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Note of Analog to Digital Conversion by Srikrishna Thota

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A/D Conversion Material T.Srikrishna M.Tech, Asst Professor,GVP Degree College 1. As a technology, analogue is the process of taking an audio or video signal (in most cases, the human voice) and translating it into electronic pulses. 2. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. 3. Digital technology breaks your voice (or television) signal into binary code—a series of 1s and 0s— transfers it to the other end where another device (phone, modem or TV) takes all the numbers and reassembles them into the original signal. 4. In a CD (and any other digital recording technology), the goal is to create a recording with very high fidelity (very high similarity between the original signal and the reproduced signal) and perfect reproduction (the recording sounds the same every single time you play it no matter how many times you play it). 5. To accomplish these two goals, digital recording converts the analog wave into a stream of numbers and records the numbers instead of the wave. 6. The conversion is done by a device called an analog-to-digital converter (ADC). 7. To play back the music, the stream of numbers is converted back to an analog wave by a digital-toanalog converter (DAC). 8. The analog wave produced by the DAC is amplified and fed to the speakers to produce the sound. Converting an analogue wave to digital wave Here is a typical wave (assume here that each tick on the x-axis represents 1/1000 of a second): • When you sample the wave with an analog-to-digital converter, you have control over two variables: • The sampling rate - Controls how many samples are taken per second

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A/D Conversion Material • T.Srikrishna M.Tech, Asst Professor,GVP Degree College The sampling precision - Controls how many different gradations (quantization levels) are possible when taking the sample Convert the curve to numbers • In the following figure, let's assume that the sampling rate is 1,000 per second and the precision is 10: 1. The green rectangles represent samples. 2. Every one-thousandth of a second, the ADC looks at the wave and picks the closest number between 0 and 9. 3. The number chosen is shown along the bottom of the figure. 4. These numbers are a digital representation of the original wave. Digital reading: Binary form: 7 8 111 1000 9 and so on 1001 1. When the DAC recreates the wave from these numbers, you get the blue line shown in the following figure:

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A/D Conversion Material T.Srikrishna M.Tech, Asst Professor,GVP Degree College 2. You can see that the blue line lost quite a bit of the detail originally found in the red line, and that means the fidelity of the reproduced wave is not very good 3. This is the sampling error. You reduce sampling error by increasing both the sampling rate and the precision In these diagrams the rate and the precision have been improved

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A/D Conversion Material T.Srikrishna M.Tech, Asst Professor,GVP Degree College Terminology Analog: continuously valued signal, such as temperature or speed, with infinite possible values in between Analog signals – directly measurable quantities in terms of some other quantity Examples: Thermometer – mercury height rises as temperature rises (or) Car Speedometer – Needle moves farther right as you accelerate Digital: discretely valued signal, such as integers, encoded in binary 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 (or) Door to a room is either open or closed

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