5
Logic Families
Digital integrated circuits are produced using several different circuit configurations and production
technologies. Each such approach is called a specific logic family. In this chapter, we will discuss
different logic families used to hardware-implement different logic functions in the form of digital
integrated circuits. The chapter begins with an introduction to logic families and the important
parameters that can be used to characterize different families. This is followed by a detailed description
of common logic families in terms of salient features, internal circuitry and interface aspects. Logic
families discussed in the chapter include transistor transistor logic (TTL), metal oxide semiconductor
(MOS) logic, emitter coupled logic (ECL), bipolar-CMOS (Bi-CMOS) logic and integrated injection
logic (I
2 L).
5.1 Logic Families – Significance and Types
There are a variety of circuit configurations or more appropriately various approaches used to produce
different types of digital integrated circuit. Each such fundamental approach is called a logic family.
The idea is that different logic functions, when fabricated in the form of an IC with the same approach,
or in other words belonging to the same logic family, will have identical electrical characteristics.
These characteristics include supply voltage range, speed of response, power dissipation, input and
output logic levels, current sourcing and sinking capability, fan-out, noise margin, etc. In other
words, the set of digital ICs belonging to the same logic family are electrically compatible with each
other.
5.1.1 Significance
A digital system in general comprises digital ICs performing different logic functions, and choosing
these ICs from the same logic family guarantees that different ICs are compatible with respect to each
Digital Electronics: Principles, Devices and Applications Anil K. Maini
© 2007 John Wiley & Sons, Ltd. ISBN: 978-0-470-03214-5
Logic Families
Digital integrated circuits are produced using several different circuit configurations and production
technologies. Each such approach is called a specific logic family. In this chapter, we will discuss
different logic families used to hardware-implement different logic functions in the form of digital
integrated circuits. The chapter begins with an introduction to logic families and the important
parameters that can be used to characterize different families. This is followed by a detailed description
of common logic families in terms of salient features, internal circuitry and interface aspects. Logic
families discussed in the chapter include transistor transistor logic (TTL), metal oxide semiconductor
(MOS) logic, emitter coupled logic (ECL), bipolar-CMOS (Bi-CMOS) logic and integrated injection
logic (I
2 L).
5.1 Logic Families – Significance and Types
There are a variety of circuit configurations or more appropriately various approaches used to produce
different types of digital integrated circuit. Each such fundamental approach is called a logic family.
The idea is that different logic functions, when fabricated in the form of an IC with the same approach,
or in other words belonging to the same logic family, will have identical electrical characteristics.
These characteristics include supply voltage range, speed of response, power dissipation, input and
output logic levels, current sourcing and sinking capability, fan-out, noise margin, etc. In other
words, the set of digital ICs belonging to the same logic family are electrically compatible with each
other.
5.1.1 Significance
A digital system in general comprises digital ICs performing different logic functions, and choosing
these ICs from the same logic family guarantees that different ICs are compatible with respect to each
Digital Electronics: Principles, Devices and Applications Anil K. Maini
© 2007 John Wiley & Sons, Ltd. ISBN: 978-0-470-03214-5