ADV7125 & AD724

Question

We want to implement a system with PAL video output or VGA monitor. 
 1. For a PAL solution we want to use the ADV7125 for digital to analog conversion and the AD724 for analog to composite video. We saw in the datasheet of the AD724 (page 11) that it may be possible to use this solution because there is an example circuit using the ADV7120 (similar part to the ADV7125). 
 
 Our question is about the voltage level of the green output of the ADV7125. 
 In the datasheet of the ADV7125 you can see that BLANK level of the green output is around 0.2V and WHITE level is around 0.9V (page 11). The AD724 only supports the standard 0V for BLANK and 0.7V for WHITE. Can we use ADV7125 in conjunction with the AD724 although the level is not correct? What will the consequences be? Are there any workarounds? 
 We don’t understand how it is possible to use the ADV7120, for example, with this level of voltage. 
 2. For the same reason for VGA, can we use ADV7125 to generate the green color although the level is not the standard also? 
 What will the consequences be?

FormerMember · Accepted Answer

If you compare ADV7120 Figure 3 with ADV7125 Figure 5 you will see that the output wave forms are almost identical. The series AC blocking caps to the AD724 will level shift the voltage to the right levels for the AD724 to work. 
 Analog video is treated as an AC signal with blank to white level = 0.7 Volts. The DC offset is corrected with the blocking caps. Normally video is defined as 1Vpp when you include the sync pulses. The peak to peak pulse levels are as shown in ADV7125 Figure 5.)

FormerMember · Answer

If the analog green input is greater then that spec'd by the part then you can change the input 75 Ohm resistor into a divider network to lower its peak to peak value. As an example, we do this for the ADV7842 inputs. Check out UG-214 Figure 171 where we have a 24 Ohm series resistor and a 51 Ohm to ground to reduce the peak to peak voltage while maintaining the 75 Ohm load requirement. 
 http://ez.analog.com/docs/DOC-1712

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ADV7125 & AD724