Search results
Results from the WOW.Com Content Network
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.
The use of a cascode (sometimes verbified to cascoding) is a common technique for improving analog circuit performance, applicable to both vacuum tubes and transistors.The name "cascode" was coined in an article written by Frederick Vinton Hunt and Roger Wayne Hickman in 1939, in a discussion on the application of voltage stabilizers. [3]
This is the only first order source of mismatch in the three-transistor Wilson current mirror [8] Second, at high currents the current gain, β, of transistors decreases and the relation of collector current to base-emitter voltage deviates from = (). The severity of these effects depends on the collector voltage.
Another major drawback is the amplifier's limited high-frequency response. Therefore, in practice the output often is routed through either a voltage follower (common-drain or CD stage), or a current follower (common-gate or CG stage), to obtain more favorable output and frequency characteristics. The CS–CG combination is called a cascode ...
This configuration is used less often than the common source or source follower.However, it can be combined with common source amplifiers to create cascode configurations. . It is useful in, for example, CMOS RF receivers, especially when operating near the frequency limitations of the FETs; it is desirable because of the ease of impedance matching and potentially has lower noi
To design the mirror, the output current must be related to the two resistor values R 1 and R 2. A basic observation is that the output transistor is in active mode only so long as its collector-base voltage is non-zero. Thus, the simplest bias condition for design of the mirror sets the applied voltage V A to equal the base voltage V B.
To calculate the current and voltage in them generally requires either graphical methods or simulation on computers using electronic circuit simulation programs like SPICE. However in some electronic circuits such as radio receivers , telecommunications, sensors, instrumentation and signal processing circuits, the AC signals are "small ...
The emitter junctions of these amplifier stages are fed by the collectors of a third differential pair (Q2/Q6). The output currents of Q2/Q6 become emitter currents for the differential amplifiers. Simplified, the output current of an individual transistor is given by i c = g m v be. Its transconductance g m is (at T = 300 K) about g m = 40 I C.