What are the differences between a power supply for a TTL circuit compared to a CMOS circuit

Discussion in 'General Electronics Chat' started by Calton57, May 8, 2015.

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  1. Calton57

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    May 4, 2015
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    What are the differences between a power supply for a logic TTL circuit compared to a logic CMOS circuit?
    A power supply for a logic TTL circuit has series pass transistors but a power supply for a logic CMOS circuit doesn't use series pass transistors.

    The series pass transistors stabilizes the fluctuations and stablizes the +5 volt to be + or - 0.25 volts?

    CMOS power supplies don't have series pass transistors

    CMOS power supplies have a high noise immunity?

    The Noise Immunity is higher on logic CMOS circuit boards compared to TTL logic boards?

    In CMOS logic there is no current flowing , only leakage current flow?
     
  2. crutschow

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    Mar 14, 2008
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    CMOS circuits generally take less power, which starts as leakage current when in a static state and increases with operating frequency. It may approach the value of TTL logic at high operating frequencies.
    TTL circuits draw a significant static current which increases only a small amount with operating frequency.

    Series pass transistors can be used for any regulated linear supply.

    CMOS circuits (particularly the old CD4000 series) have a wider operating voltage range than TTL logic so may not require a regulated voltage.

    CMOS circuits have a voltage swing equal to the supply voltage, so have a higher noise immunity than TTL when operating at 5V or above.
     
  3. Calton57

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    May 4, 2015
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    What is causing the high noise immunity? is it the print circuit board traces and lay out or the power supply?

    What is causing leakage current in CMOS chips? TTL chips don't have leakage current?

    The operating frequency is determined by the clock frequency?
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    The threshold voltages of the P and N devices.
    Non-ideal characteristics of MOSFETs.
    In "simple" logic. Microprocessors have PLLs for frequency generation. Doublers, triplers, etc are possible using simpler means.

    Max operating frequency is largely determined by propagation delays.
     
  5. Calton57

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    May 4, 2015
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    where is the operating frequency coming from in TTL circuits and CMOS circuits? i thought the operating frequency was from the clock circuit

    The Threshold voltages cause noise immunity? i don't get how a threshold voltage would cause noise in a circuit
     
  6. Papabravo

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    Feb 24, 2006
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    A little homework for you.
    What is the threshold voltage of a CMOS gate with Vcc = +5VDC and Vxx = GND?
    What is the input low threshold for a TTL gate?
    What is the input high voltage for a TTL gate?
    What is the difference between the input high and the input low thresholds?
    Is it greater than or less than the CMOS threshold?
    I think you just answered your own question. Isn't that a wonderful feeling?
     
  7. crutschow

    Expert

    Mar 14, 2008
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    The operating frequency is determined by whatever is generating the signals.
    In most circuits there is a clock that determines the highest operating frequency.

    You are confused with your terms.
    Nose immunity is immunity to noise generated elsewhere that appears at the logic inputs.
    It has nothing to do with the cause of noise.
     
  8. Calton57

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    May 4, 2015
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    What else can be generating the signals besides a clock circuit

    The clock circuit determines the switching speed of each IC logic chip

    What is causing noise immunity on the logic's inputs? the printed circuit board traces or layout or power supply or components?
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Several Amps.
     
    OBW0549 likes this.
  10. crutschow

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    Why do you keep asking different variations of the same questions?
     
  11. Calton57

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    May 4, 2015
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    The IC chips input impedance and output impedance is one of the causes of noise immunity
     
  12. dl324

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    Not even close.

    This is from a Fairchild application note:
    "noise immunity is defined as the maximum noise voltage which can appear on the input without switching an inverter from one state to another"

    It is primarily a function of the input threshold voltages.

    This has been stated multiple times. Are there some phrases/words that need further explanation?
     
  13. Calton57

    Thread Starter Member

    May 4, 2015
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    dl324
    Yes I under this part

    What I don't understand, is where is the noise coming from that is being applied to the input of the IC chip?

    dl324
    Yes I know this because All these technologies has different maximum noise immunity levels or thresholds

    RTL
    DTL
    TTL
    CMOS
    ECL
    EECL
    HTL
    PMOS
    NMOS
     
  14. dl324

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    From switching logic, power supply ripple, environment (motors, microwaves, etc), ...
     
  15. Calton57

    Thread Starter Member

    May 4, 2015
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    ok i get it

    So what are the main differences between a power supply for a TTL logic circuit VS a power supply for a CMOS circuit?
     
  16. dl324

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    As previously mentioned, TTL supplies would typically need to provide more current. Additionally, CMOS has a wider range of operating voltages.
     
  17. WBahn

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    Question asked and answered... and asked and answered... and asked and answered... and asked.... Enough.
     
  18. bertus

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