Gain Compression for Converters (GCX)

Gain Compression is measured on Converters in the same manner as it is measured in Amplifiers. Also, the Mixer/Converter setup is very similar to that of SMC (Scalar Mixer Converter application).

In this topic (unique for GCX):

The following Gain Compression for Amplifiers information is relevant for learning about GCX:

The following dialog setup tabs are shared with other applications:

Frequency tab (GCA topic)
Power tab (GCA topic)
Compression tab (GCA topic)
- Safe Sweep Mode dialog (GCA topic)
Mixer Frequency tab (separate topic)
Mixer Setup tab (separate topic)
Mixer (LO) Power tab (separate topic)

Requirements and Limitations

GCX requires Option S93086A/B (Gain Compression).

Limitations:

Number of points limited to 100,001 for two-dimensional acquisitions, 50,000 points for SMART Sweep.
Linear and CW sweep ONLY - No Power, Log, or Segment sweep. Learn more.
GCX does NOT provide any built-in image rejection techniques. You should provide image rejection hardware if necessary.
Stepped sweep mode only.
Does NOT support Narrowband Pulse measurements using the integrated Pulse setup dialogs.

The following VNA features are NOT available with Gain Compression on Converters:

ECal User Characterization
Time Domain
Balanced measurements
Save Formatted Citifile data.
Save SnP data.
Port extensions
Some Fixturing Features
External Test Set Control (Option S93551A/B)
Integrated Narrowband or Narowband Pulse App
Independent IFBW, Power Levels, or Sweep Time in a segment table is NOT supported.

Using GCX

The following is a general procedure for performing a GCX measurement. The challenge with GCX is configuring a measurement that yields the true compression performance of YOUR DUT. This requires knowledge of the Gain Compression and Mixer settings, and knowledge of the DUT.

See specific dialog boxes below for details.

Disconnect the DUT if preset or default power levels may damage the VNA or DUT.
Preset the VNA, or configure a suitable User Preset that will be safe in case the DUT is connected.
Create a GCX channel. Learn how. The default trace is SC21.
Start the GCX Setup dialog and configure the measurement settings based on the DUT, adapters, attenuators, booster amplifiers, and fixtures to be used in the measurement. To start the dialog, click Stimulus, then Frequency, then GCX Setup. Learn about the setup dialogs.
Save the instrument state (optional).
Connect the DUT. Inspect the measurement to ensure the DUT is operating as expected.
Add GCX compression and mixer parameter traces. Learn more.
Adjust the measurement settings to yield satisfactory compression results. See GCA Measurement Tips.
Start and complete the GCX Calibration wizard.

Create a GCX Measurement

Press Meas > S-Param > Meas Class....
Select Gain Compression Converters, then either:
- OK delete the existing measurement, or
- New Channel to create the measurement in a new channel.

A default SC21 measurement is displayed. To select additional parameters to display, press Trace, select a trace, press Meas, then select a parameter. Learn more about GCX Parameters.

How to start the Gain Compression for Converters Setup dialog
Using Hardkey/SoftTab/Softkey	Using a mouse
Press Freq > Main > GCX Setup....	Click Stimulus Select GCX Setup...

Valid Mixer Configuration / Sweep Type Combinations

The following are the Valid Sweep Type / Mixer Configurations.

Sweep Type	Input	LO	Output
Linear	Swept	Fixed	Swept
Linear	Swept	Swept	Fixed
CW	Fixed	Fixed	Fixed
CW	Fixed	Swept	Swept

For determining a valid mixer configuration with 2 LOs, one Fixed LO and one Swept is equivalent to having a single-stage Swept LO.

If you create an invalid Sweep Type / Mixer Configuration, a red message appears like the following:

If this occurs, change the Sweep Type on the Frequency tab.

See other rules for configuring a mixer.

GCX Measurement Parameters

Note: The following table assumes: DUT Input = VNA port 1 and DUT Output = VNA port 2.

When the Port mapping is different, the parameters in GCX are updated accordingly. For example, with Input = port 2 and Output = port 1, then "CompIn12" would be displayed.

Parameter	Description
Mixer Parameters
SC21	Linear Conversion Gain
SC12	Reverse Conversion Gain
S11	Input Match
S22	Output Match
Compression Parameters
CompIn21	Input power at the compression point.
CompOut21	Output power at the compression point.
CompGain21	Gain at the compression point.
CompS11	Input Match at the compression point.
RefS21	Linear Gain value used to calculate the compression level. This is calculated differently depending on the compression method.
DeltaGain21	CompGain21 MINUS Linear Gain (in Log Mag format). This trace can be used to learn a lot about the DUT compression point. Learn more.
Unratioed - Absolute test port receiver measurements. Learn more.
IPwr	Input power measured at DUT-IN @ Input frequency
OPwr	Output power measured at DUT-OUT @ Output frequency
RevIPwr	Input power measured at DUT-OUT @ Output frequency
RevOPwr	Output power measured at DUT-IN @ Input frequency
ADC Parameters - Learn more.
AI1	Measured at the specified Linear Input level.
AI2	Measured at the specified Linear Input level.
CompAI1	AI1 at Compression
CompAI2	AI2 at Compression

GCX Setup Dialogs

All of the GCX Setup tabs are shared with other applications.

GCX Calibration

A GCX Cal is conceptually the same as a Gain Compression Calibration. This includes the ability to perform or downgrade to an Enhanced Response Cal. Learn how.

The following Guided Cal Wizard pages are unique to GCX:

GCX Calibration Setup dialog box help

Waveguide/In-fixture/On-Wafer Setup Starts the following dialog box.

Independent power cals for input and output ports (no thru) Check if a Thru standard is NOT available. During the power cal, you will be prompted to connect the power sensor to the Input, then the Output port.

Additional Power Cal Steps

Enable LO1 / LO2 Power Cal Check when LO1 / LO2 is controlled (on the Mixer Setup tab) to perform a Power Cal on the source.

Note: Phase Correction is NOT allowed for GCX measurements.

Waveguide/In-fixture/On-Wafer Setup dialog box help

This dialog box appears ONLY if you checked the Waveguide/In-fixture/On-Wafer Setup box in the previous Cal Setup dialog.

Allows you to embed or de-embed circuit networks on the input and output of your mixer under test.

For Network1 (Input) and Network2 (Output) select Embed, De-embed, or None.

Browse Click to navigate to the .S2P file that models the network to embed or de-embed.

To Embed or De-embed

De-Embed when there is a 2-port network that needs to be connected during the measurement, but it is NOT present during the calibration. An example might be when you do not have standards for a characterized test fixture, so you calibrate without the fixture, and make measurements with the DUT in the fixture. De-Embedding during the calibration extends the calibration reference plane to include the 2-port network.
Embed when there is a 2-port network that to be disconnected during the measurement, but is present during the calibration. An example might be when a characterized adapter is required during the calibration but NOT present during measurements of the DUT. Embedding during the calibration retracts the calibration reference plane to exclude the 2-port network during the measurement.

Notes

The S2P file for Network1 (on the input of the mixer), must cover the Input frequency range.
The S2P file for Network2 (on the output of the mixer), must cover the Output frequency range.
The frequency range of the S2P file must be the same, or larger than, the frequency range of the measurement. If more frequencies are included in the file, and the data points do not exactly match those of the measurement, interpolation will be performed.
As in the image on the dialog (above), in all cases:

- Port 1 of each network is assumed to be connected to the VNA.
- Port 2 of each network is assumed to be connected to the DUT.

Select DUT Connectors and Cal Kits dialog box help

Allows you to specify the connector type and Cal Kit for each DUT port.

Port n For each listed VNA port, specify the DUT connector type and gender, and the Cal Kit to use.

input pwr sensor Specify the connector type of the power sensor. Select Ignored to not compensate for the effects of the adapter that may be necessary to connect the power sensor to the input reference plane.

output pwr sensor Available when Independent power cals for input and output ports is checked on the GCX Calibration Setup dialog. Specify the connector type of the power sensor. Select Ignored to NOT compensate for the effects of an adapter that may be necessary to connect the power sensor to the output reference plane.

De-embed input power sensor adapter Check to measure, then remove the effects of the adapter that is used to connect the power sensor to the calibration reference plane.

Source Cal Settings Click to start the Source Cal Settings dialog. These settings allow you change ALL Source Cal and Power Meter settings.

Note: If your DUT connectors are:

Waveguide Change the system impedance to 1 ohm before performing a calibration. See Setting System Impedance.
Not listed (male and female) Select Type A as the connector type. Type A requires a calibration kit file containing the electrical properties of the standards used for calibration (see Calibration kits).
Unspecified (like a packaged device) Select Type B as the connector type. Type B requires a calibration kit file containing the electrical properties of the standards used for calibration (see Calibration kits).

Modify Cal Check, then click Next, to start the Modify Frequency Cal dialog.