Active Reset Research Articles

Active reset of digitized preamplifiers for ionizing-radiation sensors

In this paper, we propose a new add-on circuit structure that swiftly desaturates a digitized charge preamplifier for ionizing-radiation detectors when an energetic event occurs, or when a burst of piled up events puts it into saturation. The amplitude of the energetic event can even be reconstructed with a time-over-threshold (TOT) measurement of the fast-reset transient. With an analog-to-digital converter (ADC) range of 10 MeV, we were able to measure events of up to 100 MeV. The circuit is conceived for experiments where a spurious background of energetic particles and photons exists, such those with exotic beams in the new generation of nuclear-physics research facilities.

INVESTIGATION ON THE INFLUENCE OF BACK SCATTERED PROTONS IN PIXE SPECTRUM

The pre-amplifier with an active reset system was examined to carry out PIXE analysis under the condition that X-rays and back scattered protons are detected simultaneously. Rejection of false signals produced by back scattered protons is discussed, and it is confirmed that false signals can be completely rejected by using an inhibit signal of the preamplifier. Energy resolution of an X-ray detector and a live-time of measurement system were measured as a function of counting rate. As a result, energy resolution did not change and the live-time was 70 % at the high counting rate over 3kcps. The pile-up effect on the X-ray signal with the proton signal tail is also discussed.

Analysis of the step response of the saccadic feedback: computational models.

We present results of theoretical analysis and computational simulations of two models of the saccadic burst generator: the Scudder model and the Jurgens model. We used the experimental paradigm of prolonged stimulation in monkey superior colliculus (SC) to compare the performance of the two models. We excluded the Scudder model since it was not capable of reproducing the experimentally observed staircase movements. We modified the Jurgens model by replacing the originally proposed feedback integrator with an active reset mechanism by a leaky integrator. With this modification we have shown that the staircase movement elicited by prolonged stimulation in the SC can be modeled as a damped oscillatory step response of this model. Furthermore, to replicate the changes in the kinetic profiles of the staircase movements with increased stimulation we modified the functionality of the model. Our results suggest that prolonged stimulation of the SC dynamically changes the gains and time constant of the saccadic feedback.

Compact active quenching circuit for fast photon counting with avalanche photodiodes

A compact and flexible circuit for operating avalanche photodiodes in Geiger mode was designed, fabricated, and tested. A new voltage driver stage, based on fast n-channel double-diffused metal–oxide–semiconductor (DMOS) transistors in a bootstrap configuration, makes it possible to obtain quenching pulses up to 25 V amplitude and fast active reset of the detector. At 20 V excess bias voltage above the photodiode breakdown level, an overall deadtime shorter than 36 ns is attained. The avalanche pulse charge is minimized by means of a mixed passive–active quenching approach, thus reducing self-heating and afterpulsing effects in the photodiode. A user-controllable hold-off time is available for further reducing the afterpulsing effect. The saturated counting rate of the circuit exceeds 25 Mcounts/s, but, by working with avalanche photodiodes with high breakdown voltage (250–400 V) and high avalanche current (10–40 mA), a practical limit is set at about 9 Mcounts/s by thermal effects in the detector. Gated-detector operation with gate times down to 10 ns is provided. The suitability of the new active-quenching circuit for the development of compact, all-solid-state instruments for high-performance photon counting was verified in experimental tests.

Acute baroreflex resetting: differential control of pressure and nerve activity.

This study evaluated acute resetting of carotid baroreflex control of arterial blood pressure and renal or thoracic sympathetic nerve activity in thiopental-anesthetized mongrel dogs with the use of a vascularly isolated carotid sinus preparation, the experimental model used previously to characterize acute resetting in carotid baroreceptor afferent fibers. Carotid baroreceptors were conditioned with a pulsatile pressure for 20 minutes at three pressure ranges: low (50 to 75 mm Hg), mid (100 to 125), or high (150 to 175). Blood pressure and nerve activity were recorded in response to slow ramp increases in sinus pressure; nonlinear regression and best-fit analyses were used for determination of curve fit parameters of the blood pressure and nerve activity versus sinus pressure response curves. Carotid sinus pressure thresholds for blood pressure and renal nerve activity responses at all conditioning pressures were significantly different; however, only the pressure threshold for thoracic nerve activity at the low conditioning pressure was significantly different from the responses at other conditioning pressures. Average renal activity resetting (0.506 +/- 0.072) was significantly greater than blood pressure resetting (0.335 +/- 0.046) in the same dogs, and thoracic activity (0.200 +/- 0.057) was not different from blood pressure resetting (0.194 +/- 0.031) in the same dogs. In a previous investigation, our laboratory had demonstrated that type 1 carotid baroreceptors acutely reset at a value of about 0.15. These results indicate that (1) renal and thoracic nerve activities and blood pressure acutely reset to a greater degree than type 1 carotid baroreceptors and that (2) renal activity acutely resets to a greater degree than blood pressure and thoracic nerve activity.

INTEGRATED ADAPTIVE THRESHOLD BURST MODE RECEIVERS FOR OPTICAL DATA LINKS—AN ANALYSIS

This paper provides a detailed analysis of the principles of the adaptive threshold, burst mode receiver circuit, covering architectures for both current and voltage input modes. In it we derive the circuit’s fundamental operating equations, and look at steady-state and dynamic stability issues. The paper also describes techniques for active threshold reset, and reviews factors affecting performance of the circuit over temperature.

Activity of neurons in anterior inferior temporal cortex during a short- term memory task

Inferior temporal (IT) cortex of primates is known to play an important role in visual memory. Previous studies of IT neurons during performance of working memory tasks have found modulation of responses when a current stimulus matched an item in memory; however, this effect was lost if other stimuli intervened in the retention interval. To examine how IT cortex retains memories while new stimuli are activating the cells, we recorded from IT neurons while monkeys performed a delayed matching-to-sample task, with multiple intervening items between the sample and matching test stimulus. About half of the cells responded differently to a test stimulus if it matched the sample, and this difference was maintained following intervening stimuli. For most of the affected cells, the responses to matching stimuli were suppressed; however, for a few cells the opposite effect was seen. Temporal contiguity alone could not explain the results, as there was no modulation of responses when a stimulus on one trial was repeated on the next trial. Thus, an active reset mechanism appears to restrict the memory comparison to just the stimuli presented within a trial. The suppressive effects appear to be generated within or before IT cortex since the suppression of response to matching stimuli began almost immediately with the onset of the visual response. The memory of the sample stimulus affected not only the responses to matching stimuli but also those to nonmatching stimuli. There was suggestive evidence that the more similar a nonmatching stimulus to the sample, the more the response was suppressed. About a quarter of the cells showed stimulus-selective activity in the delay interval following the sample. However, this activity appeared to be eliminated by intervening stimuli. Thus, it is unlikely that delay-interval activity in IT contributed to the performance of this particular version of delayed matching to sample. To determine how much information about the match-nonmatch status of the stimulus was conveyed by individual neurons, we analyzed the responses with discriminant analysis. The responses of an individual IT neuron could be used to classify a stimulus as matching or nonmatching on about 60% of the trials. To achieve the same performance as the animal would require averaging the responses of a minimum of 25 IT neurons. There was no evidence that mnemonic information was carried by temporal variations in the spike trains. By contrast, there was a modest amount of temporal variation in sensory responses to different visual stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)