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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 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.
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 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.
Can you use a pull down resistor on an analog input?
A 10k ohm resistor is recommended. See related links for more information on pull-down resistors. Adding a resistor may have an impact on your analog input readings since they will change the load going to the ADC. If you add a pull-down resistor, check your readings after to make sure that it has not affected them.
Why is a resistor added to a long input cable?
If you are not careful sizing the cap correctly, you may end up with ripple on the supply feed to the device which may have a detrimental effect on its operation. Sometimes a resistor, or other load, is added in parallel to a discrete digital input to compensate for the distributed capacitance in a long input cable.
What makes a cap different from a resistor?
It’s different from a cap because a cap will draw a lot of current on a digital edge (for a short but sometimes non-negligible time), having the opposite effect of a resistor.
Can you put a resistor in a circuit backwards?
There is no backwards. I think this applies perfectly to the definition of the resistor as a circuit element and should therefore be the accepted answer. However, the comment by @RussellMcMahan brings up the point that it may “matter” during an optical inspection process (visual or machine-based) as part of circuit board assembly.
Why is a series resistor used in a capacitor?
However, they often cannot handle all the current that can potentially be sourced by the higher voltage output, so a series resistor is used to limit the current through the diode. Yes, signal integrity is the reason.