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DAC Coding Schemes

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For 2's complement binary, codes from 0 to 2N-1-1 act just the same as they do for straight binary. But what about from 2N-1 to 2N-1? The output needs to be negative AND the coding isn't as direct as for the previous two codings. How did we handle binary subtraction when we talked about two's complement binary? By complementing, incrementing, and adding. Hey, we can play that game again! If the most significant bit is set,

a) set the ladder switches based on complemented and incremented remaining bits.

b) switch the output of the ladder from the inverting input of the summing amplifer to the non-inverting input.

That's it! And because this technology has been around for many years, it's all done in a nice, compact package. The point is that the coding of the DAC and the coding sent to the DAC from the computer have to match.

   
 

 

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