3.3 Impedance Detection

The following figure shows the response in ON operation mode, where the system updates its response depending on the impedance detected in reception and following the objective of transmitted signal level, compared to the fixed modes:

This adaptation is achieved by defining thresholds to switch from HI to VLO mode, and vice versa, which determine the points where Transmission mode is changed.

These thresholds are defined such that the switch from HI to VLO is done in a lower impedance than the switch from VLO to HI, obtaining a hysteresis window to avoid continuous switching between states which will lead to a continuous change in signal injection, which is an undesirable scenario.

The following figure illustrates such thresholds and the hysteresis window they achieve:

As shown in the figure, the Auto response has been obtained sweeping from high to low impedance; this is why the switch is done near the lower value of the hysteresis window (some point between 10 and 15Ω). If the sweep is done in the opposite way, from low to high impedance, the transition will be done near the higher value of the hysteresis window, so the curve will follow the VLO curve inside the window and then switch to HI curve just above 20Ω.

It is also seen that the Auto curve does not follow the trend of the forced ones exactly. This is because the algorithm performs a fine tuning in each transmission according to the detected signal value, trying to adjust more closely to the signal injection objectives.