Automatic Calibration Module

Automatic calibration module (ACM) is a special device, which allows for automating of the process of calibration. ACM is shown in Figure 65.

Figure 65 Automatic Calibration Module

ACM offers the following advantages over the traditional SOLT calibration, which uses a mechanical calibration kit:

• Reduces the number of connections of standards. Instead of connecting seven standards, it requires connecting only two ACM connectors;
• Reduces the calibration time;
• Reduces human error probability;
• Provides higher accuracy potentially.

ACM has two RF connectors for connection to the Analyzer test ports and a USB connector for control. ACM contains electronic switches, which switch between different reflection and transmission impedance states, as well as memory, which stores precise S-parameters of these impedance states.

After you connect the ACM to the Analyzer, the Analyzer software performs the calibration procedure automatically, i.e. switches between different ACM states, measures them, and computes calibration coefficients using the data stored in the ACM memory.

Automatic Calibration Module Features

Calibration Types:

ACM allows the Analyzer software to perform full two-port or full one-port calibrations with the click of a button. We recommend that you terminate the unusable ACM port with a load while performing one-port calibration.

Characterization:

Characterization is a table of S-parameters of all the states of the ACM switches, stored in the ACM memory. There are two types of characterization: user characterization and factory characterization. ACM has two memory sections. The first one is write-protected and contains factory characterization. The second memory section allows you to store up to three user characterizations. Before calibration you can select the factory characterization or any of the user characterizations stored in the ACM memory. The user characterization option is provided for saving new S-parameters of the ACM after connecting adapters to the ACM ports.

The software enables you to perform a user characterization and save the data to ACM with the click of a button. To be able to do this, you should first calibrate the Analyzer test ports in configuration compatible with the ACM ports.

Automatic Orientation:

Orientation means relating the ACM ports to the test ports of the Analyzer. While the Analyzer test ports are indicated by numbers, the ACM ports are indicated by letters A and B.

Orientation is defined either manually by the user, or automatically. The user is to select the manual or automatic orientation method. In case of automatic orientation, the Analyzer software determines the ACM orientation each time prior to its calibration or characterization.

Unknown Thru (expect Planar 304/1):

The Thru implemented by the electronic switches inside the ACM introduces losses. That is why you should know the exact parameters of the Thru or use an Unknown Thru algorithm to achieve the specified calibration accuracy.

The software allows using the both options. ACM memory stores S-parameters of the Thru, which are used to compute calibration coefficients. In case if an Unknown Thru algorithm is applied, such parameters are disregarded.

Thermal Compensation:

The most accurate calibration can be achieved if the ACM temperature is equal to the temperature, at which it was characterized. When this temperature changes, certain ACM state parameters may deviate from the parameters stored in the memory. This results in reduction of the ACM calibration accuracy.

To compensate for the thermal error, the ACM features thermal compensation function. Thermal compensation is a software function of the ACM S-parameter correction based on its temperature dependence and the data from the temperature sensor inside the ACM. The temperature dependence of each ACM is determined at the factory and saved into its memory.

The function of thermal compensation can be enabled or disabled by the user.

Confidence Check:

ACM also implements an additional state – an attenuator, which is not used in calibration. The attenuator is used to check the current calibration performed by ACM or any other method. Such test is called a confidence check.

The confidence check consists in simultaneous display of the measured and stored in memory S-parameters of the attenuator. The measured parameters are shown as the data trace and the parameters saved in the ACM memory are shown as the memory trace. You can compare the two traces, evaluate their differences and determine the accuracy of the calibration performed.

For a detailed comparison you can use the math (division) function for data and memory.

Automatic Calibration Procedure

Before calibrating the Analyzer with ACM, perform some settings, i.e. activate a channel and set channel parameters (frequency range, IF bandwidth, etc.).

Connect the ACM to the Analyzer test ports, and connect the USB port of the ACM to the USB port of the computer.

User Characterization Procedure

User characterization of ACM is required in case of ACM connectors modification by the use of adapters. The characterization is performed for the new ACM configuration, which includes adapters. To ensure calibration accuracy it is not recommended to disconnect and reconnect the adapters back.

Before you perform the user characterization of the ACM, perform full two-port calibration of the Analyzer in configuration of the test ports compatible with the configuration of ACM ports.

Connect the ACM to the Analyzer test ports, and connect the USB port of the ACM to the USB port of the computer.

After the ACM measurement is completed, the following dialog box will appear:

Fill in the following fields:

• User name;
• Analyzer name;
• Characterization location;
• Connectors (types of adapter connectors);
• Adapter description (description of adapters).

Use Save softkey to complete the user characterization of the ACM.

Confidence Check Procedure

In case you need to verify the reliability of the current calibration, perform the confidence check. This function can be used to check the accuracy of either calibration performed with an ACM or with a mechanical calibration kit.

Connect the ACM to the Analyzer test ports, and connect the USB port of the ACM to the USB port of the computer.

Enable the display of the data trace for the needed parameter, for example S21. It is possible to enable several data traces simultaneously, for example, S11, S22, S21, S12.

After the measurement is completed, two traces for each S-parameter will be displayed. The measured parameters will be shown as the data trace, and the ACM parameters will be shown as the memory trace.

Compare the data trace and the memory trace of the same parameter, for example S21. To perform more accurate comparison, enable the function of math operations between data and memory traces. In the logarithmic magnitude or phase format use the Data / Memory operation. In the linear magnitude format use the Data – Memory operation.

The conclusion on whether the current calibration provides sufficient accuracy or not is made by the user.

Erasing the User Characterization

In case you need to erase the user characterization in the ACM, there is possibility to perform this. The procedure erases all data of selected user characterization overwriting it by zeros. Factory characterization cannot be erased.