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TRF370417: LPF between TRF370417 and DAC5670IGDJ

Pradeep Kumar68
Intellectual 420 points
Part Number: TRF370417

Hello,

We are using TRF370417 modulator. For this IQ signal is generated by DAC5670IGDJ. Between this I need to design a Bessel LPF with 550MHz  -1dB bandwidth. This Filter must reject 1.2GHz DAC clock.

But DAC output pin impedance and Modulator Baseband input pin is different. So we are unable to finalise on the LPF topology. Could you please help us out.?

  • 0
    TI__Mastermind 18065 points
    Check out this app note that addresses this situation: www.ti.com/.../slaa399.

    The DAC is a current sink DAC operating on a 3.3V common mode. The TRF370417 modulator operates with a 1.7V common mode. You can implement a passive translation network to get the common modes to line up right. Since the modulator is high impedance, you can place a termination resistor to bound its impedance. Typically the translation network is designed to have 100 ohm differential input and output impedance to make the filter design easy.

    --RJH