Differential pair routing basics in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This table shows PCB trace nets with their lengths, impedance, and whether they form a differential pair.

Cell	Value
A1	Net Name
B1	Length (mm)
C1	Impedance (Ohms)
D1	Differential Pair?
A2	USB_D+
B2	50
C2	90
D2	Yes
A3	USB_D-
B3	50
C3	90
D3	Yes
A4	CLK
B4	30
C4	50
D4	No
A5	DATA
B5	30
C5	50
D5	No

Formula Trace

=IF(AND(D2="Yes", D3="Yes", ABS(B2-B3)<=5, ABS(C2-C3)<=5), "Good Pair", "Check Routing")

Step 1: D2="Yes"

Step 2: D3="Yes"

Step 3: ABS(B2-B3)

Step 4: ABS(B2-B3) <= 5

Step 5: ABS(C2-C3)

Step 6: ABS(C2-C3) <= 5

Step 7: AND(TRUE, TRUE, TRUE, TRUE)

Step 8: IF(TRUE, "Good Pair", "Check Routing")

Cell Reference Map

    A       B       C       D
1 | Net   | Length | Imped. | Diff? |
2 | USB_D+|  50    |  90    | Yes   |
3 | USB_D-|  50    |  90    | Yes   |
4 | CLK   |  30    |  50    | No    |
5 | DATA  |  30    |  50    | No    |

Arrows: Formula checks D2, D3, B2, B3, C2, C3 for conditions.

The formula references cells D2 and D3 to check if nets form a differential pair, and B2, B3, C2, C3 to compare length and impedance differences.

Result

    A       B       C       D        E
1 | Net   | Length | Imped. | Diff? | Status     |
2 | USB_D+|  50    |  90    | Yes   | Good Pair  |
3 | USB_D-|  50    |  90    | Yes   |            |
4 | CLK   |  30    |  50    | No    |            |
5 | DATA  |  30    |  50    | No    |            |

The formula result 'Good Pair' appears in cell E2 indicating the USB_D+ and USB_D- traces form a good differential pair based on length and impedance.

Sheet Trace Quiz - 3 Questions

Why does the formula check if D2 and D3 equal 'Yes'?

A To verify impedance values

B To check if the nets have the same length

C To confirm both nets are part of a differential pair

D To calculate the length difference

Key Result

IF all conditions for differential pair (status, length difference, impedance difference) are met, return 'Good Pair', else 'Check Routing'.