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Difference Between CMOS and TTL

cmosCMOS vs TTL

TTL stands for Transistor-Transistor Logic.It is a classification of integrated circuits. The name is derived from the use of two Bipolar Junction Transistors or BJTs in the design of each logic gate. CMOS (Complementary Metal Oxide Semiconductor) is also another classification of ICs that uses Field Effect Transistors in the design.

The primary advantage of CMOS chips to TTL chips is in the greater density of logic gates within the same material. A single logic gate in a CMOS chip can consist of as little as two FETs while a logic gate in a TTL chip can consist of a substantial number of parts as extra components like resistors are needed.

TTL chips tend to consume a lot more power compared to CMOS chips especially at rest. The power consumption of a CMOS chip can vary depending on a few factors. One major factor in the power consumption of a CMOS circuit is the clock rate, with higher values resulting to higher power consumption. Typically, a single gate in a CMOS chip can consume around 10nW while an equivalent gate on a TTL chip can consume around 10mW of power. That is such a huge margin, which is why CMOS is the preferred chip in mobile devices where power is supplied by a limited source like a battery.

CMOS chips are a bit more delicate compared to TTL chips when it comes to handling as it is quite susceptible to electrostatic discharge. People often unwittingly damage their CMOS chips from simply touching the terminals as the amount of static electricity needed to damage CMOS chips are too minute for people to notice.

The prominence of CMOS chips has pushed TTL chips to the background. Instead of being the primary IC of choice, it is now used as components that link the whole circuit as ‘glue logic’. CMOS chips that emulate the TTL logic has also gained prominence and is slowly replacing most TTL chips. These chips have similar name to their TTL equivalent so that users can easily identify them.

Summary:

1. TTL circuits utilize BJTs while CMOS circuits utilize FETs.

2. CMOS allows a much higher density of logic functions in a single chip compared to TTL.

3. TTL circuits consumes more power compared to CMOS circuits at rest.

4. CMOS chips are a lot more susceptible to static discharge compared to TTL chips.

5. There are CMOS chips that have TTL logic and are meant as replacements for TTL chips.


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3 Comments

  1. the difference of TTL and CMOS is very short! so please insert some meterials for me…

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