(FPGA) high throughput inverse tangent 2 input

[Betty Boop]

Hello! I would just like to ask what is the effect of having a 'negative x' on the high throughput inverse tangent (2 input)? It's because when I have 'negative y' (and 'positive x'), the answer is correct. However, whenever I have 'negative x' (regardless of the sign of y), the answer would always be wrong. Thank you for your time!

[Ether]

Originally Posted by Betty Boop

Hello! I would just like to ask what is the effect of having a 'negative x' on the high throughput inverse tangent (2 input)? It's because when I have 'negative y' (and 'positive x'), the answer is correct. However, whenever I have 'negative x' (regardless of the sign of y), the answer would always be wrong.

Please give a specific (numerical) example of 2 inputs which gave a wrong output. Give the three numbers X, Y, output.

[Betty Boop]

*The output is not yet multiplied to pi so that it is expressed in pi radians.

input: y = 1, x = 2
output: 0.1482 (correct)

input: y = -1, x = 2
output: -0.1482 (correct)

input: y = 1, x = -2
output: 0.8542 (even the sign is wrong)

input: y = -1, x=-2
output: -0.8518 (sign is again wrong and from my observation, it doesn't take into account the sign of x)

[Ether]

Originally Posted by Betty Boop

*The output is not yet multiplied to pi so that it is expressed in pi radians.

input: y = 1, x = 2
output: 0.1482 (correct)

input: y = -1, x = 2
output: -0.1482 (correct)

input: y = 1, x = -2
output: 0.8542 (even the sign is wrong)

input: y = -1, x=-2
output: -0.8518 (sign is again wrong and from my observation, it doesn't take into account the sign of x)

Those outputs are all correct. See attachment.

Starting from the +X axis and going counterclockwise, atan2 goes from 0 to +pi

Starting from the +X axis and going clockwise, atan2 goes from 0 to -pi.

[Betty Boop]

ohh! sorry, sir, but can you please explain the last two cases I've tried manual calculation using calculator

[Ether]

Originally Posted by Betty Boop

ohh! sorry, sir, but can you please explain the last two cases I've tried manual calculation using calculator

I edited my original response to add some detail. Please re-read it.

Then read this article:
http://en.wikipedia.org/wiki/Atan2

Then ask me a specific question and I'll gladly help.

[Betty Boop]

Hi! Now I understand THANK YOU VERY MUCH!

[Ether]

Originally Posted by Betty Boop

Hi! Now I understand THANK YOU VERY MUCH!

You're welcome.

May I ask: What is your interest in atan2? Are you taking a math class, or are you using it for FRC?

[Betty Boop]

No, Sir. I'm using it in determining the phase of a signal given its I and Q data.