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Figure 1: Top: Ideal voltage buffer

Bottom: Ideal current buffer

Buffer amplifierFrom Wikipedia, the free encyclopedia

A buffer amplifier (sometimes simply called a buffer) is one that provides electrical impedance transformation from one circuit to anoth

main types of buffer exist: the voltage buffer and the current buffer.

Contents

1 Voltage buffer

2 Current buffer

3 Voltage buffer examples

3.1 Op-amp implementation

3.2 Single-transistor circuits

3.2.1 Impedance transformation using the bipolar voltage follower

3.2.2 Impedance transformation using the MOSFET voltage follower

3.2.3 Chart of single-transistor amplifiers

3.3 Integrated buffer amplifiers

3.4 Speaker array amplifiers

4 Current buffer examples

4.1 Single-transistor circuits

5 See also

6 External links

Voltage buffer

A voltage buffer amplifier is used to transfer a voltage from a first circuit, having a high output impedance level, to a second circuit with a l

input impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interferin

its desired operation. In the ideal voltage buffer in the diagram, the input resistance is infinite, the output resistance zero ( impedance of an

voltage source is zero). Other p roperties of the ideal buffer are: perfect linearity, regardless of s ignal amplitudes; and instant output resp on

regardless of the speed of the input signal.

If the voltage is transferred unchanged (the voltage gainAv is 1), the amplifier is a unity gain buffer; also known as a voltage follower be

the output voltagefollows or tracks the input voltage. Although the voltage gain of a voltage buffer amplifier may be (approximately) unity

usually provides considerable current gain and thus power gain. However, it is commonplace to say that it has a gain of 1 (or the equivalenreferring to the voltage gain.

As an example, considera Thvenin source (voltage VA, series resistanceRA) driving a resistor loadRL. Because of voltage division (also re

as "loading") the voltage across the load is only VA RL / ( RL + RA ). However, if the Thvenin source drives a unity gain buffer such as tha

Figure 1 (top , with unity gain), the voltage input to the amplifier is VA, and with no voltage division because the amplifier input resistance

infinite. At the output the dependent voltage source delivers voltageAv VA = VA to the load, again without voltage division because the out

resistance of the buffer is zero. A Thvenin equivalent circuit of the combined original Thvenin source andthe buffer is an ideal voltage so

with z ero Thvenin resistance.

Current buffer

Typically a current buffer amplifier is used to transfer a current from a first circuit, having a low output impedance level, to a second circui

high input impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interwith its desired operation. In the ideal current buffer in the diagram, the input impedance is zero and the output impedance is infinite (imp

of an ideal current source is infinite). Again, other properties of the ideal buffer are: perfect linearity, regardless of signal amplitudes; and in

output resp onse, regardless of the speed of the input s ignal.

For a current buffer, if the current is transferred unchanged (the current gain i is 1), the amplifier is again a unity gain buffer; this time kn

a current follower because the outp ut currentfollows or tracks the input current.

As an example, consider a Norton source (current IA, parallel resistanceRA) driving a resistor loadRL. Because of current division (also ref

as "loading") the current delivered to the load is only IA RA / ( RL + RA ). However, if theNorton source drives a unity gain buffer such as

Figure 1 (bottom, with unity gain), the current input to t he amplifier isIA, with no current division because the amplifier input resistance i

At the outp ut the dependent current source delivers currenti IA = IA to the load, again without current division because the outp ut resist

the buffer is infinite. A Norton equivalent circuit of the combined original Norton source andthe buffer is an ideal current sourceIA with in

Norton resistance.

http://en.wikipedia.org/wiki/Input_impedancehttp://en.wikipedia.org/wiki/Buffer_amplifier#External_linkshttp://en.wikipedia.org/wiki/Buffer_amplifier#See_alsohttp://en.wikipedia.org/wiki/Buffer_amplifier#Single-transistor_circuits_2http://en.wikipedia.org/wiki/Buffer_amplifier#Speaker_array_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Integrated_buffer_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Integrated_buffer_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Chart_of_single-transistor_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Single-transistor_circuitshttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_buffer_exampleshttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_buffer_exampleshttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_buffer_exampleshttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/Buffer_amplifier#Current_bufferhttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_bufferhttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_bufferhttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svghttp://en.wikipedia.org/wiki/Current_divisionhttp://en.wikipedia.org/wiki/Norton%27s_theoremhttp://en.wikipedia.org/wiki/Gainhttp://en.wikipedia.org/wiki/Input_impedancehttp://en.wikipedia.org/wiki/Output_impedancehttp://en.wikipedia.org/wiki/Voltage_divisionhttp://en.wikipedia.org/wiki/Thevenin%27s_theoremhttp://en.wikipedia.org/wiki/Gainhttp://en.wikipedia.org/wiki/Input_impedancehttp://en.wikipedia.org/wiki/Output_impedancehttp://en.wikipedia.org/wiki/Buffer_amplifier#External_linkshttp://en.wikipedia.org/wiki/Buffer_amplifier#See_alsohttp://en.wikipedia.org/wiki/Buffer_amplifier#Single-transistor_circuits_2http://en.wikipedia.org/wiki/Buffer_amplifier#Current_buffer_exampleshttp://en.wikipedia.org/wiki/Buffer_amplifier#Speaker_array_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Integrated_buffer_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Chart_of_single-transistor_amplifiershttp://en.wikipedia.org/wiki/Buffer_amplifier#Impedance_transformation_using_the_MOSFET_voltage_followerhttp://en.wikipedia.org/wiki/Buffer_amplifier#Impedance_transformation_using_the_bipolar_voltage_followerhttp://en.wikipedia.org/wiki/Buffer_amplifier#Single-transistor_circuitshttp://en.wikipedia.org/wiki/Buffer_amplifier#Op-amp_implementationhttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_buffer_exampleshttp://en.wikipedia.org/wiki/Buffer_amplifier#Current_bufferhttp://en.wikipedia.org/wiki/Buffer_amplifier#Voltage_bufferhttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/File:Ideal_Buffers.svg