I'm having some trouble understanding how the diode-connected device M3 maintains a fixed voltage difference between VDD (source) and node X (drain)? In other words, why is it called a diode?
I know that diode-connected devices are always in saturation if they are turned on. But who says that their Vgs will be equal exactly to their Vth. Can't Vgs be greater than Vth for a diode connected deivce?, so then the Vdd to Vx difference will no longer be a constant Vth.