Digital to Analog (DAC) design with MOS transistors
You can look into a current steering DAC. It is basically a differential pair (5Pack) amplifier. Razavi has a introductory paper on this in his Circuit for all seasons issue. 

This is the IEEE link:
https://ieeexplore.ieee.org/document/8275558

This should be the same uploaded on the UCLA website:
http://www.seas.ucla.edu/brweb/papers/Journals/BRWinter18DAC.pdf

However, these DACs are very high speed and consume a lot of power even when idle.
You may not meet the power budget of your project using this architecture.