The role of parallel resistance and capacitance in signal lines

GUOYUAN

The role of parallel resistance and capacitance in signal lines [Copy link]

Hello everyone, As shown in the figure below, a small resistor (such as 33 ohms) is connected in series with the signal line to match the impedance and reduce reflection, but what is the purpose of connecting a 1K resistor and a 22pF capacitor in parallel? I hope someone who knows can help explain it. Thank you.

maychang

Without seeing the specific circuit, we can only guess. It is estimated that this is to ensure that the signal line is grounded, has a certain impedance to the ground, and the high frequency is attenuated quickly to avoid interference.

qmycy

If the signal is at a low level for a long time, it is preferred to pull down, and if it is at a high level for a long time, it is preferred to pull up. The capacitance of the capacitor is very small and it is a filter. From the input signal end, it is to reduce the input internal resistance of the subsequent stage. From the perspective of EMS, the lower the input impedance, the greater the current provided by the signal end, and the stronger the anti-interference. From the perspective of EMI, the capacitor provides a loop to the ground for high frequencies. Avoid excessively high input impedance of the subsequent stage, turning the signal line into an antenna.