KEYWORDS: Analog electronics, Signal processing, Optical amplifiers, Amplifiers, CMOS technology, CMOS sensors, Digital signal processing, Device simulation
-In this paper, an ultralow and high speed photocurrent analog signal readout circuit in order to amplify and process the output of SPAD(single-photon avalanche diodes) photocurrent is presented. The four main parts of the ASIC are low temperature coefficient(7.85ppm/°C) bandgap reference circuit, high linearity and high common-mode rejection ratio(120.6dB) operational amplifier, filter circuit and low-delay(63ns/1MHZ) comparator circuit. The SPAD readout chip is fabricated in a standard 0.5um CMOS process and size of 672um*780um. The simulation results indicate the chip successfully amplifies and processes 80nA and 1MHZ photocurrent analog signal. The circuit is fit for processing fleetness change and faint signal in CMOS image sensor of acquisition technology.
A single-photon avalanche diode (SPAD) device with P+-SEN junction, and a low concentration of N-type doping circular virtual guard-ring was presented in this paper. SEN layer of the proposed SPAD has high concentration of N-type doping, causing the SPAD low breakdown voltage (~14.26 V). What’s more, an efficient and narrow (about 2μm) guard-ring of the proposed SPAD not only can withstand considerably higher electric fields for preventing edge breakdown, but also offers a little increment in fill factor compared with existing SPADs due to its small area. In addition, some Silvaco TCAD simulations have been done and verify characteristics and performance of the design in this work.
The charge transfer efficiency improvement method is proposed by optimizing the electrical potential distribution along the transfer path from the PPD to the FD. In this work, we present a non-uniform doped transfer transistor channel, with the adjustments to the overlap length between the CPIA layer and the transfer gate, and the overlap length between the SEN layer and transfer gate. Theory analysis and TCAD simulation results show that the density of the residual charge reduces from 1e11 /cm3to 1e9 /cm3, and the transfer time reduces from 500 ns to 143 ns, and the charge transfer efficiency is about 77 e-/ns. This optimizing design effectively improves the charge transfer efficiency of 4T pixel and the performance of 4T high speed CMOS image sensor.
A behavior mode for simulating single-photon avalanche diodes is presented. The model is developed using Verilog-A
description language. The derived model is able to describe the static, the dynamic behavior, the triggering, the
self-sustaining and the self-quenching processes, and it also correctly characterizes the reverse current-voltage curve.
Simulation results confirmed the validity of the proposed model.
In this paper, a new UV and blue-extended photodiode with an octagon-ring-shaped structure is proposed, which have
increased responsivity for the UV and blue light, high responsive speed with short rise and fall time and UV/blue
selectivity. TCAD simulation approach is used to analyze the structural characteristics and photoelectric characteristics
of this new photodiode. For the structural characteristics, doping profile, potential distribution and Electric field
distribution are analyzed simply. For the photoelectric characteristics, the influences caused by doping concentration of
n-well on dark current, avalanche breakdown voltage and transient response are discussed in detail. The finger distance
(D) between two adjacent P+ anodes, the width (W) of P+ anode and the ratio of D/W are analyzed, witch affects the
spectral response, DC characteristic and transient response obviously. The work of TCAD simulation in this paper is
conducive to extract model parameters and process parameters of this new photodiode, which will further be used for
numerical simulation to analyze its photoelectric characteristics, noise characteristics more accurately. This work is also
a significant and helpful guide for device design and chip fabrication.
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