7 Reasons for Poor Signal Integrity
1. The influence of the voltage drop of the line resistance - the increase of the low level caused by the ground level (0 level) DC
The dotted line in the figure is the case of increase. The increase is related to the power consumption of the IC, the density of the IC, the feeding method, the ground wire resistance (R), and the total current of the ground wire fed. ΔV ground = ΔI × ΔR
2. The influence of the voltage drop of the signal line resistance
a) The IC output pin goes through the printed wire or cable to the input pin of another IC, and the output low-level current causes a low-level rise on the printed wire or cable resistance, and its value is ΔVOL=IOL×R . See the upper dashed line in the figure.
Obviously, the rise of the low level is related to the resistance value of the printed wire and the output low-level current, as shown in the following figure:
The low level at point B is higher than the low level at point A
Note: When the IC output pin is low level, if the device is not a driver, but a general device, because the output low level current is too large, much larger than the value given in the device manual, the output transistor will exit the saturation region and enter the work. area, so that the output low level is raised a lot. As shown by the dotted line above in the figure below:
Determining factors: Termination method Termination resistance size Output tube saturation depth Output tube β value
b) The IC output pin passes through the printed wire or cable to the input pin of another IC, and the output high-level current causes a high-level reduction on the printed wire or cable resistance, and its value is ΔVOH=IOH×R, See the dashed line below on the high level in the image below:
IOH is determined by the following factors: termination method, termination level, termination resistance R is determined by the following factors: line width, line thickness, line length are obvious, the reduction of high level is related to the resistance value of printed conductors or cables and the output High-level current is related, as shown in the following figure:
