Test Cases TA137 or TB137 Fail Due to Faint LMA in Certain Locations

Issue Details

My PCD under test is failing test cases TA137 or TB137 in certain locations. When I look at the analog traces, it looks like the load modulation amplitude (LMA) is very small, which seems to be causing my PCD to fail to detect it, which causes the test to fail.

Why is the load modulation amplitude so small on this test case?

Solution

The over-the-air (OTA) capture of the LMA signal is not a conclusive means of determining test performance in these LMA sensitivity cases, because the overall OTA is a superposition of the PCD signal and the subcarrier. If the LMA value is small relative to other positions, this is likely due to a "communication hole", where the coupling, carrier signal, and subcarrier signal combine to result in destructive interference at the particular test location.

The distortion of the load modulation signal results in the PCD being unable to properly detect the subcarrier, and thus leads to a failure in these test cases.

Our recommended solution is to adjust the tuning of your PCD's coil to improve the performance at this location.