Digital Signal

The digital signal is only valid in two ranges of voltage; one to represent logic '1' and the other to represent logic '0'. Vmax is often the power supply voltage and Vmin ground or 0V. The symbol Vhmin is used as minimum voltage and is taken to be a logic '1'. Vlmax is used as maximum voltage and is taken to be a logic '0'. Thus a logic '1' is any voltage between Vhmin and Vmax, and logic '0' is between Vmin and Vlmax.

 

 

The waveforms associated with four signals are shown in Figures a, b, c and d above. Which of these figures could be:

• the output of a temperature sensor
• the data being transmitted on a serial link between a computer and a terminal
• the output of an audio amplifier
• the output of a circuit driving a digital clock?

  For each of your choices, write a short explanation.

 

For five different common household appliances, make a list of the
analog and digital components.

For example:

Gas Oven:

• clock - analog (or digital)
• burner control valves and knobs - analog
• gas ignition button - digital
• oven temperature control - analog
• oven light - digital

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Basic Logic Gates

A logic gate is a circuit which produces an output from one or more inputs. The inputs and outputs are logical values, ie. '1's and '0's. It is true that these logical values are often represented by particular voltage ranges, but when we draw or analyse a logic circuit made up of logic gates we are primarily interested in the '1's and '0's, not the voltage levels. However, if we actually have a real circuit in front of us, we can only check its operation if we know what voltage levels mean '1' and what voltage levels mean '0'.