Swept IMD for Converters (IMDx)

• IMDX Concepts

• Requirements and Limitations

• How to Configure your Hardware

• Create a Swept IMDx Measurement

• Valid Mixer Configuration / Sweep Type Combinations

• Setup Dialog

• How to specify IMDx Parameters

• IMDx Calibration

• Saving IMDx Data (Swept IMD topic)

Other IMD Topics

IMDx Concepts

Conceptually, Swept IMD for Converters (IMDx) is like IMD for Amplifiers, except that there are two sets of products on the DUT output.

This image shows the simplest measurement configuration: the Input, LO, and Output are all CW frequencies.

• DUT INPUT - two fundamental tones (f1 and f2)

• DUT LO - a single frequency.

• DUT OUTPUT - two sets of frequencies

With IMDx, you can view EITHER the High side or Low side products; NOT BOTH.

Make this selection on the Mixer Frequency tab.

Requirements and Limitations

Swept IMDx requires Swept IMD (Opt S9x087A/B).

The following VNA features are NOT available with Swept IMDx:

• Analog Sweep (Stepped sweep mode only)

• Log frequency sweeps

• Unratioed receiver measurements (A, B, R)

• ECal User Characterization

• Time Domain

• Balanced measurements

• Save Formatted Citifile data.

• Save SnP data.

• Port extensions

• Some Fixturing Features

• Independent IFBW, Power Levels, or Sweep Time in a segment table is NOT supported.

• External DC Sources (DC Meters ARE supported).

• See Frequency Limitations

How to Configure your Hardware

The VNA is extremely versatile, and can be configured in many ways to make IMDx measurements. While not all conceivable configurations are documented here, a few of the most common examples are provided to show the basic concepts.

DUT Configuration

• The DUT Input must be connected to VNA Port 1 which have been configured as DRA configuration.

• See LO Source configuration below.

Source Configuration

Three sources are required to make IMDx measurements: Two sources are VNA internal; the third could be either an internal or external source.

• F1 tone - Must come out VNA Port  which have been configured as DRA configuration  

• F2 tone - Must come out VNA Port that has independent source other than the F1 tone This source can come from an internal or external source.  Default is the internal Src 2.

• LO - Can come from internal or external source. Default is Not controlled, set to 0 Hz.

1. • If the VNA system has 3 or more sources, the LO can come from internal source.

   • If the VNA system has only 2 sources and the LO uses one source, the f2 tone must come from an external source.

   • If using an external source, it can be connected directly to the DUT.

Configuration Examples

DRA configuration for ports 1 to 3 is required.

Note: Above 40 GHz, high pass filter to block 2/3 sub-harmonics is required. Low pass filer to block 4/3 sub-harmonics is recommended.

1. Default Configuration  

• f1 -  Internal Src1 which is from the DRA port

• f2 -  Internal Src2

• LO - Internal Src3

2. External LO

Use this configuration to monitor LO power using R3 or R4. (Future parameters)

• f1 -  Internal Src1

• f2 -  Internal Src2

• • LO - Connect external source to the LO directly

This configuration is commonly used for FCA measurements where the internal second source is used as the LO.

• f1 -  Internal Src1

• f2 -  External f2 to one input of the combiner .

• LO - Internal Src2

Create a Swept IMDx Measurement

1. Press Meas > S-Param > Meas Class....

2. Select Swept IMD Converters, then either:

   • OK delete the existing measurement, or

   • New Channel to create the measurement in a new channel.

3. A Swept IMDx measurement is displayed. To select additional parameters to display, click Response, then Measure, then select a parameter from the list.

Valid Mixer Configuration / Sweep Type Combinations

The following are the Valid Mixer Configurations in table format:

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 Tone Frequency tab.

• See other rules for configuring a mixer.

• The following is an explanation of the table:

SWEPT Input - Sweeps the center frequency of the tones, but the tone spacing remains fixed.  

On the Tone Frequency tab, select Sweep fc

• Either the LO or Output MUST also be swept.

• On the Mixer Frequency tab, select Start/Stop, or Center/Span for each range to be swept.

FIXED Input  - The center frequency of the tones is fixed.

On the Tone Frequency tab select Fixed for the following sweep type:

• CW - Tones do NOT change. The LO and Output frequencies CAN be swept.

All Ranges FIXED - The center frequency of the tones is fixed.

On the Tone Frequency tab select Fixed for the following sweep types:

• Sweep Delta F  Tone separation changes.

• Power Sweep - Tone power changes.

• LO Power Sweep - The LO power is swept.

• CW - Tones do NOT change.

Setup Dialog

The following tabs are shared with the Swept IMD Setup dialog:

• Tone Frequency tab

• Tone Power tab

The following tabs are shared with all Mixer / Converter Applications

• Mixer Frequency tab

• Mixer (LO) Power tab

• Mixer Setup tab (NOT shared)

IMDx Calibration

Calibration for IMDx is exactly the same as calibration for IMD with the following exception:

• You can choose to perform a source power cal of the LO source.  If the LO is a fixed frequency, this step is performed very fast.

The results of an IMDx calibration are very similar to the results that are achieved from an SMC calibration.