Extracting I & Q phase component in labview FPGA

[Navin4561]

Hai everyone,

i am trying to demodulate the baseband signal by using FM DEMODULATOR block in FPGA.

This FM DEMODULATOR needs Inphase and Qphase component as a Input. 

i dont have much exposure on LABVIEW.

can any please direct me how to go  about this.

thanks

regards

Navin

[mcduff · Accepted solution]

To get I & Q you need a pair of mixers, cos and sin, multiplying the passband frequency, then a pair of low pass filters with the appropriate bandwidth. The FM demodulation is just a phase unwrap.

In the FPGA, create a cos and sin wave at your FM frequency, then multiply each by your input, low pass filter and then you have I & Q.

Mcduff

[Navin4561]

Hai Mcduff,

thank you for your response.

Is there way to change the frequency of the sine & cosine signal with  " High throughput sine & cosine function" in LABVIEW FPGA..?

For example if i want generate the sine wave with 100KHz, what are the chages to made..?

i am loking for your suggestions.

thanks

Navin

[mcduff]

I will be onsite tomorrow and have access to my computer, I'll try to post a screenshot.

I don't think I used the high speed sin/cos, just the normal FPGA function that gives sin and cos. That function was tied into the FPGA clock such that I could generate the correct frequency wave for multiplication/mixing stage.

1. Do things in parallel via pipelining. Don't try to demodulate in a single loop, spread it out. The first few sample will be garbage, but then it will operate much smoother.
2. Don't use the ATAN2 for phase unwrapping, too much overhead. There is a DSP approximation that is a division which is much less overhead.

mcduff

[mcduff]

Here's the First Stage of my input that is pipelined.

1. In the Sequence Structure have an appropriate delay then acquire signal on myRio channel. At the same time generate a phase synchronous sin/cos at the carrier frequency (.002 times 40MHz equals 80kHz) Note it takes 2 iterations of the loop before real data is sent to the mixer.
2. Convert to 32 bit and shift the numbers, my Rio 12 Bits (This is done for later processing)
3. Filter out any low frequency noise, then Multiply(Mix) the sin and cos with the signal.
4. Send data to another loop for low pass filtering.

The output of the loop above is I & Q; that can be sent to any other loop you want.

For the pipelined approach the first few samples will be garbage, but afterwards there will a signal that is slightly delayed to your input. Don't try to do sequentially.

mcduff

[DeepakDSPEngineer]

Please, me how to do Phase unwrapping using some other methods with using arctan2 function. bascaily how to do demodulation of fm in fpga?

[mcduff]

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@DeepakDSPEngineer wrote:

Please, me how to do Phase unwrapping using some other methods with using arctan2 function. bascaily how to do demodulation of fm in fpga?

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(Q0-Q2)I1 - (I0-I2)Q1 where the subscripts are sample delays, that is, 0 is the current sample, 2 would be the sample two time periods previous. Can't find the reference for this.

[Deepak.k]

Hi mcduff,

Please Help me, I'm really trying since 1 week. For FM demodulation in FPGA. If you have any idea how to do it. Please suggest me or please provide source code for it. Thank you in advance.

[mcduff]

Everything I did is in this thread. Read all of the posts.

Mix Signal

Get I&Q

Demodulate

mcduff

[DeepakDSPEngineer]

Please tell me, What is the redfilterDataIn here. Will I need to pass the IQ Demodulation signal to any filter again?