lecture-week7 - 2/18/2009 ADC and DAC Analog-to-Digital...

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2/18/2009 1 CprE 288: Introduction to Embedded Systems 1 Zhao Zhang Spring 2009 Iowa State University ADC and DAC Analog-to-Digital Conversion (ADC) and Digital-to-Analog Conversion (DAC) Why do we need ADC and DAC? Analog sensors: Temperature pressure light 2 Analog sensors: Temperature, pressure, light, humidity, compass, and so on Audio applications: Microphone and speakers Image and video applications: Digital cameras, camcorder ADC and DAC Analog sensor: Convert a physical signal into an analog electrical signal 3 Temperature Sensor $3.95 Photoresistor $1.95 (Light Sensor) Sensor pictures and prices from http://www.parallax.com Passive IR sensor $9.95 for motion detection ADC and DAC Notes on typical ADCs in microcontroller –A l s o w o r k s a s DAC Located inside microcontrollers, with a dozen of ADC pins going outside to support multiple channels Mostly 10 bit resolution (the higher the better 4 Mostly 10-bit (the higher the better, e.g. 14-bit in high-end digital cameras) Supports continuous mode and one-shot mode conversion Sampling rate in continuous mode ranges from tens of KHz to hundreds of KHz (the faster the better) Analog-to-Digital Conversion Terminology analog: continuously valued signal, such as temperature or speed, with infinite possible values in between digital: discretely valued signal, such as integers, encoded in binary 5 analog-to-digital converter: ADC, A/D, A2D; converts an analog signal to a digital signal digital-to-analog converter: DAC, D/A, D2A An embedded system’s surroundings typically involve many analog signals. Analog-to-digital converters V max = 7.5V 1111 1110 1000 1010 1100 1001 1011 1101 40V 4.5V 5.0V 5.5V 6.0V 6.5V 7.0V 4 3 2 1 analog input (V) 4 3 2 1 nalog output (V) 6 proportionality 0V 0000 0010 0100 0110 0001 0011 0101 0111 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V analog to digital t1 t2 t3 t4 0100 1000 0110 0101 time a Digital output digital to analog 0100 1000 0110 0101 t1 t2 t3 t4 time an Digital input Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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2/18/2009 2 Proportional Signals Simple Equation Assume minimum voltage of 0 V.
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This note was uploaded on 10/16/2009 for the course CPR E 288 taught by Professor Staff during the Spring '08 term at Iowa State.

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lecture-week7 - 2/18/2009 ADC and DAC Analog-to-Digital...

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