WHat is the main difference between CMOS and TTL IC's?

[avinsinanan]

Hi,

I am trying the find out what is the main difference between CMOS and TTL IC's?

Also I saw that there is something call a monochronic IC or something like thats... I don't know if splet it correct.. I only got a glimpse of the paper.

Can anyone give me any info plz.

Thanks...

Yousr Repectfully
Avin Sinanan

 

[Agent 009]

The first thing that comes into my mind abt the difference b/w TTL & CMOS is 3 things:

CMOS TTL
-------- -----
speed slower faster
size smaller larger
power less much more power needy

 

[Vaibhav Birit]

CMOS are better as compared to TTL, in most of the respects like
power saving etc. They consume extremely negligible power. Hence used in Battery operated devices.

Also you may have read about monolithic IC's (not monochrome) . THey are IC's built on single Base or Substrate

 

[Agent 009]

sorry abt the last post, it seems we can't have many successive spaces...
But I meant that CMOS are slower, smaller and cheaper, whereas TTL are faster, larger and more expensive...

 

[avinsinanan]

what is the physical diffrence?

I was also wondering the difference between the components and materials used in making the TTL and CMOS.

Thanks for all the help so far.

Yours Respectfully
Avin SInanan

 

[fsahmed]

CMOS Ics are based upon Metal Oxide Semiconductor based Field Effect Transistors (MOSFETs for short). Mosfets are voltage controlled transistors, unlike Bipolar Junction Transistors (BJTs), whose working is current dependent. The circuits integrated in TTL ICs use BJTs for logic operations, & due to the current consumption, the over all power consumption is greater in TTL. CMOS, using voltage based transistors for logic operations, consumes much less power.

On the other hand, since TTL has very little parasitic capacitance, the time delay is very small, & TTL is faster. MOSFETs, based on voltage operations, have much greater capacitances, the charging & discharging of which consumes time (Ref: RC time constant), hence CMOS is slower.

 

[mstechca]

According to Sayal Electronics in Canada, CMOS devices are generally cheaper then TTL devices.

 

[mstechca]

Let me point out too that:

TTL stands for Transistor-Transistor Logic
CMOS stands for Carbon Metal Oxide Semiconductor

Correct me if Carbon is wrong.

 

[fsahmed]

Let me point out too that:

TTL stands for Transistor-Transistor Logic
CMOS stands for Carbon Metal Oxide Semiconductor

Correct me if Carbon is wrong.

Indeed, the carbon is incorrect, for the C stands for 'Complementary', making the name "Complementary Metal Oxide Semiconductor". The complementary comes from the fact that a NOT gate (inverter) fabricated in CMOS technology is based upon a PMOS (MOSFET with source & gate of Ptype Semiconductor) & an NMOS (MOSFET with source & gate of Ntype Semiconductor). The rest of the gates r just modifications in the basic inverter circuit.

 

[ljcox]

CMOS has a very high input resistance.

The 74AC series is faster than TTL.

The advantages of CMOS are such that I never use TTL.

Len

 

[fsahmed]

CMOS has a very high input resistance.

The 74AC series is faster than TTL.

The advantages of CMOS are such that I never use TTL.

Len

I beg ur pardon but dont u mean 74HC is faster than TTL?
Fayez

 

[TekNoir]

CMOS (4000 series) General Characteristics

* Supply: 3 to 15V, small fluctuations are tolerated.
* Inputs have very high impedance (resistance), this is good because it means they will not affect the part of the circuit where they are connected. However, it also means that unconnected inputs can easily pick up electrical noise and rapidly change between high and low states in an unpredictable way. This is likely to make the chip behave erratically and it will significantly increase the supply current. To prevent problems all unused inputs MUST be connected to the supply (either +Vs or 0V), this applies even if that part of the chip is not being used in the circuit!
* Outputs can sink and source only about 1mA if you wish to maintain the correct output voltage to drive CMOS inputs. If there is no need to drive any inputs the maximum current is about 5mA with a 6V supply, or 10mA with a 9V supply (just enough to light an LED). To switch larger currents you can connect a transistor.
* Fan-out: one output can drive up to 50 inputs.
* Gate propagation time: typically 30ns for a signal to travel through a gate with a 9V supply, it takes a longer time at lower supply voltages.
* Frequency: up to 1MHz, above that the 74 series is a better choice.
* Power consumption (of the chip itself) is very low, a few µW. It is much greater at high frequencies, a few mW at 1MHz for example.

74LS series TTL Characteristics:

* Supply: 5V ±0.25V, it must be very smooth, a regulated supply is best. In addition to the normal supply smoothing, a 0.1µF capacitor should be connected across the supply near the chip to remove the 'spikes' generated as it switches state, one capacitor is needed for every 4 chips.
* Inputs 'float' high to logic 1 if unconnected, but do not rely on this in a permanent (soldered) circuit because the inputs may pick up electrical noise. 1mA must be drawn out to hold inputs at logic 0. In a permanent circuit it is wise to connect any unused inputs to +Vs to ensure good immunity to noise.
* Outputs can sink up to 16mA (enough to light an LED), but they can source only about 2mA. To switch larger currents you can connect a transistor.
* Fan-out: one output can drive up to 10 74LS inputs, but many more 74HCT inputs.
* Gate propagation time: about 10ns for a signal to travel through a gate.
* Frequency: up to about 35MHz (under the right conditions).
* Power consumption (of the chip itself) is a few mW.

Edit: It should be noted that I got my information nearly verbatim from the Kelsey Park School Electronics Club website. It contains a nice wealth of information in a format easily assimilated.

 

[ljcox]

CMOS has a very high input resistance.

The 74AC series is faster than TTL.

The advantages of CMOS are such that I never use TTL.

Len

I beg ur pardon but dont u mean 74HC is faster than TTL?
Fayez

Yes, 74HC is faster than TTL and 74AC is faster than 74HC.

Len

 

[marago10]

Want to know more about TTL?

So can anyone pls explain to me what is 74HC & 74AC ; why 74AC is faster than 74HC & 74HC is faster than TTL. :? [/b]

 

[ljcox]

TTL is old technology.

The 74LS series is also TTL but faster than the original TTL.

The 74AC14 has a typical delay of 7 ns.

The 74HC14 has a typical delay of 12 ns.

The 74LS14 has a delay between 5 and 22 ns. (My data sheet does not state the typical delay)

74AC is an improved version of CMOS and is faster than 74HC.

Len

 

[marago10]

"74AC, 74LS, 74HC" can I know which one is TTL & CMOS; the abreviation AC..HC..LS stands for what?

 

[fsahmed]

"74AC, 74LS, 74HC" can I know which one is TTL & CMOS; the abreviation AC..HC..LS stands for what?

Whichever has a 'C' in it is CMOS.
S:Shottky
LS: Low power Shottky

HC: High Speed CMOS
AC: Advanced CMOS

H/A CT: High/Advanced CMOS with TTL compatibility

 

[ljcox]

The 74LS series is a faster version of TTL, it is faster than the original TTL.

There is also the 74F series which is a very fast TTL