## Course Edit

This page is for the course ELEC3106 - Electronics and is based on the lectures of Torsten Lehman senior lecturer at the University of New South Wales.

## Overview Edit

Non linearity is a situation where a real life analogue amplifier is unable to produce an output voltage which linearily follows the input voltage. This is of concern when designing an amplifier as a non linear amplifier has the following traits:

- Input signal is distorted, this means the output signal can't reflect the input signal making the amplifier essentially useless.

- The designer is unable to accurately predict the output of a non linear circuit.
- The circuit is unable to measure or receive signals with accuracy

## Prerequisites Edit

The reader of this page is assumed to have a basic mathematical knowledge (concerning linearity), and a basic knowledge of analogue circuitry, such as that gained from the course ELEC2133 - Analogue Electronics.

## Non Linearity Edit

### Causes and Effects Edit

In this section the various causes of non linearity are discussed as well as their effect on the output signal of the amplifier. Note that unless shown otherwise in the figures the input voltage is a pure sine wave.

**Clipping**

**Crossover Distortion**

**Soft Saturation**

### Quantification of non linear circuits Edit

To quanitify non linear circuits we examine the ouput voltage in the frequency domain. This is because it is very hard to accurately put a number on non linearity in the time domain. The main method of quanitfying non linear circuits is to claculate the total harmonic distortion (THD). This is done by plotting the frequency response of the output and measuring the peaks as V1, V2, ..., VN, where V1 is the fundamental frequency (the expected frequency). We then use the following equation:

$ \mathrm{THD} = \sqrt{\frac{V_2^2 + V_3^2 + \ldots + V_N^2}{V_1^2}} = \frac{1}{V_1}\left(\sum_{i=2}^N{V_i^2}\right)^{1/2} $

Usually the THD is expressed as a percentage. Typical values are around 1%.

### Fixing Non Linearity Edit

One very good method to make a circuit linear is to incorporate a high gain negative feedback into the circuit. The effect of this is that Vo is brought closer in line to Vin by the feedback mechanism, in much the same way as feedback eliminates noise. See figure 5 for an example.

## Further Reading Edit

It is recommended that the reader visits https://subjects.ee.unsw.edu.au/elec3106/ and reads the lecturers scribbles as an alternative source.

## See Also Edit

The page on electrical noise coming to an elsoc.wikia page near you!