WhatisADC.ppt

What is ADC ?;What is ADC ?;What is ADC ?;Most signals we want to process are analog i.e.: they are continuous and can take an inifinity of values ;Digital systems require discrete digital data ADC converts an analog information into a digital information ;Voltmeter ;3 steps: Sampling Quantification Coding These operations are all performed in a same element: the A to D Converter;xs(t=k*Ts);The signal can only take determined values Belonging to a range of conversion (ΔVr) Based on number of bit combinations that the converter can output Number of possible states: N=2n where n is number of bits Resolution: Q= ΔVr/N;Assigning a unique digital word to each sample Matching the digital word to the input signal ;The accuracy of an ADC can be improved by increasing: The sampling rate (Ts) The resolution (Q);t;What is ADC ?;What is ADC ?;What is ADC ?;Types of ADCs;“parallel A/D” Uses a series of comparators Each comparator compares Vin to a different reference voltage, starting w/ Vref = 1/2 lsb ;Comparator is one use of an Op-Amp;Advantages Very fast ;Oversampled input signal goes in the integrator Output of integration is compared to GND Iterates to produce a serial bitstream Output is serial bit stream with # of 1’s proportional to Vin;Advantages High resolution No precision external components needed;The sampled signal charges a capacitor for a fixed amount of time By integrating over time, noise integrates out of the conversion. Then the ADC discharges the capacitor at a fixed rate while a counter counts the ADCs output bits. A longer discharge time results in a higher count. ;Advantages Input signal is averaged Greater noise immunity than other ADC types High accuracy;Sets MSB Converts MSB to analog using DAC Compares guess to input Set bit Test next bit;Advantages Capable of high speed Medium accuracy compared to other ADC types Good tradeoff between speed and cost;Type;HC11 ADC;PE0 AN0 PE1 AN1 PE2 AN2 PE3 AN3 PE4 AN4 PE5 AN5 PE6 AN6 PE7 AN7;0;CCF;4 channels ar