Model 4200A-SCS Parameter Analyzer Reference Manual Section 5: Pulse measure and pulse generator units4200A-901-01 Rev. C / February 2017 5-11Shield connectionsFor multiple PMU channels, you should connect the shields (common LO) from all PMU channels asclose as possible to the DUT. You reduce inductance by minimizing the loop area of the shieldconnections. The figure in Using a SMA to SSMC adapter cable to connect pulse card to DUT (onpage 5-16) and the Local sensing (on page 5-18) figures illustrate proper shield connection schemesusing the supplied cabling.Cable lengthUse the shortest possible cable length to achieve the highest frequency output, the best pulse shape,and the best results. Here are reasons to avoid using longer cable lengths:• Longer cable lengths have longer reflection times, which can slow down transmission times.• Longer cables may have impedance mismatches, which can cause distortions.• Higher capacitance in longer cables causes higher capacitive charging effects during the pulsetransitions (see PMU capacitive charging/discharging effects (on page 5-42)).Only use the white SMA coaxial cables that are supplied with the PMU and RPM. These are 50 Ωcables that match the internal 50 Ω resistance of the PMU. The PMU is supplied with 6.5 ft (2 m) SMAcables and the RPM is supplied with 8 in. (20 cm) SMA cables. Always use the 8 in. (20 cm) SMAcables with the RPM.High frequency connectionsUse these connection guidelines for high-speed testing (pulse width <1 μs).• Use cables and connectors optimized for high frequency (at least 150 MHz). The SMA coaxialcables supplied with the PMU and RPM are rated for high frequency.• Probe manipulators must be rated at least 150 MHz.• Properly connect the shields of the coaxial cables and minimize the loop area of the shieldconnections (see Shield connections (on page 5-11)).• Minimize cable length (see Cable length (on page 5-11)).• Use a signal path that matches the impedance of the instrument (50 Ω). The SMA cablessupplied with the PMU and RPM are 50 Ω.
