Managing Electrical Parasitics and Capacitance in Extended Bus Sensor Harnesses
Managing sensor harness parasitics demands fluoropolymer dielectrics, matched line termination, active buffer acceleration, and strict shield grounding topology.
Series Termination
Impedance Matching
Signal reflections at the source of a transmission line are prevented by placing a resistor in the signal path. Series termination involves adding a component with a value that, when combined with the driver’s internal resistance, matches the characteristic impedance of the cable. This technique is commonly used in point to point digital links to maintain signal integrity.
Waveform Effect
The use of series termination creates a voltage divider that initially sends a half amplitude pulse down the line. When the pulse reaches the high impedance receiver, it reflects and doubles back to the full logic level. This reflected wave travels back to the source where the series resistor absorbs the energy.
Power Consumption
A primary advantage of series termination is the low power consumption compared to parallel termination methods. Because the resistor is in series with the load, no DC current flows once the line has reached its final state. This makes it ideal for battery powered devices and low power CMOS logic.
The resistor is placed as close to the output pin of the driver as possible to minimize parasitic effects.
Component Placement
Proper series termination requires precise matching of the resistor to the specific impedance of the printed circuit board trace.