U9400A/C Solid State FET Transfer Switches

U9400A/C Solid State FET Transfer Switches

Keysight Technologies, Inc. U9400A/C solid state FET transfer switches offer superior performance in terms of isolation and video leakage across a broad operating frequency range. The U9400A/C enable high-perfor­mance testing from frequencies as low as 300 KHz up to 8 GHz with the U9400A and 18 GHz with the U9400C. These transfer switches are used to increase system flexibility and simplicity, and are easily controlled with an integrated TTL-compatible driver.

The U9400A/C switches offer unmatched isolation performance between ports, as high as 100 dB at 8 GHz and 90 dB at 18 GHz. In addition, Keysight U9400A/C FET switches provide low video leakage of 90 mVpp which ensures safe testing of sensitive components. High video leakage can degrade measurement accuracy and possibly damage sensitive components or equipment. Low video leakage makes these switches particu­larly suited for measuring sensitive devices and components such as mixers and amplifiers.

The U9400A/C also feature an industry-leading settling time of 0.35 ms, measured to 0.01 dB of the final value (the typical settling time of FET switches is > 50 ms). This equates to a 500 ns switching speed making the U9400A/C ideal for RF and microwave switching applications in instrumentation, communication, radar, switch matrices and various other test systems where speed and lifetime of a switch are critical.

Gallium Arsenide (GaAs) FET switches have inherently low video leakage which make them more suitable for measuring devices that have low maximum input power ratings. Sensitive components such as receivers, traveling wave tubes (TWT) and handset power amplifiers typically have maximum input power ratings of < 13 dBm and can be easily damaged or over-driven by the high video leakage. Keysight U9400A/C switches have 90 m Vpp video leakage compared to common PIN switches in the market which typically have ≥ 1 V video leakage.

The ON and OFF switching of PIN diode switches use the same path as the RF which make them perform poorly below 10 MHz.

Historically, the main drawback of GaAs FET switches has been a long settling time.

Typical GaAs FET switches have settling time in the order of tens of milliseconds largely due to the slow transients or the “gate lag” effect. Gate lag occurs when electrons become trapped at the surface of the GaAs device. The conventional method of reducing gate lag in GaAs devices is usually achieved by controlling the gate trough geometry so that the gates fit “tightly” in the bottom of the trough. However, this approach reduces the breakdown voltage and power handling of the device. As shown in Figure 1, the typical transient behavior of FET switches from OFF state to ON state has a slow tail effect that increases the settling time.

Keysight has managed to counteract this drawback with a patented design that eliminates the gate lag effect resulting in a much faster settling time of 350 μs. You can now have the benefits of FET switches without a reduction in switching speed.

A 0.01 dB settling time of 350 μs makes U9400A/C switches suitable for signal routing in EGSM/GSM power amplifier testing since each slot of a GSM signal is 577 μs. Figure 2 shows a timing diagram for a GSM/EDGE signal, and as you can see one slot equals 577 μs. Switches used in the test system must switch and settle within 577 μs so that the system itself can start to capture data within the time frame of the slot 1 signal to ensure accurate measurements.

Video leakage also plays a vital role in switch selection for this specific applica­tion. High video leakage can potentially cause permanent damage to power amplifiers because their maximum input power is typically < 13 dBm. The alterna­tive is to use electro-mechanical switches with low or no video leakage, but the switching speed (typically in ms) is usually too slow for this application.

Keysight U9400A/C have a very fast settling time and negligible video leakage making them particularly well suited for routing signals in this test system.

Keysight U9400A/C solid state transfer switches can be used in numerous ways to enhance system flexibility and simplicity. The following five examples show how U9400A/C can be used to route the signals: as a drop-out switch, as an SPDT switch, for signal reversal, to bypass an active device, and to switch between multiple instruments and DUTs.