[SI-LIST] Re: Question about Broadcom's PHY differential pairs termination
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Dennis Han <Dennis.Han@xxxxxxxxxxxxxxx>
- Date: Sun, 29 Jul 2007 13:46:20 -0700
Dennis, it's an ENet driver. These things have to tolerate open cables
of up to 100 meters. No sane person is going to use a driver without a
source termination.
Steve
Dennis Han wrote:
> ... And I bet this transmitter is a current source, which is why the
>
> resistor is needed, but the receiver still has to be terminated.
>
>
>
> -----Original Message-----
>
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>
> On Behalf Of steve weir
>
> Sent: Sunday, July 29, 2007 10:03 PM
>
> To: jasonleehan@xxxxxxxxx
>
> Cc: SI LIST
>
> Subject: [SI-LIST] Re: Question about Broadcom's PHY differential pairs
>
> termination
>
>
>
> Han, the driver is source terminated w/ the termination resistors. They
>
> need to be as close to the driver as possible.
>
>
>
> Steve.
>
> Han Li wrote:
>
>
>> Hi, experts,
>>
>
>
>> I'am designing with Broadcom PHY BCM5461s, I have a question
>>
>
>
>> about this phy's differential pairs termination.At Twisted pairs
>>
>
>
>> interface side(interface between PHY and Transformer),ASIC's Datasheet
>>
>
>
>
>
>> and Application note says "place differential pair termination
>>
>
>
>> resisters near PHY side as close as possible"
>>
>
>
>> It seems clear that we put differential paris termination neart
>>
>
>
>> the end of receiver(Rx direction), this method is also recommended by
>>
>
>
>> Dr. Howard Johnson in his book"High-Speed Digital Design-a handbook of
>>
>
> black magic "
>
>
>> pp-244,
>>
>
>
>> But why put termination also near driver side?(Tx direction) ,
>>
>
>
>> Could any one provide a deeper explanation? Thanks a lot!
>>
>
>
>> PS: A picture is inside illustrating a reference termination.
>>
>
>
>
>
>
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>
>
>> -- Binary/unsupported file stripped by Ecartis --
>>
>
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>> -- Type: image/jpeg
>>
>
>
>> -- File: termination.JPG
>>
>
>
>
>
>
>
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> --
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> Steve Weir
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