High-Capacitance Mode; Overview; Understanding High-Capacitance Mode - Keithley 2601B Reference Manual

Series 2600B System SourceMeter® Instrument Reference Manual

High-capacitance mode

Overview

The Keithley Instruments Series 2600B System SourceMeter
mode.
Because the source-measure unit (SMU) has the ability to measure low current, issues can arise
when driving a capacitive load. The pole formed by the load capacitance and the current range
resistor can cause a phase shift in the SMU voltage control loop. This shift can lead to overshoot,
ringing, and instability. Due to the large dynamic range of current measurement and wide range of
internal resistors, the operating conditions for a given capacitive load can vary.
Based on the type, some test applications may require capacitors larger than 10 nF. While running
test scripts, it may not be possible to disconnect the capacitor from the IC (integrated circuit) and
extract accurate data. For this purpose, you can use the high-capacitance mode to minimize
overshoot, ringing and instability.
This section provides the details that you need to estimate performance based on load capacitance
and measurement conditions.

Understanding high-capacitance mode

The source-measure unit (SMU) in the Series 2600B drives 10 nF of capacitance in normal operation.
Typically, an internal capacitor across the current measuring element provides phase lead to
compensate for the phase lag caused by the load capacitance on the output. This internal
capacitance across the range resistance limits the speed for a specific measurement range.
It is important to note that the SMU in the Series 2600B implements frequency compensation to
achieve the highest throughput possible for a 10 nF or less load. In addition, you must consider the
settling time, voltage range, measure delay, the quality of the capacitor, the current measure range
resistor, and the load resistor.
In normal operation, the SMU in the Series 2600B can drive capacitive loads as large as 10 nF. In
high-capacitance mode, the SMU can drive a maximum of 50 µF of capacitance.
2600BS-901-01 Rev. B / May 2013
Figure 84: Synchronous output trigger
Section 3: Functions and features
®
instrument has a high-capacitance
3-65