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AD9173 output signal conditioning.

Hello!

We are designing a DAC module based on the AD9173. You can see the desired schematics on the picture below. We need frequencies on the output to be from 10 kHz all the way up to 6 GHz.
We understand that output of the DAC needs to be terminated with inductors to ground but lower frequencies are not possible with an inductive termination.

How could we use this DAC at lower frequencies? Is this even possible with the AD9173 and particular schematics using ADRF5024 to switch between bands? Datasheet only specifies characteristics over 100 MHz

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  • AD9176 datasheet has details on DC-coupling application.

    Ideally, the common-mode voltage at the analog outputs is kept near 0 V or GND, while the load impedance seen by the analog outputs is matched to their internal impedance. Replacing the RF chokes used in ac-coupled operation with 50 Ω resistors to GND is not recommended because this results in an excessive common-mode voltage, near 250 mV. Instead, tie the 50 Ω resistors to a −0.6 V reference supply, thus maintaining proper dc bias at the analog output devices internal to each DAC output.

  • Hi Biao;

         Our previous generation of high speed TxDACs which are generally interfaced to modulator requires 0.5V common mode voltage. And this 0.5V common mode voltage is generally setup by the external 50 ohm resistors. So when it comes to the AD916x/7x high speed DAC, do we change the internal current source design that requires the common mode voltage as 0V?

          Thanks a lot!

  • Hello,

    The AD916x/7x family of DAC's are meant to synthesize direct RF signals without use of a mixer or modulator hence its common-mode can be referenced to VDD25_DAC for AD916x family or AGND for AD917x family since most AC waveform reconstruction applications due not require DC or near DC operation.  Proper choice of balun will allow one to cover lower frequencies down to a few KHz.  Unfortunately such low cost baluns that provide low frequency coverage do not provide very good high frequency coverage.....hence customer issue above.  Marki baluns such as the BALH-0006 and -0009 are some of the best baluns in the market albeit at a high price (i.e. closest to idea in performing amplitude/phase balance over a wide frequency range with lower frequency being 500 KHz).

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  • Hello,

    The AD916x/7x family of DAC's are meant to synthesize direct RF signals without use of a mixer or modulator hence its common-mode can be referenced to VDD25_DAC for AD916x family or AGND for AD917x family since most AC waveform reconstruction applications due not require DC or near DC operation.  Proper choice of balun will allow one to cover lower frequencies down to a few KHz.  Unfortunately such low cost baluns that provide low frequency coverage do not provide very good high frequency coverage.....hence customer issue above.  Marki baluns such as the BALH-0006 and -0009 are some of the best baluns in the market albeit at a high price (i.e. closest to idea in performing amplitude/phase balance over a wide frequency range with lower frequency being 500 KHz).

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