I am designing a schematic with TI ADC12DJ3200.
This ADC is differential 100 Ohm input impedance ADC.
Signal from SMA is directly connected to input of Balun.
But sometimes I see that a 50 Ohm pull down is placed at SMA and then a capacitor and then signal is connected to Balun as shown below as example although pull down resistor in this example is DNP: Which configuration should I use in my schematic?
Does this 50 Ohm pull down at SMA helps to see the balun a 50 Ohm impedance at input so that 100 Ohm impedance can be maintained at Output of balun?
I have seen that in some schematics a 50 Ohm pull down is used at SMA and in some schematics no pull down is used at SMA.
I am confused how to know when to use a 50 Ohm pull down at SMA and when to not?