想問咩係linear circuit

A linear circuit is an electric circuit in which, for a sinusoidal input voltage of frequency f, any output of the circuit (the current through any component, or the voltage between any two points) is also sinusoidal with frequency f. Note that the output need not be in phase with the input.

Another equivalent way of defining a linear circuit is that it obeys the superposition principle. This means that the output of the circuit F(x) when a linear combination of signals ax1(t) + bx2(t) is applied to it is equal to the linear combination of the outputs due to the signals x1(t) and x2(t) applied separately:
F(ax1+bx2)=aF(x1)+bF(x2)

Examples
Examples of linear circuits are amplifiers, differentiators, and integrators, or any circuit composed exclusively of ideal resistors, capacitors, inductors, op-amps (in the "non-saturated" regime), and other "linear" circuit elements.

Some examples of circuits and components that operate in a nonlinear way: diodes, transistors when they are operated in saturation, iron core inductors and transformers when the core is saturated, mixers, modulators, and digital logic circuits.
Because they obey the superposition principle, linear circuits can be analyzed with powerful mathematical frequency domain techniques, including Fourier analysis and the Laplace transform. These also give an intuitive understanding of the qualitative behavior of the circuit, using terms such as gain, phase, resonance, bandwidth, Q, poles, and zeros. The analysis of a linear circuit can often be done by hand using a scientific calculator.


hope this can help you

2008-11-12 13:18:47 補充：
In contrast, nonlinear circuits usually don't have exact solutions. They must be analyzed using approximate numerical methods by electronic circuit simulation languages such as Spice, if accurate results are desired.

2008-11-12 13:19:07 補充：
These can give solutions for any specific circuit, but not much insight into the operation of the circuit in general with different component values or inputs. Linear circuit element (resistors, capacitors, inductors) behavior can be specified by a single number.

2008-11-12 13:19:17 補充：
In comparison, nonlinear elements' behavior is specified by the device's detailed transfer function which may be given as a graph, so more information is needed to specify nonlinear circuits' characteristics.

2008-11-12 13:19:29 補充：
Linear circuits and systems form a separate category within electronic manufacturing. Manufacturers of transistors and integrated circuits divide their product lines into 'linear' and 'digital' lines, for example.

2008-11-12 13:19:36 補充：
In their linear components, manufacturers work to reduce nonlinear behavior to a minimum, to make the real component conform as closely as possible to the 'ideal' model used in circuit theory.

2008-11-12 13:19:51 補充：
Nonlinear elements such as transistors tend to behave linearly when small AC signals are applied to them. So in analysing many circuits where the signal levels are small, for

2008-11-12 13:20:02 補充：
example those in TV and radio receivers, nonlinear elements can be replaced with a linear small signal model, allowing linear analysis techniques to be used.

2008-11-12 13:20:11 補充：
Conversely, many linear circuit elements show nonlinearity as the signal level is increased. If nothing else, the power supply voltage to the circuit usually puts a limit on the magnitude of voltage output from a circuit

2008-11-12 13:20:21 補充：
Above that limit, the output ceases to scale in magnitude with the input, failing the definition of linearity.

2008-11-12 13:20:32 補充：
hope these can help you

linear 意思係線性, 直線關係。數學上
1. f(x y z) =f(x) f(y) f(z), x,y,z variable
2. f(kx ky kz)=kf(x y z) k constant
簡單講電路上元件功能(I,R,V,f)可以直接相加減, 就係linear circuit.
例如 ohm's law. V=IR 夠線性啦, 串連電阻(R=R1 R2....)
V=I(R1 R2..)=IR1 IR2...

就算電容,線圈, 如果電係sinosoidal ac都用ohm's law.加多左個jw(omega),亦係線性加減. 都係linear circuit. 如果個電唔係sinosoidal, 就唔係linear circuit.

二極管, 三極管 都唔係linear, 例如二極管絛VI curve都唔係直線, 三極管三個極都唔係。所以計算比較復雜。

結論: 所有元件都係linear, 就係linear circuit.
唔知我講得好唔好？中文好難表達。

2008-11-12 22:09:08 補充：
http://en.wikipedia.org/wiki/Linear_circuit