walters

Whats it called when a waveform starts BELOW the zero crossing point?

example: triangle waveform

starts from -6 goes up to +4

or starts -10 goes up to +2


Mostly DC offset Raises the Waveform up ABOVE the zero crossing point what makes the waveform go Below the zero crossing point? what would cause the circuit to do this?

Superimposed is taking a DC voltage and having AC waveforms riding on top
making the AC waveform go "Above the Zero crossing point

Is there anything else like a network or circuit that would make the AC waveform go 'Above" or "Below the zero crossing point?

Whats the inverse of superimposing?

akg

As u know the Zero is referance point for voltage

Suppose two terminals A and B and B is the referance point (gnd/0v) now if A is more positive than B we say its +1V and if it is lees than B we say its -1V

the flow of the current will also reverse according to this.

superimposing a +ve voltage will make a waveform go up above zero , likewise a -ve voltage superimposing will drag it down below Zero .

Think of Zero/Ground only as a common reference point only..

walters

Thanks

yes the zero crossing is 0 zero volts

So what is it called when having waveforms start under zero volts?

When start waveforms under zero volts is have -ve or a negative power supply i don't get it ?

This changes the Reference points

akg

take a very small time slice of a waveform that starts at -6v ok..

now as earlier consider two terminals A nd B with B as reference(0v) . now -6v at a moment means the Termonal A have 6v 'lower' potential than B , and we donote it by - . it doesn't mean that it has a -ve power supply.

walters

but how do i start the wave at -6 or -12 thats my problem is what makes the waveform start at -4 or -6 ,-8,-12 how do i get the waveform below the zero voltage do i use a negative power supply or what circut does this?

akg

have u understood the 'reference point' concept clearly?
u don't require a '-ve' power supply for this .
if a waveform oscillates above the '0' (means it has static dc component) . just pass the wave thru a capacitor . u will get a bipolar wave.

mstechca

logically speaking, anything below 0 is negative, and anything above 0 is positive.

Seeing that kind of waveform means that your circuit must be starting in the inverted mode. For example, if you had a circuit whichs turns a light on and off, then in the inverted mode, the light will start off, and then turn on. I am making the assumption that the light is connected to 0V.

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evandude

mstechca, I don't think he was talking about a logic circuit, since his example was a triangle wave...

you can add a DC offset to an AC signal using a simple op-amp circuit (or perhaps an AC-coupling cap and a couple biasing resistors, in some cases) There is no real difference in adding a positive or negative DC offset, it's just in how you set up the circuit. of course, you would need to have a negative supply voltage to run the op-amp.

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walters

Thanks guys

Analog circuit not logic

Triangle waveform starting at -4 or -6 ,-8,-12 how do i do this?

Most common triangle or square waves start on the Zero reference point

examples most common

starts at 0 voltage and goes to +5 volts
so the triangle waveform or square wave
just goes from 0 to 5 volts

I'm not talking about this at all

How do i get Negative DC offset?
What circuit would make Negative DC offset?
Would i need a negative power supply to get Negative DC offset?

Triangle waveform starting at -4 or -6 ,-8,-12

example:

Triangle Waveform starts at -12volts and ramps up to +5 volts

how do i get the Triangle waveform or a Square waveform to start below
like starting with -12volts? or -8volts? or starting at -6volts?

The triangle waveform or square waveform is outputing negative voltages how do i do this?

Russlk

This is the type of circuit you want. If the gain is less than one, you will need an input attenuator.

Attached Images

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mstechca

my god, thats old style printing.

Is that a copy from the 1980's?

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evandude

there's a date right at the top of the printout :roll: :lol:

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walters

Thanks

So if i put in a +5 volt waveform it will output -12 ?

Do i just experiment with the resistor values?

How do i get different transform ranges?

Inputs are +6 or +8 but the outputs are -12 or -10

akg

yes u can
for different transforms u ned to adjust the bias and resistor values
(remember the op-amp shld be dual powered).

walters

so its the Ratios of the resistor valuse that makes the difference?

From using different Ratios i can get Negative DC offset?