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How should the ground wires between the test coupon and the boards be connected?

o-leading.com o-leading.com 2017-09-22 20:09:39
About test coupon.
The test coupon is used to measure whether the characteristic impedance of the PCB plate produced by TDR (Time, Domain, Reflectometer) meets the design requirements. Generally, the impedance to be controlled has a single line and a differential pair of two cases. Therefore, the line width and line distance of the test coupon are the same as those of the line to be controlled. 

The most important thing is to measure the location of the site. In order to reduce the grounding wire (ground lead) of the inductance, TDR probe (probe) ground areas are usually very close to the local signal (probe tip), so test coupon measurement signal to ground distance and approach to meet the probe. 

How should the ground wires between the boards be connected to a number of PCB systems?
Each PCB board connected signal or power in the action, such as the A board has the power or signal is sent to the B board, the current must be equal from the formation to flow back to the A board (the Kirchoff current law). The current on this layer will flow back where the impedance is least. 

Therefore, in each power or signal interface, the number of pins allocated to the formation can not be too small to reduce the impedance, which can reduce the noise on the formation. In addition, can also analyze the current loop, especially the larger part of the current adjustment, the formation or wire connecting method, to control the current law (for example, somewhere in the low impedance, make the most of the current from the place to go), to reduce the influence of other sensitive signal.