#BIASING TRANSISTOR AMPLIFIER FULL#
However, because the relationship between input and output for a transistor is not linear across its full operating range, the transistor amplifier only approximates linear operation. In linear amplifiers, a small input signal gives a larger output signal without any change in shape (low distortion): the input signal causes the output signal to vary up and down about the Q-point in a manner strictly proportional to the input. As an example of the need for careful biasing, consider a transistor amplifier. Linear circuits involving transistors typically require specific DC voltages and currents for correct operation, which can be achieved using a biasing circuit. In magnetic tape recording, the term bias is also used for a high-frequency signal added to the audio signal and applied to the recording head, to improve the quality of the recording on the tape. For vacuum tubes, a grid bias voltage is often applied to the grid electrodes for the same reason. For example, a bias voltage is applied to a transistor in an electronic amplifier to allow the transistor to operate in a particular region of its transconductance curve. In electronics, 'biasing' usually refers to a fixed DC voltage or current applied to a terminal of an electronic component such as a diode, transistor or vacuum tube in a circuit in which AC signals are also present, in order to establish proper operating conditions for the component. A bias circuit is a portion of the device's circuit that supplies this steady current or voltage. The operating point of a device, also known as bias point, quiescent point, or Q-point, is the DC voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied. The AC signal applied to them is superposed on this DC bias current or voltage. Many electronic devices, such as diodes, transistors and vacuum tubes, whose function is processing time-varying ( AC) signals, also require a steady (DC) current or voltage at their terminals to operate correctly. In electronics, biasing is the setting of DC ( direct current) operating conditions (current and voltage) of an electronic component that processes time-varying signals.
A graphical representation of the current and voltage properties of a transistor the bias is selected so that the operating point permits maximum signal amplitude without distortion.
For the safety discharge resistor, see Bleeder resistor.
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