An Over Voltage condition occurs when a signal far exceeds the normal operating input range. Because an excessive voltage on the inputs can damage the device, automatic protection mechanisms are provided.
An Over Voltage event results in the automatic shutdown of the input buffer to protect it. The Over Voltage circuit monitors each of the signals of the differential inputs independently, and flags the condition when any individual input signal exceeds the maximum input voltage or is less than the minimum input voltage of the RF-ADC input buffer.
The Over Voltage feature offers protection for signals in the range defined in the Zynq UltraScale+ RFSoC Data Sheet: DC and AC Switching Characteristics (DS926). Signals exceeding this maximum are not permitted, and care must be taken externally to ensure that such voltages are not presented to the RF-ADC inputs.
When an Over Voltage condition is detected, the signal is flagged by both the interrupt mechanism and by asserting the Over Voltage real-time output signal. The Over Voltage real-time output is asserted and deasserted asynchronously, and provides immediate notification of the event. As a result, the Over Voltage output self-clears when the Over Voltage condition is no longer present. The associated interrupt is sticky, so requires clearing by the API interrupt handling routines.
After an Over Voltage event the input buffer automatically re-enables and the RF-ADC resumes operation as before. However, an over voltage condition should be considered as grounds to stop the traffic and restart the receiver chain. In the event of an Over Voltage condition, the buffer shuts down and the resulting RF-ADC output digital codes are mostly just noise. As a result, the threshold information become irrelevant and this can affect an AGC implementation. Therefore it is important that an AGC implementation takes account of the Over Voltage signal and sets up the two threshold detectors accordingly.
The following figure shows the Over Range, and Over Voltage levels and the response of these with an increasing input analog signal.