Digital logic, an Inverter or NOT gate Digital logic, an Inverter or NOT gate | Page 5

improved due to the relatively low resistance compared to the NMOS-only or
PMOS-only type devices. Inverters can also be constructed with bipolar
junction transistors (BJT) in either a resistor–transistor logic (RTL) or a
transistor–transistor logic (TTL) configuration.
Digital electronics circuits operate at fixed voltage levels corresponding to a
logical 0 or 1 (see binary). An inverter circuit serves as the basic logic gate to
swap between those two voltage levels. Implementation determines the actual
voltage, but common levels include (0, +5V) for TTL circuits.