IF you have used any of the microcontroller, you must have gone through the pain of limited DAC resolution which at some point of time must have forced you to use an external DAC, which is a little complicated to code. You can obviously extend the range of the DAC by using a sigma-delta converter on the software side but it can be a bit slowly. To extend the DAC, a LTC1665 8-bit 8-channel DAC and a 8-bit 6-channel digital potentiometer with a nominal resistance of 10K is used. Since the current flowing through the potentiometer is in the sub-µA range, a precision rail-to-rail opamp (AD8603) is added as a voltage follower to ensure the accuracy of the voltage divider.
The resolution is extended by using two DAC with a potentiometer using which we can adjust the output voltage continuously. If the potentiometer is replaced by a digital one the number of bits at the output is effectively the sum of the DAC resolution and that of the digital potentiometer. The effective output is that we have a 16 bit resolution at a cheaper cost. For those interested, a circuit diagram along with the schematic has been provided with the project.