LTC2267-14_Terminating resistors in Fig. 12 and Fig. 13

Question

I had a question from a customer about LTC2267-14. 
 
 In Figure 12 of the LTC2264-14, there is a 100&Omega; termination resistor in addition to the 50&Omega; x 2 termination resistors, which is not evident from the evaluation board schematic. Is this a 100&Omega; resistor for impedance matching?

Also, in the connection diagram in Fig. 13, a termination resistance of 100&Omega; cannot be confirmed. Is a terminating resistor built-in?

Best Regards

ADIApproved · Accepted Answer

Figure 12 shows a single ended signal generator going thru a single ended to differential translation and then driving the ADC clock. The signal source is assumed to the 50ohms. So with the two 50ohms resistors in parallel with the 100 ohms, the termination after the transformer is 50ohms, so it is matched. The 50ohm resistors provide common mode termination, and the 100ohm resistors provides differential mode termination. 
 Figure 13 shows the drive for PECL or LVDS clock drive. Both of these clock source would need termination somewhere, but should be located before the final capacitors. The ADC will set the common mode voltage required.)

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LTC2267-14_Terminating resistors in Fig. 12 and Fig. 13