What is buffer and its use, when doing circuitry design?

[theenes]

what is buffer?

what is buffer and the use of buffer,when doing circuitry design?
for example..when i use photodiode to detect the intensity of optic source..and the output current changes linearly with incident light and the voltage output changes lagarithmaically with incident light poer?so do i need buffer for the output signal and i need to amplify the signal and connect it later to PIC(a/d port)..
what is the function of buffer?anybody can explain?

 

[electron_boy]

Re: what is buffer?

a buffer is a unity gain amplifier. it may be used for impedance matching problems. for the example u have given buffer is not needed as per my knowledge. but if u see the signal going down after connecting the output to the next stage then u might need a buffer.

 

[thedesolatesoul]

Re: what is buffer?

Buffers are used for a variety of purposes. However in your case it seems that a buffer is needed to source enough current to your PIC. Either way it shouldnt be harmful to use one.

 

[zahrein]

Re: what is buffer?

A buffer amplifier is one that provides buffering 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.

If the voltage is transferred unchanged, the amplifier is a unity gain buffer.

A unity gain buffer amplifier may be constructed very simply by connecting the output of an operational amplifier to its inverting input, and using the non-inverting input.

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.

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. Therefore it is erroneous (though commonplace) to say that it has a gain of 0 dB.

Frequency response of buffer amplifier: normally it allows input signal from DC to AC of few KHz. But at very low frequiencies gain (dB) becomes slighty negative.

 

[tuza2000]

what is buffer?

when i design the sample/hold circuit for a pipeline adc,using a emitter follower to buffering the sampled voltage with the next circuit ,but i only can take 92% of source voltage.and i it is affect the function of the ciucuit with 6bit pipeline adc

 

[zhaoshibin]

what is buffer?

could anybody can make a deeply description about the current buffer?

 

[Meridian]

Re: what is buffer?

what is buffer and the use of buffer,when doing circuitry design?
for example..when i use photodiode to detect the intensity of optic source..and the output current changes linearly with incident light and the voltage output changes lagarithmaically with incident light poer?so do i need buffer for the output signal and i need to amplify the signal and connect it later to PIC(a/d port)..
what is the function of buffer?anybody can explain?

Additional to all answers already given, a buffer is used to temporarily store data until needed. It makes data flow smoothly instead of waiting for the next bit it is already in-the-buffer for fast retrieval...

 

[azaz104]

Re: what is buffer?

What are buffer amplifiers?

What exactly is a buffer amplifier, what is its purpose in life?

This class of amplifier is designed to follow low level stages, one example is a crystal oscillator. An oscillator for optimum performance can NOT be loaded down, it needs an intermediate stage following. This will then present a sufficiently high enough input impedance so it is not considered a significant load to the oscillator. The intermediate or buffer stage, while not representing a load must then have a sufficiently low output impedance to drive successive stages.

If these concepts of impedance confuse or worry you then look at my other page "what is impedance?" it's a rough and ready explanation, followed by a more technical explanation of impedance matching but hopefully you will come back with a considerably better understanding.

From what I said above, two desirable traits of a buffer amplifier are high input impedance and low output impedance. Obviously succeeding stages should also be linear because we don't want to introduce distortion.

As a matter of interest a buffer amplifier is not solely limited to following an oscillator. You could have a requirement of wanting to sample the output of the first mixer for what is called a "Panadaptor", a means of visually seeing adjacent signals on an oscilloscope. Also a high quality agc system should be derived from the last i.f. stage, it should be buffered before going to the agc amplifier and then on to the agc detector.

Other examples are low level outputs of audio amplifier stages such as microphone inputs where the microphone is a high impedance type. Although not so common now, phono inputs to audio ampliers also needed buffering.
A practical example of a buffer amplifier

Here I'm going to use a very practical example where one has a requirement for a voltage controlled oscillator operating at 1.8 - 2.0 Mhz (amateur radio band 160M). This is to be part of a frequency synthesiser.

The design requirements were:-

(a) frequency coverage 1.8 - 2.0 Mhz

(b) voltage controlled by a frequency synthesiser with an output level sufficient to drive the input of a Phase Locked Loop (PLL)

(c) a further buffered output for a digital frequency readout.

(d) another buffered out put to drive succeeding amplifier stages.

We can look at two types of active devices for use in buffer amplifiers, FET transistors and bipolar transistors. Choice is largely a matter of opinion but more often it depends on what you have on hand. Bipolar types are referred to as "emitter followers".




https://www.electronics-tutorials.com/amplifiers/buffer-amplifiers.htm