SelectingTheCorrectADC - Selecting the proper ADC for your...

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Unformatted text preview: Selecting the proper ADC for your application. anEss 2 Objectives Objective: Examine analog to digital converters (ADCs) to help better understand their operation. Review different ADC parameters and show how they effect performance. Both DC and AC performance. Discuss accuracy, resolution and the number of bits. Show specific practical examples. 3 Selecting ADCs Freedom of Choice, Burden of Choice With PSoC, users are given many choices for ADCs and frankly many do not have a clue of what type and resolution they need. With less choice you took what you got. Engineers developed rules of thumb to help choose. These rules may not have any real foundation. Before PSoC the firmware team would rely on some old guy to do this selection for them. There are fewer of them with each passing year. Fear of risk often influences ADC choice. 4 Ideal ADC Parameters 5 Ideal ADC The Ideal ADC-1-0.5 0.5 1 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 5 0 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 6 0 6 1 6 2 6 3 6 4 6 5 t V(t) 6 Ideal ADC The Ideal ADC Quantizes the Signal Amplitude-1-0.5 0.5 1 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 5 0 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 6 0 6 1 6 2 6 3 6 4 6 5 t V(t) Definitions: Range := The allowable input voltage. Resolution := Range / Number of Quantization Steps For a n bit converter: Number of Quantization Steps := 2 n Resolution also known as LSB or 7 Ideal ADC The Ideal ADC Quantizes the Signal Amplitude Quantizes the Time Domain-1-0.5 0.5 1 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 5 0 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 6 0 6 1 6 2 6 3 6 4 6 5 n V(n) Definitions: Sample Rate f s Expressed as samples per second sps. Not Hz! 8 ADC Parameters 9 ADC Errors Ideal ADC Input is quantized into uniform steps. Transitions at +/- 50% of Ideal ADC-8-6-4-2 2 4 6 8-8-6-4-2 2 4 6 8 Analog Input Digital Output 10 ADC Errors Offset Error Defined as a constant difference, over the whole range of the ADC, between the actual output value and the ideal output value. Expressed in LSBs. Offset Error-8-6-4-2 2 4 6 8-8-6-4-2 2 4 6 8 Analog Input Digital Output Offset error can be removed be measuring a reference point and subtracting that value from future samples. 11 ADC Errors Gain Error Defines as the difference of the slope of the actual output values and the ideal output values....
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This note was uploaded on 09/21/2010 for the course ECE 4180 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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SelectingTheCorrectADC - Selecting the proper ADC for your...

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