In the process of determining the track width/separation of differential pairs for a board design
that needs to route usb2, pcie(90R) , gigabit ethernet(100R), CSI/DSI(100R), HDMI
im looking a a four layer board with a stackup of
GND
PWR/Signal
PWR/Signal
GND
euro circuits does an impedance controlled stackup, based on is400, of
copper
prepreg PR2116 0.12mm
copper (35 um)
Core fr4-improved 1.2 mm
copper (35 um)
prepreg PR2116 0.12mm
copper
i can calculate the pairs using https://saturnpcb.com/pcb_toolkit/
i can't find a second calculator for (internal) asymmetric edge coupled microstrip or the actual equations for them
im trying to understand why when moving a track from surface to internal the track separation has to increase to get the same differential
e.g
Target 100R
surface W = .125 S = .2 H = .12 zDiff = 95.457
internal W = .125 S = .787 H = .12 h2 = 1.2 zDiff = 95.463