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AFE5809EVM: AFE5809EVM Digital Demodulator

Part Number: AFE5809EVM
Other Parts Discussed in Thread: AFE5809

Hello,

I am trying to use AFE5809EVM Demodulator feature.

1.  If possible, Can you guys please help me to design filter for 40/32 = 1.25 MHz ?

2. If possible I would like to set filter cut-off freq to 350 KHz.

Please let me know if you need any further information.

Thank you.

  • Hello Vatsal,

    We will look into this and provide details by May 16th.

  • Hi Praveen,

    Thank you.  Also, I would like to know this, How to set Down conversion frequency in GUI ? I can see there is a manual frequency EN for downconversion.

    Can you please tell me how to set it to 300KHz ? I found some information in Data-sheet but not sure how to use it.

    Thank you.

  • Hi Praveen,

    Any updates yet? thank you.
  • Hello Praveen,

    I am wondering that do you have any progress yet?
    Thanks.
  • Hello TI people,

    Any progress yet?

    Thanks
  • Hi Vatsal,

    I believe the reason for the problems using the digital demodulator on the AFE5809EVM GUI is an MSB/LSB mismatch between HSDC Pro GUI and the AFE5809EVM GUI.

    The user guide needs to be updated to reflect this. Unfortunately, I won't get around to taking an in-depth look at it until maybe the end of next week.

    We apologize for the delay and appreciate your patience.

    Sincerely,

    Olu

  • Hi Olu,

    Thank you for your reply. Let me know when you have any updates.

    Thanks.
  • Hi Vatsal,

    Thank you for your patience. Please answer the following questions so we can correctly address your problem.

    Have you been able to successfully get the default demodulation features outlined in the user guide working using the AFE5809 board?
    Furthermore, what do the numbers '40' and '32' refer to when you mention '40/32 = 1.25 MHz'?

    Sincerely,
    Sahana
  • Hi Sahana,

    My requirement changed since. Now We are using the 20MHz clock for AFE5809. So I am looking to configure profile RAM and coefficient RAM for that.

    1.) I am looking to Downconvert with 350KHz. So I am using register for that. In GUI Manual_Freq_EN = 1 and Manual_Freq = 47B, which gives me almost 350KHz mixing frequency for downconversion. Is this the correct way to do it?

          1.A)  Also, Is there a way that I can only get In Phase information from downconversion? I don't need Q.

    2.) I want to decimate with 32. My Fs = 20MHz so after decimation I will get Fs= 20MHz/32 = 625KHz. So for that, I need low pass filter coefficients for a coefficient vector. ( I am looking for 0 to 300KHz passband for the filter).

    3.) What is the Demod Freq window in GUI? just above the Fs. please see attached screenshot.

    4.) I have attached a screenshot for GUI setting that I'm trying please let me know if you have any questions. 

    Please let me know If you have any questions. 

    Thank you,

    Vatsal

  • Hi Vatsal,

    We are working on getting your issues resolved but I had some questions!

    1) There is a formula in the data sheet that reads: (N*Fs)/2^16. This formula can be used to calculate the oscillator frequency. Is the oscillator frequency what you want to change and set to 350 kHz? Using this formula, I would also like to know what numbers you are putting in for both N and Fs.

    Sincerely,
    Sahana
  • Hi Sahana,

    I am using 0x47B(1147 decimal) as a value for N. my Fs = 20 MHz. Which brings my mixer frequency to ~350KHz. The problem I am having is with the Decimation.

    I want to use 32 decimation factor. and 200KHz as LPF cut-off frequency, 

    THanks

  • Hi Vatsal,

    Please find some responses below.

    (1) You had previously asked a question about only getting In-Phase information from down conversion. This can be done by setting the value of the register with address '0x0A'. This is a 16-bit register with bit 15 as the MSB and bit 0 as the LSB. Bit 14 of the register (MODULATE_BYPASS bit) controls the channel output mode which can be selected as IQ modulated or single channel output.
    When bit 14 = 1, only the I channel data appears on the LVDS line
    When bit 14 = 0, both I and Q channel data appear on one LVDS line

    (2) The decimation factor and cut-off frequency can be set by generating appropriate coefficients that can be used to program the RAM. Section 8.6.2.1.3 (Programming the Coefficient RAM) in the AFE5809 data gives some details on this. The coefficients are symmetric so there will need to be eight 14-bit coefficients in 2's complement format. I am still looking into how to generate these coefficients.

    I hope this helps!

    Sincerely,
    Sahana
  • I also forgot to mention for (2) in my previous reply: There is an ‘fir1’ function in Matlab used to design filters. It takes in the filter order and corner frequency as parameters. I am still looking into how we can utilize this function in order to generate the coefficients.
  • Hi Sahana,

    1. Thanks for the information.

    2. yes, I got the filter coefficients! The question I have is, Does a number of coefficients depend on Decimation factor? In the datasheet, It is given that coefficient should be 8 x decimation factor. So what happens if I use less or In the datasheet, It is given that coefficient should be 8 x decimation factor. So what happens if I use less or more number of coefficients?

    I am usign 32 decimation factor so, 256 coefficients are enough, but I can increase coefficient for some better filter! 

    Regards,

    Vatsal

  • Hi Vatsal,

    The device has only been tested as per the specifications in the datasheet. So, for a decimation factor M, it expects 8M coefficients to be stored in the coefficient RAM. We have not verified what will happen if less or more information needs to be stored in this space!

    Sincerely,
    Sahana