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ADV7802 issue: low gain when using the AGC

Question asked by phil.evertz on Sep 17, 2012
Latest reply on Sep 18, 2012 by DaveD

Hi,

 

Our group is having trouble getting the AGC on the ADV7802 to give our signals a near expected gain:

 

- the gain for RGB is too low in given a SD or HD component input signal
- the gain for YPbPr is too low given a HD component input signal
- the gain for YPbPr is perfect given a SD component input signal
The AGC is setting the gain to approximately 0x15F (351 decimal) for RGB SD/HD and YPbPr HD, and 0x2AF (678 decimal) for YPbPr SD. This was read from CP_AGC_GAIN[9:0]. The gain level of YPbPr SD was very close to the gain we saw on ALL of the input signals which is why the term “too low” is being used for the rest (the output gain is almost half of the input gain (~678 vs ~351)).

 

To use the AGC the following values were set: AGC_MODE_MAN = 0/1 (tried both, no difference) and GAIN_MAN = 0.

We were able to achieve similar gains for all input / output signals using manual mode (AGC_MODE_MAN = 1, GAIN_MAN = 1).

 

To select the RGB colour space the following values are being set: INP_COLOR_SPACE = 0x00, and to select the YPbPr colour space: INP_COLOR_SPACE = 0x03, CSC_ALT_GAMMA = 0.

 

We have read through section 6.3 “CP Gain Operation” in the hardware manual, as well as the corresponding section in the software manual and haven’t been able to find a solution. Any insight you could provide would be appreciated.

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