|
Biasing in electronics is the method of establishing predetermined voltages or currents at various points of an electronic circuit for the purpose of establishing proper operating conditions in electronic components. Many electronic devices such as transistors and vacuum tubes, whose function is processing time-varying (AC) signals also require a steady (DC) current or voltage to operate correctly — a ''bias''. The AC signal applied to them is superposed on this DC bias current or voltage. The operating point of a device, also known as bias point, quiescent point, or Q-point, is the steady-state voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied. The term is also used for an alternating current (AC) signal applied to some electronic devices which is similarly required for correct operation, such as the tape bias signal applied to magnetic recording heads used in magnetic tape recorders. ==Overview== In electronic engineering, the term ''bias'' has the following meanings: # A systematic deviation of a value from a reference value. # The amount by which the average of a set of values departs from a reference value. # Electrical, mechanical, magnetic, or other force (field) applied to a device to establish a reference level to operate the device. # In telegraph signaling systems, the development of a positive or negative DC voltage at a point on a line that should remain at a specified reference level, such as zero. :''Note:'' A bias may be applied or produced by (i) the electrical characteristics of the line, (ii) the terminal equipment, and (iii) the signaling scheme. Most often, bias simply refers to a fixed DC voltage applied to the same point in a circuit as an alternating current (AC) signal, frequently to select the desired operating response of a semiconductor or other electronic component (forward or reverse bias). 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. For vacuum tubes, a (much higher) grid bias voltage is also often applied to the grid electrodes for precisely the same reason. A hot bias can lower the tube life span, but a "cool" bias can induce crossover distortion. Bias is also the term used for a high-frequency signal added to the audio signal recorded on magnetic tape. See tape bias. Bias is used in direct broadcast satellites such as DirecTV and Dish Network, the integrated receiver/decoder (IRD) box actually powers the feedhorn or low-noise block converter (LNB) receiver mounted on the dish arm. This bias is changed from a lower voltage to a higher voltage to select the polarization of the LNB, so that it receives signals that are polarized either horizontally or vertically, thereby allowing it to receive twice as many channels. We still need to determine the optimal values for the DC biasing in order to choose resistors, etc. This bias point is called the quiescent or Q-point as it gives the values of the voltages when no input signal is applied. To determine the Q-point we need to look at the range of values for which the transistor is in the active region. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Biasing」の詳細全文を読む スポンサード リンク
|