DDR3 Clock Differential Impedance

wuchy143

Member
I am trying to figure out what the differential impedance for a clock on DDR3 memory should be. The part number for the DDR3 I am referencing is W3J128M72G-1066PBI. It's a microsemi part with a 1066MB/s, so the clock is 533MHz.

Exactly how should I go about calculating this?
 
Thank you.

Yes, what's interesting is the NXP recommendation is saying 75 to 95 ohm differential impedance. The TI says 100 ohm diff. imp.

I thought there would be a standard or something. Meaning, if you are using X speed use Y diff. impedance.

Sadly I'm a noob when it comes to high speed
 
wuchy143 said:
Meaning, if you are using X speed use Y diff. impedance.
Click to expand...
The impedance of a transmission line (coax or PCB traces) should be some what independent of speed. Like watching TV on channel-2 or on channel-12; the transmission line is the same impedance.
 
Awesome, thanks, makes sense.

I'm looking at a designs board file and see that they did not match the length of the diff pair. There is a delta of 3 mils. For some reason I remember .001" difference in trace length will create a 1 nano second difference between the positive and negative signals. Is that right?
 
You must log in or register to reply here.

Similar threads

M
  • Question Question
Bird Clock Repair
Replies
3
Views
1K
Tony Stewart
A
  • Question Question
Reading Clock Pulses of a Master Clock with Arduino.
Replies
12
Views
2K
Nigel Goodwin
W
  • Question Question
Permanent magnet clock
Replies
13
Views
2K
Nigel Goodwin
W
  • Solved
1 sec alternating polarity circuit
3 4 5
Replies
91
Views
19K
Nigel Goodwin
T
  • Question Question
Non-overlapping Two-Phase Clock Generator Layout
Replies
8
Views
6K
TW1
T
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…