Analogue to Digital Conversion © D Hoult 2010 ODWSC

Analogue to Digital Conversion

© D Hoult 2010 ODWSC

analogue signal

© D Hoult 2010 ODWS

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.



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



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.


Vs is the value of the signal voltage at the instant of sampling


The sampling process is assumed to take a very short time.




The precision of the process is limited by the “size of the steps”


This depends on the number of bits used by the counter


3 bit precision and sampling frequency 1 Hz










digital signal



digital signal

binary coded output



digital signal

binary coded output 110 110 110 etc









digital signal

binary coded output



digital signal

binary coded output 110 001 110 001 etc





digital signal













binary coded output



1011 1100 1011 0110 0010 0000 0010 0110 etc



1011 1100 1011 0110 0010 0000 0010 0110 etc

Binary coded digital output corresponding to the first four samples


1011 1100 1011 0110 0010 0000 0010 0110 etc



1011 1100 1011 0110 0010 0000 0010 0110 etc



1011 1100 1011 0110 0010 0000 0010 0110 etc



1011 1100 1011 0110 0010 0000 0010 0110 etc



1011 1100 1011 0110 0010 0000 0010 0110 etc


In some systems, logic 1 (“true”) is represented by zero volts and logic zero (“false”) by 5 V


1011 1100 1011 0110 0010 0000 0010 0110 etc


In some systems, logic 1 (“true”) is represented by zero volts and logic zero (“false”) by 5 V


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Analogue to Digital Conversion © D Hoult 2010 ODWSC