In forward bias operation, the PXIe-4133 outputs sequences of current pulses and returns current and voltage measurements for the diode under test. The settings for each pulse in a pulse sequence can be configured individually.

Pulse Parameters

The following parameters can be configured independently for every pulse.

  • Current Level—The current level of the pulse.
  • Pulse Width—The duration of the pulse.
  • Measurement Delay—The delay between the start of the pulse and the start of the measurement. Measurement delay is supported with an external pulse trigger.
  • Aperture Time—The duration for a single measurement. Increase this time to improve measurement resolution.
  • Dead Time—The time between the end of the pulse and the start of the next pulse.

    • The following figure illustrates the features that make up each pulse in a sequence of multiple pulses.

    Figure 4. Individual Pulse Parameters


    Pulse Parameter Limits

    Consult the PXIe-4133 Specifications for minimum and maximum parameter values for each operating mode. In addition, note the following relative limits on pulse parameters:

    • Measurement start time is determined by measurement delay.
    • Measurement start time for the current pulse cannot follow the start (pulse high) of the next pulse, as illustrated in the following figure.
    • Measurement end time is determined by the combination of measurement delay and aperture time duration.
    • Measurement end time cannot occur after the measurement start time of the next pulse, as illustrated in the following figure.
    • Measurements (aperture times) cannot overlap.
    Figure 5. Measurement Aperture Constraints


    Terminal Disconnect

    When a pulse sequence is completed, an output switch on the PXIe-4133 disconnects the pulsing circuitry from the triaxial terminal so that the output is in a true high-impedance state.

    Wait for the pulse sequence to finish to ensure there is no current flow while disconnecting the DUT.

    Understanding Idle Current and Return-to-Zero Behavior

    The voltage across a diode may settle to any voltage below the forward voltage, including negative voltages, once the current disconnects. In diode test applications, the diode current alone is generally too low to discharge the voltage across the diode and return sysrtem capacitance to zero during the dead time between pulses.

    To avoid this uncertainty, the PXIe-4133 actively returns the diode voltage to a known state between pulses. To define the idle state, specify the idle current level parameter for the MeasurePulsedCurrentAndVoltage function.

    Returning the Diode Under Test to Zero Volts between Pulses

    When an idle current level of zero is specified, the PXIe-4133 discharges the voltage between Force HI and Force LO to zero volts. Positive voltages are discharged with a current source into Force HI of 7.5 mA (or 0.5 mA in the 0.1 A range). Negative voltages are discharged with a current source in the opposite direction. The output current reaches zero as the output voltage is discharged to zero volts.

    The following figure illustrates the current into the Force HI pin as a function of the output voltage with a specified idle current level of zero:

    Figure 6. Output Discharge Current vs. Voltage during Pulse Dead Time

    Holding the Diode Under Test Near Its Forward Voltage Between Pulses

    You can set a non-zero idle current level to specify the current out of the Force HI pin between pulses (during the pulse dead time). Use this feature to ensure the diode under test retains a slight bias between pulses. In this condition, the voltage across the diode under test will be determined by its I-V characteristic at the programmed current level. Setting the idle current to a non-zero value increases the average output current, which may limit the allowable duty cycle or pulse sequence length. See Duty Cycle Limitations for more information.