Let’s describe each component so that you know its need or function within the input matching network to the ADC:

• C1, C2. Typically 0.1µF, these components block DC from being fed into the balun or transformer. Some balun designs lead to ground, DC, or both, and may aggravate the balun’s function, leading to poor performance.
• R1. This component enables back termination near the outputs of the balun after the DC blocking capacitors. If your trace lengths are long enough, you may need this component. Assuming that no perfect match across the band of interest is achievable, you may need to back terminate in order to handle any standing waves that accumulate as the imperfect match rolls back and forth across your frequency range.
• R2, R3, R4. These components enable you to employ various matching techniques and can take the form of several combinations in order to solve a balun and ADC matching conundrum. For the widest band matches, R2, R3 and R4 are generally configured as a matching pad, which helps dissolve the standing waves between the balun and ADC and provides a “stiff” 50Ω impedance that both the balun and the ADC need. Though these components are represented as resistors, they can take the form of capacitors or inductors as well.
• C3. This capacitor, typically 0.1µF, ties the center point of the R3s together and enables an AC current path. Adding C3 is also a good idea, because when over-ranging the ADC’s input full scale, C3 allows this AC current to go somewhere. C3 could also be located at R5 instead.
• R5. This component allows back termination on the opposite side near the ADC’s inputs, and is not always necessary. R5 provides the same function as R1, but from the opposite perspective in order to help resolve standing waves that may accumulate. Typically, R1 or R5 are required when trace connections are ≥300mils in length.
• R6. This is a kickback component, typically in the form of resistors, but in some cases inductors or low-Q ferrite beads that can help snub any residual charge kickback that comes back onto the analog input network from the internal sampling circuit in the ADC. These component placeholders are essential when using unbuffered ADCs.

Again, be wary if you just plan to run two traces from the output of the balun to the inputs of the ADC. Even if you collect S-parameters, simulate and prove the design to your colleagues, this methodology could prove to be costly unless you have previous experience with the balun and ADC combo.