RF switch matrix

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An RF switch matrix is a system of discrete electronic components that are integrated to route radio frequency (RF) signals between multiple inputs and multiple outputs. Popular applications requiring RF matrices are ground systems, test equipment, and communication systems.

Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around twenty thousand times per second to around three hundred billion times per second. This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies; these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range.

Contents

An RF matrix is used in test systems, in both design verification and manufacturing test, to route high frequency signals between the device under test (DUT) and the test and measurement equipment. In addition to signal routing, the RF/Microwave Switch Matrix may also contain signal conditioning components including passive signal conditioning devices, such as attenuators, filters, and directional couplers, as well as active signal conditioning, such as amplification and frequency converters. Since the signal routing and signal conditioning needs of a test system differ from design to design, RF/Microwave Switch Matrices typically are custom designed by the test system engineer or by a hired contractor for each new test system.[ dubious ]

A device under test (DUT), also known as equipment under test (EUT) and unit under test (UUT), is a manufactured product undergoing testing, either at first manufacture or later during its life cycle as part of ongoing functional testing and calibration checks. This can include a test after repair to establish that the product is performing in accordance with the original product specification.

Electronic filter electronic circuit that removes unwanted components from the signal, or enhances wanted ones, or both

Electronic filters are a type of signal processing filter in the form of electrical circuits consisting of discrete (lumped) electronic components. Such filters remove unwanted frequency components from the applied signal, enhance wanted ones, or both. Electronic filters can be:

The Switch Matrix is made up of RF switches and signal conditioners that are mounted together in a mechanical infrastructure or housing. Cables then interconnect the switches and signal conditioners. The switch matrix then employs a driver circuit and power supply to power and drive the switches and signal conditioners. The switch matrix uses connectors or fixtures to route the signal paths from the sourcing and measurement equipment to the DUT. The switch matrix is typically located close to the DUT to shorten the signal paths, thus reducing insertion loss and signal degradation.

RF switch

An RF Switch or Microwave Switch is a device to route high frequency signals through transmission paths. RF 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.

Power supply electronic device that converts or regulates electric energy and supplies it to a load

A power supply is an electrical device that supplies electric power to an electrical load. The primary function of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power.

Matrix benefits

Switch Matrix Block diagram.gif
Switch Matrix

The purpose of a switch matrix is to move the signal routing and signal conditioning to one central location in the test system versus having it all distributed at various places in the test system. Moving the signal routing and signal conditioning to a single location in the test system has the following advantages:

Making it vs buying it

Switch matrices present a unique problem to test system designers as the signal conditioning needs, the frequency range, the bandwidth, and power aspects change from application to application. Test and measurement companies cannot provide a "one size fits all" solution. This leaves test system designers with two choices for their switch matrix design: Insourcing or outsourcing.

Outsourcing is an agreement in which one company hires another company to be responsible for a planned or existing activity that is or could be done internally, and sometimes involves transferring employees and assets from one firm to another.

Insource advantages

  1. Proprietary concerns are a big issue especially in the Aerospace Defense industry. Creating a switch matrix in-house removes this issue.
  2. Internal human resources may be less costly.
  3. A company is in control of the amount of daily man hours spent in development.
  4. Being the first to develop an emerging technology into a finished product can be very profitable. Insourcing bypasses the time spent shopping around for the right contractor.
  5. Successive switch matrix designs can be highly leveragable from one design to another. The switch driver hardware and software, the mechanical designs, the power supply, etc. can all be reused in other designs with little or no modification.

Outsource advantages

  1. Only way to obtain device if the company lacks or cannot spare human resources.
  2. System integrators (contractors) tend to have more experience and expertise.
  3. System integrators can design within tight specs and can handle complicated designs.
  4. System integrators can provide guaranteed work and product support.

Signal routing

A PIN Diode RF Microwave Switch Microwave Switch.png
A PIN Diode RF Microwave Switch

There are two types of switches typically used in switch matrices: Coaxial Electromechanical Switches and Solid State Switches, also known as electronic switches. Coaxial electromechanical switches can be further divided into two categories based on their architecture, latching relay and non-latching relay.

Coaxial

In geometry, coaxial means that two or more three-dimensional linear forms share a common axis. Thus, it is concentric in three-dimensional, linear forms.

In electronics, an electronic switch is an electronic component or device that can switch an electrical circuit, interrupting the current or diverting it from one conductor to another.

In electrical engineering, a switch is an electrical component that can "make" or "break" an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving object such as a door, or may be operated by some sensing element for pressure, temperature or flow. A switch will have one or more sets of contacts, which may operate simultaneously, sequentially, or alternately. Switches in high-powered circuits must operate rapidly to prevent destructive arcing, and may include special features to assist in rapidly interrupting a heavy current. Multiple forms of actuators are used for operation by hand or to sense position, level, temperature or flow. Special types are used, for example, for control of machinery, to reverse electric motors, or to sense liquid level. Many specialized forms exist. A common use is control of lighting, where multiple switches may be wired into one circuit to allow convenient control of light fixtures.

Solid state switches come in three types: PIN diode, FET, and hybrid. The advantages of solid state switches over EM switches are:

A PIN diode is a diode with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts.

On the other hand, since solid state switches have non-linear portions over their frequency range their bandwidth is limited.

An electromechanical switch (EM) provides better:

For these reasons EM switches are used much more often in switch matrix designs.

Example applications

Custom Switch Matrices are used extensively throughout test systems in the wireless and aerospace defense sectors for design verification and for manufacturing test. They have a wide range of complexity, from the simple to the complex.

RF Switch Matrices are also used heavily in the Television Broadcast market for the reception and re-broadcast of TV Channels. Typically a cable television headend will contain a matrix to enable multiple dishes that are aligned to different satellites to be routed to a bank of receivers. The RF Switch Matrix allows channel changes to be made remotely, without any interruptions.

Design challenges

There are six main challenges when designing a custom RF/Microwave Switch Matrix from beginning to end:

  1. Mechanical Design: design of an electrically shielded enclosure or box, internal component mounting brackets, with a component and cabling layout.
  2. RF/Microwave Design: a signal routing and signal conditioning design and testing plan. A calibration plan for the switch matrix would need to be developed to properly characterize the signal paths.
  3. Power and Control Hardware: The power supply and switch driver circuitry will need to be designed and developed.
  4. Software Control: A software driver will need to be developed to provide an interface between the control hardware and test system program.
  5. Documentation: The whole switch matrix design needs to be documented to support maintenance and possible future design leveraging.
  6. Servicing Plan: A servicing plan needs to be developed to ensure the life of the switch matrix lasts as long as the life of the test system.

Test equipment manufacturers offer instruments that provide a power supply, driver circuitry, and software drivers that essentially saves a test system designer time and cost by eliminating two of the six switch matrix design challenges: power and control hardware design as well as software driver development.

Many companies have introduced new product concepts that aid in custom switch matrix design. These new products offer test system designers a power supply, driver circuitry, and software drivers all wrapped together in a mainframe. The mainframe provides flexible mounting for switches and other components as well as blank front and rear panels that can be easily modified to fit a design need. These new products eliminates 3 of the 6 design challenges: mechanical design, power and control hardware design, and software driver development

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