- Small-signal model
**Small-signal modeling**is a common analysis method used inelectrical engineering to describenonlinear device s in terms oflinear equations . This linearization is done by first calculating (possibly by aniterative process if the circuit is complex) the DC bias point (that is, thevoltage /current levels present when no signal is applied), and then forming linear approximations about this point.**Motivation**Electronic circuits generally involve small time-varying signals carried over a constant bias. This suggests using a method akin to approximation by

differentials to analyze relatively small perturbations about thebias point .Any nonlinear device which can be described quantitatively using a formula can then be 'linearized' about a bias point by taking partial derivatives of the formula with respect to all governing variables. These partial derivatives can be associated with physical quantities (such as

capacitance , resistance andinductance ), and a circuit diagram relating them can be formulated.Small-signal models exist fordiode s,field-effect transistor s (FET) andbipolar transistors , notably thehybrid-pi model and varioustwo-port network s.**Notation*** Large-signal DC quantities are denoted by uppercase letters with uppercase subscripts. For example, the DC input bias voltage of a transistor would be denoted $V\_\{IN\}$.

* Small-signal quantities are denoted using lowercase letters with lowercase subscripts. For example, the input signal of a transistor would be denoted as $v\_\{in\}$.

* Total quantities, combining both small-signal and large-signal quantities, are denoted using lower case letters and uppercase subscripts. For example, the total input voltage to the aforementioned transistor would be $v\_\{IN\}(t)=V\_\{IN\}(t)+v\_\{in\}(t)$.

**Example: PN junction diodes**The (large-signal) Shockley equation for a diode can be linearized about the bias point or quiescent point (sometimes called

Q-point ) to find the small-signalconductance , capacitance and resistance of the diode. This procedure is described in more detail under diode modeling, which provides an example of the linearization procedure followed in all small-signal models of semiconductor devices.**ee also***

Diode modelling

*Hybrid-pi model

*Early effect

*SPICE ... (Simulation Program with Integrated Circuit Emphasis) is a general purpose analog electronic circuit simulator capable of solving small signal models.**References**

*Wikimedia Foundation.
2010.*

### Look at other dictionaries:

**Large-signal model**— Large signal modeling is a common analysis method used in electrical engineering to describe nonlinear devices in terms of the underlying nonlinear equations.In circuits containing nonlinear elements such as transistors, diodes, and vacuum tubes … Wikipedia**Signal integrity**— or SI is a measure of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage (or current) waveform. Over short distances and at low bit rates, a simple conductor can transmit this with… … Wikipedia**Model 45A**— Image Type Battle rifle Light machine gun Place of origin … Wikipedia**Small-angle neutron scattering**— (SANS) is a laboratory technique, similar to the often complementary techniques of small angle X ray scattering (SAXS) and light scattering. These are particularly useful because of the dramatic increase in forward scattering that occurs at phase … Wikipedia**Signal transduction**— In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another. Most processes of signal transduction involve ordered sequences of biochemical reactions inside the cell, which are… … Wikipedia**Model aircraft**— A die cast Boeing 747 400 model. Model aircraft are flying or non flying models of existing or imaginary aircraft using a variety of materials including plastic, diecast metal, polystyrene, balsa wood, foam and fibreglass. Flying designs range… … Wikipedia**Model rocket**— A typical model rocket during launch A model rocket is a small rocket that is commonly advertised as being able to be launched by anybody, to, in general, low altitudes (usually to around 100–500 m (300–1500 ft) for a 30 g (1 oz.) model) and … Wikipedia**Model lipid bilayer**— A model lipid bilayer is any bilayer assembled in vitro, as opposed to the bilayer of natural cell membranes or covering various sub cellular structures like the nucleus. A model bilayer can be made with either synthetic or natural lipids. The… … Wikipedia**Signal Hill, California**— Infobox Settlement official name = City of Signal Hill, California settlement type = City nickname = motto = imagesize = image caption = image imagesize = image caption = image mapsize = 250x200px map caption = Location of Signal Hill in Los… … Wikipedia**Model car**— For the term referring to delineation of (non model) car ranges, see car model. This Norev model car is a good miniature representation of a real Renault 4CV and would have been sold as a children s toy. A model car or toy car is a miniature… … Wikipedia