6240B DC Voltage Current Source/Monitor Operation Manual
5.1.3 Preventing Oscillation
5-5
5.1.3.2 Preventing DUT Oscillation
The DUT itself may oscillate due to the stray capacitance of cables and a test fixture. Particularly a high
h
FE transistor or a high gm FET has a higher probability of oscillation.
Take the following measures to prevent oscillation.
• Attach a ferrite bead near the DUT as in Figure 5-4
• For the transistor it is effective to attach the ferrite bead at the base, and for the FET at the gate.
• To minimize a current leak, be careful that the ferrite bead does not touch other terminals, the DUT
case, lead wires, or other ferrite beads.
Figure 5-4 Preventing DUT Oscillation
• For a high frequency device such as a GaAS FET, take the following measures.
• Separate the ground line of the gate power supply from that of the drain power supply.
• Insert ferrite beads and by-pass capacitors both at the gate and the drain so that high frequency
signals do not enter the power supplies.
• Insert matching resistors both at the gate and the drain or make the pattern length /4 for match-
ing.
Figure 5-5 Preventing 6240B Oscillation
(Note) Insert a resistor with a value in a tolerable range.
6240B
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