Noise And Source Impedance - Keithley 4200A-SCS Reference Manual

Hide thumbs Also See for 4200A-SCS:

Table of Contents

Model 4200A-SCS Parameter Analyzer Reference Manual

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

1 pA to 100 pA

1 nA to 100 nA

1 μA to 100 μA

1 mA to 100 mA

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.

4200A-901-01 Rev. C / February 2017

Figure 497: Effects of voltage burden

Minimum recommended

source resistance

1 GΩ to 100 GΩ

1 MΩ to 100 MΩ

1 kΩ to 100 kΩ

1 Ω to 100 Ω

Section 12: Maintenance