Inverse kinematics computations with modified CORDIC iterations

The paper presents hardware solutions for the computation of inverse kinematics. They are based on an existing pipeline arithmetic processor which employs the CORDIC algorithm. It is shown that a slight modification of the standard CORDIC algorithm enables fast and efficient computation of the joint angles for the inverse kinematics. Due to this modification, the hardware amount and the computation time for the inverse kinematics computations are considerably reduced. The method yields an extended convergence range and a reduced number of iterations in comparison to the original CORDIC design. Another advantage of this method is that it yields an enhanced CORDIC functionality. Finally, a novel architecture for a new kinematic processor based on the modified CORDIC method is presented

Modelling of SPAD-based time-of-flight measurement techniques

For applications like autonomous driving a fast and reliable monitoring of the vehicle's environment is essential. With the possibility of fabricating single-photon avalanche diodes in standard CMOS processes, small and cost-efficient time-of-flight sensors can be realized. To estimate the performance of such a sensor a general theoretical model taking into account the properties of the light source, the sensor, and the environment is of key importance. In this paper we will present a model to predict the performance parameters like achievable range and precision of different time-of-flight measurement techniques

CMOS SiPM with integrated amplifier

The integration of silicon photomultiplier (SiPM) and frontend electronics in a suitable optoelectronic CMOS process is a promising approach to increase the versatility of single-photon avalanche diode (SPAD)-based singlephoton detectors. By integrating readout amplifiers, the device output capacitance can be reduced to minimize the waveform tail, which is especially important for large area detectors (>10 × 10mm2). Possible architectures include a single readout amplifier for the whole detector, which reduces the output capacitance to 1:1 pF at minimal reduction in detector active area. On the other hand, including a readout amplifier in every SiPM cell would greatly improve the total output capacitance by minimizing the influence of metal routing parasitic capacitance, but requiring a prohibitive amount of detector area. As tradeoff, the proposed detector features one readout amplifier for each column of the detector matrix to allow for a moderate reduction in output capacitance while allowing the electronics to be placed in the periphery of the active detector area. The presented detector with a total size of 1.7 X 1.0mm2 features 400 cells with a 50 μm pitch, where the signal of each column of 20 SiPM cells is summed in a readout channel. The 20 readout channels are subsequently summed into one output channel, to allow the device to be used as a drop-in replacement for commonly used analog SiPMs

Dead time effects in the indirect time-of-flight measurement with SPADs

Indirect time-of-flight measurement with SPADs is performed by counting incident photons in several time windows. Since SPADs exhibit dead time not all incident photons can be counted within a given time window. This affects the expected values and, hence, the variance of the distance measurement. For photon detection rates close to the inverse of the dead time, which defines the maximum count rate of a SPAD, the probability of photon detection cannot be assumed constant within the window anymore. In this paper the effects of dead time on the photon counts are analyzed by employing statistical calculations. Based on these a model to correct such effects can be derived

Coincidence in SPAD-based time-of-flight sensors

High ambient illumination reduces the range and target detection reliability in light-based 3D sensors. Raising the optical power of the artificial illumination source to overcome the influence of high ambient light is often not possible for systems with flash illumination due to eye safety constraints. The high timing resolution of single-photon avalanche diodes enables the search for photon concurrences in incident photon streams. In this paper a theoretical analysis of coincidence and its benefits for 3D sensors with single-photon avalanche diodes is presented

Expected value and variance of the indirect time-of-flight measurement with dead time afflicted single-photon avalanche diodes

Indirect time-of-flight (TOF) measurement with single-photon avalanche diodes (SPADs) is performed by counting incident photons in several time windows. Since SPADs exhibit dead time not all incident photons can be counted within a given time window. This affects the expected values and, hence, the variance of the distance measurement. For photon detection rates close to the inverse of the dead time, which defines the maximum count rate of a SPAD, the probability of photon detection cannot be assumed constant within the window anymore. In this paper, the effects of the dead time on the photon counts as well as the corresponding variances are analyzed by employing statistical calculations. Based on these a model which can be used to correct systematic error is derived. In addition, the detailed analysis of the variance is useful to estimate the performance of an indirect TOF system in the design phase

Modeling of the charge transfer in a lateral drift field photo detector

In this article a model is introduced that describes the charge transfer in pixels of an image sensor. The model is suitable for image sensors where lateral drift field photo detectors were implemented and considers the effects of thermal diffusion, drift due to the built-in potential gradient, and self-induced drift. The analytical result is compared with a numerical solution and confirmed by measurements. With this model it is possible to predict the amount of collected charge at the sense node for very short integration times in comparatively long pixel structures. This is particularly important for indirect time-of-flight applications with CMOS image sensors. This approach enables the optimization of the pixel layout as well as an advanced calibration that might possibly enhance the distance precision. The model can also be applied to image sensors featuring pinned photodiodes