Difference Between CMOS and TTL

TTL (transistor-transistor logic) and CMOS (complementary metal-oxide semiconductor) are two common types of digital logic families used in electronic circuits. CMOS is a popular method of constructing digital integrated circuits. TTL is a widely used digital logic family in the design of integrated circuits.

Read this article to find out more about CMOS and TTL and how they are different from each other.

What is CMOS?

CMOS (complementary metal-oxide semiconductor) is a popular method of constructing digital integrated circuits. Its low power consumption, good noise immunity, and compatibility with a wide range of voltage levels distinguish it. Here's a more in-depth description of CMOS technology:

  • MOSFET Transistors: MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used to construct CMOS logic gates. MOSFETs have three terminals and are made up of a metal gate, an insulating layer (oxide), and a semiconductor channel. NMOS (n-type MOSFET) and PMOS (p-type MOSFET) transistors are used in CMOS.

  • Complementary Pair: In CMOS, the use of both NMOS and PMOS transistors in each logic gate is referred to as "complementary." Low-voltage logic levels (0 or ground) are handled by NMOS transistors, whereas high-voltage logic levels (1 or power supply voltage) are handled by PMOS transistors. This arrangement makes optimal use of power and decreases static power usage.

  • CMOS Logic Gates: Combinations of NMOS and PMOS transistors are used to construct CMOS logic gates. The CMOS inverter, NAND gate, NOR gate, and XOR gate are the most common CMOS gates. These gates can be connected together in order to create more complicated digital circuits

Due to its low power consumption, good noise immunity, compatibility with various voltage levels, and adaptability in circuit design, CMOS technology has become the preferred choice for designing digital integrated circuits. It is used in a variety of applications, including microprocessors

What is TTL?

TTL (transistor-transistor logic) is a widely used digital logic family in the design of integrated circuits. It is well-known for its durability, fast performance, and compatibility with a wide range of input and output devices. TTL technology is described below:

  • Bipolar Transistors: Bipolar junction transistors (BJTs) are used to construct TTL logic gates. These transistors have three terminals: a base, an emitter, and a collector. TTL gates make use of bipolar transistors that are NPN (negative-positive-negative) or PNP (positive-negative-positive).

  • Bipolar Transistor Operation: TTL transistors operate in the active region, where the transistor's base-emitter junction is forward-biassed. The current flowing through the transistor's collector-emitter circuit defines the output of a TTL gate.

  • Voltage Levels: The voltage levels of the TTL logic levels are fixed. A low logic level (0) is normally represented by a voltage near 0 volts, whereas a high logic level (1) is typically represented by a voltage near the power supply voltage (typically 5 volts). TTL devices are not designed to function at different voltage levels.

  • Power Consumption: Even while idle, TTL circuits require a large amount of electricity. This is because current is flowing through the transistors in the active zone. As a result, TTL is less energy-efficient than CMOS.

Difference between CMOS and TTL

The following table highlights the major differences between CMOS and TTL:




Voltage Levels

Wide range of voltage levels

Fixed voltage levels (typically 5V)

Power Consumption





Bipolar Junction Transistor (BJT)

Noise Immunity



Fan-Out Capability

High fan-out capability

Lower fan-out capability


Slow propagation delays

Fast propagation delays

Power Supply

Typically operates at 5V or 3.3V

Typically operates at 5V


Battery-operated devices, high-density ICs

High-speed applications, memory systems


In conclusion, CMOS and TTL are two different families of digital logic with differences in technology, power consumption, voltage levels, noise immunity, fan-out capabilities, speed, and compatibility.

CMOS circuits are based on MOSFET technology, need very little power, operate at a variety of voltage levels, have excellent noise immunity, and have a high fan-out capability, but may have significantly longer propagation delays. TTL circuits use bipolar transistors, drain significant power even when idle, have fixed voltage levels, a good noise margin, and lesser fan-out capabilities than CMOS, but have faster propagation delays in general.

The decision between CMOS and TTL depends on the application's specific requirements, such as power consumption, noise immunity, speed, and interface requirements. For precise information and to assure optimal design and compatibility in electronic circuits, research the datasheets and technical specifications of specific CMOS and TTL devices.

Updated on: 13-Jul-2023

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