Walk Error Research Articles

A high sensitive 66 dB linear dynamic range receiver for 3-D laser radar

This study presents a CMOS receiver chip realized in 0.18 μm standard CMOS technology and intended for high precision 3-D laser radar. The chip includes an adjustable gain transimpedance pre-amplifier, a post-amplifier and two timing comparators. An additional feedback is employed in the regulated cascode transimpedance amplifier to decrease the input impedance, and a variable gain transimpedance amplifier controlled by digital switches and analog multiplexer is utilized to realize four gain modes, extending the input dynamic range. The measurement shows that the highest transimpedance of the channel is 50 k , the uncompensated walk error is 1.44 ns in a wide linear dynamic range of 66 dB (1:2000), and the input referred noise current is 2.3 pA/ (rms), resulting in a very low detectable input current of 1 μA with SNR = 5.

Signal restoration method for restraining the range walk error of Geiger-mode avalanche photodiode lidar in acquiring a merged three-dimensional image.

The fluctuation in the number of signal photoelectrons will cause a range walk error in a Geiger-mode avalanche photodiode (Gm-APD) lidar, which significantly depends on the target intensity. For a nanosecond-pulsed laser, the range walk error of traditional time-of-flight will cause deterioration. A new signal restoration method, based on the Poisson probability response model and the center-of-mass algorithm, is proposed to restrain the range walk error. We obtain a high-precision depth and intensity merged 3D image using this method. The range accuracy is 0.6cm, and the intensity error is less than 3%.

A Wide Dynamic Range CMOS Laser Radar Receiver With a Time-Domain Walk Error Compensation Scheme

This integrated receiver channel designed for a pulsed time-of-flight (TOF) laser rangefinder consists of a fully differential transimpedance amplifier channel and a timing discriminator. The amplitude-dependent timing walk error is compensated by measuring the width and rise time of the received pulse echo and using this information for calibration. The measured bandwidth, transimpedance and minimum detectable signal (SNR ~10) of the receiver channel are 230 MHz, $100~\text {k}\Omega $ and ${\sim } 1~\mu \text {A}$ respectively. The single-shot precision of the receiver is ~3 cm at an SNR of 13 and the measurement accuracy is ±4 mm with compensation within a dynamic range of ~1:100 000. The receiver circuit was realized in a $0.35~\mu \text {m}$ CMOS process and has a power consumption of 150 mW. The functionality of the receiver channel was verified over a temperature range of -20 °C to +50 °C.

Influence of rough surface on the ranging distribution of constant fraction discriminator

Aiming effect of the rough surface on the pulse laser ranging distribution of Constant fraction discriminator (CFD), based on the traditional laser radar equation and rough surface characteristic, incoherent pulse laser detection equation of plane target is derived considering launch process as the shock response of linear system. Based on principle of CFD, the probability density function of ranging distribution of CFD is derived. The pulse laser CFD distribution with rough plane is deduced with the echo equation and probability density function. The influence of different plane angles, reflectivity, noise characteristics and pulse width on the distance distribution is analyzed by simulation. The simulation results show that CFD can effectively suppress walk error caused by different angles of rough plane.

Restraint of range walk error in a Geiger-mode avalanche photodiode lidar to acquire high-precision depth and intensity information.

There exists a range walk error in a Geiger-mode avalanche photodiode (Gm-APD) lidar because of the fluctuation in the number of signal photoelectrons. To restrain this range walk error, we propose a new returning-wave signal processing technique based on the Poisson probability response model and the Gaussian functions fitting method. High-precision depth and intensity information of the target at the distance of 5 m is obtained by a Gm-APD lidar using a 6 ns wide pulsed laser. The experiment results show that the range and intensity precisions are 1.2 cm and 0.015 photoelectrons, respectively.

Multi-resolution model correction for improving the accuracy of flying laser ranging sensor

More and more unexpected incidents come out currently. Static sensor networks can not satisfy the increasing need for emergency response due to lack of adaptivity and limited coverage, thus mobile sensor networks become the research focus for overcoming above drawbacks. With excellent performances including autonomy, flexibility, stability and low-cost, micro-unmanned air vehicles (MUAVs) play a greater pole in mobile sensor networks. Ranging is one of the most critical sensing functions for mobile sensor networks. In this paper, a flying laser ranging sensor is proposed, essentially, an airborne pulsed time-of-flight (TOF) laser rangefinder (LRF) is realized. Because of the influence from walk error, time jitter, temperature drift and other factors, there is still room to improve the measurement precision of pulsed TOF LRFs. So the more important contribution of the paper is to present a novel interval time amendment approach for higher ranging precision. Based on leading-edge time discrimination, this method first employs wavelet multi-resolution analysis to compute compensation time values, which are computed mainly from local modulus maxima (LMMs) position differences. With approximations signals similarity and measurement relative error (MRE), a fusion evaluation is built to select the best wavelet parameters, and optimal corrected measurement model is obtained. Results show that MRE of the improved model is reduced by 73.41%. Therefore, the performance of flying laser ranging sensor is improved significantly with multi-resolution model correction.

A continuous wavelet transform-based modulus maxima approach for the walk error compensation of pulsed time-of-flight laser rangefinders

Semiconductor pulsed time-of-flight (TOF) laser rangefinders (LRFs) have been the main distance measurement components equipped by many radar systems of Micro Unmanned Air Vehicles (MUAVs). A novel approach is proposed to improve the measurement accuracy of pulsed TOF LRFs. This approach adopted traditional single-threshold leading edge detection firstly, then employed continuous wavelet transform (CWT)-based local modulus maxima (LMMs) to detect singularities of emitting pulses and receiving echoes of LRFs, and obtained the compensation time with detected singularities to revise the measurement model. A series of experiments were done in a proposed pulsed TOF LRF prototype, and the measurement model is built by linear fitting. With the compensation values of various wavelets, the optimum revised measurement model is obtained. It is demonstrated that the single-shot precision of the pulsed TOF LRF achieves 195ps (∼29mm) with SNR=7, and the absolute error is reduced from 9.25 to 6.32mm. Therefore, the proposed approach can better compensate the walk error of the existing pulsed TOF LRFs and improve the performance of TOF LRFs.

Improved time-of-flight range acquisition technique in underwater lidar experiments.

This paper presents an underwater lidar time-of-flight ranging system that combines the variable forgivable factor recursive least-squares (VFF-RLS) adaptive filter algorithm and the constant fraction discriminator (CFD) timing technology. The effectiveness of suppressing the backscattering and increasing timing accuracy is experimentally verified in the water basin under the different target distances, especially near the detection limit. The classical RLS is creatively transformed by introducing the VFF, which is highly correlated to the target echo at any distance. The improvement of the signal-to-backscatter ratio always exceeds 18.9dB. The Monte Carlo simulation proves the applicability of the proposed method in the media of different turbidity. The influences of the selective timing methods on the walk error and time jitter are compared, and the optimum zero point of CFD is achieved by the slope analysis of leading (falling) edge in experimental target pulses.

A High-Sensitivity and Low-Walk Error LADAR Receiver for Military Application

An integrated receiver with high sensitivity and low walk error for a military purpose pulsed time-of-flight (TOF) LADAR system is proposed. The proposed receiver adopts a dual-gain capacitive-feedback TIA (C-TIA) instead of widely used resistive-feedback TIA (R-TIA) to increase the sensitivity. In addition, a new walk-error improvement circuit based on a constant-delay detection method is proposed. Implemented in 0.35 μm CMOS technology, the receiver achieves an input-referred noise current of 1.36 pA/√Hz with bandwidth of 140 MHz and minimum detectable signal (MDS) of 10 nW with a 5 ns pulse at SNR=3.3, maximum walk-error of 2.8 ns, and a dynamic range of 1:12,000 over the operating temperature range of -40 ° C to +85 ° C.

Role of CSPG receptor LAR phosphatase in restricting axon regeneration after CNS injury

Extracellular matrix molecule chondroitin sulfate proteoglycans (CSPGs) are highly upregulated in scar tissues and form a potent chemical barrier for CNS axon regeneration. Recent studies support that the receptor protein tyrosine phosphatase σ (PTPσ) and its subfamily member leukocyte common antigen related phosphatase (LAR) act as transmembrane receptors to mediate CSPG inhibition. PTPσ deficiency increased regrowth of ascending axons into scar tissues and descending corticospinal tract (CST) axons into the caudal spinal cord after spinal cord injury (SCI). Pharmacological LAR inhibition enhanced serotonergic axon growth in SCI mice. However, transgenic LAR deletion on axon growth in vivo and the role of LAR in regulating regrowth of other fiber tracts have not been studied. Here, we studied the role of LAR in restricting regrowth of injured descending CNS axons in deficient mice. LAR deletion increased regrowth of serotonergic axons into scar tissues and caudal spinal cord after dorsal over-hemitransection. LAR deletion also stimulated regrowth of CST fibers into the caudal spinal cord. LAR protein was upregulated days to weeks after injury and co-localized to serotonergic and CST axons. Moreover, LAR deletion improved functional recovery by increasing BMS locomotor scores and stride length and reducing grid walk errors. This is the first transgenic study that demonstrates the crucial role of LAR in restricting regrowth of injured CNS axons.

Recent advances in dental optics – Part II: Experimental tests for a new intraoral scanner

The object of this paper is testing the performance of a new device for 3D oral scanning: a two channel PTOF (pulsed time-of-flight) laser scanner, designed for dental and industrial applications in the measurement range of zero to a few centimetres. The application on short distances (0–10cm) has entailed the improvement of performance parameters such as single shot precision, average precision and walk error up to mm-level and to µm-level respectively.The single-shot precision (σ-value) has resulted to range from 43 to 63ps (9–10mm), having considered the measurement range (6.5–10mm) corresponding to 1–2V signal; this result agrees well with estimates made from simulations. The average precision has resulted to be dependent on the number of measurements and can reach a value equal to ±25µm, whenever the measurements frequency is sufficiently high. For example, if the required scanning speed is 1000 points/s and the required average precision is ±25µm, then a pulses frequency of 30–50MHz is needed, considering signal amplitude varying between 1–2V.On the whole, the performance of this new device, based on PTOF has proven to be adequate to its employment in the field of restorative dentistry.

A correction method for range walk error in photon counting 3D imaging LIDAR

A correction method for the range walk error is presented in this paper, which is based on a priori modeling and suitable for the GmAPD photon counting three-dimensional(3D) imaging LIDAR. The range walk error is mainly brought in by the fluctuation in number of photons in the laser echo pulse. In this paper, the priori model of range walk error was established, and the function relationship between the range walk error and the laser pulse response rate was determined using the numerical fitting. With this function, the range walk error of original 3D range image was forecasted and the corresponding compensated image of range walk error was obtained to correct the original 3D range image. The experimental results showed that the correction method could reduce the range walk error effectively, and it is particularly suitable for the case that there are significant differences of material properties or reflection characteristics in the scene.

A Multichannel High-Precision CMOS Time-to-Digital Converter for Laser-Scanner-Based Perception Systems

A multichannel time-to-digital converter (TDC) implemented with 0.35-μm complementary metal-oxide-semiconductor technology that uses a low-frequency crystal as reference and measures the time intervals with counter and delay line interpolation techniques is described. The multichannel measurement architecture provides information on the time intervals between several timing signals. The circuit can be used for laser time-of-flight distance measurements, e.g., where it can determine time intervals between a transmitted laser pulse and several reflected pulses and also pulsewidths or rise times, to compensate for the timing walk error. This paper shows how several measurement channels can be integrated into one TDC without losing the measurement performance. The circuit offers a measurement precision that is better than 8 ps and a measurement range of up to 74 μs. In terms of laser distance measurement, its performance is equivalent to millimeter-level precision within an 11-km range.

A wide dynamic range laser rangefinder with cm-level resolution based on AGC amplifier structure

A pulsed time-of-flight (TOF) laser rangefinder with a pulsed laser diode and an avalanche photo diode (APD) receiver is constructed and tested. Trigged by an avalanche transistor, the laser diode can emit a periodic pulse with rise time of ∼2ns. A new structure with auto gain control (AGC) circuits both in the pre-amplifier and the post-amplifier is presented. Through this technology, not only the dynamic range of the receiver is extended, but also the walk error of timing discriminators is reduced. Large measurement range from 5m to 500m is achieved without any cooperative target. The single-shot precision is 3cm for the weakest signal. Compared with previous laser rangefinders, the complexity of this system is greatly simplified.

Cell phones change the way we walk

Cell phone use among pedestrians leads to increased cognitive distraction, reduced situation awareness and increases in unsafe behavior. Performing a dual-task, such as talking or texting with a cell phone while walking, may interfere with working memory and result in walking errors. At baseline, thirty-three participants visually located a target 8m ahead; then vision was occluded and they were instructed to walk to the remembered target. One week later participants were assigned to either walk, walk while talking on a cell phone, or walk while texting on a cell phone toward the target with vision occluded. Duration and final location of the heel were noted. Linear distance traveled, lateral angular deviation from the start line, and gait velocity were derived. Changes from baseline to testing were analyzed with paired t-tests. Participants engaged in cell phone use presented with significant reductions in gait velocity (texting: 33% reduction, p=0.01; talking: 16% reduction, p=0.02). Moreover, participants who were texting while walking demonstrated a 61% increase in lateral deviation (p=0.04) and 13% increase in linear distance traveled (p=0.03). These results suggest that the dual-task of walking while using a cell phone impacts executive function and working memory and influences gait to such a degree that it may compromise safety. Importantly, comparison of the two cell phone conditions demonstrates texting creates a significantly greater interference effect on walking than talking on a cell phone.

Analysis of Noise Failure Characteristics for Superluminescent Diode Fiber-Optic Gyroscopes in Space Applications

Noise failure, particularly due to random walk error (RWE) degradation behavior, is one of the critical failure modes for fiber-optic gyroscopes (FOGs) in space applications. In this paper, firstly, the analytical model of RWE is presented and the affected parameters are listed according to the gamma irradiation damage mechanism. In addition, the influence of temperature is also included. The deterioration of affected parameters is determined through a 60Co radiation experiment on optic and optoelectronic components. Based on the parameters’ deterioration range and assumed distribution properties, their importance to the noise failure is calculated through the Sobol method, a global sensitivity analysis method. In the computation steps, the Latin Hyper Sampling (LHS) based Monte-Carlo numerical simulation technique is adopted. It is determined from calculation results that the detected light power (DLP) is the noise failure characteristic which is the most sensitive parameter in the space environment. Finally, another 60Co radiation experiment with the same conditions is performed on a superluminescent diode (SLD) FOG. The original noise degradation behavior is compared to the simulated RWE, calculated according to DLP, and the result shows that they follow trend almost identical. This supports the conclusion that DLP is the most sensitive noise failure characteristic for SLD-based FOGs.

Natural error patterns enable transfer of motor learning to novel contexts

Successful behavior demands motor learning to be transferable in some cases (e.g., adjusting walking patterns as we develop and age) and context specific in others (e.g., learning to walk in high heels). Here we investigated differences in motor learning transfer in people learning a new walking pattern on a split-belt treadmill, where the legs move at different speeds. We hypothesized that transfer of the newly acquired walking pattern on the treadmill to natural over ground walking might depend on the pattern of errors experienced during learning. Error patterns within a person's natural range might be experienced as endogenous (i.e., produced by the body), encouraging general adjustments that transfer across contexts. On the other hand, larger errors might be experienced as exogenous (i.e., produced by the environment), indicating unusual conditions requiring context-specific learning. To test this, we manipulated the distribution of errors experienced during learning to lie either within or outside the normal distribution of walking errors. We found that restriction of errors to the natural range produced transfer of the new walking pattern from the treadmill to natural walking off the treadmill, while larger errors prevented transfer. This result helps explain how transfer of motor learning is controlled, and it offers an important strategy for clinical rehabilitation, where transfer of motor learning to other contexts is essential.

Time Discriminating Design for High Precision Pulsed TOF Laser Rangefinder

The purpose of a time discriminator is to decide when the input is something you are interested in. It does this by putting out a logic pulse when the input signal meets an adjustable threshold value. A low cost high performance constant fraction discriminator (CFD) for laser rangefinder using pulsed TOF (time of flight) is proposed with the accuracy been improved. The theory of CFD is deduced and discussed and a distance measuring system has been established and experimental evidence is presented to show the feasibility of solving the time walking error problem to amend the precision and improving the environmental applicability, the distance error of +/-0.5mm was observed in the lab condition. The advantages of this instrument are highlighted and the experimental results are presented.

Research on lock-in correction for mechanical dithered ring laser gyro

Although a sinusoidal bias method is introduced to avoid working in the death band for a majority of time, the mechanical dithered ring laser gyro (RLG) still encounters information loss when crossing the zero rate point. A novel lock-in error correction method is proposed which can pick up the lost information and remove the random walk error radically. The lost information at the zero rate crossing can be expressed by such parameters as the phase and phase acceleration of a beat frequency signal. These parameters are sampled every time the phase crosses the zero rate point, and two correction trains are formed. Using the minimum variance method, the correction trains are properly scaled to compensate the output of RLG. Experiment shows that even in a bad working condition, this method can achieve satisfactory results.

An Integrated Laser Radar Receiver Channel Utilizing a Time-Domain Walk Error Compensation Scheme

An integrated receiver channel for a pulsed time-of-flight (TOF) laser rangefinder has been designed and fabricated in a 0.35-μm SiGe BiCMOS process. The receiver channel generates a timing mark for the TDC by means of a leading-edge timing discriminator that detects the crossover of the received pulse with respect to a set reference level. The walk error generated by the amplitude variation is compensated in the time domain on the basis of the measured dependence of the walk on the length of the received pulse. The measurement accuracy is ±15 ps with compensation within a dynamic range of 1:100000, and the single-shot precision and power consumption are 120 ps for a minimum detectable signal of ~1 μA and 115 mW, respectively.