# BEING COMPLEMENTARY

The breakthrough comes when we use both types of transistor together. Consider this circuit. It has a P-channel FET at the top and an N-channel one at the bottom, and they work alternately.
When the input is high, the top transistor turns off and the bottom one turns on, pulling the output low. When the input is low, the bottom transistor turns off and the top one turns on, pulling the output high.
So we have an inverter again, but it doesn't suffer from any of the problems of the previous ones. The transistors are never both on at the same time, except for a brief instant when the input is changing, so it uses much less power. And there are no resistors to slow things down, so the output switches from low to high and high to low equally fast.
This type of circuitry is called CMOS, because the transistors are always used in complementary pairs. It's really good stuff, so good that we'll be using it for all of our logic circuits.

## Experiment 6

Build a CMOS inverter as shown. Observe how the output switches both high and low nice and sharply. Notice that all parts of the circuit show up as either red or blue under the Q-Goggles, indicating that no power is being wasted in resistances.

## Graduation

You know enough now to tackle your first real design job. When you're ready, press the Next Level button below and you will receive further instructions.