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Level shifter/ moving 0V to -15V

  1. Nov 25, 2013 #1
    Hi all
    I have a CMOS inverter, from which i can produce something like 0V or 15V out - I don't think I can make it -15 to +15, which is what i need
    I believe what i need is a device called a level shifter, which would go in after but any searches online have yielded very little
    Can anyone even point me in the right direction? (before anyone says it, an op-amp based Schmitt trigger (or something similar), which is an obvious choice, is not an option). I dont need the whole thing done out, just some idea of what kind of circuit i need

    (also diodes are not an option)
     
    Last edited: Nov 25, 2013
  2. jcsd
  3. Nov 25, 2013 #2

    AlephZero

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    Telling us two things that are "not an option" isn't very helpful.

    Tell us what are the constraints on your design that exclude those options, e.g. operating frequency, power requirements, physical size of the circuit, etc.

    Otherwise, trying to answer is just a guessing game.
     
  4. Nov 25, 2013 #3
    Fair answer, i was being intentionally vague because i would like to figure most of it out myself, i just hagve no idea where to start.
    The circuit can contain 6 MOSFETs, + resistors and capacitors, has to operate at 200MHz, and can be any size, but the smaller the better, as it has to go onto silicon after.

    Also the circuit its intended for is modeled on an ADG201A analog switch
     
  5. Nov 25, 2013 #4
    Sorry about this:
    Thinking further, what i have detailed above isn't actually enough - when the inverter output is high, i need both +15 AND -15V available, and when the output is low, (0v) i need the same outputs but in the opposite places, if that makes sense. Neither will need to supply any current if that's an issue.
    Again, sorry - I'm even more confused now
     
  6. Nov 25, 2013 #5

    NascentOxygen

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    You have a logic signal x (0V, 15V). You want it level-changed (-15V, +15V) and also make available its complement ¬x ?

    You want this constructed using discrete high-speed MOSFETS?

    A fan out of 0 is acceptable???
     
  7. Nov 26, 2013 #6

    Baluncore

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    Sounds to me like an H bridge.

    Digital switching between +15V and -15V = 30Vpp square wave signal at 200MHz is quite a tall order. The problem is the current needed to charge and discharge the stray capacitance.

    The solution to your problem would be obvious to an experienced electronics engineer who knew what you were trying to achieve.
     
  8. Nov 26, 2013 #7
    This is unhelpful - if i was or had and experienced electronics engineer, i would be posting here :-/

    In the end i solved it by myself - i used a Cmos source follower to boost the TTL signal to 0 to +15V, then 2 cmos inverters with +/-15V supplies. the first had a +ve switching point, bringing the signal to +/-15, and the second inverter gave the opposite output
     
  9. Nov 26, 2013 #8

    Baluncore

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    But you do not get 200MHz bandwidth.

    There are experienced electronics design engineers on this forum. If you specified your circuit's environment rather than ideal goal posts, then an engineer could select goal posts that best satisfied the circuit's environment for the minimum power / cost.

    If we assume it drives a 150 ohm transmission line then for 30Vpp, current = 30 / 150 = 200 mA.
    If it drives 50 pF at 200 MHz then since c = i . t / v we get i = c . dv / dt = 50e-12 * 60 / 5e-9 = 600 mA.

    Without I/O details it is hard to design a solution that meets the specification.
     
    Last edited: Nov 26, 2013
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