An RF switch or microwave switch is a device to route high frequency signals through transmission paths. RF (radio frequency) and microwave switches are used extensively in microwave test systems for signal routing between instruments and devices under test (DUT). Incorporating a switch into a switch matrix system enables you to route signals from multiple instruments to single or multiple DUTs. This allows multiple tests to be performed with the same setup, eliminating the need for frequent connects and disconnects. The entire testing process can be automated, increasing the throughput in high-volume production environments.
Like other electrical switches, RF and microwave switches provide different configurations for many different applications. Below is a list of typical switch configurations and usage:
Single pole, double throw (SPDT or 1:2) switches route signals from one input to two output paths.
Multiport switches or single pole, multiple throw (SPnT) switches allow a single input to multiple (three or more) output paths. Transfer switches or double pole, double throw (DPDT) switches can serve various purposes. Bypass switches insert or remove a test component from a signal path.
RF CMOS switches are crucial to modern wireless telecommunication, including wireless networks and mobile communication devices. Infineon's bulk CMOS RF switches sell over 1billion units annually, reaching a cumulative 5billion units, .
Technologies
The two main kinds of RF and microwave switches have different capabilities:
Electromechanical switches are based on the simple theory of electromagnetic induction. They rely on mechanical contacts as their switching mechanism.
A solid state switch is an electronic switching device based on semiconductor technology (e.g. MOSFET, PIN diode). It functions similarly to an electromechanical switch except that it has no moving parts.
{ | class="wikitable" |- ! Parameters !! Electromechanical !! Solid state |- | Frequency range || from [DC] || from kHz |- | Insertion loss || low || high |- | Return loss || good || good |- | Repeatability || good || excellent |- | Isolation || excellent || good |- | Switching speed || in ms || in ns |- | Settling time || < 15 ms || < 1 μs |- | Power handling || high || low |- | Video leakage || none || low |- | Operating life || 5 million cycles || infinite |- | ESD immunity || high || low |- | Sensitive to || vibration || RF power overstress |}
Parameters
Frequency range
RF and microwave applications range in frequency from 100 MHz for semiconductor to 60 GHz for satellite communications. Broadband accessories increase test system flexibility by extending frequency coverage. However, frequency is always application dependent and a broad operating frequency may be sacrificed to meet other critical parameters. For example, a network analyzer may perform a 1 ms sweep for an insertion loss measurement, so for this application settling time or switching speed becomes the critical parameter for ensuring measurement accuracy.
Insertion loss
In addition to proper frequency selection, insertion loss is critical to testing. Losses greater than 1 or 2 dB will attenuate peak signal levels and increase rising and falling edge times. A low insertion loss system can be achieved by minimizing the number of connectors and through-paths, or by selecting low insertion loss devices for system configuration. As power is expensive at higher frequencies, electromechanical switches provide the lowest possible loss along the transmission path.
Return loss
Return loss is caused by impedance mismatch between circuits. At microwave frequencies, the material properties as well as the dimensions of a network element play a significant role in determining the impedance match or mismatch caused by the distributed effect. Switches with excellent return loss performance ensure optimum power transfer through the switch and the entire network.
Repeatability
Low insertion loss repeatability reduces sources of random errors in the measurement path, which improves measurement accuracy. The repeatability and reliability of a switch guarantees measurement accuracy and can cut the cost of ownership by reducing calibration cycles and increasing test system uptime.