Some questions about circuit design
Signal integrity is basically a problem of impedance matching. The factors that affect impedance matching include signal source architecture and output impedance (output, impedance), characteristic impedance of line, load characteristic, routing topology (topology) architecture and so on. The solution is by terminating (termination) and adjusting the routing topology.
Why should differential pair routing be near and parallel?
The routing of differential pairs should be properly close and parallel. The so-called appropriate because it is close to the distance affect the differential impedance (differential impedance) value, this value is the important parameters of the differential design. Parallel is also necessary to maintain consistency of differential impedances. If the two lines are near and near, the differential impedance will be inconsistent, which will affect signal integrity (signal, integrity) and time delay (timing, delay).
Is it possible to use the microstrip model to calculate characteristic impedance on the signal line above the power plane? Can the signals between the power and ground planes be computed using a strip line model?
Yes, when calculating the characteristic impedance, the power plane and the ground plane must be regarded as the reference plane. For example, four layers: top layer, power layer, stratum bottom layer, and then the top line characteristic impedance model is a microstrip line model with power plane as reference plane.