Merging channels allows multiple channels of a single SMU to work in unison. When you connect the channels in parallel at the destination, you can use your instrument for applications that require a higher current output than any single independent channel of the SMU.

To merge channels with NI-DCPower, you designate a primary channel and combine it with compatible merge channels.

  • Primary channel—The channel you access when programming merged channels in a session.
  • Merge channels—The channels that you specify with the Merged Channels property. The merge channels work in unison with the primary channel.

    • The PXIe-4162 supports merge counts of ×2 and ×4, each of which supports multiple merge configurations.

  • Merge count—The total number of combined channels. The combined channels include the primary channel plus the merge channels.
  • Merge configuration—The combination of channels included in the merge.

    • The total current you can source from the SMU by merging channels is equal to the merge count times the normal per-channel maximum for the SMU. Refer to specifications or documentation for your instrument for information on maximum sourcing power and current ranges.

    Note
    • You cannot change the merge configuration when channels are in the Running state.
    • You cannot merge channels across different physical instruments.
    • You cannot use secondary channels in a merge if those secondary channels are in the Committed or Running state.

    Choosing a Valid Merge Configuration

    Choose a valid merge configuration that supports the output current that you need.

    Each merge count supports only certain combinations of the primary channel and merge channels. The potential merge configurations depend on how many and which channels you want to merge. Complete the following steps to determine your merge configuration.
    1. Select the primary channel and determine the possible merge counts for that channel. The primary channel that you select must be a multiple of the merge count.
      Possible Merge CountsPrimary Channel
      ×2 0, 2, 4, 6, 8, 10
      ×4 0, 4, 8
    2. Determine the merge channels based on the primary channel you select and the desired merge count. Use the following formulas to determine the range of merge channels.
      1. To determine the beginning range of merge channels, use Primary Channel + 1.
      2. To determine the end range of merge channels, use Primary Channel + Merge Count - 1.

    For example, if you want to use a merge count of ×4 with primary channel 0, then the valid merge channels are 1,2,3.

    If you want to use a merge count of ×2 with primary channel 4, then the only valid merge channel is 5.

    Input the range of merge channels when setting the Merged Channels property.

    Designing Merge Circuitry

    To use merged channels for a higher maximum current, you must design an interconnect. The interconnect must combine the current output from the SMU physical channels as specified in the merge channel configuration.

    Ensure your test system that is using merged channels includes the following general components:
    • The SMU to source the current.
    • Cabling or wiring to convey current from the SMU.
    • An interconnect between the SMU cabling and the destination device.
    • The destination device to which you are delivering the current.

    The specific interconnection design depends on your application needs. Refer to the following guidelines for designing these elements:

    • Ensure that your design corresponds to a valid merge configuration for the SMU.
    • Connect the merged channels at the destination in parallel.
    • If your application does not involve switching between merge configurations, short the Output HI pins of the primary channel and merge channels together. Otherwise, your application requires the use of an external switching circuitry.
    • Tie the Sense HI and Sense LO pins of the primary channel only. Do not tie together the Sense pins of the merge channels. You can leave the Sense HI and Sense LO pins of the merge channels floating.
    • If your application uses screw terminal connectivity, ensure that you are using the correct size wire for the Output HI and Output LO. The output current that you configure is distributed between the channels in the merge configuration.
    • If your application uses Guard terminals, connect the Guard terminal for the primary channel only.
    Important Avoid wiring together the Guard terminals for more than one channel.
    Note
    • Connect only the channels that you intend to merge.
    • If using external switching circuitry, ensure your switching circuitry presents as little resistance as possible when merging channels.

    Programming the PXIe-4162 for Merged Channels

    Use the NI-DCPower API to program the SMU for merged channels.

    Before you program your SMU for merged channels using the NI-DCPower API, ensure you connect your channels appropriately.
    1. Based on the merge configuration you choose, initialize your NI-DCPower session using Initialize With Independent Channels.
      You can use merged channels while the session is open to an arbitrary set of channels, as long as the primary channel is in the session.
      Note If you are using Initialize With Channels (deprecated), open the session to only the primary channel.
    2. Depending on your merge configuration, use the Merged Channels property to specify the required merge channels.
      Note You can enter the range of merge channels using commas, a hyphen, or a colon. For example, 1,2,3, 1:3, or 1-3. If you are using a multi-instrument session, you must specify the instrument name with the merge channels in the following format: <instrumentname>/<mergechannels>. For example, if the instrument name is PXI1Slot3 and you want to specify merge channel 1, enter PXI1Slot3/1.
      1. To configure properties on the primary channel in LabVIEW, write the Active Channel property to the primary channel.
        Note You do not need to configure any properties on the merge channels that are part of a merge configuration. Configure properties only on the primary channel.
    3. Use Commit With Channels to apply the merge configuration to the SMU.
      Note Call functions only on the primary channel. NI-DCPower returns an error if you attempt to commit or initiate a merge channel.
      Committing the session properties reserves the channels you specified for merging that prevents the channels from being used independently.
    4. Call Initiate With Channels to begin sourcing current according to the merge configuration.
      Note To acquire measurements from the combined channels, call the niDCPower_MeasureMultiple function or the niDCPower_FetchMultiple function on the primary channel only. Attempting to call these measurement functions on the merge channels returns an error.
    The maximum current you can now source from your SMU in this merge configuration is equal to the merge count times the per-channel maximum of your instrument.
    Note If you have multiple active merge configurations on the same instrument (without any overlapping merge configurations that use the same primary and merge channels), you can configure properties or call functions on multiple primary channels simultaneously. You do not need to configure properties or call functions on merge channels.

    Merging Channels in Practice

    For example, for a 12-channel SMU that can source up to 100 mA on an independent channel, designating channel 0 as the primary channel and using the Merged Channels property to specify channel 1 as the merge channel yields a merge count of ×2.

    This configuration allows you to source up to 200 mA from the combined channels.

    You can then either use the remaining 10 channels independently or combine them into multiple other merge configurations.

    Note If you want to change the merge configuration, first disable the outputs of any sourcing channels before initiating the new merge configuration in order to avoid output glitches.

    Effect of Merging Channels on Performance Specifications

    Merging channels of the PXIe-4162 impacts your instrument specifications as defined in the following sections.

    Note Specifications not mentioned in the following sections remain the same and maintain the same classification (warranted, typical, etc.) as described in the specifications document for your instrument.

    The calibration procedure for your instrument does not explicitly verify the specifications for merged channels. The merged channel specifications are ensured by design and assume the following about your merge configuration:

    • The individual channels perform within their calibration limits
    • The external interconnects that you design for the merge circuitry do not contribute more error than the verification connections assumed for single channel calibration

    Low Frequency Noise

    The Noise (0.1 Hz to 10 Hz, peak-to-peak, typical) specifications increase proportionally to the square root of the number of channels in the merged configuration.

    Note Some instruments have a combined specification for resolution and low frequency noise, while other instruments have individual specifications. Resolution is a loosely defined specification that does not lend itself well to generalized quantitative guidelines.

    For example, if the noise specification for a single channel is x and your merge configuration includes four channels, the new specification for the configuration is: √4 · x = 2 · x

    Accuracy and Temperature Coefficient

    The offset term of the accuracy and tempco specifications increases directly proportional to the number of channels in your merge configuration.

    For example, if the accuracy specification for a single channel is ± (x% + y), and your merge configuration includes four channels, the new specification for the configuration is: ± (x% + 4 · y)

    If the tempco specification is ± (x% + y)/ ℃ and your merge configuration includes four channels, the new specification for the configuration is: ± (x% + 4 · y)/ ℃

    Current RMS Noise Versus Aperture Time

    The plots in the specifications maintain the same shape, but the y-axis values increase proportional to the square root of the number of channels in your merge configuration.

    For example, if the noise specification for a single channel is x and your merge configuration includes four channels, the new specification for the configuration is: √4 · x = 2 · x

    Current Load Regulation

    The current load regulation specification increases directly proportional to the number of channels in your merge configuration.

    For example, if the current load regulation specification for a single channel is x, and your merge configuration includes four channels, the new specification for the configuration is: 4 · x

    Effect of Merging Channels on Other Functions and Properties

    When you merge channels of the PXIe-4162, the normal values you can specify or behaviors for certain functions and properties change accordingly.

    Merging channels affects the following aspects of programming the PXIe-4162 with NI-DCPower.

    Setting the Current Levels, Limits, and Ranges

    For relevant functions or properties that control current, the maximum current that you can source increases as follows:

    Without Merged Channels With Merged Channels
    Per-Channel Maximum Per-Channel Maximum × Merge Count
    Note Current Limit Autorange and Current Level Autorange also account for the increased current values that you can specify when merging channels.

    Setting the Programmable Output Resistance

    The behavior when channels are merged depends on the output function.

    With DC Voltage, output resistance range decreases; with DC Current, output resistance range expands. Refer to the following table for details.

    Table 13. Effects of Merged Channels on DC Voltage and DC Current
    Output Function Without Merged Channels With Merged Channels
    DC Voltage Valid Range Valid Range / Merge Count
    DC Current Output resistance <0 Ω (-∞, Upper Negative Limit] (-∞, Upper Negative Limit / Merge Count]
    Output resistance >0 Ω [Lower Positive Limit, +∞) [Lower Positive Limit / Merge Count, +∞)

    Operating in Compliance

    In addition to the normal criteria for operating in compliance, merged channels may operate in compliance when their outputs are poorly balanced, such as when one of the channels being merged is physically disconnected.

    Use Fetch Multiple or Query In Compliance to identify whether a channel is operating in compliance.

    Unmerging Merged Channels

    Merging channels reserves the primary channel and merge channels for use in the merge configuration you choose. To use merged channels independently again, you must unreserve the channels first.

    Complete the following steps to unreserve merged channels and use the channels independently.
    1. Complete any of the following steps based on your desired unreserve outcome.
      Desired Unreserve OutcomeHow To
      Continue sourcing current from the channels according to the merge configuration Call Close in a session that includes the primary channel
      Stop the channels from sourcing current Complete one of the following steps:
      • Set Merged Channels to "" for the primary channel and then call Commit With Channels
      • Call Reset With Channels on the primary channel
      • Call Disable, if the session is initialized with a single primary channel only
      • Self-calibrate the instrument
      The channels are now unreserved. You can now access the channels and configure the channels independently of one another.
    2. Configure the channels independently.
    3. Call Commit With Channels on the channels that you intend to use.
      Committing the independent configuration unmerges the channels and applies the independent configuration.
      Note When you change the merge configuration upon calling Commit With Channels, the outputs of all channels that were in the previous merge configuration are disabled; this is equivalent to using Configure Output Enabled to disable the outputs of those channels.
    The new merge configuration is applied at commit. You can use each channel independently of the others (or in a new merge configuration), and each channel might source current up to its normal per-channel or merged maximum. If the merge configuration remains unchanged, the merged channels continue sourcing based on their previous configuration.
    Once you commit a new configuration to the channels, call Initiate With Channels to begin sourcing according to your new configuration.