Common mode differential mode signals

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SUMMARY

This discussion clarifies the distinctions between common mode and differential mode signals, emphasizing that both can be either AC or DC. A common mode signal appears identically on both inputs of a differential amplifier, while a differential mode signal varies between the two inputs. The conversation also highlights the relevance of operational amplifiers (opamps) and comparators, which have specific common mode and differential mode range specifications that determine their performance in rejecting common mode signals.

PREREQUISITES
  • Understanding of common mode and differential mode signals
  • Familiarity with operational amplifiers (opamps)
  • Basic knowledge of circuit simulation using SPICE
  • Concept of signal types: AC and DC
NEXT STEPS
  • Research the specifications of opamps regarding common mode and differential mode ranges
  • Explore how to simulate common and differential mode signals in SPICE
  • Learn about noise reduction techniques in twisted pair cables
  • Investigate the effects of common mode signals in real-world applications
USEFUL FOR

Electronics engineers, circuit designers, students learning about signal processing, and anyone interested in understanding the behavior of common mode and differential mode signals in amplifiers.

FOIWATER
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I am having trouble getting this.

I have been introduced to common mode and differential mode signals.

I assumed the inputs to a differential amplifier is an ac signal...

my instructor gave instruction on how to input such a signal to a circuit using SPICE, he used DC.

is the common mode dc while the diff mode is ac? can the diff mode be dc as well
 
Last edited:
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Common mode is a signal component that appears on both inputs. It can be AC or DC. An AC example would be 60Hz noise from a transformer coupled into a twisted pair cable. The twisted pair could be carrying any sort of signal, but they are both changing in unison from the 60 Hz common mode signal.

Differential mode signals are when the two signals are changing (or not) differently. One is more positive that the other. It could be around an AC or DC common mode voltage, or even ground.

Common mode and differential mode signals can be AC or DC or any combination.

opamps and comparators have both differential and common mode range specifications. The common mode range would be the range over which the amplifier can reject the common mode signal.
 
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Excellent, thanks
 

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