PXIe-4135 Theory of Operation

One significant advantage of SourceAdapt is the ability to make precise adjustments to the control loop to customize the SMU transient response to any load, so you can achieve an ideal transient response with minimum rise times and no overshoots or oscillations.

The PXIe-4135 can operate in either CV mode or CC mode:

• In CV mode, the device acts as a precision voltage source that holds the voltage across the selected voltage sense points constant with respect to load changes as long as load current is below the programmed current limit.
• In CC mode, the device acts as a precision current source that holds the current across the load constant with respect to load changes as long as load voltage is below the programmed voltage limit.

A measurement circuit on the PXIe-4135 can simultaneously read the voltage and current values using two integrating analog-to-digital converters. Voltage is measured differentially between the HI and LO terminals (local sense) or between the Sense HI and Sense LO terminals (remote sense) based on the programmed voltage sense location. Remote sense is used to compensate for voltage drop that results from resistance in cables, connectors and switches. Current is measured using shunt resistors in series with the HI terminal.

Additionally, the PXIe-4135 features a Guard terminal on the output connector. You can use the Guard terminal to implement guarding techniques against parasitic leakage resistance and capacitance in cabling and test fixtures.

There are several protection mechanisms built into the PXIe-4135 that guard against common faults. The output has an over-current protection (OCP) circuit that will open the Output Disconnect switch when an over-current condition is either too severe or lasts too long.

The PXIe-4135 continuously monitors voltage between HI and LO or HI Sense and LO Sense and protects against over-voltage faults. If an excessive voltage is detected, the over-voltage protection (OVP) circuit opens the Output Disconnect switch to protect the PXIe-4135 from excessive over-voltage.

The output may also be configured to automatically disconnect from the DUT if a user-defined limit is exceeded. The Output Cutoff feature supports configurable limits for voltage, voltage slew rate, current, current slew rate, and current over-range.

In the event the Sense terminals are left disconnected during remote sense operation, the 1 MΩ open-sense protection resistors provide a voltage feedback path to prevent the output voltage from saturating to a large voltage level.

The output terminals of the PXIe-4135 are electrically isolated from chassis ground through a 250 V DC, Category I isolation barrier. This allows any SMU terminal to float ±250 V DC with respect to chassis ground.

The PXIe-4135 includes flexible source and measurement units that enable multiple programming modes and timing options:

Single Point Source Mode—Use for software-timed source or measurement operation.

Sequence Source Mode—Use for basic hardware-timed operation where the user specifies a set of setpoint steps and source delays between each step while other parameters are held constant. You can modify this mode with the sequence step delta property to use a fixed time between points which enables sampled waveform generation.

Advanced Sequencing Mode—Use for hardware-timed operation where full control of all the supported parameters is available for each step.

You can use hardware triggers in all modes to control operation of the source and measure units with other channels or devices in the system. The measurement engine operation can operate in waveform acquisition mode and can be decoupled from the sequence engine. Refer to Sourcing Voltage and Current for more information about triggerable events in each programming mode.