IC Gates and MSI Chips

 

An Integrated Circuit (IC) is a set of electronic circuits on one small plate (i.e.chip) of semiconductor material. A standard logic IC is a single and small integrated package carrying basic components and common functionalities for a logic circuit. These ICs are key components of logic circuits. ICs can be made much smaller than a discrete circuit made from independent components. It has functionality of logic AND or amplifying of a signal. 

These are mainly of two types: Digital or Analog. Analog ICs focus on continuous signals such as audio signals whereas Digital ICs focus on discrete signals such as binary values. Digital ICs do not have to know the precise amplitudes of their input signals but just simply recognize them as being in either a low or a high state.

Different ICs for Different Applications

Digital ICs come in many different types (around 600 types). Following are some basic IC types used for various applications.

1. Microcomputers: ICs that carry out various types of processing
2. Memory: ICs that store data
3. Standard Logic ICs: ICs put together in various combinations to implement particular functionalities
4. Custom Logic ICs: Original dedicated circuitry implemented by or for the needs of a particular user

Families of Integrated Circuits

A logic family is a group of various electronic logic gates. Every family has its own discrete logic level, power supply, individual components, characteristic, advantages and disadvantages. Also they have a range of voltage which may be low level or high level.

Below we have been provided with the list of families of ICs:

Diode Logic (DL)

Registers and diodes are used to implement the logic. The functionality of diode is performing OR and AND operation, and logic switch. Diode must be forward biased, or else it will not conduct. But diodes hold a disadvantage of not being able to perform NOT operation. Also, they cannot work for multiple states,i.e. only one stage at a time. Hence, they tend to degrade signals quickly.

Resistor-Transistor Logic (RTL)

Registers and transistors are also used to implement logic. Transistors are generally used to combine signals which are inverted and amplified inputs. Being economical and easy to design they hold an advantage, but they are slower in speed. Also, these require great amount of current from supply. RTL gates are very useful as interface between linear and digital circuits.

Diode Transistor Logic (DTL)

Registers and diodes also are used to implement logic. It holds an advantage over DL and RTL. Diode can perform AND and OR operation along with a transistor and output signal can be amplified. It has logic inversion, i.e., signal can be restored to full logic level, if we add a transistor at output of logic gates. OR operation can be performed using diodes instead of resistors which removes interaction between input signals. Since input resistor to transistor, switching speed of the transistor is limited. Diode Transistor Logic was used in tube computers.

Transistor - Transistor Logic (TTL)

Transistors are used to implement logic and also Bipolar transistors to contract integrated circuits. These have different types thatj are standard TTL, high speed TTL, low power TTL, and schottky TTL. TTL is a popular family of ICs

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Emitter Coupled Logic (ECL)

ECL is a non-structured logic that holds an advantage of speed, and very low propagation delay.

Complementary Metal Oxide Semiconductor Logic (CMOS)

CMOS is known for high fan-out, low power consumption and hence, is the most reliable logic family.

IC’s Generations

As humans have evolved through different generations, same goes by the ICs. Below is a list of IC's generations:  

• SSI: SSI stands for Small Scale Integration. These were the first integrated circuits containing only a few transistors.These are digital circuits containing transistors numbering in the tens provided a few logic gates. Complexity level between one and 10 gates.
• MSI:  MSI stands for Medium Scale Integration. These were the next step in the development of integrated circuits. It introduced devices which contained hundreds of transistors on each chip. Complexity level between 10 and 100 gates.
• LSI: LSI stands for Large Scale Integration. Further development of integrated circuits led to Large-Scale Integration with tens of thousands of transistors per chip. Complexity level between 100 and 1,000 gates.
• VLSI: VLSI stands for Very Large-Scale integration. The final step in the development process, was Very Large-Scale integration. The development started with hundreds of thousands of transistors, and till now continues beyond several billion transistors. Complexity level between 1,000 and 10,000 gates.

Popular MSI Chips

One of the most popular MSI arithmetic circuits is the 74283 4-bit adder. Several of them could be wired in series to perform 8-bit, 16 bit or even 32-bit operations. Example: 74HC283 from Philips.

Another widely used MSI chip was the 74181 bit-slice arithmetic logic unit. It is more complex than a simple 4-bit adder, and could perform all the traditional add / subtract / decrement operations with or without carry, as well as AND / NAND, OR / NOR, XOR, and shift. This chip was used in the core of the CPU of such computers as the PDP-11 and VAX 11/780.