Control of PCB track impedance by adequate buffering, proper termination, careful routing strategies establishes signal quality in microprocessor based system
Approximate methods have been suggested for improving the speed performance of a microprocessor based system. This can be achieved by providing adequate buffering, termination, and careful routing of the tracks. This paper addresses the problems encountered in signals where the the effective line length is larger or capacitive loading is high (data bus, address, etc.). The effective characteristic impedance (Ze) of a PCB track can vary from 25 ohms to 300 ohms. A line with a characteristic impedance of 25 ohms might be good for a power supply line but it will degrade the rise time in a data line, resulting in a reduction of the overall speed performance of the system. The output impedance of CMOS and TTL ICs vary from 45 ohms to 150 ohms, so it is better to keep Ze above 25 ohms.