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  • TI Thinks Resolved

DAC5681: DAC5681+THS3215

Prodigy 220 points

Replies: 5

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Part Number: DAC5681

We are in the designing phase of  a zero-IF based transmitter using DAC5681 with THS3215.

Our required output frequency range is from 1MHz to 50 MHz.

The DAC samples are at 122.88 MSPS with modulated signal with information bandwidth occupying 48 KHz.

We want to generate transmit signal with the combination of DAC5681 and THS3215. We want an output level of 30 dBm from this circuit to drive next Power amplifier stage, which has 50 Ohm input impedance.

Please suggest, whether we can go ahead with this design or any other recommendations..

Please suggest if any documents like schematics and HDL driver available for this application..

  • Hi Ch Ramakrishna,

    We are looking into this, and will be back with you soon.

    Best Regards,

    Dan

  • In reply to dBrock:

    Hi Ch,

    Here is the document that talks about the connection of DAC with the amplifier.

    Regards,

    Neeraj

  • In reply to Neeraj Gill:

    Hi Niraj,

    Thank you for your support.

    The attached document is more generic, which explained about the interfacing of high speed current DAC to Op-Amp.

    The technical inputs are good for carrying out the design process.

    However we are looking into the specific chip set DAC5681 with THS3215. Whether with this combination, can we able to achieve an output power of 30dBm within 1MHz to 50 Mhz frequency range. The THD we are looking for is around 60 dBC. And IMD components should be better than 50 dB within a tx BW of 48KHZ.

    Any ready available circuit (schematic) is more helpful.

    Thank you once again..

  • In reply to Ch Ramakrishna:

    Hi Ramakrishna,

    Achieving 30dBm output power within 1MHz to 50MHz frequency range would be tough using just the THS3215. You will have to cascade output of the THS3215 with THS3491 in-order to get 30dBm output power into 50-ohm load.

    You may want to look at the following TI-Design in-order to realize such as circuit.

    One thing you need to be careful is that the DAC5681 output CM is 1.8V which needs to be properly brought down to 0V using the THS3215. Since, your care-about is only for frequency greater than 1MHz, I believe you should be able to ac-couple between the DAC output and THS3215 input which will isolate any CM issue between the two.

    Best Regards,

    Rohit

  • In reply to Rohit Bhat:

    Hi Rohit,

    We thank for your support. We are looking for the similar application note from TI.

    We will proceed with the Channel-2 Configuration (THS3217 + 2 X THS3091) configuration, which can able to generate upto 50 MHZ output frequency.

    1. As per your suggestion, in order to block the CM output of DAC5681, we will use DC blocking capacitors 100 nF each on OUTA+ and OUTA- outputs of DAC5681. then we will feed this input to the 500 MHZ Low pass filter.

    2. As per TIDA-00684, the DAC is capable of 30 mA full scale output, where as DAC5681 is 20 mA full scale capable. Any precauations or suggestions from your end to use DAC5681 along with THS3217 + 2 X THS3091 ?

    3. The Power supply for 2 X THS3091 is shown EXTV in the application and is fed from outside. We are planning to use +5 V and -5V supplies on our board , which will power THS3217 and 2 X THS3091. Any care and precautions to be taken to use this configuration?

    Regards

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