| ??? 02/20/07 20:39 Read: times |
#133363 - Why Vss is positive and Vdd is negative Responding to: ???'s previous message |
Back when dinosaurs ruled the earth and PMOS was king....
In a PMOS device, the source is positive, and the drain is negative. The power supply connected to the sources was called Vss. The power supply connected to the drains was Vdd. And in all PMOS circuits, Vss = 0 volts, and everything worked off of negative voltages. When the evil, mammalian NMOS devices evolved with positive drains, Vdd became positive. And the rest is history. |
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