![]() The two most common forms of transistor biasing are: Beta Dependent and Beta Independent. One of the most frequently used biasing circuits for a transistor circuit is with the self-bias of the emitter-bias circuit where one or more biasing resistors are used to set up the initial DC values of transistor currents, ( IB ), ( IC ) and ( IE ). In this simple transistor biasing tutorial we will look at the different biasing arrangements available for a Common Emitter Amplifier. Base bias networks can be used for Common-base (CB), common-collector (CC) or common-emitter (CE) transistor configurations. Since the transistors Base bias currents are steady-state DC currents, the appropriate use of coupling and bypass capacitors will help block bias current setup for one transistor stage affecting the bias conditions of the next. This steady-state or DC operating point is set by the values of the circuits DC supply voltage ( Vcc ) and the value of the biasing resistors connected the transistors Base terminal. The function of the “DC Bias level” or “no input signal level” is to correctly set the transistors Q-point by setting its Collector current ( IC ) to a constant and steady state value without an input signal applied to the transistors Base. So how do we set this Q-point biasing of a transistor? – The correct biasing of the transistor is achieved using a process know commonly as Base Bias.īut before we start looking at the possible different transistor biasing arrangements, lets first reminder ourselves of the basic transistor circuit and associated voltages and currents as shown on the left. In other words, the output current flows for the full 360o of the input cycle. This mode of operation allows the output current to increase and decrease around the amplifiers Q-point without distortion as the input signal swings through a complete cycle. When a bipolar transistor is biased so that the Q-point is near the middle of its operating range, that is approximately halfway between cut-off and saturation, it is said to be operating as a Class-A amplifier. ![]() ![]() This central operating point is called the “Quiescent Operating Point”, or Q-point for short. The correct biasing point for a bipolar transistor, either NPN or PNP, generally lies somewhere between the two extremes of operation with respect to it being either “fully-ON” or “fully-OFF” along its load line. Transistor Biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor.Ī transistors steady state of operation depends a great deal on its base current, collector voltage, and collector current and therefore, if a transistor is to operate as a linear amplifier, it must be properly biased to have a suitable operating point.Įstablishing the correct operating point requires the proper selection of bias resistors and load resistors to provide the appropriate input current and collector voltage conditions.
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