A Sensitive Dynamic and Active Pixel Vision Sensor for Color or Neural Imaging Applications

Abstract

Applications requiring detection of small visual contrast require high sensitivity. Event cameras can provide higher dynamic range (DR) and reduce data rate and latency, but most existing event cameras have limited sensitivity. This paper presents the results of a 180-nm Towerjazz CIS process vision sensor called SDAVIS192. It outputs temporal contrast dynamic vision sensor (DVS) events and conventional active pixel sensor frames. The SDAVIS192 improves on previous DAVIS sensors with higher sensitivity for temporal contrast. The temporal contrast thresholds can be set down to 1% for negative changes in logarithmic intensity (OFF events) and down to 3.5% for positive changes (ON events). The achievement is possible through the adoption of an in-pixel preamplification stage. This preamplifier reduces the effective intrascene DR of the sensor (70 dB for OFF and 50 dB for ON), but an automated operating region control allows up to at least 110-dB DR for OFF events. A second contribution of this paper is the development of characterization methodology for measuring DVS event detection thresholds by incorporating a measure of signal-to-noise ratio (SNR). At average SNR of 30 dB, the DVS temporal contrast threshold fixed pattern noise is measured to be 0.3%-0.8% temporal contrast. Results comparing monochrome and RGBW color filter array DVS events are presented. The higher sensitivity of SDAVIS192 make this sensor potentially useful for calcium imaging, as shown in a recording from cultured neurons expressing calcium sensitive green fluorescent protein GCaMP6f.

In-vivo imaging of neural activity with dynamic vision sensors

“…The experiments performed with SDAVIS and BSIDAVIS suggest the development of a sensor that combines their main advantages. The SDAVIS has lower event threshold (13% in the experiments) and acceptable signal quality for fast spiking neurons [8] but a large amount of noise at low intensity. The BSIDAVIS increases the QE to 89%, improving the performance in dark conditions and reducing the background noise, but has higher minimum event threshold.…”

“…These have latencies below 0.2ms, allowing studies of voltage dynamics in cellular compartments, resolution of individual spikes in fast spike trains, and precise estimates of spike timing. Although current GEVIs have a much lower temporal contrast of typically ΔF/F0 below 2% [8], upcoming technologies could result in sub-millisecond GEVI dynamics and contrasts exceeding 50%/100mV [3].…”

“…Here, two improved versions of the DAVIS sensor have been investigated: the Sensitive Dynamic and Active Pixel Vision Sensor (SDAVIS) [8], and the Back Side Illuminated Dynamic and Active Pixel Vision Sensor (BSIDAVIS). Table I.…”

“…This BSIDAVIS works better at low level of illumination, due to the higher QE. In the SDAVIS the dark background is out of the intrascene dynamic range which results in the pixels exposed to be noisy and self-oscillate [8], resulting in uninformative data that is difficult to filter.…”

“…Feasibility studies of the application of event-based sensor in neural imaging was first reported in a mock experiment in [7] and in in-vitro slices in [8] (currently under review). This paper improves upon [8], by comparing the SDAVIS used in [8] with a previously unpublished back-side-illuminated BSIDAVIS sensor (see next section). We demonstrate recordings from neurons expressing GCaMP6f in brain slices and in awake mice, using a cranial window preparation allowing optical access to the brain.…”