The DAC provides an analog output voltage or current that is proportional to the product of its digital input word and its analog reference.
Here is an example of a 3-bit D/A converter. Because it has 3 bits, there are 23 = 8 possible input codes, each producing a different output voltage or current. The difference between each output voltage is, in the ideal case, the size of the LSB, which is G x VREF / 2n, where "G" is the DAC gain factor and VREF is the DAC reference voltage, assuming the reference is a voltage
- Assuming that the output response has no errors, every time you increase the input code by one count, the output voltage or current will increase by one LSB. This means, in this example, that the least significant bit (LSB) represents 1 Volt, which is the smallest increment that this converter can resolve.
- If the reference voltage were reduced to 0.8V, the LSB size would then be 100mV, allowing the output to take on a smaller range of voltages (0 to 0.8V) with greater accuracy.
- The Resolution of a D/A converter is the number of input bits it has (3 bits, in this example). Resolution may also be defined as the size of the smallest output voltage or current step, or one LSB (Least Significant Bit), which is 1 Volt, in this example.
- When we speak of the resolution of a DAC we usually are referring to the number of input bits it has.
