Digital circuits possess a unique property called “regeneration.” In contrast to analog circuits, where the signal-to-noise ratio typically degrades from input to output, digital circuits can improve the quality of an incoming signal. This regeneration process occurs as the signal progresses through a chain of digital components.
Example of Regeneration
Imagine a chain of inverters, where the initial input signal is noisy and uncertain. As this signal moves through each inverter in the chain, it progressively becomes “cleaner” and approaches the expected or nominal value. In essence, digital circuits have the ability to extract the clean signal from the noise and amplify it at the output.
Continuous vs. Binary
Digital circuits operate in a binary manner, dealing with discrete values (usually represented as logic “0” and logic “1”) rather than continuous, analog values. However, it’s important to note that the electrical values corresponding to each logic value have a certain range of acceptable values
What is Noise Margin
This range of acceptable electrical values for a logic input is referred to as the “noise margin.” For example, while a gate might expect 0 volts as the nominal representation of logic “0,” it will still consider a range of voltage values within the noise margin as valid “0” inputs.
What is Noise Immunity
The regenerative property and the concept of noise margins together contribute to the remarkable noise immunity of digital circuits. Because digital gates can tolerate a range of input values within the noise margin and produce a clean or nearly clean logic output, digital circuits are highly resistant to noise and can reliably operate in noisy environments.
In summary, digital circuits have the unique ability to regenerate and improve the quality of signals as they pass through, thanks to their discrete binary nature and the concept of noise margins. This noise immunity has been a key factor in the widespread adoption and success of digital technologies.