Voltage Levels
Below is a list of voltage levels that are specified in certain documents as official, as well as examples of consoles or systems that output different voltage level standards.
I will define two voltage levels, terminated (connected to receiver like TV) and floating. This will presume the system is using a 75R resistor in order to form a 50/50 voltage divider when connected to a receiver, but if the system is different and using another termination resistor value, you would have to calculate the expected output voltage from that new voltage divider or just connect it to a receiver to measure the voltages.
Composite has all of its signal on a single pin, and its voltage range is 1V terminated / 2V floating.
This comprises of the Sync pulse expected to be 0.3V terminated / 0.6V floating, and the luma/chroma expected to be 0.7V terminated / 1.4V floating.
For composite the voltage level standard is called IRE (Institute of Radio Engineers).
The signal should be 75ohm terminated.
RGBs is RGB and CSync signals.
Similar to composite, but not quite, RGB voltage levels are slightly different.
There are 2 standards of expected voltage level for RGB. The RGB information is always 0.7V terminated / 1.4V floating for the actual color information, but the difference comes in if the RGB signal standard being used by the receiver are expected to have a 0.3V offset for the sync information or not.
The rule of thumb is set the voltage level to 0.7V terminated / 1.4V floating if you don't want to risk clipping colors, or to 1V terminated / 2V floating if you want to make sure regardless of receiver you have the full brightness.
If you set the levels to 1V for example instead of 0.7V and use something like an OSSC you can simply change the pre-gain to lower than default to compensate if you get too much brightness, but then on receivers that expect a 1V level it will still be full brightness.
A good application note on the RGB standards is here.
RS343A is typically used for 50Hz PAL signals.
This standard expects no sync assertion on the RGB pins, so it excludes the 0.3V offset as part of the RGB signals, and so expects a 0V to 0.7V terminated / 0V to 1.4V floating where the entire signal is color information with no offset.
In simple terms this means the RGB signals should be 0.7V terminated / 1.4V floating from 0 to 100% saturation.
The CSync voltage should be 1V terminated / 2V floating like the RGB pins.
The signal should be 75ohm terminated.
RS-170A is typically used for 60Hz NTSC in the US and Japan primarily.
This standard expects the RGB signals to include an offset of 0.3V where the Sync signal would be present, and so expects a 0V to 1V terminated / 0V to 2V floating signal where the first 0.3V terminated / 0.6V floating is ignored for sync.
In simple terms this means the RGB signals should be 1V terminated / 2V floating from 0 to 100% saturation, where the color information sits between 0.3V to 1V terminated or 0.6V to 2V floating.
The CSync voltage should be 1V terminated / 2V floating like the RGB pins.
The signal should be 75ohm terminated.
There is a variant of the CSync signal called TTL, where the voltage should be 2.5V terminated / 5V floating. This is used in systems like arcade machines typically.
The RGB voltages are also usually then 2.5V terminated / 5V floating for the RGB also.
The signal should be 75ohm terminated.
