CMOS is faster than TTL?

Discussion in 'General Electronics Chat' started by watsongrey, Nov 3, 2014.

  1. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    Is CMOS Logic faster , faster switching than TTL logic?
    CMOS switching time is faster and less propagation delay time?
    Why did designers switch from TTL to CMOS?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Yes, but you have a troll-like name and you're asking very troll like questions.
    Got any autopilot schematics?
     
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  3. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    Any reason why CMOS is faster than TTL?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Some varieties of CMOS are faster than some varieties of TTL and vice versa.
    The reason for changing from TTL to CMOS is that CMOS uses less power.
     
  5. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    how about propagation delay times , is it true that CMOS has less propagation delay time compared to TTL propagation delay time?
     
  6. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    Any reason why a CMOS take less power or current draw compared to a TTL Ic chips?
    What makes a CMOS IC chip takes less power and current draw
     
  7. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Have you considered Wikipedia?
     
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  8. ScottWang

    Moderator

    Aug 23, 2012
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    The fets were inside of the CMOS IC and they work by voltage, the bjts were inside of the TTL and they work by current, so the COMS IC just need less power, but the TTL need more current and power.

    You can see the R values of TTL circuit are more less then the CMOS circuit, and the CMOS circuit can using a resistor with higher value as 1M or some more.
     
  9. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    ok i get it thanks scott wang
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    BCD counter:

    CD4518 - CMOS
    5V - Fmin = 1.1Mhz
    10V - Fmin = 3Mhz
    15V - Fmin = 4Mhz
    http://pdf.datasheetcatalog.com/datasheets/120/109587_DS.pdf

    74HC4518 - CMOS
    5V - Fmax = 61Mhz
    http://pdf.datasheetcatalog.com/datasheet/philips/74HCT4518.pdf

    74HC390 - CMOS
    Fmax = 66Mhz
    http://pdf.datasheetcatalog.com/datasheet/philips/74HC_HCT390_CNV_2.pdf

    74AC390 - CMOS
    Fmax = 160Mhz
    http://pdf.datasheetcatalog.com/datasheet/toshiba/4247.pdf

    74LS90 - TTL,5V
    cp0 : Fmin = 32Mhz
    cp1 : Fmin = 16Mhz
    http://pdf.datasheetcatalog.com/datasheet/motorola/SN54LS92J.pdf
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    74F160 -TTL 5V 120MHz
     
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  12. ScottWang

    Moderator

    Aug 23, 2012
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    The ECL Translator Guide
    PECL • LVPECL • NECL • TTL •
    LVTTL/LVCMOS • CMOS
    Prepared by: Paul Shockman
    ON Semiconductor
    Objective
    This application note is intended to provide the basic
    device selection and connection information to enable signal
    translation interface between ON Semiconductor’s ECL
    logic operating in various supply modes This document also
    provides information regarding translation between our
    ECL devices and TTL (5 V), CMOS (5 V), or
    LVTTL/LVCMOS (3.3 V) devices. For translation interface
    with LVDS, see AN1568.

    The ECL Translator Guide APPLICATION NOTE.
     
  13. alfacliff

    Well-Known Member

    Dec 13, 2013
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    and high current counters like ecl with only a half volt from 1 to 0 count to over 1000 mhz, but at the expense of high current. different families of logic have different reasons, some are fast, some use very low power, and some mimic other families like the FC series uses cmos to mimic ttl, but with cmos power levels.
     
  14. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    But is CMOS faster at switching from input to output compared to TTL logic chips, and CMOS has less Rise time and fall time, less delay from input and ouput?
     
  15. alfacliff

    Well-Known Member

    Dec 13, 2013
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    cmos has oless current drive capability. so arise time and fall time is slower.cmos, being voltage driven, and cmos transistors having more capacitance on gate to source, have slower times. cmos can be made to be similar to ttl, but still, the main advantage for cmos is power disapation.
     
  16. BobTPH

    Active Member

    Jun 5, 2013
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    The TTL and CMOS logic chips that you see still being used today are decades old. Intel's version of CMOS, used in its microprocessors, is orders of magnitude faster any TTL or CMOS logic chips, running as high as 4GHz clock speeds. The propagation delays are in the picosecond range.

    Bob
     
  17. watsongrey

    Thread Starter Member

    Oct 31, 2014
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    So a FET switching time , rise time and fall time is "slower at switching" compared to a Transistor switching time? so a transistor switches faster then a FET? a transistor has less rise time then a FET?
     
  18. BobTPH

    Active Member

    Jun 5, 2013
    782
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    No. There are extremely wide overlapping ranges of switching time of different kinds of transistors.

    In practical use, most high speed logic is now CMOS because bipolar logic of any kind uses too much power. Bipolar transistors are probably still used in some specialty hardware for speed where power is not a problem.

    Bob
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    The increase in speed is primarily a result of lower operating voltage and smaller feature sizes: less charge to move around.
     
  20. BobTPH

    Active Member

    Jun 5, 2013
    782
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    Yep.

    One difference between CMOS and any bipolar logic is that in CMOS there is not current flowing in the steady state, since you have two complementary transistors with one on and the other off going from Vdd to Vss. (okay, there is leakage current, but this is small) So, current flows only when they switch. With bipolar transistors you have to have current flowing all the time to make the speed of switching reasonable.

    Bob
     
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