ADC converter ppt

analog to digital converter ppt presentation and advantages and disadvantages of adc
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Dr.MattWood,United States,Teacher
Published Date:25-07-2017
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Analog to Digital Converters By: Dapeng Zhu Todd Sifleet Travis Nunnally Yachun HuangIntroduction of ADC By: Dapeng Zhu  What is ADC(Analog to Digital Converter)  Why ADC is needed  Application of ADC  A/D conversion processWhat is ADC  An electronic integrated circuit which transforms a signal from analog (continuous) to digital (discrete) form.  Analog signals are directly measurable quantities.  Digital signals only have two states. For digital computer, we refer to binary states, 0 and 1.Why ADC is needed  Microprocessors can only perform complex processing on digitized signals.  When signals are in digital form they are less susceptible to the deleterious effects of additive noise.  ADC Provides a link between the analog world of transducers and the digital world of signal processing and data handling.Application of ADC  ADC are used virtually everywhere where an analog signal has to be processed, stored, or transported in digital form.  Some examples of ADC usage are digital volt meters, cell phone, thermocouples, and digital oscilloscope.  Microcontrollers commonly use 8, 10, 12, or 16 bit ADCs, our micro controller uses an 8 or 10 bit ADC.… ADC process Output digital Output digital Input analog Input analog signal signal signal signal D Quantizing n 1 u (t) I & S D Encoding 1 u ′(t) C I D 0 S/H circuit 2 steps  Sampling and Holding (S/H)  Quantizing and Encoding (Q/E)Sampling and Holding Continuous Signal  Holding signal benefits Sampling pulse the accuracy of the A/D conversion  Minimum sampling rate Sampled signal should be at least twice the highest data frequency of the analog signal Sampled and held signalQuantizing and Encoding Resolution: The smallest change in analog signal that will result in a change in the digital output. V r V = N 2 V = Reference voltage range N = Number of bits in digital output. N 2 = Number of states. ∆V = Resolution The resolution represents the quantization error inherent in the conversion of the signal to digital formQuantizing and Encoding Analog Signal Digital output in binary • Quantizing: Partitioning the reference signal range into a number of discrete quanta, then matching the input signal to the correct quantum. • Encoding: Assigning a unique digital code to each quantum, then allocating the digital code to the input signal. V =1V 1 "%&%'(&")+",)'-..,.=± V =±0.5V 2Accuracy of A/D Conversion There are two ways to best improve the accuracy of A/D conversion:  increasing the resolution which improves the accuracy in measuring the amplitude of the analog signal.  increasing the sampling rate which increases the maximum frequency that can be measured.Accuracy of A/D Conversion  Low Accuracy  Improved Time Time Resolution ResolutionTypes of A/D Converters By: Todd Sifleet  Dual Slope A/D Converter  Successive Approximation A/D Converter  Flash A/D Converter  Delta-Sigma A/D Converter  Other  Voltage-to-frequency, staircase ramp or single slope, charge balancing or redistribution, switched capacitor, tracking, and synchro or resolverDual Slope A/D Converter  Fundamental components  Integrator  Electronically Controlled Switches  Counter  Clock  Control Logic  ComparatorHow does it work A dual-slope ADC (DS-ADC) integrates an unknown input voltage (V ) for IN a fixed amount of time (T ), then "de-integrates" (T ) using a INT DEINT known reference voltage (V ) for a variable amount of time. REF The key advantage of this architecture over the single-slope is that the final conversion result is insensitive to errors in the component values. That is, any error introduced by a component value during the integrate cycle will be cancelled out during the de-integrate phase.How Does it Work Cont.  At t0, S is set to ground, S is closed, and 1 2 counter=0.  At t=0 a conversion begins and S is open, and S 2 1 is set so the input to the integrator is V . in  S is held for T which is a constant 1 INT predetermined time interval.  When S is set the counter begins to count clock 1 pulses, the counter resets to zero after T INT  V of integrator at t=T is V T /RC is linearly out INT IN INT proportional to V IN  At t=T S is set so -V is the input to the INT 1 ref integrator which has the voltage V T /RC stored IN INT in it.  The integrator voltage then drops linearly with a slop -V /RC. ref  A compartor is used to determine when the output voltage of the integrator crosses zero  When it is zero the digitized output value is the state of the counter.Dual Slope A/D Converter Pros and Cons PROS CONS  Conversion result is insensitive  Slow to errors in the component  Accuracy is dependent on the values. use of precision external  Fewer adverse affects from components “noise”  Cost  High AccuracyFlash A/D Converter  Fundamental Components (For N bit Flash A/D) N  2 -1 Comparators N  2 Resistors  Control LogicHow does it work N  Uses the 2 resistors to form a ladder voltage divider, which N divides the reference voltage into 2 equal intervals. N N  Uses the 2 -1 comparators to determine in which of these 2 voltage intervals the input voltage V lies. in  The Combinational logic then translates the information provided by the output of the comparators  This ADC does not require a clock so the conversion time is essentially set by the settling time of the comparators and the propagation time of the combinational logic.Flash A/D Converter Pros and Cons PROS CONS  Very Fast (Fastest)  Expensive  Very simple  Prone to produce operational theory glitches in the output  Speed is only limited  Each additional bit by gate and of resolution comparator requires twice the propagation delay comparators.SIGMA-DELTA A/D Converter Main Components  Resistors  Capacitor  Comparators  Control Logic  DAC

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