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Engineering

Published on April 27, 2014

Author: RonakMachhi

Source: slideshare.net

A part of active learning assignment. An initiative by GTU. Prepared by, Ronak Machhi Parth Tank Prince Jain Dhaval Darji Electrical Department SVIT, Vasad. Guided by: Prof. Krishna B. Chauhan Prof. Surbhi S. Bhatnagar Basic Electronics

Analog to Digital Converter

Outline  Introduction: Analog vs. Digital  Examples of ADC Applications  Types of A/D Converters  Examples of Analog to Digital Signal Conversion  Successive Approximation ADC

Analog Signals Analog signals – directly measurable quantities in terms of some other quantity Examples:  Thermometer – mercury height rises as temperature rises  Car Speedometer – Needle moves farther right as you accelerate  Stereo – Volume increases as you turn the knob.

Digital Signals Digital Signals – have only two states. For digital computers, we refer to binary states, 0 and 1. “1” can be on, “0” can be off. Examples:  Light switch can be either on or off  Door to a room is either open or closed

Examples of A/D Applications  Microphones - take your voice varying pressure waves in the air and convert them into varying electrical signals  Strain Gauges - determines the amount of strain (change in dimensions) when a stress is applied  Thermocouple – temperature measuring device converts thermal energy to electric energy  Voltmeters  Digital Multimeters

4.7 Pulse-code modulation  Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals.  PCM consists of three steps to digitize an analog signal: 1. Sampling 2. Quantization 3. Binary encoding  Before we sample, we have to filter the signal to limit the maximum frequency of the signal as it affects the sampling rate.  Filtering should ensure that we do not distort the signal, i.e. remove high frequency components that affect the signal shape.

4.8 Components of PCM encoder

4.9 Three different sampling methods for PCM

A/D Converter Types  Converters  Flash ADC  Delta-Sigma ADC  Dual Slope (integrating) ADC  Successive Approximation ADC P.S. : Flash and Delta-Sigma ADC not being in curriculum, will not be presented. Thank you.

Dual Slope Converter  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 with the counter counts the ADC’s output bits. A longer discharge time results in a higher count t Vin tFIX tmeas

Dual Slope Converter Advantages  Input signal is averaged  Greater noise immunity than other ADC types  High accuracy Disadvantages  Slow  High precision external components required to achieve accuracy

Successive Approximation ADC  A Successive Approximation Register (SAR) is added to the circuit  Instead of counting up in binary sequence, this register counts by trying all values of bits starting with the MSB and finishing at the LSB.  The register monitors the comparators output to see if the binary count is greater or less than the analog signal input and adjusts the bits accordingly

Output

Successive Approximation Advantages  Capable of high speed and reliable  Medium accuracy compared to other ADC types  Good tradeoff between speed and cost  Capable of outputting the binary number in serial (one bit at a time) format. Disadvantages  Higher resolution successive approximation ADC’s will be slower  Speed limited to ~5Msps

References  Text book of Basic Electronics (Tech-max Publications )  Image representation : www.google.co.in  All the excerpts taken from the respective book were used for academic purpose only. No commercial purpose was entertained.

Thank You.

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