Contents
When to use series termination?
Series termination is effective in reducing the driver’s edge rate, and it consumes low power. It is recommended for single receiver, point-to-point and star topologies. Series termination provides good signal quality by damping overshoot and undershoot, and effectively reducing line noise and EMI.
How does series termination work?
The series termination scheme works by introducing a resistor placed in series between the driver and receiver. The driver impedance and series resistance become the total effective driver impedance. The transmission line impedance has to match the driver impedance to minimize reflection and manage overshoot.
Can common mode termination?
A common mode termination helps to reduce EMI emissions and susceptibility to EMI by properly terminating common mode energy that can exist on a twisted pair cable. This technique is used for unshielded twisted pair (UTP) which, due to lack of shielding, is susceptible to common mode noise.
What are the two factors that influence resistance?
Resistance is the property of the material that restricts the flow of electrons. There are four factors affecting resistance which are Temperature, Length of wire, Area of the cross-section of the wire, and nature of the material.
Why do you put a resistor on a signal line?
Adding a resistor to a line may limit damaging current flows that would otherwise result from short high-voltage transients, such as those caused by electrostatic discharge (ESD). A low-value resistor in line with the power-supply input to a chip will drop a voltage which is proportional to the chip’s supply current.
What should be the resistor length of a digital line?
Typical values are 20, 30, and 50 ohms respectively. An excellent book is: High-Speed Digital Design, A Handbook of Black Magic, by Howard Johnson and Martin Graham. According to the book: If the line length exceeds one-sixth of the electrical length of a rising edge, terminators are needed.
Where does the series termination resistor need to go?
BTW the series termination resistor needs to go as close as possible to the DRIVING end of the line. This is important. Although they are somewhat related, the edge rate is more important than the frequency.
What is the purpose of a source resistor?
The purpose is to match the source end of the transmission line formed by the track. This means that when the unterminated far end of the line reflects the signal, those reflections will be absorbed in the source resistor, resulting in a clean signal received at the far end.