Low Slew Rate Research Articles

Current Context and Research Trends in Linear DC–DC Converters

With the introduction of switch-mode power supplies (SMPS) in the mid-1970s, the efficiency of DC–DC conversion rose from 60 to 80% and SMPS became a popular power supply solution. However, linear regulators have not become obsolete. The modern power management system in portable devices supports a complex mix of DC–DC converters, combining switch-mode power supplies (SMPS), switched capacitor converters (SCCs), and linear regulators in the form of low-dropout regulators (LDOs). LDOs are used to supply low-voltage DC power rails with very low noise and high current slew rate capability, which are usually fed by the output rail of SMPS. This paper provides a comprehensive review of the evolution of the application scope of linear-type DC–DC converters in the power supply context and the present research trends. First, we review the context of linear DC–DC converters in detail, particularly in portable device power supplies. Then, the details of LDO regulators and their recent industry development and research trends are discussed. Then, the discussion focuses on supercapacitor-assisted low-dropout (SCALDO) regulator design and its scope in the portable device power management together with SCALDO-based dual output and reduced switch designs, and finally, the conclusions follow.

Current Control Strategies for Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply With Two Switched-Mode Converters to Achieve Optimal Power Allocation

Switch-linear hybrid (SLH) envelope tracking (ET) power supply is one of the mainstream structures for achieving both high efficiency and high bandwidth. When tracking a high bandwidth envelope signal, the overall efficiency of SLH ET power supply with the single switched-mode converter is limited. This paper adopts two switched-mode converters with different tracking bandwidths instead of the single switched-mode converter. The switched-mode converter with low tracking bandwidth is called slow switched-mode converter (SSMC), which aims for providing the low-frequency load current components with low slew rate; while the switched-mode converter with high tracking bandwidth is called fast switched-mode converter (FSMC), which copes with the high-frequency load current components with high slew rate. The rest load current components are processed by the linear amplifier. The class-A linear amplifier is employed for reducing the complexity of the circuits, which works as a voltage regulator that does not sink the load current. The SSMC provides the majority of the load current with low switching frequency. Thus, the switching loss of the SSMC is not high. The FSMC is operated at high switching frequency but provides the minority of the load current, and thus the switching loss of the FSMC is not high. The valley-point current control and peak current control with critical continuous current mode are proposed for the SSMC and FSMC, respectively, achieving the desired power allocation among the SSMC, FSMC, and the linear amplifier. Finally, a prototype is fabricated in the lab aiming for tracking a 10-MHz envelope signal and 20-W average output power. Experimental results are provided to verify the effectiveness of the proposed configuration and its current control strategies. The efficiency of the proposed SLH power supply is 77.0%, a 4.5% efficiency improvement compared with the SLH ET power supply with the single switched-mode converter.

Accelerated insulation aging due to fast, repetitive voltages: A review identifying challenges and future research needs

Although the adverse effects of using power electronic conversion on the insulation systems used in different apparatuses have been investigated, they are limited to low slew rates and repetitions. These results cannot be used for next-generation wide bandgap (WBG)-based conversion systems targeted to be fast (with a dv/dt up to 100 kV/ws) and operate at a high switching frequency up to 500 kHz. Frequency and slew rate are two of the most important factors of a voltage pulse, influencing the level of degradation of the insulation systems that are exposed to such voltage pulses. The paper reviews challenges concerning insulation degradation when benefitting from WBG-based conversion systems with the mentioned dv/dt and switching frequency values and identifies technical gaps and future research needs. The paper provides a framework for future research in dielectrics and electrical insulation design for systems under fast, repetitive voltage pluses originated by WBG-based conversion systems.

Fuzzy logic based Truly Random number generator for high-speed BIST applications

Communication security is a major concern in the developed world. A key feature of security is the facility to detect the person on the other side of communication with almost 100% inevitability. This concern can be disabled by using the random number generators, that generating exclusive identities for each person in a network. The same random number generators find application in the field of testing to apply test patterns for the circuit under test. One such method is proposed here. The proposed work is the implementation of three ring oscillator based truly random number generators with application of fuzzy logic concept. The randomness from this type of generator instigates from phase noise in a ring oscillator. The proposed fuzzy based random number generators were intended to ensure a low slew rate at the inverter switching threshold. The output of the proposed system depicts a great increase in timing compared to the existing design. The ring oscillator based Truly Random Generator is used as a Test pattern generator in Built in Self Test (BIST) applications and the results are compared with other existing approaches.

An Enhanced Scheme of Multi-Stage Amplifier With High-Speed High-Gain Blocks and Recycling Frequency Cascode Circuitry to Improve Gain-Bandwidth and Slew Rate

With the existing circuit topologies, the conventional multi-stage amplifiers (MSA) can only achieve low gain-bandwidths (<;5 MHz) and low slew rates (<;10 V/μs). These specifications are not satisfied by most operational amplifier (OPA) related circuit designers. To solve this issue, a novel enhanced scheme of multi-stage (ESMS) amplifier is proposed by this study. The scheme of the proposed ESMS includes a recycling frequency cascade (RFC) amplifier with a shunt current source and high-speed current mirrors, a high-speed block (HSB), and a high-gain block (HGB). Briefly, the circuitry mechanism of the ESMS amplifier demonstrates two key functions. Firstly, when an input signal is feeding into the first stage, the RFC amplifier along with the shunt current source and the current mirrors, play an important role to enhance the slew rate. Secondly, as the signal goes to the consecutive stage, low and medium frequency signals go through to the direct-coupled high-gain block (HGB), and the high-frequency signal goes to the high-speed block (HSB). Thus, the total DC gain and gain-bandwidth are improved. To test the gain-bandwidth and slew rate characteristics, the proposed ESMS amplifier was simulated by using a TSMC 0.18-μm CMOS process standard technology with a 1.8 V power supply. The results of the experiment showed that when driving a 5-pF/1-kΩ load, the proposed ESMS amplifier achieved 105.5 dB DC gain, 231.77 MHz gain-bandwidth, and 13.25 V/μs average slew rate. Compared to the NMC amplifier, one of the most well-known conventional MSAs, the proposed ESMS amplifier boosted the gain-bandwidth by 55.32 times and improved the average slew rate by 1.55 times.

Optimized MR Simulation Protocol for Framed Stereotactic Radiosurgery at 3T

Magnetic resonance imaging is often the primary imaging modality for framed stereotactic radiosurgery (SRS). However, eddy currents, chemical shift, gradient nonlinearities, and the magnetic susceptibility distribution of the patient can all contribute to geometric distortions that may affect the accuracy of SRS if not properly controlled. The goal of this work was to establish an optimized MR simulation protocol for framed SRS at 3T, and assess the severity of any residual geometric distortions. Imaging was performed on a 3T scanner using an SRS phantom (CIRS, model 603A). A titanium Leksell head frame was secured to the phantom. The fiducial box was then affixed to the head frame. The combined, phantom, head frame, and fiducial box assembly were then immobilized in treatment position using a holder of our design. The combination of two flexible phase-array coils and the integrated spine RF coil was used for signal reception. Magnetic field mapping was performed using a dual echo GRE sequence. Different shimming modes (tune up, standard, standard + local shim, standard + brain shim, advanced, advanced + local shim, advanced + brain shim) were applied prior to acquisition of each field map. In addition, 3D T1 FLASH images were acquired with different gradient slew rate modes (whisper, normal, fast) and readout bandwidths. Vendor-provided 3D gradient nonlinearity distortion correction was applied to all images prior to them being sent to a commercial deformable registration algorithm system for analysis. Large magnetic field variations were observed with tune up and standard shim modes. The advanced + brain shim mode resulted in smallest magnetic field variations over the brain. Shimming over the brain did not affect the geometric accuracy of the fiducial markers. The low slew rate whisper gradient mode reduced eddy current-induced distortion by 1.5mm compared to normal gradient mode. Reducing the readout bandwidth from 980 Hz/pixel to 440 Hz/pixel reduced eddy current-induced distortion further by 2mm and increased SNR, while minimizing the severity of chemical shift. Eddy currents induced by the gradients in the titanium frame can result in geometric distortions of fiducial that exceed 1mm in regions of the fiducial box within 2cm of the SRS frame. We established an optimized MR simulation protocol for framed SRS at 3T. Our recommendations include: 1) use of low slew rate gradient modes to reduce eddy current induced distortions, 2) reduce readout bandwidths to 440 Hz/pixel as a tradeoff between eddy current induced distortions and water-fat shift, 3) scan with the prescription volume centered at isocenter, 4) perform advanced high-order shimming with shim volume localized to brain, 5) confirm A-P phase encode direction to avoid flow artifacts, 6) apply 3D gradient nonlinearity distortion correction prior to using images for treatment planning, 7) avoid registering images in treatment planning system using fiducials within 2cm of the SRS frame.

Low Offset and High Slew Rate Buffer amplifier for LCD Application

The proposed buffer achieves low offset and high slew rate in proposed circuit NMOS folded cascode operation amplifier is used instead of rail to rail operation amplifier, use of only NMOS folded cascode operation amplifier reduces the number of MOS used in circuit and using auto zero negative feedback will provide full swing for positive and negative feedback polarity pixel, and to decrease the offset a current distributed load is used which increases DC gain of operational amplifier and as DC gain increases it reduces offset voltage and increases slew rate with same bias current used in folded and summing stage of operational amplifier. The proposed circuit is simulated and verified in LT-spice and Microwind simulation tool using 350nm CMOS TSMC foundry with 3.3 V supply voltage the offset calculated is around .2mV and slew rate is 14V/μs.

Design of a Low Voltage High Symmetrical Slew Rate Opamp Based on Self Cascode in UMC 0.18 &lt;I&gt;μ&lt;/I&gt;m

Design of a Low Voltage High Symmetrical Slew Rate Opamp Based on Self Cascode in UMC 0.18 &lt;I&gt;μ&lt;/I&gt;m

Acoustic-noise-optimized diffusion-weighted imaging.

This work was aimed at reducing acoustic noise in diffusion-weighted MR imaging (DWI) that might reach acoustic noise levels of over 100 dB(A) in clinical practice. A diffusion-weighted readout-segmented echo-planar imaging (EPI) sequence was optimized for acoustic noise by utilizing small readout segment widths to obtain low gradient slew rates and amplitudes instead of faster k-space coverage. In addition, all other gradients were optimized for low slew rates. Volunteer and patient imaging experiments were conducted to demonstrate the feasibility of the method. Acoustic noise measurements were performed and analyzed for four different DWI measurement protocols at 1.5T and 3T. An acoustic noise reduction of up to 20 dB(A) was achieved, which corresponds to a fourfold reduction in acoustic perception. The image quality was preserved at the level of a standard single-shot (ss)-EPI sequence, with a 27-54% increase in scan time. The diffusion-weighted imaging technique proposed in this study allowed a substantial reduction in the level of acoustic noise compared to standard single-shot diffusion-weighted EPI. This is expected to afford considerably more patient comfort, but a larger study would be necessary to fully characterize the subjective changes in patient experience.

Dual output Rail to Rail CMOS Buffer Amplifier with Low Power and High Slew Rate for LCD Source Driver IC

Dual output Rail to Rail CMOS Buffer Amplifier with Low Power and High Slew Rate for LCD Source Driver IC

Single Echo MRI

PurposePrevious nonlinear gradient research has focused on trajectories that reconstruct images with a minimum number of echoes. Here we describe sequences where the nonlinear gradients vary in time to acquire the image in a single readout. The readout is designed to be very smooth so that it can be compressed to minimal time without violating peripheral nerve stimulation limits, yielding an image from a single 4 ms echo.Theory and MethodsThis sequence was inspired by considering the code of each voxel, i.e. the phase accumulation that a voxel follows through the readout, an approach connected to traditional encoding theory. We present simulations for the initial sequence, a low slew rate analog, and higher resolution reconstructions.ResultsExtremely fast acquisitions are achievable, though as one would expect, SNR is reduced relative to the slower Cartesian sampling schemes because of the high gradient strengths.ConclusionsThe prospect that nonlinear gradients can acquire images in a single <10 ms echo makes this a novel and interesting approach to image encoding.

SU‐FF‐I‐66: MRI Relaxometry BMD Measurements Using Conventional Phase Symmetrized Rapid Increased Flip Spin Echo and Standard Gradient Echo and Its Correlation with DXA

Purpose: Recently, several special MRI protocols have been developed for BMD measurements for deriving R2(=1/T2), R2*(=1/T2*) and R2′(=R2*‐R2) applied in several cross sectional studies. But, due to high slew rate gradients with high amplitudes in small periods, such protocols can be used only in system with high slew rate (22 mT/m.s or greater). However, our main aim in this study was to develop optimized versions of standard GE and conventional SE protocols using in existing MRI systems for BMD measurements, as most systems do not support such newly high slew rate protocols. Method and Materials: This study was performed by 1.5T‐MRI system(Picker Vista‐Q800, slew rate=13mT/m.s), SNR phantom (1.25g/l , T2=200ms) for calibration, a body RF‐Coil, cross sectional study with 12 normal, 12 osteopenia, 12 osteoporosis volunteers done with a Lunar DXA system‐(DPX‐MD). To determine R2* and R2, simple standard‐GE and conventional phase‐symmetrized‐rapid‐increased‐flip‐SE(PRISE) protocols with different TE/TR were applied. Then in coronal section of femoral‐neck, relaxation rates were compared with BMD from DXA. The optimized conditions of the protocols for R2* measurement standard‐GE protocol with TE=13.42/18/26.8ms, TR=800ms and ST=8mm(CV(R2*)=2.96%) and for R2 measurement PRISE protocol with TE=36/54/63/72ms, TR=800ms and ST=8mm(CV(R2)=3%), receiver bandwidth of 21.2 kHz for PRISE, 31.75kHz for GE, Matrix=190×256, FOV=45cm leading to good SNR. Results: The overall Pearson's correlation coefficient of R2*, R2′ and R2 vs. BMD were calculated as 0.62(p&lt;0.003), 0.62(p&lt;0.003) and 0.03(p&lt;0.9), respectively. Based on the R2* and R2′ parameters, significant difference between normal and abnormal groups (osteopenia and osteoporosis) were found. However, there was no significant difference between osteopenia and osteoporosis groups using the relaxation parameters. Conclusion: R2* and R2′ showed a significant positive correlation with BMD. Therefore, in accordance with DXA values, the results showed standard‐GE and conventional‐SE(PRISE) could be proper protocols for BMD‐measurements in femoral‐neck even in low slew rates systems.

Endothelial cell dynamics under pulsating flows: significance of high versus low shear stress slew rates (d(tau)/dt).

Shear stress modulates endothelial cell (EC) remodeling via realignment and elongation. We provide the first evidence that the upstroke slopes of pulsatile flow, defined as shear stress slew rates (positive d(tau)/dt), affect significantly the rates at which ECs remodel. We designed a novel flow system to isolate various shear stress slew rates by precisely controlling the frequency, amplitude, and time-averaged shear stress (tau(ave)) of pulsatile flow. Bovine aortic endothelial cell (BAEC) monolayers were exposed to three conditions: (1) pulsatile flow (1 Hz) at high slew rate (293 dyn/cm2 s), (2) pulsatile flow (1 Hz) at low slew rate (71 dyn/cm2s), and (3) steady laminar flow at d(tau)/dt = 0. All of the three conditions were operated at tau(ave) = 50 dyn/cm2. BAEC elongation and alignment were measured over 17 h. We were able to demonstrate the effects of shear stress slew rates ((tau)/dt) on EC remodeling at a fixed spatial shear stress gradient (d(tau)/dx). We found that pulsatile flow significantly increased the rates at which EC elongated and realigned, compared to steady flow at d(tau)/dt = 0. Furthermore, EC remodeling was faster in response to high than to low slew rates at a given tau(ave).

A high-resolution multibit Sigma Delta ADC with digital correction and relaxed amplifier requirements

A second-order multibit Sigma Delta (sigma-delta) analog-to-digital converter (ADC) with a 4-b internal quantizer is described. It uses a simple and fast digital correction scheme. A correlated-double-sampling (CDS) fully differential integrator was used, in which the op amp needed only a low slew rate and moderate bandwidth for a sampling rate of 5.25 MHz. A second-order modulator was fabricated in the standard MOSIS p-well 2- mu m CMOS process. The excellent measured linearity and high S/(N+D) ratio (95 dB with an oversampling ratio of only 128) of the corrected converter verified the practical advantages of the proposed architecture. >

Switching probability of QFP comparators as a function of exciter slew-rate

The current noise (inferred from switching probabilities) of quantum flux parametron (QFP) comparators has been measured as a function of exciter slew rates. It was found that at high slew rates the switching probability follows an error-function distribution quite closely. However, at low slew rates, the distribution resembles a Fermi-Dirac distribution. Good agreement with Monte-Carlo simulations for high slew-rates is seen with a current noise proportional to the Johnson noise of the damping resistors. The current noise decreases with decreasing slew rate and is in good agreement with thermal activation calculations in the limit of slow slew rates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimal pacemaker sensing with respect to amplitude and slew rate of intracardiac electrograms: theoretical analysis by computer simulation.

The optimal amplitude and slew rate of intracardiac electrograms for pacemaker sensing were examined on a theoretical basis by computer simulation. The simulation was based on the concept that it is the voltage at the position of the pacing electrode in an electrical field of a moving electrical dipole. By changing the distance between the electrode and the myocardium and the moving velocity of the electrical dipole, simulated ECGs with arbitrary amplitudes and slew rates were generated by the computer and fed to a bandpass filter. This filter was equivalent to those assembled in some models of permanent pacemakers and had a center pass-band frequency of 50 Hz and a Q of 1.0. The outputs of the filter were measured. The results showed that, for pacemakers sensing, simulated intracardiac electrograms with high amplitude should have high slew rates and those with low amplitudes should have low slew rates, although the absolute values depend on the characteristics of the bandpass filter and the sensing threshold of the pacemaker.