RF components are available in multiple sizes and shapes and as such coaxial connectors are not as useful. With the variety of components, one single size of connector is not fit for the all. In such a case, test fixtures in Orlando act as mechanical and electrical interface from the Radio Frequency system (RF) to the device-under-test (DUT). Radio frequency integrated circuits are marketed as packaged components and not as die and so a high-performing die in an inferior package will cause the application to underperform. Some RF packages cannot be directly probed as well and in this situation, a test fixture becomes the most viable solution. They are super flexible and are more affordable than wafer probe stations. However, test fixtures have a characteristic of adding parasitics to characterization schemes like RF reflections and DUT and so correct de-embedding is important. In this article you will learn more about the different types of RF test fixtures.
The Basic Structure Of A RF Test Fixture
RF test fixtures has three main component parts:
- RF launcher which is usually a coaxial cable connector.
- RF interconnecting lines which are usually microstrips that lead to the device-under-test.
- A block housing to accommodate the entire body of the test fixture.
Types Of Test Fixtures
- Test Fixtures For Active Components
This type of test fixture design depends on the RF application it is used for. Say for example, you are using it to test an amplifier, in this case, the amplifier can overcome the loss by the test fixture by adding a certain decibel to the output. However, this can also generate a lot of heat and the heat dissipation is done by cooling the test fixture or by pulsing the bias. For testing low noise amplifiers, the DUT needs to be shielded from stray fields. There will be fixture mismatches even after calibration, which are mathematically de-embedded from the measurement and not physically. As power amplifiers have a low-output impedance so to maintain their integrity, the loss of the test fixture should be little but somewhat higher than that of the DUT.
- Test Fixtures For Passive Components
Passive components usually show some amount of loss and as such, the loss of the fixture should not impact the sensitivity of measurement. Also, passive components do not have any gain over the losses seen by a test fixture, unlike the active components. For example, in the measurement of a filter, the parasitics presented by the test fixtures affect the zeroes and the poles of the filter which shifts its frequency. So, when there is excessive inductance or incompetence, the filter will easily degrade around the band edges or the skirts.if it is a high-reject filter, that only sees a small amount signal through then the leakage can impact the port to port measurements.
In an attempt to reject the band frequencies, the filter imparts a highly reflective load to the fixture port and instead of tuning the port to match impedance, attenuators are usually placed in the RF path. The attenuators need to be placed close to the DUT as it will attenuate the signals as soon as they are reflected from the filters. The attenuators will also decrease the dynamic range of measurement.
- R&D Test Fixtures
This type of test fixtures are used in Research and Development environments and are used to make rugged and compliant contacts that can withstand a large number of insertion of crimping wires in Melbourne and removal. For automated loading or unloading, the test fixture is more mechanically complicated than in manual processes and they provide fast connections with long-lasting fixture life span and decent RF performance. However, R&D test fixtures are somewhat fragile and unsophisticated as they are used to test only a few devices. Since the definition of the reference planes and its measurement is very important in R&D testing, repeatability and correlation between R&D test fixtures and manufacturing can pose a problem.
