Digital to analog converter

1. A digital to analog converter (DAC), comprising:

a self-calibration signal generator receiving an output voltage of the DAC to generate a self-calibration signal;

a constant current generator determining a value of a constant current;

a first current provider, comprising a plurality of first current generating elements, and receiving the self-calibration signal, when the DAC is in a self-calibration mode, to determine amount of the first current generating elements coupling to the constant current generator to provide the constant current, wherein the first current provider further outputs a control voltage at connected control terminals of the first current generating elements;

a second current provider, comprising a plurality of second current generating elements which are controlled by the control voltage, and receiving a digital code to determine the actual working ones of the second current generating elements to generate an output current; and

a current to voltage converter, converting the output current to the output voltage,

wherein the self-calibration signal generator generates the self-calibration signal by a comparing procedure.

2. The DAC as claimed in claim 1 , wherein the self-calibration signal generator generates the self-calibration signal by comparing the output voltage with an upper limit and an lower limit, wherein the upper and lower limits of the output voltage are dependent on the digital code.

3. The DAC as claimed in claim 2 , wherein the self-calibration signal generator comprises:

a reference voltage generator generating the upper and lower limits of the output voltage; and

a comparing circuit comparing the output voltage with the upper and lower limits of the output voltage to generate the self-calibration signal.

4. The DAC as claimed in claim 3 , wherein the digital code is set to a specific value when the DAC is in the self-calibration mode and the reference voltage generator comprises:

a bandgap reference voltage generator generating a bandgap reference voltage; and

a boost/buck circuit boosting or bucking the bandgap reference voltage to generate the output voltage upper or lower limits.

5. The DAC as claimed in claim 2 , wherein the number of the first current generating elements that are coupled to the constant current generator is increased by the self-calibration signal when the output voltage is greater than the upper limit of the output voltage, and the number of the first current generating elements that are coupled to the constant current generator is decreased by the self-calibration signal when the output voltage is lower than the lower limit of the output voltage.

6. The DAC as claimed in claim 1 , wherein the first and second current generating elements are formed into a current mirror structure.

7. The DAC as claimed in claim 1 , wherein the first current provider further comprises a first switching circuit selectively coupling the first current generating elements to the constant current generator according to the self-calibration signal.

8. The DAC as claimed in claim 1 , wherein the second current provider further comprises a second switching circuit for setting the number of the actual working second current generating elements coupled to the current to voltage converter according to the digital code.

9. The DAC as claimed in claim 1 , further comprising a multiplexer operative to provide a specific digital code for the DAC to replace the digital code when the DAC is in the self-calibration mode.