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Entry  Thu Jul 18 01:03:44 2019, Ismael Garcia, Trace Impedance DRS4_Analog_IN.PNG
    Reply  Thu Jul 18 11:37:56 2019, Stefan Ritt, Trace Impedance 
       Reply  Fri Jul 19 01:37:09 2019, Ismael Garcia, Trace Impedance 
          Reply  Sat Jul 20 12:28:14 2019, Stefan Ritt, Trace Impedance 
Message ID: 767     Entry time: Sat Jul 20 12:28:14 2019     In reply to: 766
Author: Stefan Ritt 
Subject: Trace Impedance 

The DRS4 input is high impedance. So if you like you can terminate it with 100 Ohm differentially and route it with 100 Ohm. But if you keep the lines short, the reflection is negligible. That’s what we made on the evaluation board.

Ismael Garcia wrote:

When you're refering to laying a 50 Ohm trace, you're referring to the SMA input and not the interface between the output of the Op-AMP(THS4508) buffer 
and the inputs  of the DRS4(IN0-IN8). Is there a recommended diffential impedance for IN0-IN8? 


Stefan Ritt wrote:

The requiremnet is the same as for any high speed analog board, there is othing special with the DRS4. If you want to terminate your line with 50 Ohms and you want a matched impedance layout, you route all lines with 50 Ohms impedance. Truth is however that nothing is perfect. The SMA connector is not exactly 50 Ohm, the PCB gets a 10-20% variation depending on the manufacturer. So even if you try hard, you will never have a 50 Ohm matched impedance. On the evaluation board we made some compromises as you have seen, but for us the board works satisfactory even with this compromises, and you can test it yourself with real hardware (namely the evaluation board). If you can do a better job, try it. But usually these compromises have only little influence on the signal quality.


Ismael Garcia wrote:

Hi Steffan,

              I'm an engineer at UCLA developing a board with the DRS4 chip. Our team has a question on what might be the required trace impedence for the analog inputs. Can that information be provided? 

Best Regards,
Ismael Garcia




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