Download Noise

Noise
• External Noise
 Human-made
• Caused by electronic or mechanical
devices operating in proximity to
communications system
 Atmospheric
• Caused by natural phenomena occurring
either within Earth’s atmosphere or in
outer space
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Figure 1-9
Noise effect on a receiver’s first and second amplifier stages.
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Noise
• External Noise
 Space
• Arrives from outer space
• Internal Noise
 Thermal
• Result of thermal interactions between
free electrons and vibrating ions in a
conductor
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Figure 1-10
Resistance noise generator.
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Figure 1-11
Device noise versus frequency.
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Noise
• Internal Noise
 Transistor
• Shot noise results from currents flowing
within emitter-base/collector-base
diodes.
 Frequency noise effects
• Low-frequency effect (excess)
• High-frequency noise (transit-time)
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Figure 1-12 Noise figure versus frequency for a 2N4957 transistor.
(Used with permission from SCILLC dba ON Semiconductor. All rights reserved.)
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved
Figure 1-13 Noise contours for a 2N4957 transistor.
(Used with permission from SCILLC dba ON Semiconductor. All rights reserved.)
Electronic Communications: A Systems Approach
Beasley | Hymer | Miller
Copyright © 2014 by Pearson Education, Inc.
All Rights Reserved