The Quanta Image Sensor: Every Photon Counts

Abstract

The Quanta Image Sensor (QIS) was conceived when contemplating shrinking pixel sizes and storage capacities, and the steady increase in digital processing power. In the single-bit QIS, the output of each field is a binary bit plane, where each bit represents the presence or absence of at least one photoelectron in a photodetector. A series of bit planes is generated through high-speed readout, and a kernel or “cubicle” of bits (x, y, t) is used to create a single output image pixel. The size of the cubicle can be adjusted post-acquisition to optimize image quality. The specialized sub-diffraction-limit photodetectors in the QIS are referred to as “jots” and a QIS may have a gigajot or more, read out at 1000 fps, for a data rate exceeding 1 Tb/s. Basically, we are trying to count photons as they arrive at the sensor. This paper reviews the QIS concept and its imaging characteristics. Recent progress towards realizing the QIS for commercial and scientific purposes is discussed. This includes implementation of a pump-gate jot device in a 65 nm CIS BSI process yielding read noise as low as 0.22 e− r.m.s. and conversion gain as high as 420 µV/e−, power efficient readout electronics, currently as low as 0.4 pJ/b in the same process, creating high dynamic range images from jot data, and understanding the imaging characteristics of single-bit and multi-bit QIS devices. The QIS represents a possible major paradigm shift in image capture.

Megapixel time-gated SPAD image sensor for 2D and 3D imaging applications

“…Recently, a novel photon-counting image sensor called quanta image sensor (QIS) has been demonstrated [15][16][17]. The QIS inherits several advantages of CMOS image sensors such as a potentially small pixel size, high spatial resolution, low dark current, high quantum efficiency and low power consumption.…”

High Flux Passive Imaging With Single-Photon Sensors

“…Sensors with Non-Linear Response: Logarithmic image sensors [17] use additional hardware in each pixel that applies logarithmic non-linearity to obtain dynamic range compression. Quanta image sensors (QIS) obtain logarithmic dynamic range compression by exploiting fine-grained (sub-diffraction-limit) spatial statistics, through spatial oversampling [18,19,20]. We take a different approach of treating a SPAD as an adaptive temporal binary sensor which subdivides the total exposure time into random non-equispaced time bins at least as long as the dead time of the SPAD.…”

Images from Bits: Non-Iterative Image Reconstruction for Quanta Image Sensors

“…Proposition 1 shows why a simple summation $S_n/L$ is inadequate to achieve the desired result, although such summation has been used in [18,36]. By only summing the number of ones, the resulting value $S_n/L$ is the empirical average of these one-bit measurements.…”