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چكيده انگليسي :

89 Design and Simulation of Low Offset Amplifiers for Usage in Hall Effect Sensors Maryam Jenab m jenab@ec iut ac ir Date of Submission 2012 5 19 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Rasoul Dehghani dehghani@cc iut ac irAbstractThe Hall Effect sensor is a transducer which converts the magnetic field to an equivalent voltage Nowadaysmagnetic sensors based on the Hall Effect have the most widespread usage among different magnetic field sensors One group of Hall Effect sensor consists of a Hall plate with the circuitries for amplification and converting itsoutput voltage to a suitable output signal for consumers The Hall plate is a semiconductor plate with two outputcontacts showing a differential voltage in the presence of magnetic field Simplicity possibility of transformingmost of natural signals to magnetic field and feasibility of integration of Hall plate and all corresponding signalconditioning circuits on a single chip in a CMOS technology has made it a significant component from aneconomical stand point They are used in automotive and computer industry such as disk drives internal engineignition timing and antilock braking systems The Hall sensors generally consist of two main parts the sensor itself and its processing peripheral circuit Thushaving knowledge about performance of both parts is necessary to increase the performance of the sensor Thesensitivity of Hall plate is limited by its geometrical factor and some non ideal phenomena such as short circuiteffect on the other hand noise and offset strongly affect its output voltage accuracy In this thesis first the physicalparameters of the Hall plate are analyzed and numerical simulation of Hall plate is investigated Next the design of a low offset amplifier that is appropriate for Hall Effect sensors is studied Offset and noise limitthe performance of many precision electronic systems like sensors and biomedical instruments Offset originatesfrom any mismatches of different devices that are used in the circuit Noise can be classified as thermal and 1 fnoise In the past years by switching from bipolar technology to CMOS process this problem has become moreserious since CMOS technology has higher 1 f noise and the trimming technique which is widely used in bipolartechnology is less applicable to cancel 1 f noise In this thesis the chopper autozero offset stabilized operational amplifier is described which is applicable for typicalsensor output signals with amplitude in microvolt range The designed opamp has a bandwidth from DC up to a fewkilohertz that is sufficient for most Hall sensor applications Boosting such signals requires a low offset amplifierwith bandwidth of few megahertz Such bandwidth is not achievable by auto zero and chopper techniquesstraightforwardly since there is a tradeoff between bandwidth and offset compensation Chopper techniques does not affect the white noise characteristic of the input stage but shifts a large amount ofspectrum energy to chopping frequency This shifted signal needs to be filtered out and requires high order filteringblock Requiring lowpass filter makes chopper technique unsuitable for wide band applications Autozero techniquereduces 1 f noise but increases the noise power spectrum since aliasing occurs as a result of sampling of the inputsignal and folding back the wide band noise to DC frequency Also sampling of the input signal in time domainmakes autozero technique inappropriate for continuous time operation In the condition that continuous timeamplification is required auto zero structure can be duplicated and used in time shared mode Nevertheless switching the two amplifiers can result in spikes appearing at output So in this thesis we ve used a feed forwardstructure with the dynamic offset cancellation techniques in its low frequency path to have continuous time low offset amplifier which is free from spikes In addi

جناب، مريم

طراحي و شبيه سازي تقويت كننده هاي با آفست پايين براي كاربرد در حسگرهاي اثر هال

روش Auto Zero , روش چاپر , جبرانساز آفست پايدار