Logic circuits use current source or voltage source?
There are two common types:

1)   Voltage source switched logic CMOS (Very low static current )


Although not 0 Ohm voltage sources , logic families exist for 300 Ohm high V (CD4xxx) 50 Ohm 74HCxx and 25 Ohm 74ALCxx


Although dozens of CMOS families now exist, they offer different voltage ranges and speeds.  3~18V lowest speed, 5V standard speed , 3 V lower power or high speed, &lt; 3V etc  examples

2) Current Model Logic (CML) aka ECL.  at very high speed ( GHz )


CML is optimized for 50 Ohm sources and 400mV swing.
usually differential so Vcc current is constant and noise free.


Older TTL is asymmetric current bias but defined by voltage threshold and input current can tolerate floating inputs unlike CMOS but generally low current High"1", higher current low V"0". Input Threshold is 2 Vbe drops.

Logic is always defined by Voltage thresholds with std. margin for noise. so in between "0" &amp; 1" depends on temperature, supply voltage , supplier, tolerances and noise so it is switched rapidly.

Some may argue CMOS logic ( with validity) that CMOS is just Voltage controlled conductors to Vdd and Vss that conduct a known small amount of current in between and nothing unless loaded in either state or  a dynamic amount of current according to capacitance load (pF) and frequency of switching.  (Ic=CdV/dt)