Both DTL and TTL are based on the saturating BJT inverter. The transistor acts as a switch that connects or disconnects the collector and emitter. The switch is closed when sufficient base current is applied to saturate the transistor. While the BJT technologies have dominated during the 1970s, logic families based on MOSFET technology are nowmore widely used because of the advantages of fewer fabrication steps and generally lower power consumption. After PMOS and NMOS technologies, CMOS emerged as the dominant MOS technology and remains so today. Let us consider the simple MOSFET inverter with resistive load shown in Figure (a), quite similar in principle to the BJT inverter, although the circuit is rather impractical, as we shall see later. The load line for R_D = 23 k and V_DD = 7 V is shown along with the transistor I-V characteristics in Figure (b). On finding vout (= v_DS) for different values of v_in (= v_GS), the voltage-transfer characteristic (vout versus vin) is plotted in Figure (c). By choosing the low range to be 0 to 3 V (i.e., less than the threshold voltage) and the high range to be 5 to 7 V, we can see that any input voltage in the low range gives an output of 7 V (high) and inputs in the high range give outputs in the low range. Thus, the circuit is seen to be an inverter.