How to match LTC5562 LO ranging from 3GHz to 7.5GHz

How do I match LO port of LTC5562, my LO ranges from 3GHz to 7.5GHz?

  • 0
    •  Analog Employees 
    on Jul 10, 2018 5:32 PM

    Hello ,

    Due to the large change in port impedance over the range you're interested in, I don't think it's likely that a suitable match can be provided for this application. The port changes from essentially 100Ω to around 10Ω over this range. If you need an LO match over this entire range, you may want to look in to some of our other parts which have wideband LO ports (LTC5510, LTC5549, etc). The list of choices can be narrowed depending on your frequency plan and performance requirements. If you only need the LO to be matched in a couple of places across that range, then you may want to consider switching in different matching circuits for each band.

    Best Regards,

    Weston Sapia

    Sr. RF Applications Engineer

    Analog Devices

  • Table 2 shows single ended LO input impedance and reflection coefficients which are not consistent with each other. For example, at 10MHz, impedance is 195.29-j2576.34 but magnitude of reflection coefficient is shown as 0.59 (it should be 0.997 for this impedance at 50 ohms).

    Also, using a simulator to plot return loss given the table 2 impedances and table 4 matching components differs significantly from the curves shown in Figure 8.

  • 0
    •  Analog Employees 
    on Jul 11, 2018 6:58 PM

    Hi ,

    Table 2 shows the part impedance in parallel form, not series. This will make the math work out.

    Also, keep in mind that the simulator will use ideal components, so to make the results match the table, you're likely going to need to include some real component s-parameters as well as account for the losses and imperfections in the board you'll be using. Figure 8 shows measured data using the circuits from Table 4, so it should line up once all the parasitics are added in to the simulator.

    Best Regards,


    Weston Sapia

    Sr. RF Applications Engineer

    Analog Devices