I've got some doubts regarding the AD9272 design. All my questions are on the attached schematic file.
I would appreciate for the suggestions.
Hi, I came across your post and let me try to answer your questions below.
1- The coupling caps can be either 10 or 100 nF but we use 10 nF on our eval boards just fine but they just need to be the same value.
2- R2 calculation using formula 2 is correct based on the target input impedance. R3 can be enabled using register 0x2C to add more options for input impedance. When R3 is enabled then formula 2 can use R2||R3 when calculating the input impedance. This feature is useful to allow 3 different input impedance settings (R2, R2||R3, or open circuit with no termination) to fit multiple probe impedances.
3- BAS404 diodes can be used here but shotkey diodes will be better.
4- I am not sure about R1 and I assume it is up to the specs of the pulser.
Thanks for your reply. I'd like to pay your attention that formula 2 in the AD9272 datasheet is wrong!! Try to calculate according to it an example which is just below eq. 2. You will get the result 234 Ohm instead of 188.
formula 2 is actually correct but it hard codes the gain value. It should be A/2 instead of 3 in the denominator. The example value is the one that is not accurate and should be revised. However formula1 should be accurate enough for your termination calculations.
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