User:Daleyshaw/sandbox

Digital buffer

A digital buffer is a special electronic circuit element that takes digital inputs, usually the ones with a very low current, and output a value which is used to drive high-current loads.

In a nutshell, digital buffers provide power amplification to the digital signal, as they have a high fan-out capability.^[1]

The importance of digital buffer

In circuit design, buffer serves as an amplifier to amplify the signal source, when a signal source doesn't have sufficient capacity to deliver the current to load circuit. Fundamentally, a buffer is an amplifier. It takes a small signal (lightly loading the source of the signal) and provides a copy of that signal that can drive a heavy load such as a capacitance. They are used in places where connecting the heavy load directly to the source would adversely affect the signal. Such effects arise because the signal source has a non-zero output impedance, and the output may also be used for feedback in some way. Loading the output also affects the feedback, which then changes the behavior of the source in undesirable ways.

Single Input Digital Buffer

standard digital buffer

This kind of buffer performs no inversion or decision-making possibilities . It does not invert or alter its input signal in any way, or make any logical decisions or operations like the AND orOR gates do. It reads an input and output a value. Usually, the input side reads either HIGH or LOW input and outputs a HIGH or LOW value, correspondingly. Whether the output terminal sends off HIGH or LOW signal is determined by its input value. The output value will be high if and only if the input value is high. In other words, Q will be high if and only if A is HIGH.

Tri-State Digital Buffer

tri-state buffer

Unlike the single input digital buffer which has only one input, Tri-state digital buffer has two inputs: a data input and a control input. (A control input is analogous to a valve, which controls the data flow.) When the control input is active, the output value is the input value, and the buffer is not different from the single input digital buffer.

Active High Tri-state Digital Buffer

Active high Tri-state digital buffer is a buffer with control input high as an active state.

In=0 En=0

When the data input is nothing and the control input is open, the output value will be "Z", which means no current and high impedance.

In=0 En=1

Data input is nothing but control input is active. The output value will be "Z", the impedance is approaching infinity.

In=1 En=0

Data input is active but control input is inactive. The output value is 0, which means no current.

In=1 En=1

Both data input and control input is active. The output value will be 1 and current will flow through the element.

Active Low Tri-state Digital Buffer

It is basically the same as active high digital buffer except the fact that the buffer is active when the control input is at a low state.

Application

Tri-state digital buffers are used widely on a bus, which allows multiple devices communicate with each other. Ordinarily, devices always generate output, so we're in trouble merely by attaching more than one device's output to the bus because a bus can only read one data input from a device at one time. Tri-state buffer, with its control input, can prevent a bus from reading excessive input.