The 7404 contain six independent inverter or
NOT gates. An inverter takes an input signal and "reverses" it; a low input signal produces a high output while a high input
produces a low input.
Tech Tin Files: Advantage of digital circuits
An advantage of digital circuits when compared to analog circuits is that signals represented digitally can be
transmitted without degradation due to noise. For example, a continuous audio signal transmitted as a
sequence of 1s and 0s, can be reconstructed without error, provided the noise picked up in transmission
is not enough to prevent
identification of the 1s and 0s. An hour of music can be stored on a compact disc using about
6 billion binary digits.
In a digital system, a more precise representation of a signal can be obtained by using more binary digits
to represent it. While this requires more digital circuits to process the signals, each digit is handled
by the same kind of hardware, resulting in an easily scalable system. In an analog system, additional
resolution requires fundamental improvements in the linearity and noise characteristics of each step of
the signal chain.
Computer-controlled digital systems can be controlled by software, allowing new functions to be added without
changing hardware. Often this can be done outside of the factory by updating
the product's software. So, the product's design errors can be corrected after the product is in a customer's
Information storage can be easier in digital systems than in analog ones. The noise-immunity of digital systems
permits data to be stored and retrieved without degradation. In an analog system, noise from aging and wear
degrade the information stored.
In a digital system, as long as the total noise is below a certain level, the information can be recovered
Even when more significant noise is present, the use of redundancy permits the recovery of the original data
provided too many errors do not occur.
In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing
more heat which increases the complexity of the
circuits such as the inclusion of heat sinks. In portable or battery-powered systems this can limit use of
For example, battery-powered cellular telephones often use a low-power analog front-end to amplify and tune in the
radio signals from the base station. However, a base station has grid power and can use power-hungry, but very
software radios. Such base stations can be easily reprogrammed to process the signals used in new cellular
Most useful digital systems must translate from continuous analog signals to discrete digital signals.
This causes quantization errors. Quantization error can be reduced if the system stores enough digital data
to represent the signal to the desired degree of fidelity. The Nyquist-Shannon sampling
theorem provides an important guideline as to how much digital data is needed to accurately portray a
given analog signal.