Transistors is the main electronic component in any electronic system. It is used in analog and digital circuitry and it can be used as an amplifier and/ or a switch. When starting any circuit design that involves transistor is finding out what the function of the transistor is and what is supposed to do and deliver in the circuit. It may be either used as an amplifier or as a switch. When it is used as an amplifier it operates in the active region and if it is used for switch application then it operates in the saturation and cutoff region, that is, it switches between these two region.
So depending upon the transistor function requirement the transistor is based to operate in those aforementioned region. For amplification function, the transistor is designed to operate in the active region by proper biasing of the transistor.
Biasing is the process of adding external resistors in accordance to the applied voltage source supply so that the transistor operates in active region if it is used as an amplifier or in the cutoff/ saturation region if it is used as a switch. When it operates in the active region the B-E junction is forward biased and the C-B junction is revered biased. So biasing is also referred as process of making the B-E junction forward biased and C-B junction a reversed biased junction.
There are couple of different ways to bias a transistor. For example the addition of base resistor is one way, the addition of emitter resistance is another. Other popular biasing techniques are voltage divider biasing and self biasing. An example circuit of calculating biasing an amplifier is shown below-
Which biasing technique to choose? This question is answered by performance comparison and application. The biasing technique which produces output current and voltage invariant of change of temperature, transistor parameter such as current gain should be chosen. For example the fixed base biasing technique is not well suited for biasing because the output current(collector current) tend to vary with current gain. The emitter resistance biasing in comparison produces constant collector current and is less independent of the variation of current gain of the transistor.
So depending upon the transistor function requirement the transistor is based to operate in those aforementioned region. For amplification function, the transistor is designed to operate in the active region by proper biasing of the transistor.
Biasing is the process of adding external resistors in accordance to the applied voltage source supply so that the transistor operates in active region if it is used as an amplifier or in the cutoff/ saturation region if it is used as a switch. When it operates in the active region the B-E junction is forward biased and the C-B junction is revered biased. So biasing is also referred as process of making the B-E junction forward biased and C-B junction a reversed biased junction.
There are couple of different ways to bias a transistor. For example the addition of base resistor is one way, the addition of emitter resistance is another. Other popular biasing techniques are voltage divider biasing and self biasing. An example circuit of calculating biasing an amplifier is shown below-
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