90 degree phase sine wave phase shifter

Hi Mark,

It is certainly possible to create sine and cosine outputs for a given input signal, but how you go about it depends on the frequency range you are attempting to do that across. If it is a single frequency this can be accomplished with something as simple as an RC bridge circuit, or various LC, and op amp circuits can be used. However, if you are trying to cover a wider frequency range such as that covered by speech, then an active all-pass filter is commonly employed.

If you can get a hold of a copy of the "Electronic Filter Design Handbook," by Arthur B. Williams, there is a section titled Wide-band 90 degree Phase-shift Networks. The author walks you through the all-pass design process. If you can't locate the book, I suggest you do a Google images search on "all-pass filter design." Many different network images will be displayed for active all-pass filters and you can follow the images back to their home pages where more information is provided.

If just need to generate two sine waves having a quadrature relationship, here's a good resource:

www.ti.com/.../slyt164.pdf

Regards, Thomas

PA - Linear Applications Engineering

my application is for a specific frequency to be in quadrature. i am currently using an all pass filter but i read the theory about it and the input is in 90 degrees out of phase as the output is in the cut off frequency of the all pass filter or -3dB. so the amplitude of the input will be reduced.

Hi Mark,

The expectation of a all-pass filter designed for quadrature operation is that it maintains a constant gain and the quadrature output phase relationship across its usable bandwidth. Any passive, or active, filter will have output phase shift across frequency relative to the input signal. 

Regards, Thomas

PA - Linear Applications Engineering