Introduction
Rapid growth in the number of connected devices for next generation wireless applications is driving demand for faster, more innovative, and more cost-effective test solutions. The need for reduction in cost and improvement in test throughput is found both at the design verification stage as well as in high-volume production testing. Test engineers are looking for ways to reduce the number of device-under-test (DUT) connections and enable testing of multiple DUTs in parallel from a single test station.
The diversity of real-world test applications makes it virtually impossible to realize anything like a “one-size-fits-all” solution. The specifications for many test applications are often defined concurrently with the design process, forcing equipment vendors to be agile in the design and fabrication of a wide range of unique, user-defined solutions. The turnaround time on these test systems directly affects customers’ time to market, so they’re depending on suppliers to deliver solutions that are both tailored to their needs and fast.
Mini-Circuits has built its product line for test and measurement applications around principles of economy, reliability, flexibility and speed. The company’s wealth and variety of components in stock enables a building-block approach to developing custom test solutions for each customer’s unique requirements with turnaround times as fast as two weeks. Test engineers can integrate any combination of switches, splitter/combiners, attenuators, amplifiers and many other components to manage signal traffic between DUTs and test instrumentation in any lab environment. This article will focus specifically on how RF switches can be configured to improve efficiency in high-volume test applications.
Switch Matrices and Automated Signal Routing
RF and microwave switches used in real-world test applications are often configured together into a switch matrix to manage and automate signal traffic. Since all test signals pass through the switch matrix, its performance directly effects the accuracy, repeatability, and efficiency of your measurements. In building a given test setup, test engineers need to focus on getting their DUTs properly tested in the most efficient manner possible. Primary concerns are that the test solution employed delivers the correct signal at the required power level to the DUT and that the isolation between test ports maintains measurement integrity.
Some of the key performance parameters of RF switches for test applications include:
- Isolation – The degree to which the switch suppresses RF leakage from the “on” signal port to the “off” port(s)
- Insertion loss – The attenuation from input to output due to intrinsic losses along the transmission line
- Power handling – The maximum rated RF input power the switch can receive without sustaining damage
- Switching time – The time it takes for a switch transition from one state to another, typically ranging from the order of milliseconds to nanoseconds
- Switch life – The number of switch cycles a switch can complete before failure
Determining switch matrix routing and performance for complex, application-specific test systems can become very costly and time consuming, especially because system requirements tend to be unique to a given application. To support customers in this task, Mini-Circuits offers a wide range of modular and fully customized integrated solutions, including high-order switch matrices for signal routing. Whether these systems incorporate mechanical, solid state, or MEMS switching in each system is determined based on the customer’s specific system requirements.
Mechanical, Solid State and MEMS Switches Compared: Key Distinctions
Before exploring real-world examples of switch matrices for test applications, it will be beneficial to review the relative pros and cons between the different switch types available. RF switches fall into three basic design categories: electro-mechanical, solid state and MEMS (Figure 1).
Mechanical Switches
Mechanical switches tend to support higher RF power levels with lowest loss and highest isolation. However, they have slower switching times, are larger in size and typically with higher DC power consumption. Well-engineered mechanical switches can be designed with switching lifetimes in the order of millions of cycles, but even this limit can be quickly surpassed in high volume switch applications, for example semi-conductor testing. Table 1 shows examples of the TTL mechanical switches. Mini-Circuits offers mechanical switches with a wide range of form factors and control options, from individual DC or TTL controlled components, to complete integrated test racks with Ethernet and USB control.
| Model Name | Switch Type | Frequency | Insertion Loss (Typ.) | Isolation (Typ.) | Power Rating (Cold Switching) |
|---|---|---|---|---|---|
| ZK-MSP8TA-12 | SP8T | DC–12 GHz | 0.4 dB | 90 dB | 20W |
| ZK-MSP6TA-12 | SP6T | DC–12 GHz | 0.25 dB | 90 dB | 20W |
| ZK-MSP4TA-18 | SP4T | DC–18 GHz | 0.5 dB | 80 dB | 20W |
| ZK-MSP2TA-18 | SPDT | DC–18 GHz | 0.3 dB | 80 dB | 20W |
Solid State Switches
Solid state switches, by contrast, tend to have much faster switching speeds, better repeatability and significantly longer lifetimes. With no physical moving parts, the lifetime is not limited by the number of switching cycles but is instead only measured in terms of the MTTF considerations of solid-state technology. These attributes are especially desirable for high-volume production test applications, as switching speed is directly related to test throughput, and the switches need to be replaced far less often under heavy use. At the same time, they come with limitations of lower power handling and lower isolation. Isolation, in particular, is more difficult to calibrate out of a test system and is therefore an especially critical parameter for automated testing. Switches with poor isolation can allow stray signals to flow into the measurement path and degrade the integrity of the measurement. This can impair system accuracy and lead to challenges in determining uncertainties and timing requirements.
Fortunately, Mini-Circuits engineers have innovated solid-state switch designs to dramatically improve isolation performance over wide bandwidths and circumvent some of the challenges associated with lower isolation. Mini-Circuits now offers a wide variety of cost-effective, USB-controlled solid-state switches with frequencies ranging from DC to 67GHz and isolation as high as 110 dB in some cases.
The eSB and RCS Series operating up to 67 GHz was developed to support testing up to V-band. TTL controlled solid-state switches based in PIN diode with ultra-fast switching (100 ns typ), operating up to 18 GHz was optimized for 5G FR1 & FR3 telecom testing requirements. These advantages and new product innovations combined with the capabilities of a full lineup of mechanical switches give engineers a wealth of options, whether using discrete components in their native test setups or sourcing a fully integrated, customized solution.
| Model Name | Low (MHz) | High (GHz) | Switch Type | Switches | Termination | Loss | Isolation | Transitions | Power | Control Interfaces |
|---|---|---|---|---|---|---|---|---|---|---|
| U2C-1SP2T-63VH | 10 | 6 | SP2T | 1 | Absorptive | 4.0 dB | 110 dB | 700 ns | 36 dBm | USB + I2C + SPI |
| USB-SP4T-63 | 1 | 6 | SP4T | 1 | Absorptive | 1.0 dB | 50 dB | 3 μs | 27 dBm | USB |
| USB-2SP2T-DCH | DC | 8 | SP2T | 2 | Absorptive | 1.4 dB | 50 dB | 10 μs | 35 dBm | USB + Daisy-chain |
| USB-1SP16T-83H | 1 | 8 | SP16T | 1 | Absorptive | 7.5 dB | 100 dB | 5 μs | 30 dBm | USB + TTL + Daisy-chain |
| USB-4SP2T-852H | 10 | 8.5 | SP2T | 4 | Absorptive | 2.0 dB | 80 dB | 250 ns | 30 dBm | USB + Daisy-chain |
| U2C-1SP4T-852H | 2 | 8.5 | SP4T | 1 | Absorptive | 3.7 dB | 80 dB | 250 ns | 30 dBm | USB + I2C |
| USB-2SP4T-852H | 10 | 8.5 | SP4T | 2 | Absorptive | 2.5 dB | 85 dB | 5 μs | 30 dBm | USB + Daisy-chain |
| USB-1SP8T-852H | 10 | 8.5 | SP8T | 1 | Absorptive | 4.0 dB | 80 dB | 250 ns | 30 dBm | USB + Daisy-chain |
| USB-1SP2T-183 | 100 | 18 | SP2T | 1 | Absorptive | 2.0 dB | 65 dB | 50 ns | 25 dBm | USB + Daisy-chain |
| TTL-1SP4T-183 | 100 | 18 | SP4T | 1 | Absorptive | 4.0 dB | 60 dB | 50 ns | 30 dBm | TTL |
| USB-1SP4T-183 | 100 | 18 | SP4T | 1 | Absorptive | 4.0 dB | 65 dB | 20 ns | 25 dBm | USB + Daisy-chain |
| TTL-1SP8T-183 | 100 | 18 | SP8T | 1 | Absorptive | 5.7 dB | 60 dB | 50 ns | 30 dBm | TTL |
| USB-1SP8T-183 | 100 | 18 | SP8T | 1 | Absorptive | 5.7 dB | 60 dB | 25 ns | 24 dBm | USB + Daisy-chain |
| USB-1SP2T-34 | 100 | 30 | SP2T | 1 | Absorptive | 2.8 dB | 60 dB | 5 ns | 24 dBm | USB + Daisy-chain |
| USB-1SP4T-34 | 100 | 30 | SP4T | 1 | Absorptive | 4.5 dB | 60 dB | 10 ns | 24 dBm | USB + Daisy-chain |
| USB-1SP8T-34 | 100 | 30 | SP8T | 1 | Absorptive | 5.0 dB | 80 dB | 25 ns | 24 dBm | USB + Daisy-chain |
| USB-1SP2T-A44 | 100 | 43.5 | SP2T | 1 | Absorptive | 3.5 dB | 50 dB | 10 ns | 24 dBm | USB + Daisy-chain |
| eSB-1SP2T-A673 | 100 | 67 | SP2T | 1 | Absorptive | 4.0 dB | 45 dB | 600 ns | 24 dBm | USB + Daisy-chain |
| RCS-1SP2T-A673 | 100 | 67 | SP2T | 1 | Absorptive | 4.5 dB | 45 dB | 600 ns | 24 dBm | LAN + USB + Daisy-chain |
| eSB-1SP4T-A673 | 100 | 67 | SP4T | 1 | Absorptive | 6.0 dB | 45 dB | 600 ns | 24 dBm | USB + Daisy-chain |
| RCS-1SP4T-A673 | 100 | 67 | SP4T | 1 | Absorptive | 6.5 dB | 45 dB | 600 ns | 24 dBm | LAN + USB + Daisy-chain |
New Technology: MEMS Switches
To complete the portfolio of switching products, Mini-Circuits has recently launched a switch using MEMS technology. MEMS (micro-electro-mechanical system) is a new technology which aims to combine the best characteristics of both solid-state and electro-mechanical switch types. Using precision engineering, the mechanical switch topology is miniaturized into a form factor which operates like a solid-state integrated circuit.
MEM-SP4T-A18 is an SP4T absorptive switch operating up to 18 GHz. The MEMS technology enables DC passing & wideband operation with a switch lifetime orders of magnitude greater than traditional mechanical switches (30 billion switch cycles) at 1 GHz and 30 dBm power. Figure 2 shows the typical power and life de-rating curves for MEM-SP4T-A18.
Other advantages include fast switching time (15 us), excellent linearity (90dB IP3) and 25W CW power rating (cold switching at 1 GHz), all with exceptionally low DC power consumption. The MEMS switch has been developed in the same footprint as a typical mechanical switch to allow seamless transition for applications requiring extremely high switch life. Higher switch density models are considered in the roadmap.
Use Case 1: High Order Switching System for Cellular Network Testing
In our first real-world use case, a cellular network operator was building a test setup to validate new base station (BTS) equipment on their network. The test system needed to evaluate each channel of new BTS nodes to verify they were meeting specifications; it needed to confirm that new equipment worked alongside existing, heterogeneous equipment without adverse interactions; and it needed to allow validation of supported handsets with the new BTS equipment.
For this functionality, the customer required a signal routing system to connect six independent test stations to any or all of 20 base station channels. The setup needed to allow multiple users to connect to the same BTS if necessary, but also required a control mechanism to limit which test stations could access which BTS. To satisfy these requirements, Mini-Circuits developed the ZT-20X6NB, a 20 x 6 non-blocking full access switch matrix. This bi-directional switch matrix covers the key worldwide telecommunications bands from 600 MHz to 6 GHz and can be programmed to connect ports B1 – B6 (shown in Figure 3) to any combination of ports A1 – A20, such that multiple input ports may be routed to the same output port simultaneously. Because of its flexibility, this non-blocking configuration is ideal for multi-user, multi-device test systems of the kind this customer was building.
The system was designed into in a compact, 5U height, 10-inch rack-mountable chassis with all 26 RF connections (N-type) easily accessible on the front panel (Figure 4). It includes both USB and Ethernet control interfaces along with a built-in touch screen giving users a versatile range of control options. Software support is provided through Mini-Circuits’ user-friendly GUI application for remote control over a network or via USB connection. ActiveX and .NET API objects for Windows environments and HTTP / Telnet support ensure compatibility with most common programming environments.
Use Case 2: Incorporating Solid State Switching for Fast Throughput Requirements
Let’s consider another example supporting telecom test applications from 600 MHz to 6 GHz. Figure 5 highlights an 8 x 24 switch matrix subassembly. This unit was part of a larger, 24 x 48 system that also included programmable attenuators for signal conditioning. In this case, the switch matrix had to provide a maximum path loss of 12 dB and provide 120 dB of isolation between test ports. The goal was to meet throughput requirements of less than 30 millisecond DUT test time.
In order to meet the design requirements, the system utilized a combination of mechanical and solid state switches. The 8-port side used mechanical SP4T switches (MSP4TA-18+), which provided 0.2 dB insertion loss and 90 dB isolation. The MSP4TA’s 20 millisecond switching speed meets the overall test time required at this stage of the signal routing plan.
Figure 5 illustrates the elaborate switching network beyond the SP4T switches. To accomplish this signal routing and still meet the test time requirement, SPI-controlled RF SP10T solid state switches (SPI-SP10T-63) were used. With this model’s six microsecond switching speed, all the solid state switching routes can be cycled in less time than the mechanical switch takes to perform a single cycle. It also provides 80 dB isolation and +27 dBm power handling, meeting the requirements for this telecom application. The configuration in this example takes advantage of the benefits of both switching types and allows for a wide range of testing to be performed.
Extensions up to 40 GHz
The above cases are just two examples of the capability Mini-Circuits offers to build custom RF switch matrices for complex test requirements. To support 5G testing and other high-frequency test requirements, Mini-Circuits also offers mechanical switches with operating frequency ranges up to 26.5 and 40 GHz which can be configured in similar fashion.
As the industry works to develop a growing number and variety of wireless devices, the need for fast, efficient, and cost-effective solutions for RF testing will continue to grow in kind. With this trend in mind, this article has provided an overview how custom switch matrices can help test engineers optimize efficiency in their test setups. Mini-Circuits has successfully worked with many customers on systems operating up to 40 GHz, as well as on systems incorporating other functions such as attenuation control, amplification, signal distribution and more.
As the industry works to develop a growing number and variety of wireless devices, the need for fast, efficient, and cost-effective solutions for RF testing will continue to grow in kind. With this trend in mind, this article has provided an overview how custom switch matrices can help test engineers optimize efficiency in their test setups. Mini-Circuits has successfully worked with many customers on systems operating up to 40 GHz, as well as on systems incorporating other functions such as attenuation control, amplification, signal distribution and more.
Customers can view Mini-Circuits full portfolio of test solutions and configure their own modular test systems online at the link below.
Mini-Circuits Test Solutions Link
https://www.minicircuits.com/products/PortableTestEquipment.html