Design and simulation of low power amplifier for use in image sensors

Dissertation for MS.C degree

Treatment: Electronics

Abstract:

      In this thesis, the aim is to design and simulate an amplifier based on CMOS technology with low power consumption for use in image sensors. For this purpose, an amplifier that uses the ABCC circuit (intelligent bias current circuit) has been introduced. This circuit controls the input voltages and then provides the bias current of the amplifier in order to achieve stability and optimal power consumption and high speed. This circuit has been analyzed and simulated using Hspice software in 0.18 um and 90 nm technologies based on CMOS in two modes, with and without the ABCC circuit. The results of the simulation show that the design with 90 nanometer technology has better performance in terms of gain, phase margin, response speed and power consumption compared to 0.18 um technology. We also observed that by removing the ABCC circuit despite the increase in gain, the stability of the circuit will be impaired and the system will be completely unstable.

Goal

VLSI is the reduction of power loss and chip energy consumption. Various techniques have been developed based on power consumption storage modes, structure design and circuit reconstruction. Different coding systems have been developed to reduce the circuit switching work. Now the industry is moving towards nanotechnology, for this reason, in this research, it has been tried to reduce the power consumption in the circuit as much as possible by using nano-scale transistors and reducing the power supply voltage according to the technology considered at each stage.

     One of the basic and important challenges is "power consumption". The higher the chip's power consumption, the more its operating time should be reduced. For example, in image sensors, low power consumption means that it is able to capture images in a longer period of time. In this article, in order to reduce the power consumption of integrated circuits, a circuit with low power consumption is presented and using Hspice software in 90s and 90s technologies 180 nanometers have been simulated and analyzed. These simulations indicate a significant reduction in power consumption compared to other methods.

The structure of this thesis is organized as follows. In the first chapter, image sensors and their power consumption are studied. In the second chapter, the importance of reducing power consumption in circuits is discussed. In the third chapter, the background of technologies designed to reduce power consumption in integrated circuits is presented. In the fourth chapter, the amplifier circuit is presented and analyzed using simulation in the Hspice program. In the last chapter, the results of the circuit simulation in the examined technologies are compared. rtl;"> 

Chapter One - Familiarity with image sensors and their power consumption

Introduction

A digital camera is an electronic device that uses light-sensitive sensors to take pictures and save them instead of film. It usually uses CCD or CMOS type, and the image captured by the sensor is sent to the camera's memory for use in several steps. In a digital camera, imaging is not done on film but by a sensitive sensor (CCD or CMOS). Functionally, digital cameras are very similar to film or non-digital cameras. These cameras, like normal cameras, have a viewfinder, a lens to focus the image on a light-sensitive device, a device for storing and transferring several images taken in the camera, and a compartment containing all these equipments. In a normal camera, photosensitive film stores the image and after chemical treatment, it is used to preserve the image.While in a digital camera, this is done using a combination of advanced image sensor technology and its storage in memory, and allows images to be stored in digital form and quickly available without the need for special operations (such as chemical operations on the film). Small and swallowable, it is designed for painless imaging of the small intestine. The capsule is only 11 mm x 26 mm in size and contains a camera, light source, radio transmitter and battery. The patient can easily swallow it and the capsule camera can take about 2 images per second while passing through the digestive tract.

One ??of the most important challenges in this technology is "reducing circuit power consumption". Because this will increase the operating time. Various ways have been done, including the design of operational amplifiers with low power consumption. In this research, an amplifier circuit is presented that can be used to significantly reduce the amount of power consumed.

1-1) Imaging sensors and their application in the field of medical nano cameras

An imaging sensor is a device that is sensitive to light and converts light signals into digital signals (RGB information). Two common types of these sensors are CCD and CMOS and are usually used in digital cameras and other imaging devices. The applications of imaging sensors are not limited to digital cameras and imaging sensors are used in other fields such as the following:

Astronautics and related industries such as the Hubble Space Telescope

Vision machines

Ultraviolet light spectroscopy

     Both types of CCD sensors And CMOS work by using a light detection circuit that reacts to light and stores these analog signals as digital photo information, of course, each of them works in a different way to achieve this goal. Photodiode is formed. These points are actually light-sensitive sensors that convert light information into an electrical charge. When particles of light, called photons, enter the silicon body of the photosite, enough energy is generated to release negatively charged electrons. The more light enters the photosite, the more electrons are released. Each photosite has an electrical connection that when a voltage is applied to it, the silicon below receives the released electrons and acts like a capacitor for it. Therefore, each photosite has its own special charge, the more it is, the brighter the pixel will be. When the charge enters and exits these points, the information inside them is removed, and since the charge of each row is coupled with the other row, it is like the information of each row is arranged behind the previous row. The signals are then fed as noise-free as possible to the amplifier and then to the ADC.

The photosites on a CCD are only sensitive to light, not color. Color is detected using red, green and blue filters placed on each pixel. In order for the CCD to be compatible with the human eye, the proportion of green filters is twice that of red and blue filters. This is because the human eye is more sensitive to yellow and green colors. Because each pixel detects only one color, the true color is created by averaging the light intensity around the pixel, known as the color average.