What is the purpose of R40....R45 and pull-up resistors R46....R50 on SDIO lines as shown below?
Is it really necessary to have L51, C52 & C53 matching circuit for antenna?
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Lalit
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You should probably [edit your question] to include the U1 part number and link to the datasheet. – Transistor Apr 12 '20 at 20:58
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Is this a development board? The series resistors are probably to limit current in case they get configured incorrectly. – Ron Beyer Apr 12 '20 at 20:58
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You have two completely different questions bundled up to single question. – Justme Apr 12 '20 at 21:01
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@Transistor I can not share the datasheet or part number as it is a new product dev. In brief, It is a module consists of LTE, BLE & wifi. – Lalit Apr 12 '20 at 21:09
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@RonBeyer Yes, It is a dev board. – Lalit Apr 12 '20 at 21:10
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@Justme I have updated the title. – Lalit Apr 12 '20 at 21:10
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The pull-ups are there to prevent a floating bus and their resistance range is mandated by SD interface specs. SD cards start in open-drain mode so it would not work without them.
The series resistors are there to limit signal rise/fall time. It acts as source termination for driving the bus, and by reducing the bandwidth, there is less ringing and over/undershoot on the wires.
Justme
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R40-R45 are 22 ohms, right? Then they're probably what's called source termination, or back termination resistors. Their purpose is to try and match the output resistance of the driver (maybe 30 ohms?) to the 50 ohm trace impedance. 30 ohms + 22 ohms = 52 ohms, which is what a reflection coming back from those lines see. So if the traces are nominally 50 ohms, you get little or no reflection from the "right" side of those resistors.
Here's an example, where the driver output resistance is 10 ohms, and so uses 39 ohms to get a good match to the 50 ohm tranmission line.
Also, look at this post:
SteveSh
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