Measurement of output driver impedance for signal integrity design consideration

Impedance matching is crucial in high-speed digital design to ensure signal integrity (SI). Accurate information of a device´s output impedance allows precise selection of series resistor to match the device´s output to the characteristic impedance of the connecting trace. This paper proposes an in-circuit measurement technique using two current probes to extract the output impedance information of an active device under its normal operating conditions. The measured impedance has been validated with the time-domain simulation results obtained from CST Design Studio.