The cartridge heads have a super curious digital protocol - the cartridge electronics
have no power supply. There is no power rail internally either.
Instead they use the fact mosfet gates have capacitance, and can therefore store 1 'bit' of information. Through a network of hundreds of MOSFETs, the right bits can be put on all the nozzle gates as needed, and then a 'fire' pulse is sent which for around a microsecond turns on a tiny heater (or not, depending on mosfet gate state). The heater boils some ink, making a pressure wave which travels down a pipe and makes a drop of ink fly out towards the paper. That heating and cooling again can happen around 10,000 times per second per nozzle (and there are ~300 nozzles).
I suspect this decision is because the custom silicon process needed to manufacture these nozzles is cheaper if they only have n type MOSFETs - and without p type MOSFETs you can't make a typical push pull logic gate.
The nozzles themselves are quite a lot of silicon - perhaps 100mm^2, with deep etched holes, and are effectively disposable, so I assume huge efforts have been taken to reduce costs - including this curious electrical design.
The protocol also is hugely irregular, which I suspect might be to avoid any wires on the chip needing to cross eachother.