Slide Number 1Digital/Analog ConversionDigital/Analog Voltage LevelsPulse Width Modulation (PWM)PrinciplePWM SignalPWM RepresentationAnalog Circuit ControlModulation FrequencyPWM AdvantagesPWM ImplementationPWM ApplicationsDepartment of Electrical and Compute EngineeringMississippi State UniversitySherif Abdelwahed Pulse Width ModulationComputer Aided Digital Systems Design - EE 4743/6743Digital/Analog Conversion Digital 1/0 represented by high/low voltage¾ Can also define it as halfway voltage¾ 1 is above this halfway voltage¾ 0 is below We can have more divisions in a voltage range¾ Each range is assigned a digital code¾ This is an Analog to Digital Conversion Can take a digital representation and produce an Analog voltage¾ Usually a fixed value¾ So we lose resolution in the processDigital/Analog Voltage LevelsVMAXVMINVHALF01DigitalVMAXVMINV200Analog Conversion011011V1V3Pulse Width Modulation (PWM) Technique for using Digital circuit to control an Analog device PWM is a way to encode an analog voltage using a digital signal Start with a clock signal (repeating 1/0 values) If we measure a clock signal with a DC multimeter¾ We read an average voltage¾ Somewhere between VHand VL Duty cycle is varied to represent different voltage levels Given sufficient resolution, any analog voltage can be represented in PWMPrinciple Pulse-width modulation uses a square wave whose duty cycle is modulated resulting in the variation of the averagevalue of the waveform.  If we consider a square waveform f(t) with a low value ymin, a high value ymaxand a duty cycle D, the average value of the waveform is given by:6PWM Signal10%50%90%Modulating Frequency7PWM Representation 10% signal is high for 10% of the cycle¾ If a 9V supply is used, then it represents 10% of that voltage, so 0.9V. 50% signal is high for half the cycle¾ If a 9V supply is used, then it represents 50% or 4.5V PWM signal can only represent a voltage as high as the input voltageAnalog Circuit ControlSwitch LampBatteryModulation Frequency Modulating frequency depends on the response time of the analog circuit If the switch was toggled every 5s at 50% duty cycle, the lamp might simply turn on and off Faster frequencies are required to produce an average voltage¾ Dependant on capacitance and inductance Typical frequencies: 1kHz-200kHzPWM Advantages No Digital/Analog conversion of signal Increase noise immunity¾ Good for communication¾ Increases effective communication channel¾ Receiving end can switch back to analog signal with simple RC or LC circuit33% PWMSystem Clock66% PWMPWM ImplementationPWM Applications Communications¾ the widths of the pulses correspond to specific data values encoded at one end and decoded at the other. Power delivery¾ speed control of electric motors¾ Home use light dimmers  Voltage regulation¾ switching voltage to the load with the appropriate duty cycle, the output will approximate a voltage at the desired level.  Audio effects and amplification¾ sound synthesis¾ class-D