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Abstract The developmental gene regulatory networks (dGRNs) of two sea urchin species, Lytechinus variegatus (Lv) and Strongylocentrotus purpuratus (Sp), have remained remarkably similar despite about 50 million years since a common ancestor. Hundreds of parallel experimental perturbations of transcription factors with similar outcomes support this conclusion. A recent scRNA-seq analysis suggested that the earliest expression of several genes within the dGRNs differs between Lv and Sp. Here, we present a careful reanalysis of the dGRNs in these two species, paying close attention to timing of first expression. We find that initial expression of genes critical for cell fate specification occurs during several compressed time periods in both species. Previously unrecognized feedback circuits are inferred from the temporally corrected dGRNs. Although many of these feedbacks differ in location within the respective GRNs, the overall number is similar between species. We identify several prominent differences in timing of first expression for key developmental regulatory genes; comparison with a third species indicates that these heterochronies likely originated in an unbiased manner with respect to embryonic cell lineage and evolutionary branch. Together, these results suggest that interactions can evolve even within highly conserved dGRNs and that feedback circuits may buffer the effects of heterochronies in the expression of key regulatory genes.

Single-cell transcriptomics of neocortical neurons have revealed more than 100 clusters corresponding to putative cell types. For inhibitory and subcortical projection neurons (SCPNs), there is a strong concordance between clusters and anatomical descriptions of cell types. In contrast, cortico-cortical projection neurons (CCPNs) separate into surprisingly few transcriptomic clusters, despite their diverse anatomical projection types. We used projection-dependent single-cell transcriptomic analyses and monosynaptic rabies tracing to compare mouse primary visual cortex CCPNs projecting to different higher visual areas. We find that layer 2/3 CCPNs with different anatomical projections differ systematically in their gene expressions, despite forming only a single genetic cluster. Furthermore, these neurons receive feedback selectively from the same areas to which they project. These findings demonstrate that gene-expression analysis in isolation is insufficient to identify neuron types and have important implications for understanding the functional role of cortical feedback circuits.

Evidence of long-range interactions between logic transitions in unclocked FPGA circuits is reported. The relative positions of pulses traveling in digital feedback loops are observed to dynamically interact and move to equal spacing over long timescales. We confirm the presence of this interaction over different FPGA supply voltages and hypothesize the pulse interactions are due to current draw in the power distribution network of the FPGA. This pulse interaction effect is observed for different FPGA families and manufacturers, including Altera and Xilinx, and has been tested using both look-up table (LUT) and carry chain (CC) logic to realize the feedback delays.

The developmental gene regulatory networks (dGRNs) of two sea urchin species, Lytechinus variegatus (Lv) and Strongylocentrotus purpuratus (Sp), have remained remarkably similar despite about 50 million years since a common ancestor. Hundreds of parallel experimental perturbations of transcription factors with similar outcomes support this conclusion. A recent scRNA-seq analysis suggested that the earliest expression of several genes within the dGRNs differs between Lv and Sp. Here, we present a careful reanalysis of the dGRNs in these two species, paying close attention to timing of first expression. We find that initial expression of genes critical for cell fate specification occurs during several compressed time periods in both species. Previously unrecognized feedback circuits are inferred from the temporally corrected dGRNs. Although many of these feedbacks differ in location within the respective GRNs, the overall number is similar between species. We identify several prominent differences in timing of first expression for key developmental regulatory genes; comparison with a third species indicates that these heterochronies likely originated in an unbiased manner with respect to embryonic cell lineage and evolutionary branch. Together, these results suggest that interactions can evolve even within highly conserved dGRNs and that feedback circuits may buffer the effects of heterochronies in the expression of key regulatory genes. [ABSTRACT FROM AUTHOR]

A tunable Fabry-Perot interferometer (FPI) can be used as an optical band-pass filter. This type of filter is used in spectrometers and spectral imagers. The transmitted wavelength depends on the optical cavity adjusted by an electronic controller. This cavity, or the gap between the FPI mirrors, is measured using capacitive sensing. The performance of the FPI controller directly affects the FPI transmission spectrum and thus the quality of the spectral data. This work describes the design of the FPI controller for the ultraviolet channel of the ALTIUS hyperspectral imager. The ALTIUS mission is part of the Earth Watch program managed by the European Space Agency, ESA. This article presents a novel combination of building blocks to implement a low-noise, high-stability controller for piezo-actuated FPIs. Special care was taken to guarantee temperature stability and to minimize fluctuation of the FPI gap caused by the controller electronics. With the controller design presented in this paper, temperature variations ranging from–50 to $+ 50\,\,^{\circ }\text{C}$ induce FPI gap deviations of less than 0.1 nm at an electrode distance of 3000 nm, corresponding to a relative temperature drift of 0.3 ppm/°C.

A 50–GHz bandwidth traveling-wave Mach-Zehnder modulator (TWMZM) was designed with a new equalization technique, which takes advantage of the intrinsic delay in a traveling-wave electrode (TWE) and a local negative-feedback circuit. With this idea, given the availability of flip-chip bonding, a long TWE can be equalized as a single stage or be segmented into a few stages, each being equalized separately to optimize the performance of the entire device. The detailed analysis of this equalization technique is presented. As a demonstration, a 1.6–mm long equalized TWMZM was designed using a commercial silicon photonic process and a 0.13 $\mu \mathrm{m}$ SiGe process. A 2–stage cascaded design with equal equalization was adopted and optimized for high bandwidth and high extinction ratio. The circuit was designed using the multi-physics electronic-photonic integrated circuit (EPIC) design flow we developed recently, wherein both electronic and photonic parts were modeled and the EPIC circuit was simulated for system level performance evaluation. Simulation results showed that the equalization technique increased the 3-dB EO bandwidth of the TWMZM from 28 to 50.4 GHz, an 80% increase. Large signal performance with non-return to zero signals upto 100 Gb/s was evaluated and the results showed significant improvements in the eye quality with equalization. The performance evaluation with pulse amplitude modulation (PAM)-4 signal was also carried out and the results showed successful operation at 106 Gbaud PAM-4 for the equalized TWMZM, makes it a promising candidate for future 200 Gbps-per-lambda optical transceivers. [ABSTRACT FROM AUTHOR]

Integrated polarization stabilizers along with corresponding stabilizing algorithms have been investigated for years to tackle the polarization fluctuation issue in polarization dependent systems such as photonics integrated circuits and coherent optical communication systems. Here, we propose and demonstrate a novel integrated polarization stabilizer which is composed of an in-line polarimeter and two cascaded Mach-Zehnder interferometers-based polarization converter, with a footprint of 2.8 mm × 0.8 mm. Benefitting from the integrated in-line polarimeter and two controlling algorithms, namely feed-forward tracking algorithm and feedback tracking algorithm, the stabilizer can track the incoming light with arbitrary state of polarization in one-time manipulation. The whole process consumes about 30 μs, which is approaching the limitation of the response time of the adopted thermal phase shifters, making the proposed device the fastest one with thermal phase shifters on silicon photonics platform. Meanwhile, the incoming light is endlessly tracked in real time and 99% converted to horizontal linear polarized light. [ABSTRACT FROM AUTHOR]

An alternative approximate implementation of an exactly solvable chaotic oscillator circuit is presented. In this implementation, the previously used op amp based NIC sinusoidal oscillator subcircuit was replaced with a single BJT Colpitts oscillator subcircuit. Although this change resulted in an increase in the order of the chaotic system and introduced additional nonlinearities, simulation and hardware testing results indicated that its performance was equivalent to that of the mathematical model for the exactly solvable chaotic system. It also demonstrated equivalent performance to previous op amp based designs, while mitigating some of the performance limitations inherent with op amp based NICs. Evaluation of the resulting 18.9 kHz oscillator circuit demonstrated chaotic dynamics comparable to those from the ideal exactly solvable chaotic system. [ABSTRACT FROM AUTHOR]

This article shows both theoretical and experimental analyses of a fully integrated CMOS active gate driver (AGD) developed to control the high dv/dt of GaN transistors for both 48 and 400 V applications. To mitigate negative effects in the high-frequency spectrum emission, an original technique is proposed to reduce the dv/dt with lower switching losses compared to classical solutions. The AGD technique is based on a subnanosecond delay feedback loop, which reduces the gate current only during the dv/dt sequence of the switching transients. Hence, the dv/dt and di/dt can be actively controlled separately, and the tradeoff between the dv/dt and EON switching energy is optimized. Since GaN transistors have typical voltage switching times on the order of a few nanoseconds, introducing a feedback loop from the high voltage drain to the gate terminal is quite challenging. In this article, we successfully demonstrate the active gate driving of GaN transistors for both 48 and 400 V applications, with initial open-loop voltage switching times of 3 ns, due to a full CMOS integration. Other methods for dv/dt active control are further discussed. The limits of these methods are explained based on both experimental and simulation results. The AGD showed a clear reduction in the peak dv/dt from –175 to –120 V/ns for the 400 V application. [ABSTRACT FROM AUTHOR]

This brief presents a variable-gain amplifier (VGA) for automotive radar applications integrated in a 28-nm fully depleted (FD) silicon-on-insulator (SOI) CMOS technology. The amplifier operates at a power supply as low as 1 V and guarantees 30-dB linear-in-dB gain variation with a 3-dB step. The back-gate of the MOS transistors has been exploited to implement a back-gate control-based offset cancelation loop, thus avoiding the use of inter-stage coupling capacitors that introduce frequency limitations due to parasitic capacitances. The VGA exhibits a bandwidth from 100 kHz to 20 MHz, which is compliant with typical frequency-modulated continuous wave (FMCW) radars. It also guarantees a 1-dB compression point (${P} _{\mathrm{ 1dB}}$) better than −36 dBm and an input-referred noise (IRN) of 12.5 nV/ $\surd $ Hz and 7 nV/ $\surd $ Hz at 1 MHz and 10 MHz, respectively, with a power consumption as low as 1.7 mW. [ABSTRACT FROM AUTHOR]

CMOS implementations of variable gain amplifiers (VGAs) and programmable gain amplifiers (PGAs) are reviewed in this paper. They fall into two categories: Radio Frequency VGA/PGAs and Intermediate Frequency VGA/PGAs. Most approaches to realize gain tuning create linear VGAs and consequently exponential conversion are required. The CMOS circuit realizations of exponential converters are complex and are also reviewed. In contrast, PGAs benefit from their flexible gain control mode and hence have much simpler structures. However, lower distortions and higher gain accuracy can be achieved for PGAs. Therefore, PGAs are preferred in most scenarios. This paper also presents a CMOS Gilbert VGA and a novel high linearity constant bandwidth PGA with improved common mode rejection. The DC-offset cancellation methods are reviewed as well. Finally, trends of VGAs/PGAs in modern receivers are analysed. [ABSTRACT FROM AUTHOR]

Summary: The effect of coupling on the overall sensitivity to component tolerances of two second‐order resonators is compared with the sensitivity of a non‐coupled cascade of two second‐order resonators. Coupled resonators consist of two second‐order resonators "coupled" within a negative feedback loop. The resulting overall fourth‐order transfer function of the two circuits, coupled and non‐coupled, is identical. The "cascaded" poles, ie, the poles of the two cascaded resonators, are therefore identical to the poles of the coupled circuit, the coupled poles. The poles within the negative‐feedback loop, the "open‐loop" poles, will be different. We assume that the manufacturing technology used to realize the open‐loop poles of the coupled circuit is the same as that of the cascaded, non‐coupled circuit. The open‐loop poles will therefore be subject to the same component tolerances as those of the cascaded non‐coupled circuit. Our analysis leads to the optimum location in the s‐plane with regard to minimum sensitivity, for the open‐loop poles of the coupled circuit. Since resonators are essentially the equivalent of second‐order bandpass filters, the results obtained are applied to coupled second‐order active‐RC filters, or biquads, for which insensitivity to component tolerances is critical. The examples given pertain to the coupling of biquads. [ABSTRACT FROM AUTHOR]

Circuit design techniques for enhancing an efficiency of the high power feedback-type GaN-HFET (Gallium Nitride Heterojunction Field Effect Transistor) oscillator for use in the microwave oven are shown in this paper, focusing primarily on the harmonic terminations for high efficiency of power amplifiers, the coupling factor to feedback circuits and the insertion phase adjustment of feedback loops. With the use of these circuit design techniques, an output power of 263 W and an efficiency of 61.3% have been successfully achieved at 2.44 GHz. [ABSTRACT FROM AUTHOR]

We report on the design of an active feedback circuit for charge sensitive amplifiers used for reading out hybrid pixel detectors. The predominant advantages of the proposed feedback over the existing solutions are its low noise, stability, and tunability. In addition, the circuit occupies small silicon area, which is crucial for hybrid pixel detectors. This paper presents both the mathematical analysis of the proposed circuit and measurement results obtained with the test structure. [ABSTRACT FROM AUTHOR]

Feedback control is ubiquitous in biological systems. It can also play a crucial role in the design of synthetic circuits implementing novel functions in living systems, to achieve self-regulation of gene expression, noise reduction, rise time decrease, or adaptive pathway control. Despite in vitro, in vivo, and ex vivo implementations have been successfully reported, the design of biological close-loop systems with quantitatively predictable behavior is still a major challenge. In this work, we tested a model-based bottom-up design of a synthetic close-loop controller in engineered Escherichia coli, aimed to automatically regulate the concentration of an extracellular molecule, N-(3-oxohexanoyl)-L-homoserine lactone (HSL), by rewiring the elements of heterologous quorum sensing/quenching networks. The synthetic controller was successfully constructed and experimentally validated. Relying on mathematical model and experimental characterization of individual regulatory parts and enzymes, we evaluated the predictability of the interconnected system behavior in vivo. The culture was able to reach an HSL steady-state level of 72 nM, accurately predicted by the model, and showed superior capabilities in terms of robustness against cell density variation and disturbance rejection, compared with a corresponding open-loop circuit. This engineering-inspired design approach may be adopted for the implementation of other close-loop circuits for different applications and contribute to decreasing trial-and-error steps. [ABSTRACT FROM AUTHOR]

Necessary and sufficiently conditions are derived for the decomposition of a second order linear time- varying system into two cascade connected commutative first order linear time-varying subsystems. The explicit formulas describing these subsystems are presented. It is shown that a very small class of systems satisfies the stated conditions. The results are well verified by simulations. It is also shown that its cascade synthesis is less sensitive to numerical errors than the direct simulation of the system itself.

There is increasing research interest in the development of solid-state devices to provide intelligent uniform heating, spot heating, and so on. However, the use of the solid-state devices to realize the same 1-kW output power as a conventional microwave oven requires configuration complexity that, for the moment, prevents its wider adoption. Although there is a demand for microwave generators with average output power of several tens to several hundreds of watts, existing solid-state solutions cannot produce this level of power. These problems prompted us to investigate, both by analysis and prototyping, small injection-locked oscillators that use high-efficiency microwave generators to provide several hundred watts of output power. Using an imbalanced coupling resonator in the feedback circuit, we were able to achieve an output power of 210 W and an efficiency of 51% at 2.45 GHz, when injecting a reference signal at a level of less than 1/10 000 of the output power. The high-power and high-efficiency solid-state injection-locked oscillators described in this paper have the advantages of long life, tunable frequency and phase, and low-voltage operation. These characteristics are potentially useful for realizing precise temperature control in chemical reactions, as well as spot and uniform heating by microwave ovens. [ABSTRACT FROM AUTHOR]

Circuit design techniques for enhancing an efficiency of the high power feedback-type GaN-HFET (Gallium Nitride Heterojunction Field Effect Transistor) oscillator for use in the microwave oven are shown in this paper, focusing primarily on the harmonic terminations for high efficiency of power amplifiers, the coupling factor to feedback circuits and the insertion phase adjustment of feedback loops. With the use of these circuit design techniques, an output power of 263 W and an efficiency of 61.3% have been successfully achieved at 2.44 GHz.

We demonstrate an integrated circuit (IC) implemented in 28-nm CMOS technology for Mach-Zehnder modulator (MZM) bias control. Our circuit determines the optimal MZM bias voltage that provides the largest optical modulation amplitude and maintains this bias voltage by monitoring the average modulated power. The controller IC consists of digital-to-analog converter, analog-to-digital converter, trans-impedance amplifier, power detector, track-and-hold circuit, comparator, and digital controller, all of which are integrated in a single chip. With small power consumption and chip area, our approach should be applicable for future photonic electronic integrated circuits based on the Si platform. [ABSTRACT FROM PUBLISHER]

This paper presents second order band-pass filter with high quality factor. Its high quality factor is provided by feedback circuit. The used second order filter is modified so that filters outputs through capacitor can be obtained to high impedance output. Thereby, there is no need the extra active element to obtain filter outputs. Also, the output stage of current differencing transconductance amplifier have only X− terminals instead of X+ and X− terminals. Furthermore, the quality factor of the band-pass filter with feedback circuit is increased by feedback gain consisting of only four transistors. Besides, to examine effects of parasitic elements, non-ideal and sensitivity, the overall structure is investigated deeply. Working conditions and boundaries of the overall structure is also defined. The simulation demonstrates good agreement between the theoretical expectations and simulation results. [ABSTRACT FROM AUTHOR]

In this paper, we present the design and implementation of an RF bandpass ΣΔ modulator where the loop filter is a 4th order capacitively-coupled LC filter. A design methodology using coupling capacitor and the feedback Finite Impulse Response Digital-to-Analog Converter (FIRDAC) coefficients in order to obtain the desired Noise Transfer Function (NTF) is presented. The proposed capacitively-coupled bandpass LC ΣΔ is implemented in a 130 nm CMOS process. The fabricated chip, operating under a supply voltage of 1.2 V, has a varying center frequency range of 400-442 MHz with a corresponding sampling frequency range of 533-589 MHz. A maximum Signal-to-Noise Ratio (SNR) of 50 dB in a 4.5 MHz bandwidth for a power consumption of 20 mW was achieved. The effect of the clock jitter on the Analog-to-Digital Converter (ADC) performance is measured and presented. [ABSTRACT FROM AUTHOR]

Given the performance decay of high-power light-emitting diode (LED) chips over time and package condition changes, having a reliable output light for sensitive applications is a point of concern. In this study, a light feedback control circuit, including blue-selective photodiodes, for blue/ultraviolet (UV) LED, has been designed and implemented using a low-cost seven-mask BiCMOS process. The feedback circuit was monolithically integrated in a package with four high-power blue LED chips. For sensing the intensity of exact colored blue/UV light in the package, selective photodiodes at 480-nm wavelength were implemented. An opamp-based feedback circuit combined with a high-power transistor controls the output light based on real-time sensor data. The whole system is a low-cost integrated package that guarantees a stable and reliable output light under different working conditions. Output light can be also controlled linearly by a reference input voltage. [ABSTRACT FROM PUBLISHER]

A specially developed setup for precise measurement of magnetic hysteresis and Barkhausen noise is presented in this paper. A novelty of the setup consists in a unique combination of two main features: 1) an accurate local determination of the magnetic field and 2) an improved feedback control of the magnetization process. First, the magnetic field is measured by two Hall sensors at different distances above the sample. The sample field is determined by a linear extrapolation of these measured profiles of the tangential fields to the sample surface. Second, a digital feedback loop for precise control of the ac magnetization process is proposed. The feedback algorithm combines two methods of magnetizing signal adjustment: linear corrections of the magnetizing voltage amplitude and phase. The presented system is able to adjust the waveform of the magnetic induction or field to the prescribed sinusoidal or triangular shape. This provides stable and physically accurate results, which are independent of a specific experimental configuration. [ABSTRACT FROM AUTHOR]

This paper revisits the switched flow graph (SFG) technique. A general and unified equivalent SFG model of a three-terminal switcher encountered in regular and tapped inductor converters operating in the continuous conduction mode is proposed. The model can be applied to most PWM topologies and facilitates construction of a complete flow graph of a given converter. The approach can be helpful in theoretical analysis and derivation of analytical expressions of converter's small-signal transfer functions. The suggested methodology extends the previously proposed SFG analysis technique and alleviates the principal difficulties involved. Furthermore, the approach is straightforward and expeditious. Application guidelines and examples are presented and compared to simulation and earlier theoretical results. [ABSTRACT FROM PUBLISHER]

The neurobiological learning algorithm, spike-timing-dependent plasticity (STDP), is demonstrated in a simple photonic system using the cooperative nonlinear effects of cross gain modulation and nonlinear polarization rotation, and supervised and unsupervised learning using photonic neuron principles are examined. An STDP-based supervised learning scheme is presented which is capable of mimicking a desirable spike pattern through learning and adaptation. Furthermore, unsupervised learning is illustrated by a principal component analysis system operating under similar learning rules. Finally, a photonic-distributed processing network capable of STDP-based unsupervised learning is theoretically explored. [ABSTRACT FROM PUBLISHER]

Inductive power transfer (IPT) is a commonly employed technique for wirelessly supplying power to implantable medical devices. A major limit of this approach is the sensitivity of the inductive link to coupling factor variations between transmitting and receiving coils. We propose in this paper a new method for compensating these variations and improving the inductive link efficiency. The proposed technique is based on a mechatronic module that dynamically tunes the primary resonant capacitor value in order to maintain the resonance state of the IPT system. The module is able to maintain resonance state for apparent primary inductance range at least from 0.5 to 5 \mu H using a high capacitance resolution of 0.032 pF. Experimentations conducted on a 13.56-MHz IPT system showed a $65\%$ higher power transfer compared to a traditional IPT system. [ABSTRACT FROM AUTHOR]

This paper proposes a monolithic capacitor-current-controlled hysteretic buck converter with a transient-optimized feedback circuit (TOFC) for compact-sized portable devices. The proposed TOFC simultaneously optimizes both load and dynamic voltage scaling (DVS) transient responses to minimize output voltage undershoot/overshoot and settling time. In addition, a transient-hold (TH) technique, which prevents transient response optimization from being affected by the error amplifier without increasing the compensation capacitance, is also proposed to save chip area. This work is implemented in a 0.35 µm CMOS process with a chip area of 0.88 mm 2 . Measurement results show that, for a 500 mA load transient, the output voltage settles in 0.9 µs with an undershoot/overshoot of less than 35 mV. For a 0.6-V DVS transient, output voltage settles in 3 µs with negligible undershoot/overshoot. Moreover, 96% peak efficiency is measured at 500 mW output power. [ABSTRACT FROM PUBLISHER]

This paper proposes a new concept for attaining a defined switching behavior of insulated-gate bipolar transistors (IGBTs) at inductive load (hard) switching, which is a key prerequisite for optimizing the switching behavior in terms of switching losses and electromagnetic interference (EMI). First, state-of-the art gate driver concepts that enable a control of the IGBT's switching transients are reviewed. Thereafter, a highly dynamic closed loop IGBT gate driver using simple passive diC /dt and dvCE/dt feedbacks and employing a single analog PI-controller is proposed. Contrary to conventional passive gate drivers, this concept enables an individual control of the current and voltage slopes largely independent of the specific parameters or nonlinearities of the IGBT. Accordingly, a means for optimizing the tradeoff between switching losses, switching delay times, reverse recovery current of the freewheeling diode, turn-off over voltage, and EMI is gained. The operating principle of the new gate driver is described and based on derived control oriented models of the IGBT, a stability analysis of the closed-loop control is carried out for different IGBT modules. Finally, the proposed concept is experimentally verified for different IGBT modules and compared to a conventional resistive gate driver. [ABSTRACT FROM AUTHOR]

Based on new results in circuit theory, a novel approach to feedback in linear electrical networks is proposed that generalizes the elementary one and circumvents some drawbacks and limitations that may be encountered with other general methods. It applies to all linear circuits and, differently from other approaches, does not demand two-port models or the feedback to be referred to some controlled source. Also, it evades the necessity to construct an equivalent network or to use null double injection conditions. Instead, it allows the feedback to be detected virtually in any point of the network and seems to be more effective at 'opening the loop' and agevolating an analysis by inspection on less complex subcircuits. Though simple and readily applicable, the present approach is rigorous, general and provides exact formulas for overall transfer functions and immittances as well as a general model of feedback. Moreover, it allows some of the most relevant achievements of other general approaches to be generalized and rederived as particular cases. Further results, such as a generalization of the virtual short-circuit method as well as a geometric interpretation of its limits of validity and of closed-loop −3 dB band limits, are achieved. Practical examples of application and comparison with other methods are also given. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]