![]() Probably many mistakes but better having dumb ideas than being braindead Could be braindead with dumb ideas? You be the judge ^^' I was thinking of trying to do an internal solution for my 圆8000 to be able to plug directly modern monitor in it. How good is the power supply? How much of its inherent ripple or noise will get into the signal? What about the DC resistance of some of the traces and offset voltages caused by currents in the ground? Even just 500 µΩ with 100 mA thru it will cause 50 µV offset.Multisync CRTs get rare, expensive and old. Lots of little things you can usually ignore in millivolt-level circuits become significant when you are looking for 50 µV accuracy. #EGA TO VGA CONVERTER CIRCUIT FULL#Consider that one count of a 16 bit number with a full range of 3.3 V is only 50 µV. Many parts drift more than that just from a 1☌ change.ĭifferent metals in the loop can cause thermocouple effects. Then getting parts that are good to 15 ppm over whatever your temperature range is will be tricky. Small mechanical stresses to the board, even those caused by temperature change, can change part value to more than 15 ppm. Beyond that a single resistor will probably cost more than a integrated 16 bit D/A, and you still won't get 16 bit accuracy.Īt 16 bits (15 ppm) various other effects also have to be considered. 0.1% resistors can almost do 10 bits, but nowhere near 16 bits. 1% resistors are good to 1 part in 100, which is not quite 7 bits. ![]() Where are you going to find resistors matched to within 15 ppm? The only way to achieve this with current technology is have them all on the same chip with factory trimming. 16 bit implies one part in 66 k accuracy, or 15 ppm. There is no way you're going to make a "16 bit" R/2R ladder on your own. I've dropped a number of terms in here to help guide your research, INL, DNL, Monotonic and Gamma, look them up, understand them.Įxploring techniques and topologies, and learning the limits and why things are done the way they are and how they fail is an important way to learn. ![]() the shading transitions will noticeably weird). And yes, you may have posterization in your colour tones (i.e. But it is guaranteed to be Monotonic and given the human eye insensitivity to display gamma this should be mostly passible. The INL will be dominated by the resistor accuracy, and the reproducibility of the DNL will be dominated by the resistor mismatch. All the hand wringing about resistor accuracy is for the most part only important if you are looking for reproducibility from unit to unit. Slow down the edges on the input and output just to keep things well behaved. your PSRR will be 0 dB )or close enough) Simply put a digital buffer on the input that has a separate clean power supply, (shared with the O/P amplifier). The other issue you will have is the noise from the Logic levels in particular the power supply noise on the MSB will drive straight into the VGA inputs, you'll see ripples going through your screen. Make sure it's input impedance is high so this it doesn't load the R-2R network also. ![]() Choose a nice R-R (rail to rail) amplifier that is fast enough and put it on a clean supply. You're right, The standard procedure then would be to put a voltage buffer between the R-2R network and the VGA input. ![]() You suspect that the VGA input is loading the resistor network. Just don't try to put this into production. You don't give enough information so we all have to make assumptions, but you claim to have something almost working and you indicate you have your suspicions as to what is wrong so I'll use this as a learning opportunity. Is this a good method? - well it's not production worthy, but if you learn something from it then it's probably good. ![]()
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