IBIS simulations using the datasheet reference load

Hello experts,

I'm a newbie with SI simulation, this is my first attempt. Right now I'm designing the PCB for an ARM processor (AM1705 from TI). I have been performing simulations to check SI for the interconnect between the MPU and SDRAM, however I have some doubts and I would appreciate if someone can give me some directions on how to proceed.

I read from several application notes (spra839a among them) that the datasheet timing info is specified at the reference load, so with an IBIS model for the AM1705, I can do some simulations to extract the on-chip output delays so I can use them for timing analysis.

My questions are (please refer to the pictures attached below):

1) How do I have to make the measurements (in the simulator) when using the reference circuit, taking in consideration that in this circuit there is a transmission line present like the case shown in figure 1?

2) Do I have to get rid of the transmission line of figure 1 and simulate using as the reference circuit only the network comprised of the lumped components ( 1 inductor, 2 caps and one resistor) ?

3) If the answer is no for question 2, then for simulation purposes, where do I have to make the measurements, at point a, b or c? 

3a) If the answer is yes for question 2, then for simulation purposes, where do I have to make the measurements, at point a or c? 

3b) What I thought is that the "Tester Pin Electronics" section of the picture, represents the probe's cable (transmision line) and the instrument input impedance (the 2 capacitors, the resistor and the inductor). So the signal received at point (a) should be what the tester "sees" of the real signal at point (b). So for me all the timing parameters shown in the datasheet should be referenced to the at point (a). Can you please tell me if this statement is correct?

Figure 2 and 3 shows the signals simulated at the three points: (a blue and b: green and c: red)
As you can see, it is not clear how to make measurements from the signal in point (b) because of its shape produced by the transmission line delay, however in point (b) and (c) the signal is a lot better for a measurement.

I will really appreciate your observations, I’m very confused.


Figure 1.
Figure 2

Figure 3

Thank you very much for your help.

Best regards,
Patricio C.

mpat.cohen.sch 4 years 10 months 3 days

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