D.A.(Tony)Stewart
Advanced Member level 7
- Joined
- Sep 26, 2007
- Messages
- 9,070
- Helped
- 1,825
- Reputation
- 3,649
- Reaction score
- 2,222
- Trophy points
- 1,413
- Location
- Richmond Hill, ON, Canada
- Activity points
- 59,840
The best for common mode immunity in high speed is 50 Ohm differential current mode logic (CML) with microstrip and controlled matched termination impedance but this may be overkill for you.
Historically 50 years ago many old computers like PDP-8 from DEC were initially flawed for high speed communication between computers until they paid attention to common mode noise and how differential lines become unbalanced at AC line and RF rates and then standards rose out of this 50 yrs ago (for which there are hundreds) A few basic physical standards are important to you to learn.
This evolved to RS488 to differential SCSI, to Ethernet to CML and to CANBUS, each for different purposes.
Often CM Chokes are necessary to raise CM impedance on the signals to improve immunity for the effective bandwidth of ferrite used so two stages are sometimes used. For simple slow serial communication, unbalanced RS-232 is adequate but still prone to high noise transients.
You start by defining distance, transition data rates, rise times and preferred cable impedance, then consider trying to define maximum transient of EMI sources ( dv/dt and di/dt) and make selection of preferred standard interface and choose appropriate impedance of cable, shielding and filtering as required with proper active or passive termination impedance.
Historically 50 years ago many old computers like PDP-8 from DEC were initially flawed for high speed communication between computers until they paid attention to common mode noise and how differential lines become unbalanced at AC line and RF rates and then standards rose out of this 50 yrs ago (for which there are hundreds) A few basic physical standards are important to you to learn.
This evolved to RS488 to differential SCSI, to Ethernet to CML and to CANBUS, each for different purposes.
Often CM Chokes are necessary to raise CM impedance on the signals to improve immunity for the effective bandwidth of ferrite used so two stages are sometimes used. For simple slow serial communication, unbalanced RS-232 is adequate but still prone to high noise transients.
You start by defining distance, transition data rates, rise times and preferred cable impedance, then consider trying to define maximum transient of EMI sources ( dv/dt and di/dt) and make selection of preferred standard interface and choose appropriate impedance of cable, shielding and filtering as required with proper active or passive termination impedance.
Last edited: