Oscilloscope overshooting in RC high-pass filter

[tiagoft]

Hello, all

This is my first message to the forum. I am need of some assistance in the following problem.

I have mounted an RC high pass circuit, where R = 100K and C = 100nF (hence, cutoff frequency is around 15.5Hz). When I feed the circuit with a 1 Hz square wave with 0V offset and 2V peak-to-peak, the output (voltage in the resistor) should be +-1V in the edges of the square waves followed by an exponential decay to zero, right?

The oscilloscope, however, is reading a maximum voltage value of +-2V - hence, a 1V overshoot. All configurations are correct, such as probe gain, input bandwidth limitation, etc (it is possible to see both waveforms - input and output - on the screen)

My hypothesis for this are:
- The high spike is due to the high voltage variation (this should not make sense, since there is a resistor in series with the capacitor)
- The oscilloscope - a digital one - has sampling dificulties to find sudden high frequency spots while in a large time scale
- My questioning is wrong and the results are correct

What is the correct answer?

Thanks
Tiago

[Hero999]

Could yoube confusing  peak voltage and peak to peak voltage?

If the V/division setting is 1V the signal should occupy two squares.

You might also be using complementary outputs on the signal generrator (180 degree phase shift) so you'll see double the voltage, than you'd expect from the signal generator.

Failing that it could be due to inductance in a poorly/uncomensated cable causing ringing.

[indulis]

Try it with a sine wave instead...

With a square wave you're just looking at the charge/discharge of the cap