Stepper Microstep Control And Low Offset Amplifier Digital-analog Mixed Circuit Design

Stepper motor is an open loop controlled electromechanical component which converts electrical pulse signals into angular displacement or linear displacement.It is the main actuator in digital controlled electromechanical systems and is widely used in industrial and medical equipment,printer,ATM and other scenarios.The step angle is determined by the number of states per cycle and rotor teeth.The number of rotor teeth is small and limited,resulting in a relatively large step angle.This,however,would lead to vibration and noise of stepper motor during operation,as well as the inaccuracy of position control.Therefore,using micro-step subdivision control to make the stepper motor work more quietly and accurately is one of the popular research topics of the stepper motor control circuit.The traditional stepper motor micro-step subdivision controller is based on 32-bit DSP digital chip,which is too bulky,expensive and inconvenient to be used.With the development of integrated circuit technology,the stepper motor micro-step subdivision chip has gradually become the first choice for users due to its small size,easy integration,low cost and convenience.In this thesis,the necessity and principles of stepper motor micro-step subdivision control are introduced.Meanwhile,the specs are proposed depending on the requests.Based on the theory of constant amplitude current vector,a micro-step subdivision control circuit is proposed by using the combination of look up table,current sampling and other modules.This thesis focuses on the bandgap reference,voltage regulator module,clock generation module,micro-step subdivision control module and low-offset current sampling module in the circuit.Starting from the functions implemented by each module,this thesis elaborates the design principle and topology structure of each module,and combined with the simulation and tested waveform to analysis the functional indicators concretely.The micro-step subdivision control module,which can achieve a maximum of 1/32 subdivision,controls the number of states per cycle and the state of power MOS.The current sampling module adopts a low offset design,so that the input offset voltage of the operational amplifier is as low as 960μV,ensuring that the overall circuit can provide accurate control of the current as required by the specs.The bandgap reference adopts a high PSRR design,and its low frequency PSRR can reach-160 d B,which effectively suppresses the influence of power supply voltage changes on the reference voltage.The circuit proposed in this thesis has taped out by using CSMC 0.25μm 60 V BCD process and HTSSOP-28 package.It has the following characteristics: 1.Six subdivision modes.This circuit uses PWM control combined with look-up table to realize the full step,half step,1/4 step,1/8 step,1/16 step,1/32 step operation of the stepper motor,and the step angle can be reduced at most 1/32 of the original.2.Adopt high input voltage,high PSRR bandgap reference,improve the accuracy of reference voltage 3.High current control accuracy.The current sampling OPAMP is designed with low offset,which improves the accuracy of controlling the winding current.The function test is carried out by using PCB test board after taped out.The test results show the specs of the circuit designed in this thesis are achieved.