mmWave RF Subsystem
Vector network analyzers (VNAs) are at the heart of any high performance mmWave test system, and GENASYS Semiconductor solutions are no exception. VNAs are specialized radio frequency (RF) analyzers that provide both amplitude and phase measurements; these instruments deliver results that are far superior to scalar network analyzers (SNAs) which only return the amplitude properties of the measured signal. <Read More> Phase measurements are essential when testing mmWave devices, as digital phase adjustments provide the ability to steer the RF energy.
Accurate and repeatable phase and amplitude measurement across the entire band of interest is another critical characteristic of the VNA. Some VNAs may be capable of analyzing signals across their entire operating band, 100 kHz to 40 GHz for example, but there may be dead bands or frequencies where the response is below levels that are acceptable for evaluating the device under test (DUT). The Keysight M980aX proved to be the ideal VNA solution delivering modularity, speed and accuracy in a multi-port instrument that shares the same measurement science as their PNAX instruments, with no dead bands across the operating spectrum.
Test speed and system throughput are essential for production mmWave test systems and this places additional demands on the RF measurement subsystem. Most beamforming devices are multi-port integrated circuits (ICs) and a common four port device would incorporate one RF feed and four RF input/output antenna ports; therefore, five VNA channels are required. The density of these devices continues to increase, and as a result the architecture of the test system will greatly impact overall throughput and scalability. For example some manufacturers have already transitioned to higher density beamformer ICs with two RF feeds and eight RF input/output antenna ports. These evolving needs clearly highlight the advantages of the MOSA approach. GENASYS Semiconductor test systems easily adapt to these changing needs through the installation of additional VNA instruments utilizing the chassis’ spare slots.
Some test architectures will reduce the overall number of independent VNA instrumentation ports by implementing a multiplexed switch (1x4 in the previous example). This approach will certainly reduce the number of required VNA ports, and their associated cost, but it will also impact reliability, measurement uncertainty and test times. Mechanical microwave relays tend to be the technology of choice when implementing these RF multiplexers, resulting in each path having slightly different insertion loss and VSWR characteristics that must be addressed through calibration. Additionally, relay actuation and settling times greatly increase test times. All mechanical relays have a finite life cycle and the performance of the relays will degrade non-linearly over time, impacting reliability and requiring additional support with the associated test system down-time.
A true multi-port, parallel test architecture allocates an independent VNA port for each port on the beamformer IC, delivering significant advantages in system throughput and reliability. Parallel, multi-site architectures not only significantly reduce test times, but also eliminate the need for external microwave switching and the issues associated with measurement uncertainty and reliability.
We'll explore the digital and power subsystems in our next post.
<Read More>5G mmWave Semiconductor Production Test Challenges