This features allow you to mathematically add (embed) or remove (de-embed) circuits to, or from, your measurements. The mathematical models are applied to specific ports for all measurements on the channel.
New fixture simulator provides more flexible and intuitive GUI for multi-port measurements. The multiple fixturing elements can be combined in any order, creating infinite combinations.
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Notes
GUI: Re-select the file in the dialog. SCPI: Re-select the file and apply updates: calc:fsim:draft:circ1:file "myFile.s2p" calc:fsim:apply Legacy SCPI: Cycle the deembedding state for the feature using the file. For example: calc:fsim:send:deem:stat OFF calc:fsim:send:deem:stat ON |
Procedures: To Embed or De-embed?
"De-embedding and Embedding S-Parameter Networks Using a Vector Network Analyzer" App note. for more conceptual information on Fixture Simulation.
See an example of how these functions can be used to de-embed unwanted effects of a test fixture, and then mathematically embed the DUT in the circuit in which it is used.
The fixturing operations are applied to the measurement results.
In the Data processing chain, the Fixture Simulator functions occur at the same time as the Apply Error Terms block.
When fixturing is enabled, all of the enabled fixturing features are applied when snp files are saved.
Source power compensation is then optionally applied to compensate for the aggregate loss through all enabled fixturing operations.
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You can configure your virtual fixtures on GUI. The calculation order is from right to left. Note: The calculation order was from left to right for A.14.70.01 to A.15.20.05.
File: Save Topology... : Save the current setup into a topology setting file (.topo). You can recall it by Load Topology. Save Topology as SnP... : Save the whole embedding, de-embedding, and port extension blocks as a SNP file. The portion of Port Z conversion is not included. The dimension N of the SNP file will be the total number of VNA's test ports. This saved SNP file can be used later in the Fixture Generator as a de-embedding block. Load Topology... : Load the topology setting file (.topo). You can load the .totp file which was saved with the VNA of equal or less number of test ports. Load Default Topology: Reset the topology setting. Edit: Allow to enable/edit/cut/copy/paste/delete/add for a block. Active Channel: Select the channel to apply the fixture simulator. Apply Fixtures: Apply all fixture blocks and all impedance transforms that are enabled. It does not affect port extensions or balanced definitions Add Block... Opens the Add Block dialog to add and define a new block. See the block types below. Right Click on each block shows a pop-up menu.
Disable (Draft) State
Enable (Active) State
Blue: Embedded, Green: De-embedded To change the ports on the fixturing device, you can drag and drop the port numbers. The port numbers on the device are highlighted if they are hovered on or selected:
Then you can move them around:
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This function specifies a SnP file to embed (add) or de-embed (remove) from the measurement results. Computation takes place BEFORE Balanced conversion. The SnP file S-Parameter data is normalized to a single File-Zo impedance as defined in the file. The VNA will re-normalize the S-Parameter data from File-Zo to the VNA System-Zo. The VNA will interpolate if the number of data points that are read is different from the current VNA setting. Note: De-embedding a component with more than 20 dB of loss becomes impractical because of an inability to accurately measure the match of the DUT through such a device. The de-embedding operation recalls an .s2p file (Touchstone format) which includes the electrical characteristics of a 2-port fixture or device. The file can be in any standard format (real-imaginary, magnitude-angle, dB-angle). Enable block as Check to apply the settings to the measurement results. Must also enable Fixturing ON/off. De-Embed/Embed Select the embed (adding the snp device virtually) or de-embedding (removing the snp device). Note: Port Matching circuits can only be "embed". File Name: Select the snp file for embeding or de-embeding If the block has high loss, then it may cause transmission measurement errors when full S-parameter correction is applied. The reason is that the DUT output match cannot be measured accurately through a high-loss path; if the fixture has a large mismatch then this error will cause errors in the transmission measurement. Zeroing the fixture reflection at the DUT will reduce this error. This problem is described in "Handbook of Microwave Component Measurements with Advanced VNA Techniques", Joel Dunsmore, John Wiley & Sons, page 592 in the First Edition and page 775 in the Second Edition.
Enable Extrapolation Check to apply a simple extrapolation when the SnP file has a narrower frequency range than the channel. The values for the first and last data points are extended in either direction to cover the frequency range of the measurement. The frequency ranges of the SnP file are displayed at the right of the dialog. When extrapolation is necessary and enabled, a message is displayed showing the frequency range to be extrapolated. When extrapolation is necessary and disabled, a message is displayed offering to enable extrapolation. Note: For DIQ application channels, the SnP file must cover all specified frequency ranges, unless extrapolation is selected. Note: For IMD and IMDX channels, you will be prompted for extrapolation as described above if the S2P file does not meet the port frequency conditions. However, if the file is valid, extrapolation will be enabled automatically. This is for compatibility reasons with the IMD/IMDX calsets, which list all frequencies for all ports. This applies only for the SnP section, NOT the ground loop section. Ground loop is not for IMD/IMDX. General (Right side of Dialog box) Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax show the maximum frequency of imported snp file Fmin show the minimum frequency of imported snp file. Number of Port show the number of port of imported snp file Reverse Ports Reverses the ports on an existing S2P file.
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Ground loop de-embedding removes the effect of a non-ideal ground connection between the DUT’s ground and the analyzer's ground reference. Typically, the non-ideal component is the parasitic inductance of the ground contacts. Ground loop embedding adds the effect of a non-ideal component on the ground contacts. The Ground Loop De-embedding / Embedding can be specified by circuit model type or touchstone file.
Enable block as Check to apply the settings to the measurement results. Must also enable Fixturing ON/off. De-Embed/Embed Select the embed (adding the snp device virtually) or de-embedding (removing the snp device) Ground Loop (RL) or (GC)Circuit (Right side of Dialog box) Inductance(L), Resistance(R) / Conductance(G),Capacitance (C) Values for the specific components of the circuit type that models your fixture. General (Right side of Dialog box) Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax Fixed at 9.9999 THz Fmin Fixed at 0 Hz Number of Ports Define the number of ports. Once the number of ports is set, it cannot be changed. VNA Fmax Maximum frequency of the VNA. VNA Fmin Minimum frequency of the VNA. Ground Loop (file)Enable Extrapolation Check to apply a simple extrapolation when the SnP file has a narrower frequency range than the channel. The values for the first and last data points are extended in either direction to cover the frequency range of the measurement. The frequency ranges of the SnP file are displayed at the right of the dialog. When extrapolation is necessary and enabled, a message is displayed showing the frequency range to be extrapolated. When extrapolation is necessary and disabled, a message is displayed offering to enable extrapolation. General (Right side of Dialog box) Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax show the maximum frequency of imported snp file Fmin show the minimum frequency of imported snp file. Number of Ports Define the number of ports. Once the number of ports is set, it cannot be changed. Reverse Ports Reverses the ports on an existing S2P file.
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This function specifies a circuit to embed (add) to the measurement results. See Order of Fixture Operations.
Enable block as Check to apply the settings to the measurement results. Must also enable Fixturing ON/off. De-Embed/Embed Select the embed (adding the snp device virtually). Type: Choose a circuit model that best emulates your fixture at the selected VNA port:The circuit diagram is shown in the dialog box. Circuit (Right side of Dialog box) Capacitance (C), Inductance(L), Resistance(R), Conductance(G) Values for the specific components of the circuit type that models your fixture. General (Right side of Dialog box) Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax Fixed at 9.9999 THz Fmin Fixed at 0 Hz Number of Ports Fixed at 2. VNA Fmax Maximum frequency of the VNA. VNA Fmin Minimum frequency of the VNA. Note: A preference setting of "Use legacy behavior for Series-C & Shunt-L fixtures " is available for backward compatibility. |
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This function allows the embedding/de-embedding of a differential matching circuit at a balanced port. Enable block as Check to apply the settings to the measurement results. Must also enable Fixturing ON/off. De-Embed/Embed Select the embed (adding the snp device virtually) or de-embedding (removing the snp device)
Circuit (Right side of Dialog box) Define the values
Note: For the *.S2P file: Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax show the maximum frequency of imported snp file Fmin show the minimum frequency of imported snp file. Number of Ports Fixed at 2 VNA Fmax Maximum frequency of the VNA. VNA Fmin Minimum frequency of the VNA. |
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This function allows the embedding/de-embedding of a ideal line. Enable block as Check to apply the settings to the measurement results. Must also enable Fixturing ON/off. De-Embed/Embed Select the embed (adding the snp device virtually) or de-embedding (removing the snp device)
General (Right side of Dialog box) Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax Fixed at 9.9999 THz Fmin Fixed at 0 Hz Number of Port Fixed at 2 VNA Fmax Maximum frequency of the VNA. VNA Fmin Minimum frequency of the VNA. |
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This function allows the embedding/de-embedding of an impedance transformer. Enable block as Check to apply the settings to the measurement results. Must also enable Fixturing ON/off. De-Embed/Embed Select the embed (adding the snp device virtually) or de-embedding (removing the snp device)
General (Right side of Dialog box) Block ID Block ID. This is the same number as the circuit number in SCPI. Fmax Fixed at 9.9999 THz Fmin Fixed at 0 Hz Number of Ports Fixed at 2 VNA Fmax Maximum frequency of the VNA. VNA Fmin Minimum frequency of the VNA. |
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Note: This feature is available in ALL measurement classes. This function adjusts the source power at the specified port to compensate for the combined amount of gain or loss through specific fixturing operations. Use this function to set the power level at the DUT input. Power Compensation adjusts the source power for the gain/loss through 2-port de-embedded fixture components.
For example:
Power Compensation affects all measurements in the channel. Enable Fixturing to use Power Compensation. Compensate Only For De-Embeds - If unchecked, the entire fixture is used to compute the power compensation value (embed + de-embed). If checked, then only the de-embed blocks are used to compute the power compensation. Note: Use caution when applying power compensation. Always test your setup without a DUT in place. If you are using S2P files, Recall your S2P file into the VNA so you can verify that the device your S2P file describes is what you intended it to be. It is too easy to misalign data in S2P files if they are constructed manually. |
The following example shows a DUT and the matching circuit with which the DUT will be used in its intended application. When the DUT is tested in a high-volume manufacturing environment, multiple test fixtures are often required. The most accurate way to test the DUT and ensure measurement consistency between the different test fixtures is to use a simple, repeatable, test fixture without the actual matching elements.
To get the desired performance data, the parasitic effects of the fixture must first be removed (de-embedded) from the measured data. Then a perfect "virtual" matching circuit must be simulated and added mathematically (embedded) to the corrected, measured data. The result is an accurate display of the DUT as though it was actually tested with a physical matching circuit, but without the uncertainties of using real components.
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Test Device and the circuit in which it will be used. |
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Circuit Simulation |
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This diagram does NOT refer to the order in which operations are performed.
Create a balanced measurement using single-ended to balanced (SE-Bal) topology. Include all relevant measurement settings (IFBW, number of points, and so forth). Once the measurement is created and calibrated, the measurement parameter can be easily changed. For example, Sdd22 to Sds21.
Calibrate the measurement at the point where the simple test fixture is connected to the VNA. Use accurate calibration standards and definitions.
Remove the effects of the three uncalibrated transmission lines of the simple test fixture. This can be done in several different methods. The easiest is to use manual or automatic Port Extensions to move the calibration reference plane to the DUT. This removes the electrical length and loss of the fixture’s transmission lines, but does not account for fixture mismatch. Another method is to de-embed previously-created *.S2p files of the 3 transmission lines. The files can be created using external ADS modeling software. Another alternative is to create the *.S2P files by independently measuring all 3 ports of the test fixture and saving the results of each to an S2P file.
With the test fixture connected to the VNA and a DUT inserted, the measurement results now appear as though calibration was performed at the connections to the DUT, and the device was measured in a 50-ohm single-ended test environment. The following steps will cause the results to reflect the performance of the device as though the device is embedded in the circuit in which it will be used.
Port 1 of the device is a single-ended port and sees a source impedance the same as the VNA system impedance, so no change is required. However, if Rs were a value other than 50 ohms, Port 1 Impedance Conversion would be used to simulate the different impedance.
Port Matching is used to simulate L1 inductance. Select any of the Shunt L circuits to embed (add) to the measurement results. Enter the value of L and R. The C and G values can be entered as 0 (zero).
Port Matching is used to simulate C1 and C2 capacitance. For both port 2 and port 3, select any of the Series C circuits to embed (add) to the measurement results. Enter the value of C and G. The L and R values can be entered as 0 (zero).
Balanced Conversion mathematically simulates the measurement in balanced mode.
Differential Port Matching is used to simulate L2 inductance. Select Shunt L- Shunt C and enter the inductance / resistance value. The C and G values can be entered as 0 (zero).
Finally, Differential Z Conversion is used to simulate a circuit termination of 200 ohms. If you are making Common Mode measurements, specify Common Mode Z Conversion.
