Editing MicroElectronics
You are currently not logged in.
To change this, fill in the following fields:
Username
Password
Who can read this page?
The World
Members
Council
Admin
You have been granted an edit lock on this page
until Tue Dec 3 17:48:25 2024.
Press
to finish editing.
Who can edit this page?
... world editing disabled
Members
Council
Admin
[[[> IMG:CMOS_NAND.png ---- |>> A *NAND* gate _ made from FETs <<| ]]] !! Preamble We've built transistors - now what? This is the level at which we build transistors into *gates:* fragments of circuitry that correspond to simple pieces of *logic.* This is also the level at which we worry about delivering enough power to our transistors, ensuring electrical signals propagate to them fast enough to keep the system working in time, and disposing of the resulting heat before our expensive chip melts a hole in our lovely new iPhone. !! Making circuits from FETs So we now need to make circuits from the FETs we described in Semiconductor Physics. Here we show how to make a *NAND* gate. !! In more detail The FET circled in blue is an on/off switch. When a signal is present on input *A* the switch is "on", connecting the links at the top and bottom. Similarly, when a signal is present on input *B,* the net result is that the output line is connected to *Vss* (ground). Thus when *A* and *B* are both "On", the output is connected to *Vss* and is therefore "Off". The FET circled in red has a little circle on its input, showing that the sense of the switch is reversed. Thus when a signal is present on *A,* the switch is "Off." Similarly for the other. So if either *A* or *B* is Off, the connection between the output and *Vss* (ground) is broken, but there is a connection between *Vdd* (positive) and the output. !! In summary ... If *A* is off, the connection is made from the output to *Vdd* (positive) and broken to *Vss* (ground) so the output is "On". If *B* is off, similarly, so the output is again "On". If *A* and *B* are both on, the output goes off. Thus we have a *NAND* gate: |>> | |>> *A* <<| | |>> *B* <<| | *Out* | | |>> *0* <<| | |>> *0* <<| | |>> *1* <<| | | |>> *0* <<| | |>> *1* <<| | |>> *1* <<| | | |>> *1* <<| | |>> *0* <<| | |>> *1* <<| | | |>> *1* <<| | |>> *1* <<| | |>> *0* <<| | <<| By forcing either *A* or *B* to *1* we have a *NOT* gate, although in that case the circuit can be simplified, and by adding extra FETs we can make an n-way *NAND* gate. In a similar fashion we can construct *OR* gates, and more. !! Next ... * MicroArchitecture