This steady-state or DC operating point is set by the values of the circuits DC supply voltage ( Vcc ) and the value of any biasing resistors connected the transistors Base terminal.
The function of the “DC Bias level” is to correctly set the transistors Q-point by setting its Collector current ( I C ) to a constant and steady state value without any external 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 known commonly as Base Bias.īut before we start looking at the possible different transistor biasing arrangements, lets first remind ourselves of a basic single transistor circuit along with its voltages and currents as shown on the left.
#Calculating resistor values for transistor biasing full#
In other words, the output is available for the full 360 o of the input cycle. This mode of operation allows the output voltage to increase and decrease around the amplifiers Q-point without distortion as the input signal swings through one 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 DC load line. Therefore, if the transistor is to operate correctly as a linear amplifier, it must be properly biased around its operating point as improper transistor biasing will result in a distorted output.Įstablishing the correct operating point requires the selection of bias resistors and load resistors to provide the appropriate input current and collector voltage conditions. The steady state operation of a bipolar transistor depends a great deal on its base current, collector voltage, and collector current values.
0 kommentar(er)
