# How to build a delay circuit?

Joined Oct 25, 2010
2
I'm a final year physics student and as part of my final year project I need a circuit that can provide me with two sine waves ∏/2 out of phase with equal maximum/minimum.

I will be using a signal generator to provide me with a steady sine wave input with constant magnitude but varying frequency.

My knowledge of electronics is very basic but I imagine I need something like a two branch circuit that has a capacitor in one branch and another branch that allows the input signal to pass through unchanged.

Basically I need two output signals ∏/2 out of phase from a single input signal.

Can anybody help?

Dan

#### Ron H

Joined Apr 14, 2005
7,014
It is very difficult to do with purely analog circuits, unless you generate the signals with a quadrature oscillator instead of a signal generator with a single output.

#### atferrari

Joined Jan 6, 2004
4,008
In my case I had one circuit generating two equal (variable) frequency signals. DDS in action.

Since everything was digitally controlled I could "steal" clock cycles to one of them until having the phase difference I wanted.

Anyway, the answer to your question is basically this - just click on it and look for page 78:

Last edited:

Joined Oct 25, 2010
2
Thanks for the replies. I'm not 100% certain of my frequency range yet as it will depend on the physical geometry of the system for which the circuit is going to be used to control (a linear synchronous motor) but I imagine it will be between 0 and 100Hz.

That document seems to be quite detailed but also suggest that I'm going to have issues with the output voltages as I vary the frequency of the input. I really need to have a constant voltage across all the frequencies I use.

It occurred to me earlier that I may be over complicating the situation. As the 1st derivative of sine is cosine, is that a circuit that essentially take the derivative of an input signal?

#### Ron H

Joined Apr 14, 2005
7,014
It occurred to me earlier that I may be over complicating the situation. As the 1st derivative of sine is cosine, is that a circuit that essentially take the derivative of an input signal?
The derivative of sine(ωt) is ωcos(ωt), i.e., the amplitude rises linearly as a function of frequency.

#### Ron H

Joined Apr 14, 2005
7,014

#### Ron H

Joined Apr 14, 2005
7,014
As Agustin suggested, the best solution is probably DDS (direct digital synthesis), but it is not simple for a novice.

#### atferrari

Joined Jan 6, 2004
4,008
Unfortunately, although the amplitude is constant, the phase shift varies as a function of frequency.
Yes, it seems that THAT could be a problem.