Regarding trace impedance matching

Hello sir,

I am using voltage-controlled oscillator HMC431. In the datasheet of this VCO, it is mentioned that we need to maintain a 50-ohm trace impedance at the RFOUT pin. On the RFOUT pin, I have connected lumped components as shown in the figure. These lumped components are changing the impedance. So, how shall I maintain 50-ohm impedance at RFOUT pin? 
  • +1
    •  Analog Employees 
    on Jan 27, 2020 9:33 PM 11 months ago

    Hi,

    The oscillator will in all likely hood continue to function fine albeit at a slightly different Vtune voltage vs frequency than would exist if you didn't have these elements in place. To minimize this effect place a 3 to 6 dB resistive attenuator between the output of the VCO and the series parallel LR circuit to improve the match and reduce the effects of pulling. 

    Please visit microwaves 101 and search transmission line impedance if you're unsure of how to derive impedance or search for system return loss and uncertainty for more information on how the return loss of cascaded elements impacts the return loss at various nodes throughout a design. 

    Best Regards,

    Marty