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