A digital buffer (or a logic buffer) is an

electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or Conductive trace, traces through which electric current can flow. It is a t ...

element used to copy a digital input signal and isolate it from any output load. For the typical case of using

voltages Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

as logic signals, a logic buffer's

input impedance In electrical engineering, the input impedance of an electrical network is the measure of the opposition to current ( impedance), both static ( resistance) and dynamic ( reactance), into a load network or circuit that is ''external'' to the elec ...

is high, so it draws little

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (hydr ...

from the input circuit, to avoid disturbing its

signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

. The digital buffer is important in

data transmission Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...

between connected systems. Buffers are used in registers (data storage device) and

buses A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a motor vehicle that carries significantly more passengers than an average car or van, but fewer than the average rail transport. It is most commonly used ...

(data transferring device). To connect to a shared bus, a tri-state digital buffer should be used, because it has a

high impedance In electronics, high impedance means that a point in a circuit (a node) allows a relatively small amount of current through, per unit of applied voltage at that point. High impedance circuits are low current and potentially high voltage, whereas ...

("inactive" or "disconnected") output state (in addition to logic low and high).

Functionality

A voltage buffer amplifier transfers a voltage from a high output impedance circuit to a second circuit with low input impedance. Directly connecting a low impedance load to a power source draws current according to

Ohm's law Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of ...

. The high current affects the source. Buffer inputs are high impedance. A buffered load effectively does not affect the source circuit. The buffer's output current is generated within the buffer. In this way, a buffer provides isolation between a power source and a low impedance. The buffer does not intentionally amplify or attenuate the input signal, and so may be called a ''unity gain'' buffer. A ''digital'' buffer is a type of voltage buffer amplifier that is only concerned about digital

logic level In digital circuits, a logic level is one of a finite number of states that a digital signal can inhabit. Logic levels are usually represented by the voltage difference between the signal and ground, although other standards exist. The range of ...

s, and thus may be non-linear. It may also act as a

level shifter In digital electronics, a level shifter, also called level converter or logic level shifter, or voltage level translator, is a circuit used to translate signals from one logic level or voltage domain to another, allowing compatibility between in ...

, with output voltages differing from the input voltages. One case of this is an ''inverting buffer'' which translates an active-high signal to an active-low one (or vice versa).

Types

Single input voltage buffer

Inverting buffer

This buffer's output state is the opposite of the input state. If the input is high, the output is low, and vice versa. Graphically, an inverting buffer is represented by a triangle with a small circle at the output, with the circle signifying inversion. The inverter is a basic building block in digital electronics. Decoders, state machines, and other sophisticated digital devices often include inverters.

Non-inverting buffer

This kind of buffer performs no inversion or decision-making possibilities. A single input digital buffer is different from an inverter. It does not invert or alter its input signal in any way. It reads an input and outputs 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

Unlike the single input digital buffer which has only one input, the 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 In digital circuits, a logic level is one of a finite number of states that a digital signal can inhabit. Logic levels are usually represented by the voltage difference between the signal and ground, although other standards exist. The range of ...

tri-state digital buffer is a buffer that is in an active state that transmits its data input to the output only when its control input voltage is high (logic 1). But when the control input is low (logic 0), the output is

(abbreviated as "Hi-Z"), as if the part had been removed from the circuit.

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.

Inverting tri-state digital buffer

Tri-state digital buffers also have inverting varieties in which the output is the inverse of the input.

Application

Single input voltage buffers are used in many places for measurements including: * In

strain gauge A strain gauge (also spelled strain gage) is a device used to measure Deformation (mechanics)#Strain, strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an Electrical in ...

circuitry to measure deformations in structures like bridges, airplane wings and I-beams in buildings. * In temperature measurement circuitry for boilers and in high altitude aircraft in a cold environment. * In control circuits for aircraft, people movers in airports, subways and in many different production operations. Tri-state voltage buffers are used widely to transmit onto shared

, since a bus can only transmit one input device's data at a time. The high-impedance output state effectively temporarily disconnects that input device from the bus, since at most only one device should actively drive the bus's shared wires.

References

{{Logical connectives Electronic circuits