It is based on comparing unknown analog input voltage (non inverting inputed) to set of reference voltages
When. 0<=V<=Vi/4. Output. 0 & 0
Vi/4<=V<=Vi/2. Output. 0 & 1
Vi/2<=V<=3Vi/4. Output 1 & 0
3Vi/4<=V<=Vi. Output 1 & 1
V is connected to non inverting part.
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