Prototype characterization of a charge-integration pixel detector readout chip with in-pixel A/D conversion

HYLITE (High dYmamic range free electron Laser Imaging deTEctor) is a hybrid pixel detector readout chip, which is designed for advanced light sources such as X-ray Free Electron Laser (XFEL) and diffraction-limited storage rings. It is a charge-integration readout chip which has three gains for different dynamic ranges and automatic gain-switching function. The full dynamic range covered by HYLITE is 1 ∼ 104 photons with an energy of 12 keV for each pixel in every shot. In-pixel ADC is designed to achieve front-end digitization and a 10 kHz continuous frame rate. HYLITE0.1 is the first prototype chip for functional verification that was produced in CMOS 0.13 μm technology. It consists of a pixel array with 6 × 12 pixels and a periphery with full standalone operation features. The size of each pixel is 200 μm × 200 μm. Three design variations of pixels with different integrating capacitance and structures were designed to optimize between area and performance. A 10-bit Wilkinson ADC is integrated in each pixel to digitize the outputs of the pre-amplifier. Therefore, analog signal transmission of long distance is avoided and a frame rate of 10 kHz can be achieved. In this paper, we present the design of HYLITE0.1 and the test results of this prototype chip.

Sensitivity to Pulse Phase Duration as a Marker of Neural Health Across Cochlear Implant Recipients and Electrodes

In cochlear implants, loudness has been shown to grow more slowly with increasing pulse phase duration (PPD) than with pulse amplitude (PA), possibly due to “leaky” charge integration. This leakiness has been recently quantified in terms of “charge integration efficiency,” defined as the log difference between the PPD dynamic range and PA dynamic range (both expressed in charge units), relative to a common threshold anchor. Such leakiness may differ across electrodes and/or test ears, and may reflect underlying neural health. In this study, we examined the across-site variation of charge integration in recipients of Cochlear© devices. PPD and PA dynamic ranges were measured relative to two threshold anchors with either a 25- or 50-microsecond PPD. Strength-duration functions, previously shown to relate to survival of spiral ganglion cells and peripheral processes, were compared to charge integration efficiency on selected electrodes. Results showed no significant or systematic relationship between the across-site variation in charge integration efficiency and electrode position or threshold levels. Charge integration efficiency was poorer with the 50-μs threshold anchor, suggesting that greater leakiness was associated with larger PPD dynamic ranges. Poorer and more variable charge integration efficiency across electrodes was associated with longer duration of any hearing loss, consistent with the idea that poor integration is related to neural degeneration. More variable integration efficiency was also associated with poorer speech recognition performance across test ears. The slopes of the strength-duration functions at maximum acceptable loudness were significantly correlated with charge integration efficiency. However, the strength-duration slopes were not predictive of duration of any hearing loss or speech recognition performance in our participants. As such, charge integration efficiency may be a better candidate to measure leakiness in neural populations across the electrode array, as well as the general health of the auditory nerve in human cochlear implant recipients.

Using Interleaved Stimulation to Measure the Size and Selectivity of the Sustained Phase-Locked Neural Response to Cochlear Implant Stimulation

We measured the sustained neural response to electrical stimulation by a cochlear implant (CI). To do so, we interleaved two stimuli with frequencies F1 and F2 Hz and recorded a neural distortion response (NDR) at F2-F1 Hz. We show that, because any one time point contains only the F1 or F2 stimulus, the instantaneous nonlinearities typical of electrical artefact should not produce distortion at this frequency. However, if the stimulus is smoothed, such as by charge integration at the nerve membrane, subsequent (neural) nonlinearities can produce a component at F2-F1 Hz. We stimulated a single CI electrode with interleaved sinusoids or interleaved amplitude-modulated pulse trains such that F2 = 1.5F1, and found no evidence for an NDR when F2-F1 was between 90 and 120 Hz. However, interleaved amplitude-modulated pulse trains with F2-F1~40 Hz revealed a substantial NDR with a group delay of about 45 ms, consistent with a thalamic and/or cortical response. The NDR could be measured even from recording electrodes adjacent to the implant and at the highest pulse rates (> 4000 pps) used clinically. We then measured the selectivity of this sustained response by presenting F1 and F2 to different electrodes and at different between-electrode distances. This revealed a broad tuning that, we argue, reflects the overlap between the excitation elicited by the two electrodes. Our results also provide a glimpse of the neural nonlinearity in the auditory system, unaffected by the biomechanical cochlear nonlinearities that accompany acoustic stimulation. Several potential clinical applications of our findings are discussed.

Pyroelectric Properties of Bismuth Borate BZBO Single Crystals

Pyroelectric properties of orthorhombic Bi2ZnB2O7 (BZBO) crystals were investigated by using the charge integration method. The primary and the secondary pyroelectric coefficients of BZBO crystals were found to be 6.4 and −6.5 µC/(m2·°C), respectively. The pyroelectric performance was evaluated by different figure of merits (FOMs), where BZBO crystals possessed relatively high current responsivity Fi (10.38 pm/V), and detectivity Fd (11.31 × 10−5/Pa1/2). In addition, the temperature dependent behaviours of primary pyroelectric coefficients and FOMs were studied from 15 °C to 155 °C; the pyroelectric properties were found to decrease with increases in temperature.

Using interleaved stimulation to measure the size and selectivity of the sustained phaselocked neural response to cochlear-implant stimulation

We measured the sustained neural response to electrical stimulation by a cochlear implant(CI). To do so we interleaved two stimuli with frequencies F1 and F2 Hz and recorded a neuraldistortion response (NDR) at F2-F1 Hz. We show that, because any one time-point containsonly the F1 or F2 stimulus, the instantaneous nonlinearities typical of electrical artefactshould not produce distortion at this frequency. However if the stimulus is smoothed, such asby charge integration at the nerve membrane, subsequent (neural) nonlinearities can producea component at F2-F1 Hz. We stimulated a single CI electrode with interleaved sinusoids orinterleaved amplitude-modulated pulse trains such that F2=1.5F1, and found no evidence foran NDR when F2-F1 was between 90-120 Hz. However, interleaved amplitude-modulated pulsetrains with F2-F1 40 Hz revealed a substantial NDR with a group delay of about 45 ms,consistent with a thalamic and/or cortical response. The NDR could be measured even fromrecording electrodes adjacent to the implant and at the highest pulse rates (>4000 pps) usedclinically. We then measured the selectivity of this sustained response by presenting F1 andF2 to different electrodes and at different between-electrode distances. This revealed abroad tuning that, we argue, reflects the overlap between the excitation elicited by the twoelectrodes. Our results also provide a glimpse of the neural nonlinearity in the auditorysystem, unobscured by the biomechanical cochlear nonlinearities that accompany acousticstimulation. Several potential clinical applications of our findings are discussed.