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TTL is considered to be less used today when considering cost , functionality and reliability on CCTV systems .
CMOS seems to be more robust yet TTL is cheaper and initially faster than CMOS .
Industry seems to have chosen CMOS more frequently over the years particularly since the speed of CMOS has advanced over the years ..It is similar to buying a car ..we ask ourselves the question ..do we judge the speed on how fast it starts up or on how long it can run at a high speed .
Characteristics of CMOS logic:
Characteristics of TTL logic:
CMOS compared to TTL:
TTL chips are typicalling less expensive than CMOS components. However, on system level CMOS is less expensive and it needs less regulations. TTL circuits needs huge power when compared with CMOS. CMOS components are liable to damage from electrostatic discharge than TTL.
CMOS components are typically more expensive than TTL equivalents. However, CMOS technology is usually less expensive on a system level due to CMOS chips being smaller and requiring less regulation
TTL (Transistor-Transistor Logic) is a name for type of logic circuits which are constructed using the bipolar transistors. In general the bipolar transistors such as the NPN and PNP transistors are current operated devices. In these types of transistors, when used for digital logic circuits, typically the input voltage is applied across the Base-Emitter junction. As a result of this a small base current is produced in that junction. This small base current is magnified by the transistor's current gain factor B(called Beta), resulting in a large amount of collector-emitter current. This is basiclly how a TTL switch works. The TTL family of circuits are generally very fast, but this speed comes at the cost of higher power dissipation. Also, a typical TTL logic gate circuit requires multiple transistors and other passive components such as resistors. This results in lower number of gates that can be put on an IC built using TTL family.The CMOS(Complimentary Metal Oxide Semiconductor) family of logic circuits are buit using Metal Oxide Semiconductor(MOS) Field Effect Transistors (FET). These types of transistors are voltage operated devices. A typical CMOS logic gate circuit can be constructed using as little as two MOSFET transistors (A CMOS Inverter) resulting in a much higher density of logic gates that can be put on an IC. Also, CMOS gates use much much lower power to operate compared to the TTL gates because no resistors are required to build such circuits. CMOS logic also allows much higher operating voltages compared to the TTL family. One drawback of CMOS family is that they are slower than the TTL family, however these days this may no longer be true