[SI-LIST] Impedance match
- From: "danielesperante1" <danielesperante1@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 30 Nov 2004 11:00:48 -0000
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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