Revision of Circuits and Electronics - Nonlinear Circuits (Lecture 6)

Non linear circuits can be analysed by the following methods

(1) Analytical method

(2) Graphical method

(3) Piecewise linear method - not a focus for the course

(4) Introduction to incremental analysis


How do we analyse them? It is possible to replace the linear part with the Thevenin equivalent.


Method 1 uses nodal analysis. From the two equations, a solution can be obtained by  by trial and error. v_D needs to be found first and this is done by substituting v_D into the arranged equation until a constant value of v_D is obtained.

Method 2 also uses nodal analysis but the equation is rearranged so that i_D becomes the main subject of the equation.  With the two equations, the graph of i_D versus  v_D is plotted.  There will be two plots representing the two equations, which intersect at a point that gives the solution.

Method 3 involves determining which of the linear region applies for the non linear component. Linear region is 1/ R_D so the  component can be replaced with a resistance value of R_D.

Method 4 in this lecture introduces incremental analysis which is also known as the small signal method. It is  a special way to make a non linear circuit,  linear. An example is  a circuit that transmit music over a light beam. The circuit consists of an input music signal, an LED, a photoresistor and an amplifier. The problem lies with the conversion at the beginning which is non linear, as the LED is  a non linear component, resulting in a distorted sound. This can be seen when i_D, the output current is plotted using the transfer characteristic and the graph of the input voltage versus time. The I_D does not look like the plot of the input voltage or v_D. So in order to work, the non linear LED needs to be turned into a linear device.


Video:- http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/video-lectures/lecture-6

Lecture notes : -  http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/lecture-notes/