John Boyd wanted learn more about ADCs, so he designed this 4-bit pipelined residue amplifier ADC using discrete components:
ADC on a Key-chain
The residue amplifier pipeline ADC consists of one key block: the residue amplifier. These residue amplifier blocks are then connected in series, forming a pipeline, hence the name.
To design this kind of ADC, I just used some opamp logic to make a residue amplifier and then cascaded four of them together to make a 4 bit ADC.
The design files are available on Github:
OSH Park 