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HMC1097 driven by quadrature hybrid

I'd like to use an HMC1097 as an image-rejection upconverter to go from 70 MHz to 500 MHz. The 70 MHz signal comes from an existing single-ended source, not a DAC. Would I be able to transformer couple the I and Q inputs as shown below to convert from single-ended to differential while also applying the 0.45V common mode voltage needed by the HMC1097?

U2 (Mini-circuits LRPQ-70) is a quadrature hybrid transformer used to generate the I and Q signals from the input IF. The T1 and T2 (Mini-circuits TC4-1TG2+) are 1:4 transformers with center tap, and the center taps are tied to the bias voltage generator, and are AC grounded through C3 and C4. R6 and R7 provide the termination resistors so that each output of U2 sees 50 ohms.

Please advise if this is will work, or if there is a better alternative to consider.

Thank you

  • Normally the IQ inputs are drive from a DAC which lends itself to a flexible configuration, but the transformers configuration you have will work. You should confirm the common mode voltage is 0.45V.

    Ideally you should get a single sided RF output signal, but the limitations on image rejection may come from the gain and phase imbalances between the two transformers. Additionally, the LO feedthough will be a function of the DC input offset mismatch on the inputs. Currently you do not have any means of adjusting the LO feedthrough or image rejection, so you will need to measure to confirm if the results are satisfactory for your application.

    Also per the datasheet, the RFOUT is DC coupled and matched to 50 ohms, so be sure to include a DC blocking capacitor.