This is how a computer counts. Look at the left side 0 - 15 numbers. Pick any number on the left and then look at the little cells across from that number. Those cells are the on/off bits.
Look at 1 and notice there is a 1 in the X1 column but all 0's in the other columns.
Now look at 4 and notice how the first 4 have 1's the others have 0's. (For those of you familiar with an actual 8 bit binary counting scheme this isn't quite correct but that's not important for this discussion.)
The point is we count by using either an on or an off in the appropriate column and the column should represent a factor of 2 (because this is all binary). OK, so each word comes in with the ability to turn on or off one of the columns and each column represents a factor of 2. Got it?
Now it's a simple matter to make each column a voltage and each successive column with twice the voltage of the one before it. Now replace the 1's and 0's with switches. When a 1 appears in any column the switch is on and when there's a 0 the switch is off. Every time a switch is on, the amount of voltage in that column is added to the output. All switches on and you get a big voltage - all switches off no voltage - a few switches on a voltage somewhere in the middle. Here's a picture of that:
So each bit can either turn on or not turn on one of the 16, 24, or 32 switches available to it in the DAC. When a switch is active, the voltage goes up.
Now, remember that our goal is to have a digital number that represents a fixed voltage? That's how the process works and in the end we wind up with what I showed you yesterday, a sine wave (or musical signal) made from small steps of voltage generated by the 1's and 0's turning on or off the little voltage switches.
That's how a classic ladder DAC works.
But today, we no longer use this type of DAC. Tomorrow we'll review and explain what's up with that!
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