Signal Transfer Function Research Articles

Classical (and quantum) heuristics for gravitational wave detection

We derive a lower bound on the sensitivity of generic mechanical and electromagnetic gravitational wave detectors. We consider both classical and quantum detection schemes, although we focus on the former. Our results allow for a simple reproduction of the sensitivities of a variety of experiments, including optical interferometers, resonant bars, optomechanical sensors, and electromagnetic conversion experiments. In the high-frequency regime, all detection schemes we consider can be characterised by their stored electromagnetic energy and the signal transfer function, which we provide. We discuss why high-frequency gravitational wave searches are especially difficult and primordial gravitational wave backgrounds might not be detectable above the sensitivity window of existing interferometers.

Impact of the fiber-optic faceplate on the imaging performance of a CMOS X-ray detector

Complementary metal-oxide-semiconductor (CMOS) active-pixel detectors are widely used in various imaging applications owing to their faster operation with lower noise and higher sensitivity than their conventional amorphous silicon-based counterparts. However, CMOS detectors are vulnerable to radiation damage owing to their crystalline structures. They also suffer from ghosting artifacts and gradual reduction of dynamic range along with their lifetime. Most CMOS detectors employ a fiber-optic faceplate (FOP) between the X-ray converter and CMOS active-pixel array to mitigate the radiation effect and increase longevity. In this study, we investigated the effect of an additional FOP layer on the imaging performance of a CMOS detector, including the modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). For X-ray energies ranging from 40 to 70 kV, we measured the large-area signal-transfer functions, MTFs, and NPSs and calculated the corresponding DQEs. The FOP degraded the MTF performance over the entire spatial frequency, but improved the NPS performance with increasing spatial frequency. Consequently, the FOP layer enhanced the DQE performance for the given energy ranges. The measured results are discussed in detail using a theoretical cascaded-systems model.

Readout circuit noise analysis and low-noise design for piezoelectric micro-machined ultrasonic transducers with large parasitic capacitance.

Readout circuits are fundamental components in many application systems that utilize piezoelectric micro-machined ultrasonic transducers (pMUTs). This study models the noise and signal transfer functions of trans-impedance amplifiers (TIAs), charge-sensitive circuits, and voltage-mode readout circuits in detail. A series of simulations and experiments were conducted to elucidate the advantages and disadvantages of these circuit types. Both theoretical and experimental results indicate that the intrinsic capacitance of large pMUTs can significantly degrade the quality of the readout signal. Furthermore, while the TIA-based readout circuit demonstrates clear gain advantages, it is also susceptible to considerable noise interference. This work proposes an improved readout circuit design that effectively mitigates noise interference while preserving the gain advantages of the TIA architecture. The implemented prototype circuit successfully reduces the noise from 73 mVp-p to 13 mVp-p.

Understanding Cerebellar Input Stage through Computational and Plasticity Rules.

A central hypothesis concerning brain functioning is that plasticity regulates the signal transfer function by modifying the efficacy of synaptic transmission. In the cerebellum, the granular layer has been shown to control the gain of signals transmitted through the mossy fiber pathway. Until now, the impact of plasticity on incoming activity patterns has been analyzed by combining electrophysiological recordings in acute cerebellar slices and computational modeling, unraveling a broad spectrum of different forms of synaptic plasticity in the granular layer, often accompanied by forms of intrinsic excitability changes. Here, we attempt to provide a brief overview of the most prominent forms of plasticity at the excitatory synapses formed by mossy fibers onto primary neuronal components (granule cells, Golgi cells and unipolar brush cells) in the granular layer. Specifically, we highlight the current understanding of the mechanisms and their functional implications for synaptic and intrinsic plasticity, providing valuable insights into how inputs are processed and reconfigured at the cerebellar input stage.

A Novel Approach for Realizing Loop-Filter in Low-Distortion Noise-Coupled ΣΔ Modulators

This paper presents an innovative general structure for a single-loop Sigma-Delta ([Formula: see text]) modulator that combines low-distortion and noise-coupled techniques to achieve high-resolution for low-power applications. The low-distortion technique adjusts the signal transfer function of the proposed structure to unity, while the noise-coupled technique enhances the order of quantization noise-shaping at the modulator output. These techniques were incorporated into the design to increase the modulator order without requiring additional operational amplifiers during its circuit implementation, resulting in a low-power modulator compared to similar structures. To reduce the number of required amplifiers, a second-order infinite impulse response (IIR) filter was used in the modulator loop filter, in place of two integrators. To assess the proposed structure’s performance, a third-order modulator sample was implemented and simulated for speech recognition applications, specifically, digital hearing aids, using 180[Formula: see text]nm complementary metal oxide semiconductor (CMOS) technology. The results indicate that for a third structure with a sampling rate of 64, an input sine signal of −6[Formula: see text]dBFS and a sampling frequency of 2.56[Formula: see text]MHz, the signal to noise plus distortion (SNDR) was 81.9[Formula: see text]dB, and the dynamic range (DR) was 88[Formula: see text]dB for a 20[Formula: see text]KHz bandwidth. The modulator’s power consumption was 126.9[Formula: see text][Formula: see text]W. Circuit and system-level simulations demonstrate the effectiveness of the proposed method.

An 8-Channel Ambulatory EEG Recording IC With In-Channel Fully-Analog Real-Time Motion Artifact Extraction and Removal.

Wereport the design, implementation, and experimental characterization of an 8-channel EEG recording IC (0.13 μm CMOS, 12 mm 2 total area) with a channel architecture that conducts both the extraction and removal of motion artifacts on-chip and in-channel. The proposed dual-path feed-forward method for artifact extraction and removal is implemented in the analog domain, hence is needless of a DSP unit for artifact estimation, and its associated high-DR ADCs and DACs employed by the state of the art for artifact replica generation. Additionally, the presented architecture improves system's scalability as it enables channels' stand-alone operation, and yields the lowest reported channel power consumption among works featuring motion artifact detection/removal. Following an experimental study on electrode-skin interface electrical characteristics for dry electrodes in the absence and presence of motions, the article presents the channel architecture, its detailed signal transfer function analysis, circuit-level implementation, and experimental characterization results. Our measurement results show an amplification voltage gain of 48.3 dB, a bandwidth of 300 Hz, rail-to-rail input DC offset tolerance, and 41.5 dB artifact suppression, while consuming 55 μW per channel. The system's efficacy in EEG motion artifact suppression is validated experimentally, and system- and circuit-level features and performance metrics of the presented design are compared with the state of the art.

A 143 dB Delta-Sigma Modulator for Biomedical Applications

This paper presents a single loop forth-order delta-sigma modulator topology of cascade of integrator with multiple feedback This paper presents a single loop forth-order delta-sigma modulator topology of cascade of integrator with multiple feedback (CIFB) . The number of levels in the quantizer increases for higher performance. The modulator noice transfer function (NTF) and signal transfer function (STF) exploited for higher performance. The out-of-band gain (OBG) of 1.5 selected considering the stability of higher order modulator. The high oversampling ratio (OSR) considered for small bandwidth applications. The maximum quantization noise is suppressed by NTF zeros optimization. A full-scale signal of the modulator is 0.55-V considering the higher order loop filter stability. Due to CIFB topology, there is no peaking in the STF while STF response is flat. The zeros of the NTF are optimized for maximum quantization noise and poles are placed inside the unit circle. The complete modulator loop filter has four integrators in the loop filter with multiple feedback digital-to-analog converter (DAC) for maximum stability. The complete modulator simulation shows it an achieve signal-to-noise (SNR) of 1.43 dB with oversampling ratio (OSR) of 128.

A 77.3-dB SNDR 62.5-kHz Bandwidth Continuous-Time Noise-Shaping SAR ADC With Duty-Cycled Gm-C Integrator

This article presents a first-order continuous-time (CT) noise-shaping successive-approximation-register (NS-SAR) analog-to-digital converter (ADC). Different from other NS-SAR ADCs in literature, which are discrete-time (DT), this ADC utilizes a CT Gm-C integrator to realize an inherent anti-aliasing function. To cope with the timing conflict between the DT SAR ADC and the CT integrator, the sampling switch of the SAR ADC is removed, and the integrator is duty cycled to leave 5% of the sampling clock period for the SAR conversion. Redundancy is added to track the varying ADC input due to the absence of the sampling switch. A theoretical analysis shows that the 5% duty-cycling has negligible effects on the signal transfer function (STF) and the noise transfer function. The output swing and linearity requirements for the integrator are also relaxed thanks to the inherent feedforward path in the NS-SAR ADC architecture. Fabricated in 65-nm CMOS, the prototype achieves 77.3-dB peak signal-to-noise and distortion ratio (SNDR) in a 62.5-kHz bandwidth while consuming <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13.5~\mu \text{W}$ </tex-math></inline-formula> , leading to a Schreier figure of merit (FoM) of 174.0 dB. Moreover, it provides 15-dB attenuation in the alias band.

A Generalized Passivity-Based Stability Criterion for Assessing Large Signal Stability of Interconnected DC Power Systems

With the growing need to support large dynamic electric loads in microgrid environments, there has been a necessary push toward highly regulated dc distribution through power electronics. Unfortunately, these systems are nonlinear by nature and provide potentially destabilizing behavior at their source interfaces. To complicate matters further, many systems are built from independently designed subcomponents with little information shared between designs. It is, therefore, necessary to have stability-driven design requirements for each subsystem to enforce stable dynamics upon system integration. Traditional techniques are currently limited to either overly conservative large signal small-gain methods or small signal transfer function approaches that are unreliable for assuring large signal stability. This article proposes a generalized passivity-based stability criterion that conservatively estimates the domain of stability for an integrated nonlinear system. Through passivity partitioning and uniquely driven domain of passivity estimation techniques, this methodology provides interface conditions that certify stability while only requiring a reduced subset of knowledge of each connected subsystem <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</b>

Intensity noise transfer properties of a Yb-doped single-frequency fiber amplifier.

In this work, the intensity noise transfer properties of a two-stage single-frequency fiber amplifier at 1µm are systematically investigated in the frequency domain. By applying an artificial modulation signal to the driving current of the first- and second-stage pump sources, the pump and signal transfer functions of the second-stage amplifier are experimentally measured from 10Hz to 100kHz. By associating the theoretical model, the effects of pump power, the operating wavelength, and the absorption coefficient of the gain fiber on the pump and signal transfer properties are analyzed based on the experimental measurements. It turns out that the gain dynamics of the last-stage amplifier play an important role in determining the noise performances of the final amplified laser. Because the pump and signal transfer functions essentially behave as a low pass and damped high pass filter, the pump intensity noise of the last-stage amplifier dominates the amplifier system's overall noise performance. In addition, the effects of amplified spontaneous emission (ASE) on the intensity noise transfer properties are nontrivial, although it is not included in the theoretical model. It is believed that the current work provides a useful guideline for optimizing the design of high-power single-frequency fiber amplifiers with low-intensity noise.

A 10-MHz 85.1-dB SFDR 1.1-mW continuous-time Delta–sigma modulator employing calibration-free SC DAC and passive front-end low-pass filter

A 10-MHz 85.1-dB SFDR 1.1-mW continuous-time Delta–sigma modulator employing calibration-free SC DAC and passive front-end low-pass filter

Simplified Simulation and Measurement of the Signal Transfer Function of a Continuous-Time Pipelined Analog-to-Digital Converter

The continuous-time pipeline (CTP) analog-to-digital converter is a power- and area-efficient realization of an anti-alias filter + ADC cascade. The signal transfer function (STF), which is the transfer function of the anti-alias filter, is an important property of the CTP ADC. It is conventionally characterized by exciting the ADC with multiple input sinusoids. We demonstrate that a single-tone excitation is enough to determine the STF of the CTP ADC over its useful frequency range. The theory is supported by measurement results from a three-stage CTP ADC designed in a 65 nm CMOS process. The converter, equivalent to a sixth-order anti-alias filter + ADC, achieves 70 dB SNDR in a 100MHz bandwidth while sampling at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{s}= 800$ </tex-math></inline-formula> MHz.

Time-domain Continuous-time Delta-sigma Modulator using VCO-based Integrator and GRO-based Quantizer

This paper presents a 3SUPrd/SUP-order time-domain continuous-time delta-sigma modulator (CTDSM) using two voltage-controlled oscillator (VCO)-based integrators and a gated ring oscillator (GRO)-based quantizer. The GRO-based quantizer has 1SUPst/SUP-order noise-shaping characteristics without the increase of the signal transfer function (STF) order and has magnificent linearity. Also, the output of the GRO-based quantizer has an intrinsic data weighted averaging (DWA)-based dynamic element matching (DEM) pattern that is less susceptible to the DAC mismatch. The PWM signal, which is the input of the GRO-based quantizer, is generated by the VCO-based integrator without additional blocks. In the pre-layout simulation, the CTDSM consumes 3.84 mW and achieves an SNDR of 71.2 dB at a 400-MSs sampling frequency and a 10-MHz bandwidth.

Optimal design of both multi‐input multi‐output loop filter and multi‐input single‐output reconstruction filter of sigma delta modulator

This paper considers a sigma delta modulator (SDM) with the outputs of the quantizers directly fedback to the inputs of the loop filter without being subtracted from the input sequence. The design of the multi-input multi-output (MIMO) loop filter is formulated as an optimization problem. In particular, the sum of the inner products between the elements in the signal transfer function (STF) and the corresponding elements in the noise transfer function (NTF) of the SDM is minimized. The constraints of the optimization problem are defined based on the specifications on the maximum absolute difference between the magnitude response of the designed STF and that of the desirable STF as well as that between the magnitude response of the designed NTF and that of the desirable NTF of the SDM. Similarly, the design of the multi-input single-output (MISO) reconstruction filter is also formulated as an optimization problem. In particular, the sum of the total absolute difference between the designed magnitude response of the reconstruction filter and the desirable magnitude response of the STF of the SDM is minimized. The constraint of the problem is defined based on the specification on maximum absolute difference between the designed magnitude response of the reconstruction filter and the desirable magnitude response of the STF of the SDM. In this paper, the genetic algorithm is employed to find a near global solution of the formulated optimization problems. In order to reduce the required computational power, the matrix inversion lemma is applied. The computer numerical simulation results show that the SDM designed by our proposed method outperforms the SDMs designed by the Matlab function in terms of the signal to noise ratio (SNR) performance.

Signal processing and noise analysis on realistic radiation detector model

In this paper, equations for signal processing and noise analysis were derived for a realistic radiation detector model, and simulations were performed under various conditions. Realistic radiation detector model was composed of silicon PIN diode detector, Charge Sensitive Amplifier (CSA), and CR-RC2 shaper. For the realistic CSA model, a finite bandwidth model with a single pole response amplifier was presented and related equations were derived. Through realistic CSA model, it was possible to calculate the signal distortion phenomena such as charge transfer loss and ballistic deficit of the actual circuit and the noise value of the CSA output stage. For the realistic shaper model, signal and noise transfer functions were derived for the CR-RC2 circuit with non-inverting amplifier. In particular, the equation for the internal noise of the shaper, which has been ignored in the current noise analysis, was derived. Through this, it was possible to analyze the effects of amplifier characteristics, resistance value, and signal gain for each stage on the overall noise in the radiation detector of the CSA–shaper structure. For comparison with the simulation, a circuit equivalent to the realistic radiation detector model was made and measurements under the same conditions as the simulation were made. As a result of the verification experiment, the measured values matched well with simulations under various conditions, and through this, the validity of this model was verified. Signal processing and noise analysis were mainly performed for PCB circuits using commercial components, but also included content for CMOS front-end detectors. This model consists only of analytic formulas for the time domain function and the transfer function, nonetheless it has been shown to give accurate results.

Study of Capacitive Coupling Sensor Fused With High Voltage XLPE Cable Joint

A capacitive coupling sensor for partial discharge detection with the fusion of high voltage XLPE cable joint is designed in this paper. The sensor is to address partial discharge signals leading to transmission attenuation and external interference causing poor field detection sensitivity. First, a coaxial waveguide transmission model was established of high-frequency electrical signals in the body and joint. The result showed that the signal transmission attenuation was minimized while the sensor electrodes were closely attached to the outer semi-conductive layer of the body. Second, the equivalent circuit model was constructed of the capacitive coupling sensor fused with the 110 kV straight passing joint. The specific installation location, main structure size, detection bandwidth, and sensitivity of the sensor in the joint area were determined, which was to maximize the coupling output signal amplitude and transfer function amplitude. Finally, a lightning surge voltage test was carried out with the integration of the fusion of the joint voltage thermal cycling. Simulation and measurement show the following: while the sensor is installed in the cable metal sleeve break and the electrodes are closed to the overall semi-conductive layer, there is excellent performance for partial discharge detection in the frequency range of 1–300 MHz, with a sensitivity of 5 pC.

A 0.8 V Multimode Vision Sensor for Motion and Saliency Detection With Ping-Pong PWM Pixel

This article presents a low-power, high-speed smart vision sensor for motion detection (MD) that realizes in-pixel frame-difference (FD) operation using a global shutter mechanism. A ping-pong pulse-width-modulation (PWM) pixel is proposed to achieve the consecutive event frame report with a balanced signal transfer function of successive FD operations. Three operating modes were implemented for varied application scenarios, such as image capture (IC) mode to capture a raw image, FD mode for MD, and saliency detection (SD) mode for low-resolution sub-block event counting. A 0.8 V 64 × 64 vision sensor prototype was fabricated and verified in TSMC 0.18-μm standard CMOS technology. In IC mode, it consumed 71.2 μW@360fps with an achieved iFoM of 48.3 pJ/pixel·frame. In FD mode, it consumed 74.4 μW@510fps with full-resolution (64 × 64) event reporting and achieved iFoMs of 35.6 pJ/pixel·frame. In SD mode, it consumed 121.6 μW@890fps with block-level (8 × 8) saliency reporting and achieved iFoMs of 2.1 nJ/block·frame.

An experimental study on the evaluation of temperature uniformity on the surface of a blackbody using infrared cameras

ABSTRACT Blackbody radiation is standardised electromagnetic energy emitted into space at a given temperature and wavelength distribution. It is used as a reference model to compare radiation emitted from various objects. This reference performance of blackbody systems should be maintained through periodic inspection and calibration. In this study, temperature uniformity on the surface of the blackbody was evaluated using infrared cameras. To this end, we divided the blackbody system measurements into ‘before’ and ‘after’ calibration sets and examined the blackbody surface in different bands, using two infrared cameras with different measurement principles. To evaluate surface temperature uniformity, we calculated the signal transfer function, equivalent noise temperature difference, and 3D noise of the infrared detector, and then comparatively analysed them.

Design, Fabrication, and Performance Evaluation of Portable and Large-Area Blackbody System.

In this study, a portable and large-area blackbody system was developed following a series of processes including design, computational analysis, fabrication, and experimental analysis and evaluation. The blackbody system was designed to be lightweight (5 kg), and its temperature could exceed the ambient temperature by up to 15 °C under operation. A carbon-fiber-based heat source was used to achieve a uniform temperature distribution. A heat shield fabricated from an insulation material was embedded at the opposite side of the heating element to minimize heat loss. A prototype of the blackbody system was fabricated based on the design and transient coupled electro-thermal simulation results. The operation performance of this system, such as the thermal response, signal transfer function, and noise equivalent temperature difference, was evaluated by employing an infrared imaging system. In addition, emissivity was measured during operation. The results of this study show that the developed portable and large-area blackbody system can be expected to serve as a reliable reference source for the calibration of aerial infrared images for the application of aerial infrared techniques to remote sensing.

Improved Continuous-Time Delta-Sigma Modulators With Embedded Active Filtering

Continuous-time ΔΣ modulators used in wireless transceivers need to digitize small desired signals that are accompanied by large out-of-band interferers. In such applications, it is desirable that the CTΔΣM have a low-pass signal transfer function whose bandwidth can be specified. Many architectures present themselves as potential candidates to realize such filtering-CTΔΣMs. This work investigates these threads and concludes that a CTΔΣM with an embedded Rauch filter is a compelling design choice. The theory is supported by measurement results from a filtering-CTΔΣM test chip that achieves a peak SNDR of 76.7dB in a 1MHz signal bandwidth. Measurements demonstrate improved power efficiency and out-of-band linearity when compared to prior art.