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LMH6586: LMH6586 Sync Detect

Manikandan M M
Prodigy 170 points
Part Number: LMH6586

I am using 4 LMH6586 Chips for Stanag3350B signals, where R, B, CSYNC channel doesn't have sync and G channel has sync. So, 

R, G Channel :

Vmin - 0 V;    Vmax - 1 V

B Channel:

Vmin - (-0.3 V);   Vmax - 0.7V

CSYNC:

Vmin - 0V;  Vmax - 2V

1)  Since, only G channel has minimum voltage of -0.3V. DC restore is needed as it is violating minimum input limit of 0V.

      But other channels input voltages are at a minimum voltage of 0V. So, is it okay to pull down Vref Clamp and Vref Sync and remove AC caps connecting to video inputs. 

 2) If i pull down Vref Clamp and Vin is (0 to 0.7V), then my Vout at Gain =1 is 0 to 0.7V and at Gain =2, Vout =0 to 1.4V. 

      I can disable the sync video and video detect for these particular channels through I2C config to avoid detection of FLAG

3) If my input signal doesn't have sync pulse(-0.3V) and I have used DC restore of 350mV, what will be my output voltage, if my input voltage is 0 to 0.7V?   is it 0V to 0.7V       or   0.3V to 1V  

4) Is there will be any degradation, if my input voltage is 0V and I have pull down DC restore Clamp?

5) Is it okay to pull down both Sync and clamp or is there should be any voltage difference?

  • +1
    TI__Genius 10552 points

    Hi Manikandan,

    1. For the R and B channels, since their input voltages are within the allowable input range of the device, it is okay to pull down Vref Clamp and Vref Sync and remove AC coupling caps. For the G channel, you should keep the DC restore as it is, since the minimum voltage is -0.3V which is outside the allowable range. 

    2.  Are you asking if you can disable the detection of flag here? If so, yes this is a good approach. 

    3. If your input signal doesn't have a sync pulse (-0.3V) and you have used a DC restore of 350mV, then the output voltage will be shifted up by 350mV. So if your input voltage range is 0 to 0.7V, your output voltage range will be 0.35V to 1.05V (0.3 to 1V as you suggested)

    4. If your input voltage is 0V and you pull down the DC restore clamp, there should not be any degradation in the signal. The purpose of the DC restore clamp is to shift the input voltage to meet the requirements of the chip. If your input voltage is already within the allowed range, pulling down the clamp should not cause any issues. 

    5. It is ok to pull down both sync and clamp, as long as input voltage is within the chips requirements. Ther doesn't need to be a specific voltage difference between sync and clamp as they serve difference purposes. Sync being used to detect and process the synchronization signals in the video input, while clamp is used to shift the DC level of the input signal to match the input requirements of the chip. 

    Thanks!

    Alex