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TRF370417: TRF370417 Input Questions

Part Number: TRF370417

I have a customer asking the following questions concerning the inputs to the TRF370417:

The single ended Input impedance of the baseband I & Q inputs of this chip TRF370417 are specified as 5 KΩ in the data sheet. In Table 1 of the data sheet, the baseband in-quadrature input: negative terminal. Optimal linearity is obtained if VCM is 1.7-V (normally terminated in 50 Ω). Also in the application example, the DAC is connected to this chip directly via a low pass filter without any transformer for impedance matching.

I'm puzzling if the differential impedance is 2 x 5 KΩ , why there is no transformer from DAC to the I & Q input of this chip in the application example?

Can you explain in detail why a transformer was not used? Can you also explain the configuration that would be used if the customer used a transformer? Would he simply need to add the proper bias voltage (1.7V)? Would this result in improved performance or would this configuration add additional losses?

Thanks for your help with this!

Richard Elmquist