In terms of signals and impedance
07/14 09:42
In terms of signals and impedance, attention should be paid to matching and power control. Regarding input power limitation, since exceeding the rated input power of a GaN power amplifier tube will cause overdriving, which in turn leads to a sudden increase in drain current, gain compression, or even burnout, the test should start with a small signal (such as 1/3 of the rated input power) in the initial stage. The output power (Pout) and drain current (Ids) should be monitored while gradually increasing the input power. Once a sudden drop in gain (with compression exceeding 1dB) or an abnormal increase in Ids (exceeding 10% of the rated value) is observed, the input power must be reduced immediately. For impedance matching and standing wave protection, since the input/output impedance of a GaN power amplifier (usually 50Ω) needs to be strictly matched with the test system, otherwise, the reflected power will cause excessive standing waves (VSWR>2:1) and damage the device. Therefore, calibration with a network analyzer (covering the operating frequency band) should be performed before the test to ensure that the VSWR of cables, connectors, and test fixtures is ≤1.5:1. If wide-band testing is required, an isolator (with isolation ≥20dB) should be connected in series to absorb the reflected power. Meanwhile, the standing wave ratio should be monitored in real-time (via a power meter or vector network analyzer), and the input should be automatically cut off when it exceeds the threshold (such as VSWR>2.5:1).
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