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In a conventional system design, there is typically one single ground node. Ground nodes for digital systems that deal with high-speed IO signals that constantly transition between 0 and 3V can be quite noisy compared to analog circuits where the output from the sensor is only on the order of 10s mV or smaller. This is the case for the acquisition of electrophysiology signals where the neural signal is on the order of 100s of µV, or in many cases less than 100 µV. Additionally, instruments relying on external AC power supplies generally are not earth-grounded.
TruGround is a unique XDAQ™ feature that maintains separated ground nodes and the corresponding electrical paths. On the animal side, there are unique grounds for signals and earth grounds that are connected to the connector shield. These ground nodes are also accessible from the ground panel behind the XDAQ™.
A common practice when debugging for noise during an electrophysiology experiment is to take a probe connected to “the ground” to touch various surfaces and observe the noise response. The idea is to identify the noise source and effectively sink it away. The problem is that if the ground is not connected to the earth, you could simply be introducing the noise back to the system. In rare cases, one might get lucky and the noise in differential inputs gets canceled. But really, this is no better than guessing.
If your surgical protocol includes building a copper mesh as a mini Faraday cage around your implant, tying the Faraday ground to the Earth ground would be a logical choice. In the X-Headstage™ and XDAQ™ solution, Earth ground is accessible on the X-Headstage™ via the connector shield. So, one could solder a pigtail to the outer shield of the µHDMI connector to tap into Earth ground.
Furthermore, the TruGround panel design in the back of the XDAQ™ makes the debugging more logical and straightforward. One can experiment with searching and grounding the noise sources to the earth ground (provided your building has earth ground). Then, if necessary, experiment with various configurations between the ground nodes. Each ground node in the TruGround system also includes two RC circuits that provide an ESD path to Earth in case of charge build-up that creates static charges. Circuit 1 includes a 1nF capacitor to ground and circuit 2 is a 1nF capacitor in parallel with a 1 MOhm resistor to ground. KonteX™ recommends turning on circuit 1 by default and experimenting with adding circuit 2 to the system to see if the ESD condition improves.
TruGround is a small but helpful design that might make optimization for noise easier and more logical.
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