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A large signal is any signal having enough magnitude to reveal a circuit's nonlinear behavior. The signal may be a DC signal or an AC signal or indeed, any signal. How large a signal needs to be (in magnitude) before it is considered a large signal depends on the circuit and context in which the signal is being used. In some highly nonlinear ...
Large-signal modeling is a common analysis method used in electronic engineering to describe nonlinear devices in terms of the underlying nonlinear equations. In circuits containing nonlinear elements such as transistors, diodes, and vacuum tubes, under "large signal conditions", AC signals have high enough magnitude that nonlinear effects must be considered.
This resistor can thus account for the finite output resistance of a simple current mirror or an actively loaded common-emitter amplifier. In keeping with the model used in SPICE and as discussed above using V C B {\displaystyle V_{CB}} the resistance becomes:
Figure 4: Small-signal circuit for N-channel MOSFET common-source amplifier. Figure 5: Small-signal circuit for N-channel MOSFET common-source amplifier using Miller's theorem to introduce Miller capacitance C M. Bandwidth of common-source amplifier tends to be low, due to high capacitance resulting from the Miller effect.
Full hybrid-pi model. The full model introduces the virtual terminal, B′, so that the base spreading resistance, r bb, (the bulk resistance between the base contact and the active region of the base under the emitter) and r b′e (representing the base current required to make up for recombination of minority carriers in the base region) can be represented separately.
[nb 2] A small-signal analysis for an op amp with finite gain A v but otherwise ideal is based upon Figure 5 (β, r O and r π refer to Q 2). To arrive at Figure 5, notice that the positive input of the op amp in Figure 3 is at AC ground, so the voltage input to the op amp is simply the AC emitter voltage V e applied to its negative input ...
Conversely, a voltage follower inserted between a small load resistance and a driving stage presents a large load to the driving stage—an advantage in coupling a voltage signal to a small load. This configuration is commonly used in the output stages of class-B and class-AB amplifiers.
For any particular circuit, a small-signal analysis is often used to find the actual impedance. A small-signal AC test current I x is applied to the input or output node, all external sources are set to AC zero, and the corresponding alternating voltage V x across the test current source determines the impedance seen at that node as R = V x / I ...