Question about the L-shaped Ground in PCB Layout of BCM20737S

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Anonymous
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Hi all,

I have a question about the PCB layout of BCM20737S, since it uses an embedded antenna, we have to make sure our layout won't affect its RF performance.

I have read the layout suggestions in BCM20737S datasheet and the reference design.

Questions:

There is a L-shaped ground around the BCM20737S chip, in datasheet it says this L-shaped ground is required for the embedded BLE antenna, and we need to keep GND continuous. My question is: should we connect this L-shaped ground to the GND pins of BCM20737S chip? Or should we just place the L-shaped ground close to the chip but not connect to any pin?

Thanks

Jingdong

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BoonT_56
Employee
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You should connect the L-shape ground to your system/motherboard ground. Although it is electrically the same, it is not a good idea to connect it to the pins of the module directly.

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Anonymous
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Hi boont,

I know the longer arm of the L-shaped GND should be connected to system ground of the board.

How about the shorter arm of the L-shaped GND? From the reference design, the shorter arm is not connecting to anything, just floating there in to the module a little bit.

L-Shaped GND.jpg

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I couldn't recall what is this. Which layer is it on? But it appears that it is a little electrically short to be of any significance.

BCM20732S layout

Anonymous
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From the reference design, this L-shaped GND is on L02_GND layer instead of the top layer. I think the L02_GND layer is the second inner ground layer of the whole four-layer PCB stack.

I am just not sure why the shorted arm is there, without connecting to anything. I think the L-shaped GND is not electrically small for a 2.4GHz signal.

Is it OK to use the third layer as ground plane layer and put L-shaped GND on that third layer? I don't know how this L-shaped GND can enhance RF performance of the embedded antenna so I am not sure about any modification I made during layout.

From the post you give to me, I still cannot see what does the shorter arm connect to. Maybe it is just floating.

second.jpg

BCM20732S layout

From the post below, I can also see the L-shaped GND in first figure.

iBeacon BCM20737S Reference Design Overview

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I still couldn't figure out what is that little short arm you have circled out. I have attached the above layout with the vias turn on. Hope it helps.

layout.jpg

Anonymous
Not applicable

Hi boont,

It looks like the short arm is connected to ground through the via.

Is it possible for you to send this layout file to me? I am a student at Missouri University so it won't be used for any commercial business. Since manufacturing the PCB will cost a lot of money for us student, I just don't want to make a mistake in layout.

It is OK to send just the local region of BCM20737S to me, because that is the only part I didn't understand. My email is sunjing@mst.edu.

Thanks

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