Standard Logic ICs: the Foundation of Digital Circuitry
There are roughly 600 types of standard logic ICs, from basic chips to highly functional arithmetic-and-logic units. There are two different types of implementation: TTL and CMOS. ◊ TTS (transistor-transistor…
The Need for Clocked Circuits
Over the last two sessions, we have explained the basics of logic circuits. In our previous session, we looked at combinational circuits, and this time we’ve looked at sequential circuits.…
Flip-Flops and SRAM
A flip-flop can store 1 bit of information: either it’s at H or it’s at L. Accordingly, SRAM can be implemented by arraying together a large number of flip-flops and…
Clocked D Flip-Flop
The D flip-flop captures the value of the D input at the time of the rising edge (L→H) and/or falling edge (H→L) of the incoming clock pulse (CK), and outputs…
Why Do We Call Them ” Flip-Flops” ?
Because they flip between two stable states, in the manner of a seesaw that comes to rest on one end or the other. So let’s use this analogy to help…
Photolithography
In order to alter specific locations on a wafer, a photoresist layer is first applied (as described in the section Deposition). Photoresist, or just resist, typically dissolves in a high-pH…
Deposition
In a process known as film deposition, a thin film of some substance is deposited onto the wafer by means of either a chemical or a physical reaction. Chemical methods…
Making a base wafer
The substrate material, or base wafer, on which ICs are built is a semiconductor, such as silicon or gallium arsenide. In order to obtain consistent performance, the semiconductor must be…
Digital design
Since digital circuits involve millions of times as many components as analog circuits, much of the design work is done by copying and reusing the same circuit functions, especially by…
Analog design
As mentioned earlier, an analog circuit takes an infinitely variable real-world voltage or current and modifies it in some useful way. The signal might be amplified, compared with another signal,…
