Analogue to Digital Conversion © D Hoult 2011

analogue signal

The analogue signal must be sampled (its voltage must be measured at regular intervals).

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.

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

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. At this point the counter is “disabled” (it stops counting).

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

3 bit precision and sampling frequency 1 Hz

3 bit precision and sampling frequency 1 Hz

3 bit precision and sampling frequency 1 Hz

3 bit precision and sampling frequency 1 Hz digital signal

3 bit precision and sampling frequency 1 Hz digital signal binary coded output

3 bit precision and sampling frequency 1 Hz digital signal binary coded output 110 110 110 etc

3 bit precision and sampling frequency 2 Hz

3 bit precision and sampling frequency 2 Hz

3 bit precision and sampling frequency 2 Hz digital signal binary coded output

3 bit precision and sampling frequency 2 Hz digital signal binary coded output 110 001 110 001 etc

3 bit precision and sampling frequency 4 Hz

3 bit precision and sampling frequency 4 Hz digital signal binary coded output 110 001 110 001 etc

4 bit precision and sampling frequency 4 Hz

4 bit precision and sampling frequency 4 Hz

4 bit precision and sampling frequency 4 Hz binary coded output 1011 0010 1011 0010 etc

4 bit precision and sampling frequency 8 Hz

4 bit precision and sampling frequency 8 Hz binary coded output

4 bit precision and sampling frequency 8 Hz 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

Binary coded digital output corresponding to the first four samples 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

Binary coded digital output corresponding to the first four samples 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

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 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 1011 1100 1011 0110 0010 0000 0010 0110 etc