What practical advantages could there be in using a logic NOT gate IC (e. g. schmit trigger hex inverters) when compared to a simple NMOS + pull-up resistor inverter? I want to invert the PWM output of an arduino, and I suspect using a dedicated inverter IC might be a bit overkill for that application.
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2 Answers
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A NOT gate will use less power. This is because the pull-up and pull-down will both be complementary transistors. This means that when the input is high and the pull-down transistor is pulling the output low, the pull-up transistor will basically be an open instead of a resistor between power and ground.
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1\$\begingroup\$ When I wrote this I had an NMOS/PMOS (CMOS) inverter in mind. The input is tied to both gates, so when the input goes high the PMOS opens and the NMOS turns on, pulling the output to ground. When the input goes low, the NMOS opens and the PMOS turns on, pulling the output to power. The reason for the low amount of power is because during either of the two steady states, the open MOSFET has an extremely high resistance from drain to source so there is no direct path from power to ground. Also, during steady state the input impedance is very high because the MOSFET gates are capacitive. \$\endgroup\$– BDPMay 9, 2014 at 19:38
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An inverter will give you more symmetrical drive (low-to-high and high-to-low). This will be important if you are using the signal to drive, for example, the gate of a MOSFET.
answered May 8, 2014 at 2:06