Author Topic: high speed traces and solving impedance control ....  (Read 714 times)

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Offline luudeeTopic starter

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high speed traces and solving impedance control ....
« on: August 16, 2023, 04:04:54 pm »
Guys,

I have a bit of a design challenge:

I have a USB 3.2 controller, on a custom PCB I am designing
for a customer.

The customer has requested that both a USB-A and a USB-C
connector be connected to that single controller, such
that the customer may choose which interface to use.

Now, this sounds simple enough, until you look at the signals.
The RX/TX lines for USB 3.2 are point to point, 90 ohm
terminated lanes.

I must admit, I am not a RF/high-speed PCB layout person.

Is there a way to make this work?  Placing the connectors
and their pins close together (on opposite sides of the PCB),
and just do the best possible impedance matching?

I am at loss, any ideas/suggestions?

Cheers,
luudee
 

Offline nctnico

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Re: high speed traces and solving impedance control ....
« Reply #1 on: August 16, 2023, 05:28:20 pm »
You can only achieve this by adding zero Ohm 0402 strapping resistors (or capacitors if you need capacitive coupling) that select which connector to route the signal to. A clever trick is to overlap the pads so the impact on the transmission lines is minimal. A good way for the signals to arrive at the strapping resistors is from a different layer. But there can only be 1 connector placed at the time. You can't have both. If there needs to be an option, then supply a USB-C to USB-A adapter with the product.

If the interface is a host, then you can opt to put a USB-C hub chip on the board to create multiple ports.
« Last Edit: August 16, 2023, 05:31:21 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: high speed traces and solving impedance control ....
« Reply #2 on: August 16, 2023, 11:10:25 pm »
The customer has requested that both a USB-A and a USB-C connector be connected to that single controller, such that the customer may choose which interface to use.
Sounds like a hub /s
 

Offline langwadt

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Re: high speed traces and solving impedance control ....
« Reply #3 on: August 16, 2023, 11:14:32 pm »
The customer has requested that both a USB-A and a USB-C connector be connected to that single controller, such that the customer may choose which interface to use.
Sounds like a hub /s

without  a hub it's only a matter of time before someone complains that they can't use both at the same time
 
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Offline luudeeTopic starter

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Re: high speed traces and solving impedance control ....
« Reply #4 on: August 17, 2023, 04:18:08 am »

without  a hub it's only a matter of time before someone complains that they can't use both at the same time

We don't need a hub, it will be an either or solution.

Has anybody used something like HD3SS6126 ?  I'ts a USB 3 mux. But now I will need some
logic to detect which connector is used ....

May be a current sense to control the mux ?!


Thanks,
luudee
 


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