[SI-LIST] Re: Why Termination at Both End ?
- From: Sen Velmurugan <sen.velmurugan@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 23 Aug 2011 16:07:14 -0700
Steve,
Here the buffer is a current source, the termination(pulldown) is the
load, the high input impedance receiver see the voltage across the load.
The foot print at destination does offer some(pf) capacitance. These
layouts are done in the absence of simulations and to clean up mismatches.
Usually done for clock and analog video signals.
Thanks
Sen
>
> Msg: #2 in digest
> Date: Mon, 22 Aug 2011 16:55:47 -0700
> From: steve weir <weirsi@xxxxxxxxxx>
> Subject: [SI-LIST] Re: Why Termination at Both End ?
>
> Sen, are you suggesting this:
>
> Tx side: Isink || (Pull-up = 2*Zline) --> Tx Line ---> (Pull-up =
> 2*Zline) Rx side
>
> In this case you are mismatched at both sides and you will have ISI due
> to reflections.
>
> If you have an RLL signal stream, from an ISI point of view you would be
> better off with:
>
> Tx side: Isink || (Pull-up = Zline) --> Tx Line ---> ( R=Zline --> C
> --> Vss ) || Receiver
>
> Where RC > 5X the maximum run length.
>
> Steve
>
> On 8/22/2011 4:17 PM, Sen Velmurugan wrote:
>
>> Rajan, When you need Xohm termination to sink a current source, you can
>> use 2Xohm termination each at source and destination.
>> This way source see, 2X || 2X = X ohm sink and voltage at load is
>> "cleaner". Basically, you have more freedom of choice to play with.
>>
>> ~Sen.Velmurugan@xxxxxxxxxx
>>
>>
>>
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