|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
173.160.222.138
In Reply to: RE: Interesting the 1st comment posted by jkeny on July 22, 2015 at 07:27:22
In general transformers are designed to reject common mode signals while passing differential mode signaling, though nothing is perfect. Based on the construction and limitations set forth by mother nature, there is no such thing as a perfect transformer. Most common mode noise will be blocked by even crappy pulse type transformers as far as I know.
A problem with Ethernet circuitry CAN be common mode noise, sure. Diff signaling in itself only increases signal to noise ratio compared with the diff noise. However, the impedance "balancing" typically used in this type of circuitry allows for some amount of common mode noise rejection. Together they work to limit the negative affects of noise of both types.
The nature of the sum of the noise (common mode noise component plus differential mode noise component = sum of noise problem) problem will depend on the noise source and the victim circuits ability to reject it. In my experience the types of power supplies and high speed digital circuitry used in typical PC's can cause significant common mode and/or differential mode problems if not treated with care. Especially with low cost power supplies the diff mode and common mode filtering often employed to reduce these emissions and there are eliminated for cost reasons.
Poorly implemented circuits will be more susceptible. Awesomely implemented circuits will be less susceptible but not to the point of zero susceptibility, that would be impossible.
Depending on the source of the noise there is no guarantee you wont have differential mode noise problems in Ethernet circuitry nor is there any guarantee you wont have common mode problems...it all depends.
Follow Ups:
I might be wrong here but aren't ethernet transformers only good for differential noise issues? To deal with common mode noise requires a CM choke - yes it's a transformer but in a different topology/configurstion to the topology of ethernet transformers.
Ethernet pulse transformers are are just transformers tuned to comply to appropriate Ethernet hardware requirements, transfer Ethernet signaling power at the appropriately low power levels required for the job with required signal integrity. Like other transformers they are designed to respond to differential signals and reject common mode signals.
In transformers current is passed through a primary winding, magnetic flux in the core couples energy to the secondary winding to accomplish power transfer for whatever reason. The idea is to couple power from one winding to the other. Most of the time transformers have a different winding ratio on the primary and secondary to condition the transferred energy in some way.
Common mode chokes used properly ideally transfer no power from one winding to the next. They are used to link equal but opposing flux from the common mode noise current noise flowing through both windings in order that they destructively interfere. Common mode chokes I've seen are 1:1 winding ratios.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: