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# How to convert 0 to VDD to -VDD/2 to +VDD/2

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##### Junior Member level 3
I have a square wave that oscillates from 0 to VDD, Can I convert this to -VDD/2 to VDD/2? How is it possible? Can a capacitor do it? It would be a great help if you can answer this.
thanks

Yes. A capacitor in series will remove DC component from a signal.

Afterward however the square waves will have slanted tops and bottoms.

The larger capacitor you use, the better it preserves square appearance.

Points: 2
is there any specification on what kind of capacitance this should be, for me to get -VDD/2 to VDD/2. or can any cap do this? when I try out in cadence, with a 1 pf cap for a square wave at 400kHz, it totally subtracts the signal by -1. Say I give in 0 to 1, square wave with 50% duty cycle, it gives me a sqare wave between -1 to 0. Not -0.5 and 0.5. That is what caused the confusion, why does that happen?. Any frequency dependance, I should know about, so as to make it oscillate between -0.5 and 0.5?

is there any specification on what kind of capacitance this should be, for me to get -VDD/2 to VDD/2. or can any cap do this? when I try out in cadence, with a 1 pf cap for a square wave at 400kHz, it totally subtracts the signal by -1.

A 1 pF is a tiny cap value and it will give you the briefest spikey looking pulses you ever saw. You may have trouble seeing them.

Experiment with increasingly greater values, each 10x the preceding value.

The spikes will start looking squarish. You're looking for a waveform that can be used by your next stage.

The degree of distortion is based on the length of each pulse and the impedance at the cap. It has to do with a formula for something called the RC time constant

Your capacitor may be marked for polarity. The lead for positive polarity must face the more positive voltage.

Say I give in 0 to 1, square wave with 50% duty cycle, it gives me a sqare wave between -1 to 0. Not -0.5 and 0.5.

Can't explain a capacitor doing this by itself. Sorry.

I have a square wave that oscillates from 0 to VDD, Can I convert this to -VDD/2 to VDD/2? How is it possible? Can a capacitor do it? It would be a great help if you can answer this.
thanks

Let us remember that any circuit (or even a component) we like to add, its design is related to what it is connected to; for example at its input and output.
In our case, one may ask:

How the 0-Vdd square wave is generated? What is the value of Vdd?
What is the load at ±Vdd/2 output?
The better the answers are real, the better the solution will be.

At least we know now that the frequency is 400KHz, right?

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