Designing high-speed signal distribution for multi-drop connection using simulations

Multi point distribution is used in many applications. Connection of multiple taps along the signal transmission line leads to impedance changes, and as a result the signal integrity may be degraded. This makes the design more challenging, especially in high speed circuits. Bus design layout that achieves both impedance matching and uniform power distribution for a multi-drop bus has been recently proposed. These designs are mostly based on resistor impedance matching for each branch. In most designs the signal´s spectrum is not taken into account when designing multidrop interconnects, and hence the input impedance may not be optimal for the working frequencies. In this paper, we present a scheme that is based on changing the line impedance of each segment of the bus, hence removing the need to add resistors in the layout. We also propose a design method to achieve constant impedance along the transmission line, using information derived from the signal spectrum. The simulation results of circuit boards design demonstrate good agreement with the theoretical results, and show reliable performance at high bit rates.