A buffer amplifier (sometimes simply called a buffer) is one that provides impedance transformation from high to low between one circuit and another.

Typically a buffer amplifier is used to transfer a voltage from a first circuit, having a high impedance level, to a second circuit with a lower impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interfering with its desired operation. In electrical engineering, Impedance is a measure of opposition to a sinusoidal electric current. ...

If the voltage is transferred unchanged, the amplifier is a unity gain buffer; also known as a voltage follower.

A unity gain buffer amplifier may be constructed very simply by connecting the output of an operational amplifier to its inverting input (negative feedback), and using the non-inverting input for the signal input. Look up one in Wiktionary, the free dictionary. ... A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. ...

Diagram of unity gain buffer amplifier

The circuit makes a copy of the input voltage at the output without drawing any current from the input. Image File history File links Unity_gain_buffer_amp. ... Image File history File links Unity_gain_buffer_amp. ...

Other unity gain buffer amplifiers include the bipolar junction transistor in common-collector configuration (called an emitter follower because the emitter voltage follows the base voltage); a pair of such transistors (Darlington pair); or similar configurations using field effect transistors, vacuum tubes, or other active devices. A bipolar junction transistor (BJT) is a type of transistor. ... Typical common collector or emitter follower circuit. ... Large power N-channel field effect transistor The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel in a semiconductor material. ... In electronics, a vacuum tube (U.S. and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ...

All such amplifiers actually have a gain of slightly less than unity, but the difference is usually small and unimportant.

Although the voltage gain of a buffer amplifier may be (approximately) unity, it usually provides considerable current gain and thus power gain. However, it is commonplace to say that it has a gain of 0 dB, referring to the voltage gain. The decibel (dB) is a measure of the ratio between two quantities, and is used in a wide variety of measurements in acoustics, physics and electronics. ...

Frequency response of buffer amplifier: normally it allows input signal from DC to AC of few kHz. But at very low frequencies gain (dB) becomes slighty negative. Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ...

See also

• Preamplifier

An example of a typical high-end stereo preamplifier. ...

External links

• Unity Gain Buffer Amplifier - Bucknell