# Signal Filtering - Want to filter an induced triangle wave out of the signal

#### Mazotti

Joined Oct 22, 2018
3
Hi All,

For a project I am inputting a triangle wave into a system and what is being output is this triangle wave with a sine wave following the triangle waves input.

I would like to filter out this triangle wave and only have the sine wave signal being output. I've thought about using a band pass filter to filter out the unwanted frequencies but am afraid that this will ruin the sine wave that is being induced by the system. (From what I have looked up a band pass filter can reduce the triangle wave to a sine wave, but I would like to completely negate the triangle wave and only have the sine signal that is output from the system)

Thanks for any input.

#### dl324

Joined Mar 30, 2015
12,783
Welcome to AAC!

What is the relationship between the input and output waveforms? Frequency? Amplitude? Phase? ??

#### Mazotti

Joined Oct 22, 2018
3
Welcome to AAC!

What is the relationship between the input and output waveforms? Frequency? Amplitude? Phase? ??

Thanks!! and thanks for the quick reply.

The relationship is Amplitude and Phase (I think). (The sine wave is basically following along the path of the triangle wave that was input)
I currently don't have any images from the oscilloscope but I drew a crude picture of what the output signal looks like compared to the input. If you need more information than this let me know and I'll try to get that information ASAP.

Thanks again!

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#### crutschow

Joined Mar 14, 2008
26,963
The best you can likely do is use a high-order band-pass filter with its center frequency equal to the sine-wave.
Need the frequency and amplitude of each of the two signals to give you a better answer.

#### BR-549

Joined Sep 22, 2013
4,938
There are a number a ways to reference your post and drawing.

One could add a triangle offset to a sine.

Or one might staircase or DAC your waveform.

But I'm not really sure what you want to do.

Joined Mar 10, 2018
4,057
Questions -

1) Frequency (range of) triangle wave ?

2) Frequency (range of) Sine wave ?

3) In DB, rejection desired of Triangle wave harmonics ?

Regards, Dana.

Last edited:

#### Mazotti

Joined Oct 22, 2018
3
Hi All,

Sorry for the delayed response but I think that a Band-Stop filter would work best for the purpose I'd be using it for, the triangle wave will always have different frequencies than the sine waves that are propagating on it.

I also think that I will be going a digital route, thank you all for your responses!

Joined Mar 10, 2018
4,057
One digital approach w/o host (CPU) intervention, leaving CPU to do other stuff
all onchip -

Regards, Dana.

#### MrChips

Joined Oct 2, 2009
23,204
If you filter any waveform with a narrow high-Q band-pass filter you will end up with a sine wave. That is because a narrow filter allows only one frequency to pass. You do have to watch out for ringing and oscillation at the center frequency. Any transient energy into the filter will result in a sine wave output at the center frequency.