Model 4200A-SCS Parameter Analyzer Reference Manual
Section 12: Maintenance
4200A-901-01 Rev. C / February 2017
12-15
Figure 497: Effects of voltage burden
Noise and source impedance
Noise can seriously affect sensitive current measurements. The following paragraphs discuss how
source resistance and source capacitance affect noise performance.
Source resistance
The source resistance of the DUT affects the noise performance of the SMU or preamplifier. As the
source resistance decreases, the current noise increases. Because decreasing the source resistance
can have a detrimental effect on noise performance, there are usually minimum recommended
source resistance values based on measurement range. The next table summarizes minimum
recommended source resistance values for various measurement ranges.
Minimum recommended source resistance values
Range
Minimum recommended
source resistance
1 pA to 100 pA
1 GΩ to 100 GΩ
1 nA to 100 nA
1 MΩ to 100 MΩ
1 μA to 100 μA
1 kΩ to 100 kΩ
1 mA to 100 mA
1 Ω to 100 Ω
Source capacitance
DUT source capacitance also affects the noise performance of the preamplifier. In general, as source
capacitance increases, the noise gain also increases. Although there is a limit to the maximum source
capacitance value, you can usually measure at higher source capacitance values by connecting a
resistor in series with the source. Note, however, that doing so increases the voltage burden. For
example, the source resistance values listed in the previous table results in a voltage burden between
1 mV and 1 V.
