# question about transistor resistor logic

Discussion in 'Homework Help' started by caoadon, Aug 11, 2014.

Jul 11, 2014
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Can an inverter logic gate invert a high frequency pulse? (1MHz)

thanks

2. ### MrChips Moderator

Oct 2, 2009
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Why not?
7404 TTL inverters are good to at least 25MHz.

3. ### alfacliff Well-Known Member

Dec 13, 2013
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but RTL inverters are a lot slower.

Jul 11, 2014
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Oh could i use a 7404 for just a single input and output? there are so many pins

Jul 11, 2014
24
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nvm dumb question. but thanks i'll look into buying a TTL

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Each gate is independent of all others. Just use one.
Or.
Buy chip that only has one gate, and meets your frequency requirement.

7. ### MikeML AAC Fanatic!

Oct 2, 2009
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Make your own: one NPN transistor and two resistors...

Jul 11, 2014
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are there two optimal resistors i can use? I've seen so many variations of it

9. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Depends on input voltage and current, and desired output voltage and current.

Jul 11, 2014
24
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5V pulse with a max current of 400μA?
I just want an exact inversion of it.
Sorry I can't think of the math right now...

11. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
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In retrospect, the 400uA makes it tough to do with a simple NPN (or with TTL or even LSTTL), I would use a 4000 series CMOS inverter.

12. ### MrChips Moderator

Oct 2, 2009
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You can get single gate components in a SMD package.

Or go with a single NPN transistor with two resistors as shown here:

The voltage source can be +5V instead of the +12V shown.

Jul 11, 2014
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i just bought an NTE7404 hex inverter. Do i need to use resistors with them?

14. ### MrChips Moderator

Oct 2, 2009
14,517
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You can use a single gate and leave the remaining five not connected.
If you want extra output power you can parallel multiple gates together.

400μA could be a limiting factor. Try it with one gate first and see what happens.

Jul 11, 2014
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It seems to be inverting fine. Do I not need to do impedance matching? THeres a 50ohm input impedance.

16. ### MrChips Moderator

Oct 2, 2009
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Where exactly is the 50-ohm impedance?

Jul 11, 2014
24
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The ultrasound im working with outputs a signal that i want to invert. so i sent it through the hex inverter. once inverted, the output of the hex inverter is the input of a laser with a 50ohm input impedance

18. ### MikeML AAC Fanatic!

Oct 2, 2009
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So this is an analog signal? If so, you need a medium fast modern opamp to invert the signal while retaining its fidelity; not a logic inverter...

19. ### MrChips Moderator

Oct 2, 2009
14,517
4,280
Perhaps you should go into more details as to what you are attempting to do.