Level shifter/ moving 0V to -15V

  • Thread starter Mauvai
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In summary, the conversation is about the need for a level shifter in a circuit involving a CMOS inverter and the limitations of using certain options such as op-amp based Schmitt triggers and diodes. The circuit must operate at 200MHz and be as small as possible. The solution is eventually found by using a CMOS source follower and two inverters with +/-15V supplies. However, there are concerns about the circuit's ability to supply current and the need for more specific details to properly design a solution.
  • #1
Mauvai
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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 don't need the whole thing done out, just some idea of what kind of circuit i need

(also diodes are not an option)
 
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  • #2
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.
 
  • #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
 
  • #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
 
  • #5
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?
 
  • #6
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.
 
  • #7
Baluncore said:
Sounds to me like an H bridge.

The solution to your problem would be obvious to an experienced electronics engineer who knew what you were trying to achieve.

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
 
  • #8
But you do not get 200MHz bandwidth.

Mauvai said:
This is unhelpful - if i was or had and experienced electronics engineer, i would be posting here
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.

Mauvai said:
Neither will need to supply any current if that's an issue.
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.
 
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What is a level shifter?

A level shifter is a device or circuit that is used to convert the voltage levels of a signal from one level to another. This is often necessary when two components or systems operate at different voltage levels and need to communicate with each other.

Why is a level shifter needed for moving 0V to -15V?

A level shifter is needed in this situation because the voltage levels are not compatible. Moving from 0V to -15V requires a change in polarity, as well as a decrease in voltage. A level shifter can take the 0V signal and convert it to -15V, allowing the two systems to communicate effectively.

What type of level shifter is best for moving 0V to -15V?

There are various types of level shifters available, but the best one for moving 0V to -15V would be a bi-directional level shifter. This type of level shifter can handle both positive and negative voltage levels, making it suitable for converting 0V to -15V.

Is it possible to use a level shifter for other voltage levels?

Yes, a level shifter can be used for a wide range of voltage levels, depending on the specific device or circuit. Some level shifters are designed for specific voltage ranges, while others have a wider range of compatibility. It is important to choose a level shifter that is suitable for the specific voltage levels needed.

Can a level shifter be used for other types of signals besides voltage?

Yes, a level shifter can be used for other types of signals, such as current, frequency, or data. The principle of converting one level to another remains the same, regardless of the type of signal. However, the specific type of level shifter needed may vary depending on the signal being converted.

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