Chopping Frequency Research Articles

Demonstration of normally OFF beta-gallium oxide monolithic bidirectional switch for AC switching applications

In this work, we report on the beta-gallium oxide (β-Ga2O3) monolithic bidirectional switch. The as-fabricated switch works on enhancement mode operation with a threshold voltage of ∼4 V. Maximum drain current density of 1.93 mA/mm is obtained with a drain voltage of 5 V. The bidirectional switch in a bidirectional mode has an ON/OFF current ratio of ∼107 with ON-resistance of 1.11 and 1.09 kΩ · mm in forward and reverse direction, respectively. However, in diode mode, the device shows an ON/OFF current ratio of 1.6 × 108 and 1.4 × 108 in forward and reverse conduction modes, respectively. The fabricated β-Ga2O3 monolithic bidirectional switch is then used to chop a 60 Hz Alternating Current signal at a chopping frequency of 1 kHz, indicating its potential applications in a range of converters.

Single pulse data collection with an X-ray chopper at in situ room temperature Laue crystallography beamline BL03HB

in situ room temperature Laue crystallography has gained increasing attention. This method is suitable for time-resolved Laue crystallography experiments to get crystal structure with only several single-frame data collections. To improve the diffraction efficiency of protein crystals at room temperature, a simple X-ray chopper combined with a fast shutter has been successfully developed and tested at in situ room temperature Laue crystallography beamline BL03HB of the Shanghai Synchrotron Radiation Facility (SSRF). This chopper is built with two aluminum blades. There are two windows on both blades, as well as an internal lead block. The width of windows for transmission of beam can be flexibly adjusted by a steel block coated with lead. The chopping frequency is controlled independently. The device allows chopping frequencies ranging from 0 to 10 Hz, and exposure times down to 100 μs can be obtained for our Laue diffraction experiment with the combination of a fast shutter. Moreover, a single pulse data collection strategy has been developed at BL03HB. The performance of our single pulse data collection method with the designed chopper for the improvement of data quality has been analyzed. Results show that the quality of diffraction data obtained from the single pulse data collection method is significantly improved, and the developed chopper is very suitable for room temperature Laue crystallography experiments at the synchrotron beamline with super bending magnet as light source.

Portable Photoacoustic Analytical System Combined with Wearable Hydrogel Patch for pH Monitoring in Chronic Wounds.

Timely diagnosis, monitoring, and management of chronic wounds play crucial roles in improving patients' quality of life, but clinical evaluation of chronic wounds is still ambiguous and relies heavily on the experience of clinician, resulting in increased social and financial burden and delay of optimal treatment. During the different stages of the healing process, specific and dynamic changes of pH values in the wound exudate can be used as biomarkers to reflect the wound status. Herein, a pH-responsive agent with well-behaved photoacoustic (PA) properties, nitrazine yellow (NY), was incorporated in poly(vinyl alcohol)/sucrose (PVA/Suc) hydrogel to construct a wearable pH-sensing patch (PVA/Suc/NY hydrogel) for monitoring of pH values during chronic wound healing. According to Rosencwaig-Gersho theory and the combination of 3D printing technology, the PA chamber volume and chopping frequency were systematically optimized to improve the sensitivity of the PA analytical system. The prepared PVA/Suc/NY hydrogel patch had excellent mechanical properties and flexibility and could maintain conformal contact with skin. Moreover, combined with the miniaturized PA analytical device, it had the potential to detect pH values (5.0-9.0) free from the color interference of blood and therapeutic drugs, which provides a valuable strategy for wound pH value monitoring by PA quantitation. This strategy of combining the wearable hydrogel patch with portable PA analysis offers broad new prospects for the treatment and management of chronic wounds due to its features of simple operation, time savings, and anti-interference.

Split ring hole metamaterial-enhanced pyroelectric detector for efficient multi-narrowband terahertz detection

Derived from infrared pyroelectric detection, typical terahertz (THz) pyroelectric detectors have low sensitivity at low-frequency THz bands. Based on the high-efficiency absorption of the metamaterial perfect absorber (MPA), a novel split ring hole metamaterial-enhanced pyroelectric detector is proposed to achieve efficient multi-narrowband THz detection. Using high frequency simulation software (HFSS), the dimensional parameters including ring radius, ring width, connection beam width, array period, and thickness, are optimized to enhance efficient multi-narrowband absorption. The as-optimized metamaterial-enhanced detectors are fabricated via micro-nano manufacturing technology. The voltage responsiveness and noise equivalent power of the metamaterial-enhanced detector are tested by THz focused optical path and compared with those of the typical pyroelectric detector and the simulated MPA absorptivity. The results indicate that the metamaterial-enhanced detector has a multi-narrowband detection capability at 0.245 THz, 0.295 THz, and 0.38 THz, which is close to the simulated MPA absorptivity. Compared to the typical pyroelectric detector, the split ring hole metamaterial-enhanced detector can simultaneously achieve thermal absorption, thermal conduction, and pyroelectricity in the same MPA structure, providing faster response speed above 100 Hz chopper frequency and two times higher detection sensitivity at multi-narrowband THz frequencies. This research can be used for THz sensing, absorption filtering, biological macromolecule detection, and other applications.

Extended X-ray absorption fine structure (EXAFS) measurement of Cu metal foil using thermal wave detector: A comparative study

In this study, we compared two methods for measuring EXAFS spectra, which provide insights into material local structures. The conventional transmission mode used a synchrotron beam as a source and ionization chambers as detectors. Alternatively, we employed thermal wave detectors, specifically a pyroelectric crystal, for a simpler approach. The experiment was conducted using a LiNbO3 crystal at a synchrotron facility operating in the hard X-ray energy range. The chopping frequency of the X-ray beam was set at 1.8 Hz to optimize data collection. We discussed the challenges of selecting the appropriate chopping frequency for EXAFS measurements and the importance of detector sensitivity. We shared results from experiments at various chopping frequencies, highlighting the suitability of pyroelectric detectors. The study demonstrated the feasibility of using pyroelectric detectors for EXAFS measurements, providing valuable data with minimal artifact effects. The findings contribute to the understanding of material local structures and open possibilities for further exploration of thermal wave detectors in continuous theta scan applications.

Design of a 0.5 V Chopper-Stabilized Differential Difference Amplifier for Analog Signal Processing Applications.

This paper presents a low-voltage low-power chopper-stabilized differential difference amplifier (DDA) realized using 40 nm CMOS technology. Operating with a supply voltage of 0.5 V, a three-stage DDA has been employed to achieve an open-loop gain of 89 dB, while consuming just 0.74 μW of power. The proposed DDA incorporates feed-forward frequency compensation and a Type II compensator to achieve pole-zero cancellation and damping factor control. The DDA has a unity-gain bandwidth (UGB) of 170 kHz, a phase margin (PM) of 63.98°, and a common-mode rejection ratio (CMRR) of up to 100 dB. This circuit can effectively drive a 50 pF capacitor in parallel with a 300 kΩ resistor. The use of the chopper stabilization technique effectively mitigates the offset and 1/f noise. The chopping frequency of the chopper modulator is 5 kHz. The input noise is 245 nV/sqrt (Hz) at 1 kHz, and the input-referred offset under Monte Carlo cases is only 0.26 mV. Such a low-voltage chopper-stabilized DDA will be very useful for analog signal processing applications. Compared to the reported chopper DDA counterparts, the proposed DDA is regarded as that with one of the lowest supply voltages. The proposed DDA has demonstrated its effectiveness in tradeoff design when dealing with multiple parameters pertaining to power consumption, noise, and bandwidth.

A 4.21-μV Offset Voltage and 42-nV/√Hz Input Noise Chopper Operational Amplifier with Dynamic Element Matching

This paper presents a high-efficiency operational amplifier (op-amp) used in the readout circuit of micro-sensor. The chopping and dynamic element matching (DEM) techniques are used in the proposed design, which greatly reduce the offset voltage and flicker noise [Formula: see text] noise) of the op-amp. By optimizing the circuit structure, the maximum chopping frequency is increased to 2[Formula: see text]MHz when the offset voltage is less than [Formula: see text][Formula: see text]V. Therefore, the maximum bandwidth of signal processing can be up to 1MHz. The proposed circuit is designed and fabricated using TSMC 0.18-[Formula: see text]m 1P5M CMOS technology. It occupies an area of 0.16[Formula: see text]mm2 and consumes [Formula: see text]A from a 1.8-V supply. When the chopping frequency is 100[Formula: see text]kHz, the input-referred offset voltage is 4.21[Formula: see text][Formula: see text]V and the input-referred noise is 42[Formula: see text]nV[Formula: see text]Hz. It achieves a noise efficiency factor of 7.82 and a power efficiency factor of 110.07.

Disentangling the Role of the SnO Layer on the Pyro-Phototronic Effect in ZnO-Based Self-Powered Photodetectors.

Self-powered photodetectors (PDs) have been recognized as one of the developing trends of next-generation optoelectronic devices. Herein, it is shown that by introducing a thin layer of SnO film between the Si substrate and the ZnO film, the self-powered photodetector Al/Si/SnO/ZnO/ITO exhibits a stable and uniform violet sensing ability with high photoresponsivity and fast response. The SnO layer introduces a built-in electrostatic field to highly enhance the photocurrent by over 1000%. By analyzing energy diagrams of the p-n junction, the underlying physical mechanism of the self-powered violet PDs is carefully illustrated. A high photo-responsivity (R) of 93mA W-1 accompanied by a detectivity (D*) of 3.1 × 1010 Jones are observed under self-driven conditions, when the device is exposed to 405nm excitation laser wavelength, with a laser power density of 36mW cm-2 and at a chopper frequency of 400Hz. The Si/SnO/ZnO/ITO device shows an enhancement of 3067% in responsivity when compared to the Al/Si/ZnO/ITO. The photodetector holds an ultra-fast response of ≈ 2 µs, which is among the best self-powered photodetectors reported in the literature based on ZnO.

Eff ect of Different Laser Irradiation Parameters on the Viability of Bacillus Species

The genus Bacillus is present everywhere in the environment, it has environmental, industrial, and medical signifi cance. This heterogeneous group of bacteria shares unique characteristics, one of these is the resistance to physical and chemical agents. Laser light is one of the most interesting physical agents with a wide range of applications in all scientifi c fi elds. It has the ability to alter bacterial growth by triggering inhibitory or stimulatory mechanisms. In this study, laser parameters were varied to evaluate the eff ect of each one on the viability of Bacillus species. CW or chopped (532 nm) laser light at diff erent irradiation periods were examined. Results showed that tested bacterial species’ response to green laser light varied. Bacterial viability was dropped with increasing chopping frequency and exposure time. In conclusion, high repetition rate and prolonged exposure time increase the lethal eff ects of this type of laser

Pyro-Phototronic Effect Enhanced Pyramid Structured p-Si/n-ZnO Nanowires Heterojunction Photodetector.

The emergence of nanomaterials has brought about the development of miniature photodetectors into a new stage, and ZnO nanomaterials are currently one of the most popular research objects. Here, the performance of a photodetector consisting of micropyramid structured p-Si/n-ZnO NWs heterojunction constructed by an anisotropic chemical etching and hydrothermal method is optimized by using the pyro-phototronic effect, and the photoresponses of the device to 405 and 648 nm lasers are investigated. The results show that, with the introduction of pyro-phototronic effect, the photoresponsivity Rpyro increases to 208 times that of Rphoto when the wavelength is 405 nm and the optical power density is 0.0693 mW/cm2. Moreover, with the increase of the chopper frequency, the photocurrent increases by more than 3 times, and the photoresponsivity is also increased by a factor of 4.5, making it possible to detect ultrafast pulsed light. In addition, in order to increase the current collection efficiency, a thin film Al layer was deposited as the back electrode on the basis of the device, and the photocurrent and photoresponsivity are significantly improved. Finally, the coupling between the pyro-phototronic effect and the piezo-phototronic effect is analyzed by applying compressive strain to the photodetector. When the compressive strain is -1.02%, the photocurrent decreases by 31.4% and the photoresponsivity decreases by 27.9% due to the opposite direction between laser illumination induced pyroelectric polarization charges and compressive strain induced piezoelectric polarization charges. This work not only demonstrates the great potential of pyro-phototronic effect in enhancing the silicon-based heterojunction photodetectors for high-performance photodetection and ultrafast pulsed light detection but also provides assistance for a better understanding of the coupling mechanism between pyro-phototronic and piezo-phototronic effects.

Large ferro–pyro–phototronic effect in 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 thin films integrated on silicon for photodetection

AbstractCoupling together the ferroelectric, pyroelectric, and photovoltaic characteristics within a single material is a novel way to improve the performance of photodetectors. In this work, we take advantage of the triple multifunctionality shown by 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCZT), as demonstrated in an Al/Si/SiOx/BCZT/ITO thin‐film device. The Si/SiOx acts as an n‐type layer to form a metal–ferroelectric–insulator–semiconductor heterostructure with the BCZT, and with Al and ITO as electrodes. The photo‐response of the device, with excitation from a violet laser (405 nm wavelength), is carefully investigated, and it is shown that the photodetector performance is invariant with the chopper frequency owing to the pyro‐phototronic effect, which corresponds to the coupling together of the pyroelectric and photovoltaic responses. However, the photodetector performance was significantly better than that of the devices operating based only on the pyro‐phototronic effect by a factor of 4, due to the presence of ferroelectricity in the system. Thus, after a poling voltage of −15 V, for a laser power density of 230 mW/cm2 and at a chopper frequency of 400 Hz, optimized responsivity, detectivity, and sensitivity values of 13.1 mA/W, 1.7 × 1010 Jones, and 26.9, respectively, are achieved. Furthermore, ultrafast rise and fall times of 2.4 and 1.5 µs, respectively, are obtained, which are 35,000 and 36,000 times faster rise and fall responses, respectively, than previous reports of devices with the ferro–pyro–phototronic effect. This is understood based on the much faster ferroelectric switching in ferroelectric thin films owing to the predominant 180° domains in a single direction out of plane.

Limitations on chopping frequency for photoreflectance spectroscopy of p-n GaAs junctions

Limitations on chopping frequency for photoreflectance spectroscopy of p-n GaAs junctions

Chopping for over 50 MHz gain‐bandwidth product current sense amplifiers achieving input noise level of 8.5 nV/√Hz

An accurate, high-speed, fully differential difference amplifier for current sensing utilizing the chopper approach was implemented in a 0.18 μm complementary metal-oxide-semiconductor (CMOS) technology. Unlike state-of-the-art solutions, we use a higher chopping frequency in the MHz range due to the bandwidth requirements of the introduced circuits for the latter application, namely, low-side phase-current measurement in motor control circuits. Except the low-pass filter (LPF) effect of the output stage, no additional LPF was integrated in hardware at the output of the circuits. We show that on the other hand a digital LPF, which can be integrated in the field-programmable gate-array (FPGA) logic or microcontroller used for the motor control, offers a higher flexibility in terms of filter design. Weak input signals of only few mV can be reconstructed with a high accuracy. This is demonstrated for a 500 kHz rectangular signal and a chopping frequency of 20 MHz. Note that an input-signal frequency of several hundreds of kHz with harmonics in the MHz region is very challenging for chopper amplifiers. Still, a significant decrease of the input-referred noise is demonstrated, especially cancelling out the 1/f-noise achieving a remaining noise floor of approximately 8.5 nV/√Hz. Overall, the input-referred noise level can be pushed far below 50 μV (root mean square). Moreover, using a quite relaxed second-order Butterworth filter with a 3 dB corner frequency of 1 MHz, input-referred noise levels of 10 μV (root mean square) can be easily achieved at the costs of reduced bandwidth. The lowest achieved input offset is 50 μV. The gain is adjusted by resistive feedback and is approximately 40 dB. Hence, the amplifier is suitable for current sensing in motor control circuits, and a significant reduction of the shunt resistance typically used for this purpose will be possible.

Rapidly frequency-tuneable, in-vacuum, and magnetic levitation chopper for fast modulation of infrared light.

We present an in-vacuum mechanical chopper running at high speed and integrated into a magnetic levitating motor for modulating optical beams up to 200kHz. The compact chopper rotor allows fast acceleration (10kHzs-1 as standard) for rapid tuning of the modulation frequency, while 1mm diameter slots provide high optical throughput for larger infrared beams. The modulation performances are assessed using a reference visible laser and the high brightness, broadband, infrared (IR) beam of synchrotron radiation at the MIRIAM beamline B22 at Diamond Light Source, UK. For our application of IR nanospectroscopy, minimizing the temporal jitter on the modulated beam due to chopper manufacturing and control tolerances is essential to limit the noise level in measurements via lock-in detection, while high modulation frequencies are needed to achieve high spatial resolution in photothermal nanospectroscopy. When reaching the maximum chopping frequency of 200kHz, the jitter was found to be 0.9% peak-to-peak. The described chopper now replaces the standard ball-bearing chopper in our synchrotron-based FTIR photothermal nanospectroscopy system, and we demonstrate improved spectroscopy results on a 200nm thickness polymer film.

Thermal Diffusivity Measurement of MoS2 & MoS2-GO Nano-Composite By Photoacoustic Spectroscopy

Photoacoustic spectrometer (PAS) is a significant technique to measure the thermal diffusivity of any material. When modulated light interact with solid sample which is covered by aluminium or other metal plate, first the light is absorbed by the sample and then thermal energy emitted due to non-radiative decay. Thereafter, acoustic wave produced due to different temperature which maintain by an optical chopper. The medium inside the cavity expands or retract according to the chopper frequency. So, the generated pressure fluctuation inside it measures by using a sensitive condenser microphone which fitted inside the cavity by a narrow path. Here the authors successfully synthesized molybdenum disulfide (MoS2) and its nanocomposite with graphene oxide (MoS2-GO) by simple hydrothermal method. The XRD and FESEM data confirm the phase and morphological structures of the synthesized material. The thermal diffusivity of MoS2 and MoS2-GO nanocomposite are obtained 10.94 mm2/s and 14.72 mm2/s respectively.

Plasma edge density fluctuation measurements via lithium beam emission spectroscopy on EAST

Accurate and stable measurements of edge density fluctuation with high spatio-temporal resolution have been achieved by the lithium beam emission spectroscopy (Li-BES) diagnostic on experimental and advanced superconducting tokamak (EAST). The new narrower band interference filter exhibits good ability to suppress background emission signal even under strong lithium coating of the tokamak. The raw data measured by channels at different spatial locations in avalanche photo diode camera with high chopping frequency show good consistency. Based on the detected experimental data, detailed information of density profile and fluctuation structures is obtained. A clear edge coherent mode in the auto-power spectrum is observed in pedestal region, which is regarded as the dominant factor for the strong pedestal density fluctuation amplitude. The cross-power spectrum analysis further excludes the additional effects of common-mode noises and non-local perturbation, demonstrating that the detected fluctuation is only caused by local density fluctuation. The normalized radial and poloidal wave-number spectra can specify the quantitative changes of radial wavenumber (k r) and poloidal wavenumber (k θ) during the pedestal density fluctuation phase. This new Li-BES system, which can provide more accurate experimental data, allows further studies of edge density fluctuation and complex transport process on EAST.

Low-power CW laser-assisted synthesis of plasmonic aluminium nanoparticles using low duty cycle optical chopper

This paper reports continuous wave (CW) laser-assisted synthesis of plasmonic aluminium nanoparticles (ANPs) by drastically reducing the laser power density from the existing 105 W/cm2to 9 W/cm2using a specially designed ultralow duty cycle chopper. The aluminium target is subjected to laser irradiation by keeping it in a liquid medium maintained at a specific temperature. The effect of chopping frequencies (F), temperatures (T), and surfactant-glucose (C) on the formation of ANPs are investigated through field emission scanning electron microscopic and UV-visible spectroscopic analyses. The energy required for the ejection of ANPs from the target is obtained from the optical source, thermal source, and the molecular collision due to convection current. The purity of the nanoparticle is determined from energy dispersive spectroscopic analysis. The analysis reveals that ANPs of sizes in the range 20–50 nm are formed when F = 30 Hz, T = 60 °C, and C = 18 mg/cc, exhibiting excellent ageing stability. The photoluminescence spectrum, power spectrum, and CIE analyses for the excitations at 350 nm and 390 nm indicate the emission to be blue, suggesting that it is a suitable fluorescence material for UV-plasmonics.

Analysis of Output Ripple Shape and Amplitude in Chopper Instrumentation Amplifier

In this brief, we analyzed the output ripple in a capacitively-coupled chopper-based instrumentation amplifier (CCIA). Our analysis found that the shape and amplitude of the output ripple of the CCIA are determined by five design parameters, namely amplifier offset, transconductance, chopping frequency, Miller compensation capacitance, and the nulling resistor. With different design specifications, the CCIA ripple appears in four different shapes, including triangular ripple, RC-settling ripple, square ripple, and step-change ripple. These findings are verified by the silicon results. As the cause of each ripple shape varies, this analysis serves as a guideline for designing practical chopper-based amplifiers and their corresponding ripple reduction techniques.

Measurement-based extrapolation of spectral responsivity by using a low-NEP pyroelectric detector

In case the primary realization of the spectral responsivity scale is not conducted at all target wavelengths but at only a small part of them, one needs to extrapolate values at the specific wavelengths to an extended range. In this work, we present a fully experimental procedure to extrapolate a single value of spectral responsivity at 633 nm into the whole working wavelength range (250–1100) nm of Si photodiodes. It is based on spectral responsivity comparison between a Si trap detector and a low-noise equivalent power pyroelectric detector of nearly flat spectral response. For this purpose, we developed a setup specialized to compare a Si-trap detector of dc-current output with a pyroelectric detector of ac-voltage output by using a modulated probing light source and a monitoring technique. To keep the probing light chopped even for the dc-photocurrent readout, we adopted a low chopping frequency of 4 Hz and a triggered readout for the Si-trap detector, which leads to a speedy comparison between the Si-trap detector and the pyroelectric detector. For the reference pyroelectric detector, we characterized the spectral absorptivity of the black-coating and the nonlinearity of the lock-in amplifier readout. Compiling all the required information, the spectral responsivity of the Si trap detector could be measured with the minimum uncertainty of 0.3% (k = 2), which was validated by comparing with that of our previous method based on a numerical extrapolation.

High-performance self-powered photodetectors achieved through the pyro-phototronic effect in Si/SnOx/ZnO heterojunctions

Coupling together the pyroelectric effect and the photovoltaic effect is a novel method to significantly enhance the performance of photodetectors. In this work, we make use of this effect through a tri-layered heterojunction of n-Si/p-SnO x /n-ZnO, which takes advantage of the pyroelectric properties of the n-type ZnO film and the photovoltaic response of the n-type Si/p-type SnO x heterojunction. The photo-response of the device, with excitation from a 405 nm wavelength laser, is carefully investigated, and it is shown that the photodetector performance is improved with increased chopper frequency owing to the coupled photovoltaic-pyroelectric effect. The Al/Si/SnO x /ZnO/ITO device exhibits an optimum responsivity and detectivity of 36.7 mA/W and 1.5 × 10 11 Jones, respectively, with a laser power density of 36 mW/cm 2 and at a chopper frequency of 400 Hz. Ultrafast rise and fall times of 3 and 2 µs, respectively, were obtained. Moreover, by using a 650 nm wavelength laser source, the responsivity and detectivity were improved up to 64.1 mA/W and 2.4 × 10 11 Jones, respectively. The performance of these photodetectors is approximately twice as fast as other pyro-phototronic devices, and exhibits comparable photodetector characteristics when compared to perovskite/Si heterojunction and transition metal dichalcogenides lateral heterojunction devices. Therefore, by combining a pyroelectric ZnO film with a solar cell into one single structure, photodetectors based on the pyro-phototronic effect have been developed that demonstrate state-of-the-art performance. The devices show great promise for visible ultrafast photosensing. • Performance of the photodetectors are enhanced by coupling the photovoltaic and pyroelectric effects. • The pyro-phototronic effect is demonstrated for the first time in a n-p-n heterojunction. • An optimum responsivity and detectivity of 36.7 mA/W and 1.5 × 10 11 Jones were achieved at zero bias. • Ultrafast rise and fall times of 3 and 2 µs were achieved for Al/Si/SnO x /ZnO/ITO devices.