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Analogue to Digital Conversion © D Hoult 2011
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analogue signal © D Hoult 2011
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The analogue signal must be sampled (its voltage must be measured at regular intervals). © D Hoult 2011
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The analogue signal must be sampled (its voltage must be measured at regular intervals). To measure the voltage, the A to D converter produces its own voltage which it increases in discrete steps until it is equal to the signal voltage. © D Hoult 2011
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The analogue signal must be sampled (its voltage must be measured at regular intervals). To measure the voltage, the A to D converter produces its own voltage which it increases in discrete steps* until it is equal to the signal voltage. * this voltage is said to be quantised © D Hoult 2011
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The analogue signal must be sampled (its voltage must be measured at regular intervals). At this point the counter is “disabled” (it stops counting). To measure the voltage, the A to D converter produces its own voltage which it increases in discrete steps until it is equal to the signal voltage. © D Hoult 2011
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V s is the value of the signal voltage at the instant of sampling © D Hoult 2011
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The sampling process is assumed to take a very short time. © D Hoult 2011
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The precision of the process is limited by the “size of the steps” © D Hoult 2011
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This depends on the number of bits used by the counter © D Hoult 2011
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3 bit precision and sampling frequency 1 Hz © D Hoult 2011
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3 bit precision and sampling frequency 1 Hz © D Hoult 2011
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3 bit precision and sampling frequency 1 Hz © D Hoult 2011
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3 bit precision and sampling frequency 1 Hz © D Hoult 2011
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3 bit precision and sampling frequency 1 Hz digital signal © D Hoult 2011
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binary coded output 3 bit precision and sampling frequency 1 Hz digital signal © D Hoult 2011
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binary coded output 110 110 110 etc 3 bit precision and sampling frequency 1 Hz digital signal © D Hoult 2011
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3 bit precision and sampling frequency 2 Hz © D Hoult 2011
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3 bit precision and sampling frequency 2 Hz © D Hoult 2011
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binary coded output 3 bit precision and sampling frequency 2 Hz digital signal © D Hoult 2011
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binary coded output 110 001 110 001 etc 3 bit precision and sampling frequency 2 Hz digital signal © D Hoult 2011
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3 bit precision and sampling frequency 4 Hz © D Hoult 2011
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binary coded output 110 001 110 001 etc 3 bit precision and sampling frequency 4 Hz digital signal © D Hoult 2011
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4 bit precision and sampling frequency 4 Hz © D Hoult 2011
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4 bit precision and sampling frequency 4 Hz © D Hoult 2011
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binary coded output 1011 0010 1011 0010 etc 4 bit precision and sampling frequency 4 Hz © D Hoult 2011
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4 bit precision and sampling frequency 8 Hz © D Hoult 2011
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binary coded output 4 bit precision and sampling frequency 8 Hz © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc 4 bit precision and sampling frequency 8 Hz © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples In some systems, logic 1 (“true”) is represented by zero volts and logic zero (“false”) by 5 V © D Hoult 2011
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1011 1100 1011 0110 0010 0000 0010 0110 etc Binary coded digital output corresponding to the first four samples In some systems, logic 1 (“true”) is represented by zero volts and logic zero (“false”) by 5 V © D Hoult 2011
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