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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. A bias circuit is a portion of the device's circuit that supplies this steady current or voltage.
A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. The current being "copied" can be, and sometimes is, a varying signal current. Conceptually, an ideal current mirror is simply an ideal ...
A load line diagram, illustrating an operating point in the transistor's active region.. Biasing is the setting of the DC operating point of an electronic component. For bipolar junction transistors (BJTs), the operating point is defined as the steady-state DC collector-emitter voltage and the collector current with no input signal applied.
It may be used as a Wilson current source by applying a constant bias current to the input branch as in Fig. 2. The circuit is named after George R. Wilson, an integrated circuit design engineer who worked for Tektronix .
Current mode logic (CML), or source-coupled logic (SCL), is a digital design style used both for logic gates and for board-level digital signaling of digital data. The basic principle of CML is that current from a constant current generator is steered between two alternate paths depending on whether a logic zero or logic one is being represented.
Current in the reference transistor Q 1 is held constant, thereby fixing the compliance voltage. Plots assume I C1 = 10 mA, V A = 50 V, V CC = 5 V, I S = 10 fA, β 1, = 100 independently of current. The current dependence of the resistances r π and r O is discussed in the article hybrid-pi model. The current dependence of the resistor values is:
The bias network is designed to preserve the applied AC signal. Similarly, amplifiers using field-effect transistors or vacuum tubes also have bias circuits. The operating point of an amplifier greatly affects its characteristics of distortion and efficiency; power amplifier classes are distinguished by the operating point set by the DC bias.
Signal is applied at V in, output taken from node V out may be a voltage or a current. Figure 2: Basic NPN common base circuit (neglecting biasing details). Current source I C represents an active load. In Figure 1 the load is a resistor, and the current through the resistor is determined by Ohm's law as: