AD9364 baseband digital filter design

We are using AD9364 in one of the project where we need to achieve around 58 - 60dB ACPR (Adjacent Channel Power Ratio) for 6MHz OFDM waveform with PAPR(Peak to Average Power Ratio) of 12dB. We are passing the input baseband samples to a mask filter whose output has 65dB ACPR in baseband. This filtered output is given to AD9364 input. 

We used ADI's MATLAB filter wizard to generate the FIR coefficients with the sampling rate of 6.912MSPS at the AD and base-band interface. At AD9364 Tx output, we are getting ACPR of 50dB only, irrespective of the Tx attenuation of 5 and 10dB. Now, we tried to increase the rejection in AD9364 filter by using the wizard. In wizard, it shows the rejection of 70dB at 3.1MHz away from the center frequency. But when we loaded those coefficients in the Evaluation board, we are getting a rejection of just 20dB at 3.1MHz away from center frequency.

Why are we seeing this mismatch between the filter response plot by MATLAB wizard and eval board response when loaded with the same coefficient?

Is there anyway to get 58dB ACPR in AD9364? 

We ensured that the input baseband signal has the ACPR of 65dB. 

Parents
  • 0
    •  Analog Employees 
    on Jul 23, 2019 6:08 PM over 1 year ago

    Can you provide the generated filter and a screenshot of TX and RX configurations of the Wizard.

    -Travis

  • I've attached the filter wizard screenshot for the coefficients we are using,

    The screenshot of Wizard window,

    The screenshot of the filter response,

    The filter coefficients are attached below,

    # Generated with AD9361 Filter Design Wizard 16.1.3
    # MATLAB 9.2.0.556344 (R2017a), 23-Jul-2019 18:55:25
    # Inputs:
    # Data Sample Frequency = 6912000 Hz
    TX 3 GAIN 0 INT 2
    RX 3 GAIN -6 DEC 2
    RTX 884736000 110592000 55296000 27648000 13824000 6912000
    RRX 884736000 110592000 55296000 27648000 13824000 6912000
    BWTX 6421171
    BWRX 6337804
    -82,101
    -183,96
    -248,16
    -155,-38
    24,-70
    130,65
    53,48
    -89,12
    -99,-112
    39,-15
    126,72
    23,100
    -125,-73
    -95,-119
    91,-8
    153,161
    -18,69
    -186,-130
    -77,-164
    166,80
    179,215
    -94,29
    -250,-241
    -31,-147
    268,192
    175,271
    -207,-87
    -310,-346
    71,-81
    384,356
    126,267
    -367,-264
    -334,-437
    235,81
    501,532
    -2,178
    -564,-514
    -296,-457
    482,351
    585,695
    -235,-50
    -788,-813
    -146,-353
    818,750
    599,780
    -621,-464
    -1015,-1134
    177,-38
    1272,1296
    470,706
    -1242,-1164
    -1224,-1436
    827,650
    1932,2082
    42,295
    -2397,-2451
    -1398,-1701
    2365,2302
    3302,3632
    -1434,-1210
    -6091,-6429
    -1615,-2157
    12717,12783
    25904,26752
    25904,26752
    12717,12783
    -1615,-2157
    -6091,-6429
    -1434,-1210
    3302,3632
    2365,2302
    -1398,-1701
    -2397,-2451
    42,295
    1932,2082
    827,650
    -1224,-1436
    -1242,-1164
    470,706
    1272,1296
    177,-38
    -1015,-1134
    -621,-464
    599,780
    818,750
    -146,-353
    -788,-813
    -235,-50
    585,695
    482,351
    -296,-457
    -564,-514
    -2,178
    501,532
    235,81
    -334,-437
    -367,-264
    126,267
    384,356
    71,-81
    -310,-346
    -207,-87
    175,271
    268,192
    -31,-147
    -250,-241
    -94,29
    179,215
    166,80
    -77,-164
    -186,-130
    -18,69
    153,161
    91,-8
    -95,-119
    -125,-73
    23,100
    126,72
    39,-15
    -99,-112
    -89,12
    53,48
    130,65
    24,-70
    -155,-38
    -248,16
    -183,96
    -82,101
    

  • 0
    •  Analog Employees 
    on Jul 24, 2019 12:53 PM over 1 year ago in reply to s.kannan

    What is your LO frequency? You may get better ACPR at lower LO frequency.

    As per datasheet, the typical ACPR value is around 50 dBc.

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