Hello, I currently have a design utilizing the LMH0395 (SDI Equalizer) and I was hoping to get some clarification on the "Carrier Detect" functionality. Specifically I'm trying to understand what signal/data is being "detected". I currently use the Carrier Detect to trigger an LED indicator circuit, and this appears to work. When sending a good HD-SDI signal to the LMH0395 the Carrier Detect is LOW (indicating good SDI signal received). Likewise, if the HD-SDI signal is disconnected from the LMH0395 circuit, the Carrier Detect goes High (indicating a bad SDI signal received).
Unfortunately, the Carrier Detect circuitry is not operating as expected for degraded signals. There have been many times where we have pushed the cable lengths to the limit of what is recoverable, so much so that we loose video feed completely. In these scenarios, despite the lost video feed, the Carrier Detect circuitry remains Low, indicating that the LMH0395 should be able to recover it (to my understanding). Just prior to reaching these cable limits, the Jitter characteristics observed are within SMPTE standards, so I do not believe the lost video to be caused by excessive Jitter.
In trying to understand why the Carrier Detect circuit would act this way I began to wonder what was really being "detected". If it effectively detects the sampling frequency, I could understand what is going on. Or perhaps if it looks for bit sequences such as SAVs & EAVs, this might be recoverable while the rest of the signal was lost to CRC errors.
Any insight in how to better understand and utilize the "Carrier Detect" functionality here would be very much appreciated.
Thank you, in advance, for your time and assistance.
- Jay Hardesty
