dc-offsetsignalwave
I have a square wave being generated from a waveform generator oscillating between 0 V and 5 V. The generator does not support negative DC offsets. I need to shift this signal down to be centered about the 0 V value, i.e. oscillating between -2.5 V and 2.5 V (AC Coupled?).
What are ways of doing this?
(Forgive me if I mess up any terminology I'm a software engineer by trade.)
Let me see if I understood this properly:
Your constraints are a given offset and max/min ratio, and your wave has some original minimum (m) and maximum (M) values, that you wish you scale+offset in order to meet the constraints.
If that is the case then you can simply scale with respect to the minimum and then offset.
Any point in your wave will be scaled with respect to the minimum and offset:
$$ y=scale\cdot (x-m)+m+offset $$
The offset is given, you just need the scale:
$$ ratio = \frac{max}{min} = \frac{scale\cdot (M-m)+m+offset}{scale\cdot (m-m)+m+offset} $$
You just need to solve for scale in the above equation.
Another method would be to scale with respect to zero or mid-range, and then apply the offset. I'm just not sure what your application requires.
If you scale with respect to zero, then the above equations get reduced to:
$$ y=scale\cdot x+offset $$ $$ ratio = \frac{max}{min} = \frac{scale\cdot M+offset}{scale\cdot m+offset} $$
look into this amplifier, by putting 3v on one of the input pins you can filter that out, you have the option to invert the signal to (depends on which pin you place the 3V)
http://en.wikipedia.org/wiki/Differential_amplifier#Other_differential_amplifiers
Best Answer
What you need to do is simply remove the DC offset all together, not supply a negative one. This is known as AC coupling. If you run the output of your square wave generator through series capacitor, it should do what you need. This will however be at the expense of making the square wave less square.
An example circuit is shown below for you:
And the output would look like this (Green Trace = Generator Output, Blue Trace = Voltage Across Resistor):
You will probably get a little voltage loss (meaning your peaks will be a little less that +/- 2.5V) since no capacitor is ideal, but you can get a pretty good square wave output if you get the right value capacitor. You'll have to experiment and see. Usually, the larger capacitor value you choose, the closer your output waveform will be to the original for any frequency a benchtop square wave generator is outputting.