From analog to digital circuits. A phenomenological overview. Bogdan Roman. Outline. Insulators, conductors and semiconductors Semiconductor diodes: the p-n junction The Field Effect Transistor (FET): The Junction FET (JFET) The Metal Oxide Semiconductor FET (MOSFET) The MOS Inverter
A phenomenological overview
Loosely based on the IA and 3B Engineering dept. courses
(Linear Circuits and Devices, Digital Circuits,Information Processing, Integrated Digital Electronics)
At room temperature, the thermal energy kT ~ 1/40 eV is enough to break a few covalent bonds to produce free electrons. This also leaves holes(i.e. positive net charges left by the broken covalent bond).
Both electrons and holes contribute to current flow.
At low temperatures, silicon is an insulator since there is not enough thermal energy to break the covalent bonds.
Forward biased diode:The p-n junction: The diode
Forward biased diode:The Diode (contd.)
- Proposed by Shockley in 1951
- First made by Teszner in 1958 in France
JFET Interactive (opens browser)
MOSFET Interactive (opens browser)
In CMOS technology, the output is clamped to one of the power rails by a conductive (on) device, while the other device serves as a load of effectively infinite resistance (off). This leads to static properties that approximate those of the ideal inverter.
- The PMOS devices is slower (lower mobility of holes) so it has to be larger to compensate. It is also more complex to manufacture.
The 74HC02 IC has four 2-input NOR gates
The 74HC00 IC has four 2-input NAND gates
A crucial circuit, vital for implementing functions: