NOISENoise is always present within electronic systems and is due to

fluctuations within the atomic structure of the components making up the system.

Original analogue signal

Original analogue signal

with noise

Original digital signal

with noise

Original digital signal

Noise is not related to the input signal

COMMON TYPES of NOISE

Thermal (Johnson) Noise: Caused by heat generated due to the random movement of atoms within the components. Has an infinite bandwidth with

equal noise power.

Flicker Noise: Caused by random variations in the diffusion of charge carriers within devices, transistors especially and is a low frequency noise.

Shot Noise: Caused by uneven distribution of charge carriers due to the granular nature of semiconductor materials as a result of fluctuations in the

diffusion process.

Pink Noise: A low frequency noise similar to flicker noise also known as 1/f noise since its power spectrum is inversely proportional to frequency.

White Noise: Similar to thermal noise, having noise components at all frequencies with equal noise power across the spectrum.

SIGNAL to NOISE RATIOThe signal-to-noise ratio (S/N ratio) is a quantitative method of describing the

quality of a signal in terms of its corruption by noise.

That is, the ratio of the magnitude of the signal to that of the noise, usually expressed as the ratio of signal power (Ps) to the noise power (Pn).

Manufacturers of audio equipment often like to quote the signal-to-noise ratio as a selling point for their equipment.

dBP

PratioNS

n

s10log10

The signal-to-noise ratio within a given system varies with the magnitude of the signal.

If the signal becomes very small, the relative size of the noise will increase causing the S/N ratio to decrease, (remember the noise level is independent

of signal).