Video Decoder( ADV7282A) outputting noise instead of Blue screen

Hi,

    Please find more details about the Free Run feature in the following document: ADV7280/ADV7281/ADV7282/ADV7283 Hardware Reference Manual UG-637 (Rev. B) . Kindly share the current register settings for further analysis from our side.

Thanks,

Ebin

Hi, Ebin

We dump the register setting after detected video standard at stable displayed.

Please check it. We like to keep stable output signal without internal test pattern. Like as ADV7842, can output decode video data when free run.

And, display static picture even signal is noise. Like TV tuner display behavior. 

BR

Kanter.Lin

Hi Ebin, 

Have you received our dumped register setting?  If not , we will send you agian 

B.R 

Hi Kanter,

Hi, Ebin 
Thanks for shared infomation for free-run control. Actually, we already check the sheet before. In order to display video data, we using force standard without free run. 
Because if we enable the free run, it will display ADI internal pattern, but customer requirement is keep to display video date even picture garbage. Black / Blue pattern is not acceptable.
When disable free-run mode, unstable signal will happened at low or distorted CVBS signal condition, and it will cause back-end scaler back-out picture.

And, we also confirmed ADV7842, there have free-run with decoded video, therefore we enable free-run with input video data, we can get stable signal with garbage video.
In ADV7282A, we like to improve this condition, therefore, is there any suggestion method? 

BR
Kanter

Hi Kanter,

Regarding the statement, “As the signal degrades, static is acceptable, but the monitor should not blank to a blue/black screen”:

1. Could you please adjust the gain and filter values and let us know the status?
2. To avoid signal instability, could you please increase the CVBS input signal strength and check the behavior?

Thanks,
Ebin

Hi, Ebin 
1. Could you please adjust the gain and filter values and let us know the status?
KL: What's gain and filter value?? Could you explain more detail.
2. To avoid signal instability, could you please increase the CVBS input signal strength and check the behavior?
KL: The output is from the RF module directly, it is difficult to increase input strength, is there any other suggestion?

Hi ,

The ADV7282A does not provide an equivalent gain adjustment option to that available in the ADV7842.

For gain adjustment on the ADV7282A, please refer to the Gain operation/ Filter section in the ADV728x Hardware Reference Manual (UG-637), which describes the luma and chroma gain control registers and their operation.

Reference:
https://www.analog.com/media/en/technical-documentation/user-guides/adv7280_7281_7282_7283_ug-637.pdf

Thanks,

Ebin

Hi ADI Engineer Team , 

//For gain adjustment on the ADV7282A, please refer to the Gain operation/ Filter section in the ADV728x Hardware //Reference Manual (UG-637), which describes the luma and chroma gain control registers and their operation.

I think this your suggestion and response would not improve our our problem , please find the illustration below 

We think the problem is not from Gain operation/ Filter section , we assume problem should be from sync extraction and something else  .   

Let me explain our encountered  problem again 

We are using the ADV7282A to decode an analog CVBS video stream from an FPV drone wireless receiver. The digital video is outputted via an 8-bit parallel ITU-R BT.656 interface to our backend SoC.

In our application, when the drone flies far away, the CVBS signal experiences severe static noise (snow noise) and low SNR. We noticed that a standard monitor can still show the noisy image with OSD data, but the ADV7282A frequently unstable EAV/SAV outputs to backend SoC (as shown in our attached illustrations below , left side is our benchmark , right side is using ADV7282A monitor ). This frequent switching severely disrupts the BT.656 EAV/SAV timing sequence, causing synchronization issues on our backend SoC.

Our goal: We want the ADV7282A can keep stable BT.656 EAV/SAV as much as possbile . We prefer the decoder to output pure snow/noise rather than blanking out the video stream ,keeping the BT.656 sync codes continuous.

#1  Left side : Benchmark monitor, Right side: Using ADV7282A monitor

 ADV7282A monitor is kept to display noisy image ----> Okay 

#2  ADV7282A outputs unstable to our backend SoC and then leads to black screen   --> NG 

Current key setting as below :
//DEF_VAL_AUTO_EN set to 0
//VID_SEL[3:0] set to NTSC

This problem has been troubling us for a while,we hope ADI team can give us specific recommendations as soon as you can so that we can try to see if any improvement . 

Hi ,

Thank you for providing the additional information.

Could you please provide an update on the following items?

1. What is the analog input signal amplitude level during the noisy image condition and the blank video condition (when the drone flies far away)?
2. Kindly share the system register dump captured during the blank output condition.
3. What is the measured LLC frequency values in both cases?
4. Please provide the P0 to P7 signal levels measured using an oscilloscope (CRO) during both the working and issue conditions.

Your feedback on the above points will help us further analyze the issue.

Thanks,

Ebin