A 4200-PA preamplifier adds five low current source-measure ranges to a SMU. Without a preamplifier, the 100 nA range (100 fA resolution) is the lowest current source-measure range for a SMU. With a preamplifier installed, the 10 nA, 1 nA, 100 pA, 10 pA, and 1 pA source-measure ranges are added.

If preamplifiers are ordered, the 4200A-SCS will be shipped from the factory with the preamplifiers installed on the rear panel of the mainframe. The preamplifiers can be removed from the rear panel and mounted remotely in order to reduce the effects of long cables on measurement quality (long cables can add noise to low current measurements and can cause oscillation with some devices). An installed preamplifier is matched to the SMU to which it is connected. Therefore, if you disconnect the preamplifiers to mount them at a remote location, you must ensure that you reconnect each one to its matching SMU.

Basic SMU and preamplifier circuit configuration

Basic SMU and preamp circuit configuration is shown in the next figure. This configuration is similar to
the SMU configuration discussed earlier, and the preamp, which adds low-current source-measure
capabilities.