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AFE7444EVM: Optical modulation and monitoring

Part Number: AFE7444EVM
Other Parts Discussed in Thread: AFE7422

Hello,

First some context:

I am building a fibre-optic communication system in wich I modulate an optical signal with an IQ modulator and then I detect part of that modulated signal with a photodiode pair to check for imbalances in the IQ modulator. For that I would like to use a board that integrates both DAC (to drive the IQ modulator) and ADC (to monitor the output of the photodiode pair) ports, this would basically replace a dedicated AWG and  Oscilloscope that I've been using for the same effect. So:

1 - Is it possible to use the DAC ports of the AFE7444EVM as an AWG? If yes, what sample frequencies can I use and what is the output voltage range?

2 - Is it possible to use the ADC ports of the AFE7444EVM as a real-time Oscilloscope?

Thank you for your help in advance.

  • Hi Daniel,

    Please find my answers below.

    1 - Is it possible to use the DAC ports of the AFE7444EVM as an AWG? If yes, what sample frequencies can I use and what is the output voltage range?

    Vijay: Yes. You can DAC sampling frequency of up to 9 GSPS and BW of up to 800 MHz. Output full scale at different output frequencies is given in the datasheet. If you don't have access to the datasheet, please submit a request for it at : 

    https://www.ti.com/licreg/docs/swlicexportcontrol.tsp?form_id=288371&prod_no=AFE7422-DESIGN&ref_url=asc_dc_hsc

    2 - Is it possible to use the ADC ports of the AFE7444EVM as a real-time Oscilloscope?

    Vijay: Yes. You can ADC sampling frequency of up to 3 GSPS and BW of up to 800 MHz. A digital down converter (DDC) is integrated after the ADC. If you want to bypass the DDC, you can use AFE7422.

    Regards,

    Vijay

  • Hello Vijay

    Thank you very much for your quick response, I have some follow-up questions though.

    1- How exactly does the interpolation work?

    If I understand correctly, I can give the DACs samples to output at 800MSPS (1.2GSPS in the case of the AFE7422), but it will fill in the gaps between those samples at 9GSPS. Is this correct?

    2- How exactly do the DUC and DDC work?

    Again, if I understand correctly, I can control the frequencies of the NCOs and with the oscillators obtained from them I can upconvert my signal for the DACs to some intermediate frequency using the DUC. The opposite operation can then be performed at the ADC side using the DDC. Is this correct?

    3- Can the DUCs at the DAC side be bypassed? If not, can I just set the frequency of the associated NCOs to 0?

    Same thing goes for the DDC, as an inelegant solution can I set the NCOs at the DDC to a frequency of 0, thus "bypassing" the DDC? 

    I also have some questions pertaining to the functioning of the TSW14J57, which we are also looking at acquiring, should I pose them in this thread or is it preferable to open a new thread dedicated to that?

    Thank you in advance for your help and I apologize for the large number of questions.

    Best Regards

    Daniel

  • Hello Vijay,

    One extra question. Can the DACs and ADCs of a single AFE74xx board, in conjunction with the TSW14J57, function simultaneously? That is, using the High Speed Data Converter Pro, is the board able of recording from the ADCs without stopping the output from the DACs?

    I have this question because in your training video How to configure the AFE74xx ADC in Mode 4 using the internal PLL | TI.com Video, in the moment the capture button is pressed (at 1:20 in the video) the output shown in the spectrum analyzer vanishes.

    Best Regards

    Daniel

  • Hi Daniel,

    I have answered your question in the follow-up thread you posted:

    Regards,

    Vijay