Comparing different nonlinearities in readout systems for optical neuromorphic computing networks

Nonlinear activation is a crucial building block of most machine-learning systems. However, unlike in the digital electrical domain, applying a saturating nonlinear function in a neural network in the analog optical domain is not as easy, especially in integrated systems. In this paper, we first investigate in detail the photodetector nonlinearity in two main readout schemes: electrical readout and optical readout. On a 3-bit-delayed XOR task, we show that optical readout trained with backpropagation gives the best performance. Furthermore, we propose an additional saturating nonlinearity coming from a deliberately non-ideal voltage amplifier after the detector. Compared to an all-optical nonlinearity, these two kinds of nonlinearities are extremely easy to obtain at no additional cost, since photodiodes and voltage amplifiers are present in any system. Moreover, not having to design ideal linear amplifiers could relax their design requirements. We show through simulation that for long-distance nonlinear fiber distortion compensation, using only the photodiode nonlinearity in an optical readout delivers BER improvements over three orders of magnitude. Combined with the amplifier saturation nonlinearity, we obtain another three orders of magnitude improvement of the BER.

Electrical creep and fatigue in 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramics

In this study, the creep and fatigue characterization is performed for 0.5Ba(Zr[Formula: see text]Ti[Formula: see text]O[Formula: see text]0.5(Ba[Formula: see text]Ca[Formula: see text]TiO3 (BZT-BCT) bulk ferroelectric ceramics. A function generator is used to generate the required waveform of the voltage amplifier for fatigue and creep analysis. The evolution of polarization is studied for electrical creep. The effects of temperature and electric field on the electric displacement are studied. Hysteresis–butterfly loops are analyzed for fatigue tests for different thermal loads up to 106 cycles. It inheres that the material is stable below 75[Formula: see text]C and can withstand high cycle fatigue loads (25 Hz, ± 1.5 kV/mm).

Negative feedback

Negative feedback is an essential constituent of any control system. It is illustrated for the case of an electronic voltage amplifier. Formal definitions are given of positive and negative feedback. Feedback can be used to adjust the amplifier's frequency response. Distortion, meaning generation of new and unwanted frequencies (harmonics, sums, differences), is reduced by a factor equal to the “return difference”.

A Comprehensive Survey of Readout Strategies for SiPMs Used in Nuclear Imaging Systems

Silicon photomultipliers (SiPMs) offer advantages such as lower relative cost, smaller size, and lower operating voltages compared to photomultiplier tubes. A SiPM’s readout circuit topology can significantly affect the characteristics of an imaging array. In nuclear imaging and detection, energy, timing, and position are the primary characteristics of interest. Nuclear imaging has applications in the medical, astronomy, and high energy physics fields, making SiPMs an active research area. This work is focused on the circuit topologies required for nuclear imaging. We surveyed the readout strategies including the front end preamplification topology choices of transimpedance amplifier, charge amplifier, and voltage amplifier. In addition, a review of circuit topologies suitable for energy, timing, and position information extraction was performed along with a summary of performance limitations and current challenges.

Emulation of grid-forming inverters using real-time PC and 4-quadrant voltage amplifier

A test bed for the evaluation of novel control methods of inverters for renewable power generation is presented. The behavior of grid-following and grid-forming control in a test scenario is studied and compared.Using a real-time capable control platform with a cycle time of 50 µs, control methods developed with Matlab/Simulink can be implemented. For simplicity, a three-phase 4‑quadrant voltage amplifier is used instead of an inverter. Thus, the use of modulation and switched power semiconductors can be avoided. In order to show a realistic behavior of a grid-side filter, passive components can be automatically connected as L‑, LC- or LCL-filter. The test bed has a nominal active power of 43.6 kW and a nominal voltage of 400 V.As state-of-the-art grid-following control method, a current control in the d/q-system is implemented in the test bed. A virtual synchronous machine, the Synchronverter, is used as grid-forming control method. In combination with a frequency-variable grid emulation, the behavior of both control methods is studied in the event of a load connection in an island grid environment.