6.3 Comparison Results

When comparing the eye diagram matrices of the system using PoDL and the system not using it, there are several key factors to notice.

First, there was no significant change in the shape of any of the eye diagrams. The general shape and outline as well as any effects caused by reflections did not seem to change between the tests. This means that when adding PoDL to a system, it should be expected that the eye diagram does not change significantly.

The second important thing to notice is that the system using PoDL had greater voltage noise than the system not using PoDL. This is especially significant if a mixing segment will be deployed in a noisy environment. While this may not be an issue in most cases, this becomes especially important if a node is barely within acceptable noise levels: any additional noise will push it beyond acceptable boundaries.

The increased noise may be caused by the poor filtering of the DC/DC converter on the add-on board for PoDL power. When looking at the Add-On PoDL Schematic, there is only a 1 µF capacitor as an input filter to the input pin of the converter. It may be possible to reduce the switching noise on the mixing segment by using a better filter.

Another important thing to note is that the type of noise is important. Depending on the network and line imbalances, any noise in an imbalanced systems causes mode conversion, so that the common mode noise of the power supply may have an impact on the signal quality if the connections between boards and layouts of each board are not designed and managed correctly. In this case, radiated emissions may become an issue in a noise or EMI sensitive environment.

Additionally, these measurements were done in laboratory conditions at only 3.5W power usage at maximum. There was no dynamic load. The behavior of the mixing segment may look completely different at greater power usage or when dynamic loads are present on the network.

Finally, it is important to note a major advantage of using PoDL is to power remote nodes. While performing the measurements using PoDL, applying power to the individual nodes was no issue. It was possible by simply connecting the node to the mixing segment. However, when performing the measurements without PoDL, applying power to the individual nodes became an issue. Some of the USB cables were a different length than others, a USB hub had to be found and other complications arose due to the amount of cables required. It became very clear that the overhead for routing power to the required nodes may become an issue at a larger scale.

One easy takeaway from this is that while a mixing segment using PoDL becomes more susceptible to noise, this drawback may be heavily outweighed by the simplicity and ease of use when installing and powering the mixing segment. When no large power dynamics, low noise environments or low total power requirements are present for a mixing segment, it will generally be advantageous to use PoDL in the system and save effort on cabling and overhead.