AD14.3.20 to AD16.0.6

Comparing AD14.3.20 with AD16.0.6

When new versions of Altium Designer are released I use existing designs for testing.

I run DRC checks to see if anything is being reported that was not reported for designs released using older versions of Altium Designer. 

I'm looking for backward or forward compatibility issues.

Using complex designs like Robert Feranec's iMX6 Rex is great for testing newer releases.

iMX6 Rex is an open source design.  Using an open source design gives all interested parties an opportunity to download the project and compare test results.

REX - Freescale i.MX6 - Open Source, FREE Schematic & PCB

Ok, let's get on with the test.

First the iMX6 Rex board was verified in AD14.3.20 to be DRC clean.

Then the same board file was tested in AD16.0.6.

One DRC violation was found in AD16 that was not in AD14.

The DRC is for a Diff Pair with matched length requirement of +/-0.127mm.

I took a quick look using the heads up display data.

click on image to view

According to the length data in the heads up display

CLK1_C_N = 18.431mm
CLK1_C_P = 18.425mm

And the rule was for matched lengths +/- 0.127mm.

Odd, the trace lengths appear to well matched in length ?

Check the rule, all looks normal here.

Let's do some more digging . . . 

In AD16 open the PCB panel and select the Differential Pair Editor > DIFF100 > CLK_C

Now we can see the source of the DRC.

In AD16 we have Signal Length Data and Routed length Data.

Signal Length data was introduced in AD15 to support xSignals.

Signal length data is more accurate than Routed Length data.  Signal length data is the shortest electrical distance from the center of one pin to the center of another pin.

Routed Length data includes all trace segments within a net. The Routed Length data includes trace segments that may not be following the shortest path between two points.

iMX6 Rex was originally designed using AD13 and later updated to AD14.

In AD15.1.15 the design will also pass all DRC checks.

AD15.1.15 and earlier versions do not include Signal Length data.

PCB Panel > From To Editor:

CLK1_C_N

CLK1_C_P

CLK1_C_N = 18.10653mm
CLK1_C_P = 18.11329mm

The From To Editor length data is also within the 0.127mm tolerance.


Summary:

Heads up Net Length
CLK1_C_N = 18.431mm
CLK1_C_P = 18.425mm

From To Editor Net Length
CLK1_C_N = 18.11329mm
CLK1_C_P = 18.10653mm

xSignal Length
CLK1_C_N = 18.42463mm
CLK1_C_P = 18.06434mm

AD16 uses xSignal length data for DRC checks, which is more accurate than routed length data.

When accuracy is needed, use Signal Length.

Users should not rely on Routed length data for matching trace lengths.

Users should not rely on From To Editor data for matching trace lengths.


For a more consistent user experience Altium could update the From To Editor to use the more accurate xSignal data lengths.


That's It !