User`s guide

7-18 Agilent 4155C/4156C User’s Guide Vol.2, Edition 6
Measurement Units and Functions
Measurement Units
VMU - Voltage Monitor Unit
The VMU has two measurement modes: grounded or differential. Grounded mode
uses one VMU. Differential mode uses two VMUs.
Figure 7-7 is a simplified VMU circuit diagram. The VMU can measure up to 20 V.
Table 7-13 shows the voltage measurement range of the VMU.
Figure 7-7 Simplified VMU Circuit Diagram
NOTE High Impedance DUT
A very high-impedance DUT may cause measurement error owing to the input
leakage current from the VMU.
To check the measurement error, perform voltage measurement as follows:
1. Connect the SMU to the DUT.
2. Force very low current (under 1 pA) to the DUT from the SMU.
3. Measure voltage with the SMU.
4. Compare the voltage measured with the SMU and the VMU.