Schmitt inverter CMOS or LSTTL

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I need a fast and robust schmitt inverter in 10ns-20ns propogation delay on the output pin of MCU

74HCT14 compared 74LS14

As I compare them the mosfet variant has more voltage tolerance but a little bir slower (temp dependent)

which one is more robust for time critical pulse shaper?

________________________________ We dream of a world where current does not need the voltage to flow.

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If it were critical, you wouldn't rely on the prop delay. Why would you need schmitt if you are driving with the output of a micro?
Define robust and time critical.

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The output is NCO (numeric controlled oscillator) . So I dont have the possibility to generate an inverted signal by software as can be done for PWM generation. NCO is a special module comparable to DDS. Has up to 500Khz output and 20 bit resolution (0.5Hz changing steps)

________________________________ We dream of a world where current does not need the voltage to flow.

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Well, the difference is going to be mighty small compared to microcontroler timing. What is your time constraint and which fits it closer?

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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As we have 1 output from the MCU and the time constraint is defined between the first signal and the second derived from the first signal (MCU output), the timing of the MCU should not have any effect. Because the second signal will be derived from the first one. I need a maximum deviation of 20ns. The main question is : which one is more noise immune at 5cm distance there is 60A/us di/dt and at 3cm distance there is 250V/us dV/dt.

________________________________ We dream of a world where current does not need the voltage to flow.

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LSTTL fits closer with 12ns propagation delay. But the supply range is 4.5V to 5.5V Cmos variant has 30ns and seems more temperature dependant, but has more tolerance to voltage transients (2V to 8V) and if you accept a lttle bit more propogation the range expands o
(2V to 28v)

________________________________ We dream of a world where current does not need the voltage to flow.

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Why are you limiting yourself to LS vs HCT?
Scanning TI, it looks like the SN74LVC14A would be a better fit (Tpd = 6.4ns), and AHCT is about 8ns. Single gate packages are even faster.

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Quote:
The main question is : which one is more noise immune at 5cm distance there is 60A/us di/dt and at 3cm distance there is 250V/us dV/dt.

The answer depends on the degree of coupling and the impedance of the nodes. For voltage the coupling is capacitive, current is inductive. Therefore it is highly dependant on circuit layout. You will need to answer this question yourself through testing.
My hunch is if you have coupling issues, the schmitt is the least of your problems.

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Get a single package with two dual input XOR gates.

Use one as a buffer and the other as an inverter to match delay