- Logic Families Definition: Logic families are different approaches to designing digital integrated circuits, each with identical electrical characteristics.
- Electrical Characteristics: These include factors like supply voltage range, response speed, and power dissipation, crucial for circuit performance.
- Compatibility Importance: ICs from the same logic family ensure compatibility and proper function in digital systems.
- Types of Logic Families: Major types include bipolar families like TTL and MOS families like CMOS.
- TTL and CMOS Subfamilies: TTL and CMOS have various subfamilies with specific characteristics and applications.
Different circuit configurations and production technologies are used during the production of digital integrated circuits. Each of these approaches is called a specific Logic Families. Now the idea of having different approaches or different logic families is that each ICs of same family when fabricated will have identical electrical characteristics. The characteristics which are bound to be identical are supply voltage range, speed of response, dissipation of power, input and output logic levels, current sinking capability, current sourcing capability, noise margin, fan-out etc.
Significance of Logic Families
In digital systems, digital ICs are the key components. If all ICs are from the same logic family, they are compatible, ensuring that the intended logic functions are performed correctly.
If ICs from different logic families are used in a digital system, interfacing techniques are needed to ensure compatibility. Understanding different logic families helps in choosing the best combination of ICs for a system. Using the wrong combinations may result in mismatched capabilities.
Types of Logic Family
Digital ICs are designed using either bipolar devices, MOS devices, or a combination of both. Bipolar logic families include diode logic (DL), emitter-coupled logic (ECL), resistor-transistor logic (RTL), diode-transistor logic (DTL), and transistor transistor logic (TTL). MOS families include PMOS, NMOS, and CMOS. The Bi-MOS family uses both bipolar and MOS devices.
DL, RTL, and DTL have become obsolete and are no longer used. TTL, CMOS, ECL, NMOS , and Bi-CMOS families are still in use. We will discuss some of these families in this article.
TTL subfamilies.
The TTL family consists of various subfamilies such as standard TTL, low-power TTL, high power TTL, low power Schottky TTL, Schottky TTL, advanced low-power Schottky TTL, advanced Schottky TTL and fast TTL. The ICs which belong to TTL family are designated as follows – 74 or 54 for standard TTL, 74L or 54L for low-power TTL, 74H or 54H for high power TTL, 74LS or 54LS for Low power schottky TTL and so on.
CMOS subfamilies
This is a popular logic family which includes 4000A, 4000B, 4000UB, 54/74C, 54/74HC, 54/74HCT, 54/74AC and 54/74ACT families. The subfamilies are divided on the basis of voltage difference and other parameters.
ECL Subfamilies
ECL stands for Emitter Coupled Logic family and it was introduced by ON semiconductor in 1962. The first product launched of this family was MECL-1 series. Later MECL-II, MECL-III, MECL-10K, MECL-10H series came into existence.
