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Original question:

LMK04828: Some questions about the 50ohm termination for clocking CLKinX using single-ended source.

LMK04828: About the the input impedance of OSCin.

Hui Chen
Intellectual 430 points

Part Number: LMK04828

Hi Ti experts

I have posted a question about CLKinX and OSCin Single-End Termination on e2e, as follows

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1062392/lmk04828-some-questions-about-the-50ohm-termination-for-clocking-clkinx-using-single-ended-source/3932617?tisearch=e2e-sitesearch&keymatch=%2520user%253A468450#3932617

When I used 04828 in the new design recently, I thought about Figure 27 in the specification The connection topology recommended by CLKinX and OSCin Single-Ended Termination, when a single wave source is used, in fact, the input impedance of OSCin （Rin） is parallel at both ends of the 50ohm resistor in the AC equivalent path, so my question is what is the input impedance of this OSCin? (I tried to find the answer in the specification, but it seems that it is not stated in the specification)

The reason why I ask this question is that a sine wave source generally describes its output power in the form of power level (dBm). Here I need to convert it into voltage to evaluate whether Vpp is within the specification of 2.4V. If only 50ohm impedance to ground is calculated with the input impedance of OSCin is ignored, will the estimation be inaccurate?

Thanks