What actually determines the type of bias to be used for different practical applications. Also I do not get the point of using capacitors (coupling) for emitter current and high input resistance. If input resistance is high the signal is not likely to pass through base. Please correct me if i'm wrong.

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    \$\begingroup\$ Coupling capacitors are used to interrupt the flow of DC voltage from the output of one section to another. So it would pass only the AC component of higher frequency. Amplifiers are used for amplifying the varying signals.So we want only the varying signals. en.wikipedia.org/wiki/Electronic_amplifier ,tpub.com/neets/book7/25d.htm \$\endgroup\$ – Inquisitive Jan 4 '13 at 19:15
  • \$\begingroup\$ Your actual question is a lot broader than your title. \$\endgroup\$ – user207421 Jan 5 '13 at 8:30

Biasing of amplifiers is determined by the DC current flowing through the transistor to obtain a given transconductance (Gm). This is called the DC operating point. You have to ensure that the DC component of the input signal does not disrupt this operating point. So this naturally menas that even for large signal swings it is still possible to move the amplifier out of the operating point. This can lead to distortion and other effects. This is true regardless of the topology of the amplifier.

There are biasing schemes that do not require capacitors but some performance parameters will be compromised. Each case will be have to be reviewed individually. There are many excellent texts on this issue, Sedra and Smith is but one example.

  • \$\begingroup\$ thanks 4 answering but didn't get much \$\endgroup\$ – user75736 Jan 4 '13 at 19:24
  • \$\begingroup\$ @user75736: Have you gone through the links I gave? \$\endgroup\$ – Inquisitive Jan 4 '13 at 19:27
  • \$\begingroup\$ @Inquisitive Yes i'm reading \$\endgroup\$ – user75736 Jan 4 '13 at 19:28

protected by Dave Tweed Sep 6 '14 at 17:19

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