RESUMO
A new readout architecture for single-bit quanta image sensor (QIS) consisting of a capacitive transimpedance amplifier (CTIA) before a 1-bit quantizer to improve the threshold uniformity of the readout cluster is proposed in this paper. The 1-bit quantizer in the previous single-bit QIS had significant threshold non-uniformity likely caused by the fluctuation of the common-mode voltage of the jot output. To guarantee the stability of the common-mode voltage of input signals fed to the 1-bit quantizer, the CTIA is added before the 1-bit quantizer. A pipeline operation mode is also proposed so the CTIA and 1-bit ADC can work at the same time, thereby reducing the CTIA power consumption. A 2048 × 1024 high-speed test chip was implemented with 45 nm/65 nm stacked backside illuminated (BSI) CMOS image sensor (CIS) process and tested. According to the measured D-log-H results, a good threshold uniformity in the range of 0.3 to 0.8 e- for all readout clusters is demonstrated at 500 frame per second (fps) equivalent timing with 68 mW power consumption.
RESUMO
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.
RESUMO
Superior low-light and high dynamic range (HDR) imaging performance with ultra-high pixel resolution are widely sought after in the imaging world. The quanta image sensor (QIS) concept was proposed in 2005 as the next paradigm in solid-state image sensors after charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) active pixel sensors. This next-generation image sensor would contain hundreds of millions to billions of small pixels with photon-number-resolving and HDR capabilities, providing superior imaging performance over CCD and conventional CMOS sensors. In this article, we present a 163 megapixel QIS that enables both reliable photon-number-resolving and high dynamic range imaging in a single device. This is the highest pixel resolution ever reported among low-noise image sensors with photon-number-resolving capability. This QIS was fabricated with a standard, state-of-the-art CMOS process with 2-layer wafer stacking and backside illumination. Reliable photon-number-resolving is demonstrated with an average read noise of 0.35 e- rms at room temperature operation, enabling industry leading low-light imaging performance. Additionally, a dynamic range of 95 dB is realized due to the extremely low noise floor and an extended full-well capacity of 20k e-. The design, operating principles, experimental results, and imaging performance of this QIS device are discussed.