[SI-LIST] Re: Impedance match

You can use a "bus switch" device. Check AN_11 from IDT
http://www1.idt.com/pcms/getDoc.taf?docID=7530
Ivor

on 11/30/2004 3:00 AM danielesperante1 wrote:

>Dear all
>
>Maybe somebody can help me a suggest me what I have to do dealing 
>with the problem I desribe below:
>
>I have to build a PCB board in which I have to interconnect a 5V TTL 
>device with a 3.3V TTL one. From the 5V device goes a bus of 9 lines 
>to the inputs of the 3.3V device, which is not 5V tolerant. The speed 
>of the signals is 80 MHz, but the potential problem I have is with 
>the rise time of the signals which I guess is about 1ns (I don`t have 
>the device in my hands yet), and the bus length will probably be more 
>than 7cm, so I'll have to work with the connections as they were 
>transmission lines. 
>
>How should I interconnect the devices in order to keep the integrity 
>of the signal? Lets suppose that the impedance that I implement for 
>the line is 50 Ohm, should I use a voltage divider in the source (ie, 
>in the 5V device) or in the end? and what values for the resistors in 
>order to match the impedance of the line? Or should I do someting 
>completely different?
>
>Thaks in advance
>
>
>
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