[How to find phase of signal using FFT and CORDIC IP core in vivado?]

On 9/9/2022 at 12:12 AM, D@n said:

@kalainan,

Are you sure you know what you are asking for?  Phase is one of the most meaningless and irrelevant outputs of an FFT.  Why?  Well, because phase has to be referenced to something.  Do you really want to reference phase to a local clock which can not have any calibrations of any type?

Likewise, if you are new to an FFT, then I think you will find the bit-reversed order difficult to work with.  If you weren't using a bit-reversed order, I could tell you what bins to expect an output in.  With a bit reversed order things get a bit more difficult, and I'd have to think about it.

Digging deeper, I'd never use an FFT without some amount of overlap and window function.  Unfortunately, any amount of overlap will really mess with the phase you are trying to measure.  So ... you are going to need some knowledge about what you are doing.  The FFT alone is rarely sufficient for such purposes.  This, however, is a much longer discussion to be had, and that with your DSP instructor.

Dan

Hi,

    I have to find the phase difference and gain difference of two signals which is 23.5MHz and the ADC sampling frequency is 188MHz. so can you suggest any algorithm to find these parameters from ADC sampled data? 

[How to find phase angle from ADC sample using FFT and CORDIC IP core?]

25 minutes ago, zygot said:

I don't know why you directed your post to a particular set of people but the fact is that everyone can read it and anyone can post a reply to it. I'm just the only person to take the time to reply so far.

The Digilent forum is not supposed to be a place where students can find people to do their work for them or try and get a grade that they aren't worthy of... but you'd be surprised how many try, and I imagine occasionally with success. You are certainly correct in suspecting that I'm testing you. I don't know what your motivatinos are or who you are. I can only ask for clarification.  It's all about what you say, and more importantly what you won't say, and about how the conversation progresses. Often, having a conversation is more important than supplying direct answers to questions. This is especially true when the questions don't make sense and the person asking for help is evasive when asked to clarify confusing detail that have been provided. Trying to be helpful in the context of this forum isn't an exact science.

Don't give up. Someone else might get involved with your threads. For what its worth I'm coming away from this experience only the more convinced that my approach so far has been the correct one. My view is that people asking for help have no right to complain about the service. Generally, it's all about the conversation and communication. If you are unhappy with how I'm handling your thread then I'm quite happy to end the conversation.

Thank you and I will find the solution shortly.

[How to find phase angle from ADC sample using FFT and CORDIC IP core?]

@zygot

 The ADC which I am using is 16-bit dual channel so there will be two IF input signal one is taken as reference signal which is generated onboard using PLL and another signal is received from RF receiver  from which I have to calculate the phase of the each signal and then have to find the difference between them.

IF1 = 23.5MHz with 45degree phase

IF2=23.5MHz with unknown phase

From this two signals I have to find the phase difference and gain difference.

[How to find phase angle from ADC sample using FFT and CORDIC IP core?]

@D@n @Pavel @zygot@QuailJohn @msamirh @petriggg @RCB

Hi, 

     I have to find the phase angle from ADC samples. The input signal is from the function generator which is given to ADC and then the ADC sampled data is buffered and given to FFT IP core. Then the output of the FFT IP core is given to CORDIC IP core to get the phase angle, but I am not getting correct phase angle for the respective input signal. Refer the parameters which I have given below. 

Input frequency => 23.5MHz sine wave with 45 degree phase shift which was generated by function generator

ADC sampling frequency => 188MHz

FFT samples  N=> 256 points

Frequency resolution => FS/N

                                   => 188MHz/256

                                   =>734375Hz

Frequency bin => input frequency/frequency resolution 

                         => 23500000/734375

                         => 32nd bin 

The real and imaginary value of 32nd bin is given to CORDIC IP core to get the phase angle value as 45degree but I am getting the varying phase angle.

Here I  have attached the configuration settings of FFT and CORDIC IP core. 

 

[How to find phase of signal using FFT and CORDIC IP core in vivado?]

@D@n@Pavel@zygot

I have to find the phase of a signal from the ADC sample. For simulation purpose I replaced the ADC with the DDS complier IP core the 1MHz sine wave signal with 45 degree phase is generated from the DDS core and its feed to FFT(configure as FORWARD FFT) IP core and the output of the FFT IP Core is feed to CORDIC IP core(configure for TRANSLATE function) to get the phase of the signal.

here fs=256MHz, N FFT points =256, input frequency =1MHz.

frequency resolution = 256MHz/256 =>1MHz

frequency bin = 1MHz/1MHz => 1

The magnitude of FFT output shows two bin one in 1st index and another one in 255th index. if I taken 1st bin real and imaginary value the cordic output is incorrect. If take 255 bin real and imaginary value the cordic output is correct. Iam totally confused? If anyone have done this before suggest me solution for the issue.

Here I have attached the DDS , FFT configuration settings image for clarification go through it.