class AB and class B amplifiers

[shanmukh]

i want the circit diagram for class B amplifier and also class AB amplifier.
how can we eleminate crossover distortion of class B amplifier .
i am not able to eleminate it by using diodes in PSPICE . is it possible to eleminate crossover distortion without using voltage source or current source? is class AB amplifier designed to eliminate crossover distortion in cls B amplifier . if so how is it done?

 

[TekUT]

Taken from http://www.rocketroberts.com/techart/amp.htm:

Class B: Class B amplifiers are used in low cost designs or designs where sound quality is not that important. Class B amplifiers are significantly more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion in this region of operation is called "crossover distortion"). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical. For example, a siren driver is one application of a Class B amp. Siren drivers are amplifiers that are basically driven into clipping (to produce a square wave type signal). In such a drive situation there would be little need to care about crossover distortion (the design can be less expensive due to reduced parts count).
Class AB: Class AB is probably the most common amplifier class currently used in home stereo and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the improved efficiency of class B amps and distortion performance that is a lot closer to that of a class A amp. With such amplifiers, distortion is worst when the signal is low, and generally lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated.

Other info about the polarization stage:

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part2/page3.html

Here a pratical schematic:

**broken link removed**

Lot of document and useful info can be found here:

**broken link removed**

Hope it help.

Bye
Pow

 

[Kral]

shanmukh,
Some years ago a technique call "current dumping" was developed. The idea is to augment a pure class B amplifier with a low power class A amplifier. The class A amplifier suplies only the current necessary to "fill in" the crossover region of the class B amplifier. You get the high efficiency of the class B amplifier, with the linearity of a class A amplifier with only a small decreas in efficiency, due to the small power output requirements of the class A Amplifier. See the following articles:
"Current Dumping Audio Amplifier" by Walker, P. J.
www.aes.org/e-lib/browse.cfm?elib=2440. You must be a member of the AES to download this article.
.
"Amplifier circuit - Patent EP0198478"
www.freepatentsonline.com/EP0198478.html This article is free. You will need to download a free reader in order to view the diagrams.
.
The "current dumping" technique has been used commercially in audio power amplifiers, most notably by amplifiers manufactured by Quad.
Regards,
Kral

 

[LvW]

"Current Dumping Audio Amplifier" by Walker, P. J.
www.aes.org/e-lib/browse.cfm?elib=2440. You must be a member of the AES to download this article.
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Kral

For your conviniance, here is a pdf version of the paper from P.J. Walker

 

[newtonkishore]

anyone define me chopper amplifier

 

[zhaozenghui]

thanks!