[SI-LIST] Re: termination resistor
- From: "Lynne C. Green" <lgreen22@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sat, 22 Dec 2012 20:38:30 -0800
Hello, XiaoLiang Tan,
Basically:
- Termination resistors are matched to the trace impedance, not the
driver impedance.
- Every time a trace branches, there is an impedance change seen by the
signal.
- Impedance changes lead to reflections, leading to loss of signal quality.
- A high-speed system is usually designed as a daisy-chain to avoid
these impedance changes.
A good SI simulator and Eric Bogatin's signal integrity book are useful.
Regards,
Lynne
"IBIS training when you need it, where you need it."
Dr. Lynne Green
President
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@xxxxxxxxxxxxxx
On 12/22/2012 7:01 PM, XiaoLiang Tan wrote:
> Dear Expert,
> Hello, I am designing a high speed system.Since I don't know my
> driver's output resistance, thus the termination resistor value is not
> known. Thus may I use the variable resistor? If I use the variable
> resistor, the size is big thus I am unable to put all the resistor near the
> driver.( I have more than 10 outputs needs to be terminated). Which means
> the termination resistor could not be put close to the drivers.
> However, if I use a fixed and small size resistor, I need to trim
> the resistor manually when I doing the testing.
> So may I know that which one is more suitable? Thanks.
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