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Single-stage Transistor Amplifiers
The asymptotic gain model (also known as the Rosenstark method) is a representation of the gain of negative feedback amplifiers given by the asymptotic gain relation: :G = G_ \left( \frac \right) + G_0 \left( \frac \right) \ , where T is the return ratio with the input source disabled (equal to the negative of the loop gain in the case of a single-loop system composed of Amplifier#Unilateral or bilateral, unilateral blocks), ''G∞'' is the asymptotic gain and ''G0'' is the direct transmission term. This form for the gain can provide intuitive insight into the circuit and often is easier to derive than a direct attack on the gain. Figure 1 shows a block diagram that leads to the asymptotic gain expression. The asymptotic gain relation also can be expressed as a Signal-flow graph#Example 3 Asymptotic gain formula, signal flow graph. See Figure 2. The asymptotic gain model is a special case of the extra element theorem. As follows directly from limiting cases of the gain expressio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Negative Feedback Amplifier
A negative-feedback amplifier (or feedback amplifier) is an electronic amplifier that subtracts a fraction of its output from its input, so that negative feedback opposes the original signal. The applied negative feedback can improve its performance (gain stability, linearity, frequency response, step response) and reduces sensitivity to parameter variations due to manufacturing or environment. Because of these advantages, many amplifiers and control systems use negative feedback. An idealized negative-feedback amplifier as shown in the diagram is a system of three elements (see Figure 1): * an ''amplifier'' with gain ''A''OL, * a ''feedback network'' ''β'', which senses the output signal and possibly transforms it in some way (for example by attenuating or filtering it), * a summing circuit that acts as a ''subtractor'' (the circle in the figure), which combines the input and the transformed output. Overview Fundamentally, all electronic devices that provide power ga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybrid-pi Model
Hybrid-pi is a popular Electronic circuit, circuit model used for analyzing the small signal behavior of Bipolar junction transistor, bipolar junction and Field-effect transistor, field effect transistors. Sometimes it is also called Giacoletto model because it was introduced by Lawrence J. Giacoletto, L.J. Giacoletto in 1969. The model can be quite accurate for low-frequency circuits and can easily be adapted for higher frequency circuits with the addition of appropriate inter-electrode capacitances and other Parasitic element (electrical networks), parasitic elements. BJT parameters The hybrid-pi model is a linearized two-port network approximation to the BJT using the small-signal base-emitter voltage, \textstyle v_\text, and collector-emitter voltage, \textstyle v_\text, as independent variables, and the small-signal base current, \textstyle i_\text, and collector current, \textstyle i_\text, as dependent variables. A basic, low-frequency hybrid-pi model for the bipolar tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mason's Gain Formula
Mason's gain formula (MGF) is a method for finding the transfer function of a linear signal-flow graph (SFG). The formula was derived by Samuel Jefferson Mason, for whom it is named. MGF is an alternate method to finding the transfer function algebraically by labeling each signal, writing down the equation for how that signal depends on other signals, and then solving the multiple equations for the output signal in terms of the input signal. MGF provides a step by step method to obtain the transfer function from a SFG. Often, MGF can be determined by inspection of the SFG. The method can easily handle SFGs with many variables and loops including loops with inner loops. MGF comes up often in the context of control systems, microwave circuits and digital filters because these are often represented by SFGs. Formula The gain formula is as follows: : G = \frac = \frac : \Delta = 1 - \sum L_i + \sum L_iL_j- \sum L_iL_jL_k + \cdots + (-1)^m \sum \cdots +\cdots where: *Δ = ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extra Element Theorem
The Extra Element Theorem (EET) is an analytic technique developed by R. D. Middlebrook for simplifying the process of deriving driving point and transfer functions for linear electronic circuits. Much like Thévenin's theorem, the extra element theorem breaks down one complicated problem into several simpler ones. Driving point and transfer functions can generally be found using Kirchhoff's circuit laws. However, several complicated equations may result that offer little insight into the circuit's behavior. Using the extra element theorem, a circuit element (such as a resistor) can be removed from a circuit, and the desired driving point or transfer function is found. By removing the element that most complicate the circuit (such as an element that creates feedback), the desired function can be easier to obtain. Next, two correctional factors must be found and combined with the previously derived function to find the exact expression. The general form of the extra element theor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blackman's Theorem
Blackman's theorem is a general procedure for calculating the change in an impedance due to feedback in a circuit. It was published by Ralph Beebe Blackman in 1943, was connected to signal-flow analysis by John Choma, and was made popular in the extra element theorem by R. D. Middlebrook and the asymptotic gain model of Solomon Rosenstark. Blackman's approach leads to the formula for the impedance ''Z'' between two selected terminals of a negative feedback amplifier as Blackman's formula: :Z = Z_D \frac \ , where ''ZD'' = impedance with the feedback disabled, ''TSC'' = loop transmission with a small-signal short across the selected terminal pair, and ''TOC'' = loop transmission with an open circuit across the terminal pair. The loop transmission also is referred to as the return ratio. Blackman's formula can be compared with Middlebrook's result for the input impedance ''Zin'' of a circuit based upon the extra-element theorem: :Z_ = Z^_ \left \frac\right/math> where: :Z\ is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Voltage Divider
In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (''V''out) that is a fraction of its input voltage (''V''in). Voltage division is the result of distributing the input voltage among the components of the divider. A simple example of a voltage divider is two resistors connected in series, with the input voltage applied across the resistor pair and the output voltage emerging from the connection between them. Resistor voltage dividers are commonly used to create reference voltages, or to reduce the magnitude of a voltage so it can be measured, and may also be used as signal attenuators at low frequencies. For direct current and relatively low frequencies, a voltage divider may be sufficiently accurate if made only of resistors; where frequency response over a wide range is required (such as in an oscilloscope probe), a voltage divider may have capacitive elements added to compensate load capacitance. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kirchhoff's Circuit Laws
Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirchhoff. This generalized the work of Georg Ohm and preceded the work of James Clerk Maxwell. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws. These laws can be applied in time and frequency domains and form the basis for network analysis. Both of Kirchhoff's laws can be understood as corollaries of Maxwell's equations in the low-frequency limit. They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits. Kirchhoff's current law This law, also called Kirchhoff's first law, or Kirchhoff's junction rule, states that, for any node (junction) in an electrical circuit, the sum of cur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ohm's Law
Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of proportionality, the Electrical resistance, resistance, one arrives at the three mathematical equations used to describe this relationship: V = IR \quad \text\quad I = \frac \quad \text\quad R = \frac where is the current through the conductor, ''V'' is the voltage measured across the conductor and ''R'' is the electrical resistance, resistance of the conductor. More specifically, Ohm's law states that the ''R'' in this relation is constant, independent of the current. If the resistance is not constant, the previous equation cannot be called ''Ohm's law'', but it can still be used as a definition of Electrical resistance and conductance#Static and differential resistance, static/DC resistance. Ohm's law is an empirical law, empirical rel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Using Return Ratio
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Using may refer to: Programming language keywords * In C++, for alias declarations * In C++, for using directives * In C++, for using enum declarations * In C#, for using directives * In TypeScript, for using declarations Other uses *Using Daeng Rangka (c. 1845–1927), a Makassan fisherman who had contact with Aboriginal Australians See also * Use (other) Use may refer to: * Use (law), an obligation on a person to whom property has been conveyed * Use (liturgy), subset of a Christian liturgical ritual family used by a particular group or diocese * Use–mention distinction, the distinction between ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Current Mirror
A current mirror is a circuit designed to copy a electric current, 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 ''inverting current amplifier'' that reverses the current direction as well, or it could consist of a amplifier#Ideal, current-controlled current source (CCCS). The current mirror is used to provide bias currents and active loads to circuits. It can also be used to model a more realistic current source (since ideal current sources do not exist). The circuit topology covered here is one that appears in many monolithic ICs. It is a Widlar current source, Widlar mirror without an emitter degeneration resistor in the follower (output) transistor. This topology can only be done in an IC, as the matching has to be extremely close an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Active Load
An active load or dynamic load is a component or a circuit that functions as a current-stable nonlinear resistor. Circuit design In circuit design, an active load is a circuit component made up of ''active devices'', such as transistors, intended to present a high small-signal impedance yet not requiring a large DC voltage drop, as would occur if a large resistor were used instead. Such large AC load impedances may be desirable, for example, to increase the AC gain of some types of amplifier. Most commonly the active load is the output part of a current mirror and is represented in an idealized manner as a current source. Usually, it is only a ''constant-current resistor'' that is a part of the whole current source including a ''constant voltage source'' as well (the power supply ''VCC'' on the figures below). Common base example In Figure 1 the load is a resistor, and the current through the resistor is determined by Ohm's law as: :I_C = \frac {R_C}. As a consequence of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
