Uploaded by Norman Morrison

Amplifier Noise

Module 1
Power Amplifiers
(Assignment 1)
Lecturer: Mr Hughroy Cooper
Norman Morrison
Serenae Brown
The Objectives
Explain the reason for Amplifier Noise
Outline how Amplifier noise can be reduced
Outline the purpose and function of Heat sink in
Power Amplifier design
There is no such a device as a perfect amplifier. One of the
factors which governs the performance of any amplifier system
is the noise in the system.
Noise might be defined as signals in the system which are
unwanted and which degrade the desired signal content in the
A good understanding of the underlying principles can, in
some cases, be used to reduce noise in the design of amplifiers.
Noise is any random unwanted signal
that is added to the signal being
amplified, it is also known as ‘White
It does not convey any useful
It affects performance and overall
Source can be both internal and
external to the system.
External vs Internally
As far as the amplifier system is concerned, noise can be
divided into noise it receives at its input (external) and
noise it generates itself (internal).
Externally generated
interference (non random
noise) includes mains (line)
born sources such as spikes of
interference caused by arcing
contacts when heavy currents
are switched.
This is noise generated
within the components that
make up the amplifier.
Types of Noise
There are five types of noise in power amplifiers and
associated circuitry:
1) Shot noise
2) Thermal noise
3) Flicker noise
4) Burst noise
5) Avalanche noise
Shot Noise
1) Shot noise - is created when charge carriers crosses a
potential barrier, such as a semiconductor P-N junction.
Thermal Noise
2) Thermal noise - is generated by the thermal agitation
of electrons in a conductor. The typical sound is hiss.
Flicker Noise
3) Flicker (1/F) noise - is present in all active and many
passive devices. It may be related to imperfections in
crystalline structure of semiconductors.
1/f noise
white noise
Burst Noise
4) Burst noise - also called popcorn noise, is related to
imperfections in the semiconductor production process or material
and heavy ion implants.
Noise that is produced by
erratic jumps of bias current
between two levels at
random intervals in
amplifiers and other
semiconductor devices.
Avalanche Noise
5) Avalanche noise similar to shot noise, is created when a
p-n junction is operated in the reverse breakdown mode.
Reasons for Amplifier Noise
 Bad (or misguided) earthing practices
 Signal wiring running close to magnetic field
 Harmonic generating items such as transformers and
bridge rectifiers.
 Radio frequency interference
Reducing Power Amplifier Noise
Noise cannot be removed but preventive measurement can
be taken to minimize
Op-amps can also be paralleled to get lower noise. Outputs must be combined using
low value resistors to ensure proper current sharing and prevent circulating
currents between the op-amps. The noise improvement is much the same as with
discrete transistors.
The best way of eliminating avalanche noise is to redesign a circuit to use no zener
Flicker noise - as better processing can reduce it.
Low equivalent noise at the input is better achieved using discrete transistors with
controlled collector (or drain) current rather than IC packages. Bi-polar transistors
are good for a low source resistance but FET transistors perform better for high
source resistance.
For VHF range operation RF transistors should be used which are
remarkably low noise.
Earthed shield put between the source and the victim of noise. Restricts
E-field propagation
Connecting two zener back to back.
Plastic enclosure shield is best to protect from radiation noise.
Many local induced noise can be solved by proper grounding, shielding
and filtering.(Metal box around the conductor to reduce electric field
Noise Analysis in Operational Amplifier Circuits by Kenneth
A. Kuhn
Noise source and reduction techniques by Raman K. Attri