequency of the input high‑pass filter may suffer from excessive nonlinearity, since the gate-source voltages of the transistors forming the pseudoresistors vary following the signal being amplified. Consequently, the nonlinear distortion in such circuits may be high for signal frequencies close to the cutoff frequency of the input filter. Here we propose a simple modification of the architecture of a tunable AC-coupled amplifier, in which the bias voltages Vgs of the transistors forming the pseudoresistor are kept constant independently of the signal levels, what results in significantly improved linearity. Based on numerical simulations of the proposed circuit designed in 180 nm technology we analyze the Total Harmonic Distortion levels as a function of signal frequency and amplitude. We also investigate the impact of basic amplifier parameters—gain, cutoff frequency of the AC coupling circuit, and silicon area—on the distortion and noise performance. The post-layout simulations of the complete test ASIC show that the distortion is very significantly reduced at frequencies near the cutoff frequency, when compared to the commonly used circuits. The THD values are below 1.17% for signal frequencies 1 Hz–10 kHz and signal amplitudes up to 10 mV peak-to-peak. The preamplifier area is only 0.0046 mm2 and the noise is 8.3 µVrms in the 1 Hz–10 kHz range. To our knowledge this is the first report on a CMOS neural amplifier with systematic characterization of THD across complete range of frequencies and amplitudes of neuronal signals recorded by extracellular electrodes.

Stability Analysis of Shunt Active Power Filter with Predictive Closed-Loop Control of Supply Current

This paper presents a shunt active power filter connected to the grid via an LCL coupling circuit with implemented closed-loop control. The proposed control system allows selective harmonic currents compensation up to the 50th harmonic with the utilization of a model-based predictive current controller. As the system is fully predictive, it provides high effectiveness of the harmonic reduction, which is proved by waveforms achieved in performed tests. On the other hand, the control system is prone to loss of stability. Therefore, the paper is focused on the stability analysis of the discussed control system with the additional outer control loop of the supply current with predictive control of this current. The conducted stability analysis encompasses the assessment of system stability as a function of the coupling circuit parameter identification accuracy, whose values are implemented in the current controller, as well as parameters such as the sampling frequency and proportional–integral (PI) controller coefficients. The obtained results show that the ranges of the LCL circuit parameter identification accuracy for which the system remains stable are relatively wide. However, the most effective compensation of the supply current distortion is achieved for the parameters identified correctly, and the greatest impact on the compensation quality has the value of L1 inductance.

Research on power coupling characteristics and acceleration strategy of electro-hydrostatic hydraulic hybrid power system

Aiming at the adverse effect of the peak power of the electric motor of the battery-powered rail vehicles on the battery life and the driving range when starting or accelerating, a new type of electro-hydrostatic hydraulic hybrid powertrain is designed. This article proposes a novel power form that assists the vehicle to start or accelerate through two power coupling methods: torque coupling circuit and flow rate coupling circuit which have good power performance and energy-saving performance. A mathematical model for power coupling of hybrid power system is constructed, and the effects of key parameters of the system and different power coupling ratios on electric power consumption and power coupling characteristics are studied. Based on the simulation and test platform, the power coupling characteristics of the electro-hydrostatic hydraulic hybrid powertrain are simulated and experimentally researched. The results show that compared with the traditional electro-hydrostatic series system, the novel electro-hydrostatic hydraulic hybrid powertrain can effectively avoid the impact of electric motor power and reduce the power consumption. Based on the characteristics of power coupling, the acceleration strategy of minimum peak power is studied to control the key components of the power coupling process. Simulation and experimental results show that under the control of the new acceleration strategy, the electro-hydrostatic hydraulic hybrid powertrain has good electro-hydraulic power coupling characteristics. The electric power of the power system is greatly reduced during acceleration, which has better energy-saving characteristics and value for engineering applications.

New Method of State-Space Formulation for Degenerate Circuit and Coupling Circuit

The state-space formulation overcomes many limitations of traditional differential equation approach and is utilized as alternative to many traditional approaches in the modern electrical field. This paper proposes a new method of finding the state equation for degenerate circuit and coupling circuit that have not been systematically solved now. This paper also introduces some sound improvements to solve complicated dependent-source circuits. Four comparative examples are demonstrated to show the significant merits that our method owns over the traditional approaches.