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  3. Phase Tolerance: Proper pin pair setup

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Phase Tolerance: Proper pin pair setup

Eric IntAZ
Eric IntAZ over 16 years ago

I am attempting to use phase tolerance to control some relative length rules within a differential pair. The topology is essentially 3 components which I will call A, B and C. The signal goes from a pin on comp A to one on comp B and continues on from B to a pin on comp C.

I would like to set phase tolerance to say 5mils and see the property on pin pairs from A-B and A-C though I could live with B-C being created as well.

The issue that I am having with this is that Allegro configures the pin pairs associated with a given net/diff pair based upon the PINUSE property (and apparently the part CLASS, though I haven't seen this affect anything in my situation.) The pins in question are functionally bi-directional, yet I don't get the pin pairs I would expect if I set the PINUSE property of the associated pins on A, B and C to "BI". Perhaps I'm not thinking about this correctly, but in my mind a bi-directional pin is one that can either drive or receive a signal. As such, I would expect to see 3 pin pairs created when all components are set as mentioned (pinuse = "BI"); A.pin:B.pin; A.pin:C.pin; B.pin:C.pin. Instead, Allegro will only create a pin pair based upon the longest length (A.pin:C.pin).

I decided to research this a bit further and found information essentially saying that there has to be an explicit definition of driver and receiver, otherwise the longest path will be chosen. To further complicate matters I tried the following configuration: A = TRI         B = BI         C = BI

This yielded the 3 aforementioned pin pairs I would've expected to see on a BI, BI, BI configuration. What is confusing here is that a pin pair is created between components B and C which again, were both set to BI... yet in the previous configuration (BI, BI, BI) Allegro defaulted to the longest path method of pin pair creation.

I can work around this issue by using the following: A = OUT         B = IN         C = IN. This works fine for my purposes as I will get A.pin:B.pin; A.pin:C.pin as I originally wanted, but it is functionally incorrect in terms of PINUSE which could adversely affect other disciplines interacting with the topology.

 

To summarize, I would like to know if there is a way to set this up in such a way that I can access the desired pin pairs while maintaining accurate PINUSE properties.

 

 

 

 

 

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  • annoonan
    annoonan over 14 years ago
    Deleting previous post (too difficult to read), and replacing I have several diff pairs, with each net containing 3 nodes; driver, mid-bus probe, and AC coupling cap. The diff pair property is applied to the net (I am not aware of any other way to apply the diff pair property). But the software is only calculating phase tolerance from the driver to the mid bus probe. What is happening? Electrical Constraints assigned to net prop delay: from L to S min=0.00 MIL max=12000.00 MIL diff pair positive coupled tolerance: 0.4 MIL diff pair negative coupled tolerance: 0.4 MIL diff pair min line spacing: 3.8 MIL diff pair max uncoupled length: 800 MIL diff pair phase tolerance: 2.5 MILS Constraint information: (Dly) U121.AM18 to TP19.1 max= 12000 MIL actual= 4559.36 MIL (-5984.66,-6499.99) pin U121.AM18,IN,TOP/TOP,pin=392.64 MIL 28.28 MIL cline TOP (-5984.66,-6528.27) via TOP/BOTTOM 4113.44 MIL cline T07 (-2258.46,-6475.00) via TOP/BOTTOM (-2258.46,-6450.00) pin TP19.1,UNSPEC,TOP/TOP (Dly) C1142.2 to TP19.1 min= 0 MIL actual= 3503.8 MIL (-2891.50,-3550.00) pin C1142.2,UNSPEC,TOP/TOP 34.5 MIL cline TOP (-2926.00,-3550.00) via TOP/BOTTOM 3444.3 MIL cline T07 (-2258.46,-6425.00) via TOP/BOTTOM (-2258.46,-6450.00) pin TP19.1,UNSPEC,TOP/TOP (DPTol) TP19.1 to U121.AM18 min= 4557.43 MIL max= 4562.43 MIL actual= 4559.36 MIL DPData: gap=var (-0.40,+0.40) tolerance= 2.50; max uncoupled= 800.00 (-2258.46,-6450.00) pin TP19.1,UNSPEC,TOP/TOP (-2258.46,-6475.00) via TOP/BOTTOM 4113.44 MIL cline T07 (-5984.66,-6528.27) via TOP/BOTTOM 28.28 MIL cline TOP (-5984.66,-6499.99) pin U121.AM18,IN,TOP/TOP,pin=392.64 MIL
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  • annoonan
    annoonan over 14 years ago
    Deleting previous post (too difficult to read), and replacing I have several diff pairs, with each net containing 3 nodes; driver, mid-bus probe, and AC coupling cap. The diff pair property is applied to the net (I am not aware of any other way to apply the diff pair property). But the software is only calculating phase tolerance from the driver to the mid bus probe. What is happening? Electrical Constraints assigned to net prop delay: from L to S min=0.00 MIL max=12000.00 MIL diff pair positive coupled tolerance: 0.4 MIL diff pair negative coupled tolerance: 0.4 MIL diff pair min line spacing: 3.8 MIL diff pair max uncoupled length: 800 MIL diff pair phase tolerance: 2.5 MILS Constraint information: (Dly) U121.AM18 to TP19.1 max= 12000 MIL actual= 4559.36 MIL (-5984.66,-6499.99) pin U121.AM18,IN,TOP/TOP,pin=392.64 MIL 28.28 MIL cline TOP (-5984.66,-6528.27) via TOP/BOTTOM 4113.44 MIL cline T07 (-2258.46,-6475.00) via TOP/BOTTOM (-2258.46,-6450.00) pin TP19.1,UNSPEC,TOP/TOP (Dly) C1142.2 to TP19.1 min= 0 MIL actual= 3503.8 MIL (-2891.50,-3550.00) pin C1142.2,UNSPEC,TOP/TOP 34.5 MIL cline TOP (-2926.00,-3550.00) via TOP/BOTTOM 3444.3 MIL cline T07 (-2258.46,-6425.00) via TOP/BOTTOM (-2258.46,-6450.00) pin TP19.1,UNSPEC,TOP/TOP (DPTol) TP19.1 to U121.AM18 min= 4557.43 MIL max= 4562.43 MIL actual= 4559.36 MIL DPData: gap=var (-0.40,+0.40) tolerance= 2.50; max uncoupled= 800.00 (-2258.46,-6450.00) pin TP19.1,UNSPEC,TOP/TOP (-2258.46,-6475.00) via TOP/BOTTOM 4113.44 MIL cline T07 (-5984.66,-6528.27) via TOP/BOTTOM 28.28 MIL cline TOP (-5984.66,-6499.99) pin U121.AM18,IN,TOP/TOP,pin=392.64 MIL
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