Scalable RF MEMS Switch Matrices: Methodology and Design

As product complexity continues to increase, test engineers are challenged with improving test coverage on a variety of devices while keeping costs at a minimum. When finished products incorporate hundreds or thousands of devices, developing and maintaining separate test systems for individual components lacks scalability. An approach to this problem is to standardize on a single platform and develop a small number of test systems that can each test tens or hundreds of different devices. Test engineers are increasingly seeing the benefits of developing, deploying, and supporting a reduced number of test systems that use common components. Although many factors such as system assurance and platform longevity influence the long-term success of these systems, the core requirements consist of modular, reconfigurable hardware. A switching matrix is the main hardware component that gives a single test system the flexibility to test a variety of devices. With a switching matrix, you can connect all of your instruments and test points through a series of relays and close relevant relays via software. Switching matrices provide several benefits such as simple connectivity and test repeatability; however, it's usually not practical to have a switching matrix that completely matches the I/O of your instruments. For example, if you have a 1,000 V DMM, a 2 A power supply, and a 1.5 GHz digitizer, you're unlikely to find a COTS switching matrix that maximizes those I/O points. Selecting a switching matrix involves evaluating various trade-offs between density, power, bandwidth, and so on and optimizing the cost of your test system. This paper examines the trade-offs you should evaluate when choosing a switching matrix along with considerations for reducing cost and size.

With the increased commercial availability of high channel count MR coil arrays and the associated higher number of plugs in the patient bed, it has become a common practice to include switch matrices in the receive path of MR systems. These allow the arbitrary routing of a signal from any plug to any receiver in the console. While switch matrices are standard in systems at clinical field strength and have been developed for systems operating up to 4T, they have not yet been implemented at ultra-high field (UHF). Here, we present a switch matrix suitable for operation at UHF. Crossbar switches, which are the most frequently employed forms of a switch matrix, use RF switches to connect horizontal input lines with the desired vertical output line. This leaves transmission line stubs of variable length physically connected with the selected signal path, potentially resulting in elevated signal losses. While this can be tolerated at low frequencies, and only needs partial compensation at intermediate frequencies (4T), a full compensation is required at UHF. In this study, an RF crossbar switch, which uses switchable compensation elements in both horizontal and vertical transmission lines, was implemented for a 9.4T MRI scanner. The prototype developed was evaluated for single channel and multichannel receive performance and benchmarked against a fixed wire connection.

In a generic switching problem, a switching pattern consists of a one-to-one mapping from a set of inputs to a set of outputs (i.e., a permutation). We propose and investigate a wireless switching framework in which a multi-antenna relay is responsible for switching traffic among a set of N stations. We refer to such a relay as a MIMO switch. With beamforming and linear detection, the MIMO switch controls which stations are connected to which stations. Each beamforming matrix realizes a permutation pattern among the stations. We refer to the corresponding permutation matrix as a switch matrix. By scheduling a set of different switch matrices, full connectivity among the stations can be established. In this paper, we focus on “fair switching” in which equal amounts of traffic are to be delivered for all the N(N - 1) ordered pairs of stations. In particular, we investigate how the system throughput can be maximized. In general, for large N the number of possible switch matrices N! is huge, making the scheduling problem combinatorially challenging. We show that for N = 4 and 5, only a subset of N - 1 of the N! switch matrices need to be considered in the scheduling problem to achieve good throughput. We conjecture that this will be the case for large N as well. This conjecture, if valid, implies that for practical purposes, fair-switching scheduling is not an intractable problem.

Current electronic broadband switch matrices employ discrete semiconductor devices or VLSI chips. Isolation between ON- and OFF-states degrades and crosstalk between input and output lines of these electronic switch matrices increases at high operation frequencies. These will limit electronic switch matrices to low-frequency or low-bit-rate operations. In addition, optical-to-electrical (electrical-to-optical) conversions at the input (output) ends are required for these switch matrices to be used in a fiber environment. One way to achieve broadband, low-crosstalk, and high-isolation switching and to eliminate E/O and O/E conversions is to use optical switches. This paper describes an optical broadband switching architecture using optical/optoelectronic logic gates. Input and output signals are optical. No E/O or O/E conversions are needed for this architecture. The optical/optoelectronic logic gates that can be employed in this architecture are reviewed. Performance of this architecture is evaluated by calculating the crosstalk, isolation, insertion loss, switch matrix size, drive power, and switching speed. Technologies needed for hybrid and monolithic implementations of this architecture are also identified.

A novel miniature-size switching unit is reported for application as the building block of multiport switch matrices. The cell consists of 3 cantilever-beam contact type MEMS devices coupled to CPW transmission lines. A major feature of the proposed switch cell is that in each of the operating states there is only one MEMS switch located in the path of signal inducing a similar loss for all switching states. The construction of the entire system is carried out by a six-mask fabrication process. To minimize the unwanted coupling of the RF signal through the bias lines of MEMS devices, high-resistive phosphorous-doped hydrogenated amorphous silicon (n+ a-Si:H) is selected as a material of choice for the dc bias lines. The switching unit has been employed to build a 4times4 switch matrix measuring 1.45 times 1.45 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in dimensions. The system presents an excellent RF performance with the worst-case insertion loss, return loss, and isolation of -1.8 dB, -17 dB and 26 dB up to 40 GHz, respectively.

A complementary metal–oxide–semiconductor (CMOS) trombone true-time delay (TTD) operating from 2 to 18 GHz is presented. The second-order all-pass network (APN) is used to construct the delay lines. The higher-order delay response of the APN allows for a better trade-off between the delay and bandwidth compared to the artificial transmission line structures. The all-pass characteristic of the APN further improves the matching performance of the TTD. In order to improve the insertion loss (IL) variations between different delay states, the source degeneration by resistor–capacitor structure is used for the switching amplifiers. Two 3-bit TTDs are fabricated in a standard 0.13 µm CMOS process, namely TTD 1 and TTD 2. TTD 1 is based on conventional switching amplifiers and TTD 2 adopts the proposed source degeneration technique. The measurement results show that the root-mean-square IL variation of TTD 1 and TTD 2 is better than 2 and 1.4 dB. The input and output return loss of the two TTDs is >12 dB. Delays of 270 and 265 ps are achieved by TTD 1 and TTD 2. The power consumption for TTD 1 is 2–6.2 mW and is 2–3.6 mW for TTD 2.

Single-mode integrated-optic directional couplers on electro-optic substrates can be used to realize photonic space-division multiplexers/switches with low cross-talk level and switching voltage. This paper describes briefly the methods which have been used by the present authors to design 2x2 and 4x4 switch matrices oir LiNbO3 substrates. A computer-aided analytical model has been developed to obtain the two-dimensional distribution of Ti-concentration and refractive index profiles for arbitrary waveguide geometry, Ti-film thickness and processing conditions. The matrix method which is a simple analytical tool for layered structures has been employed to study the wave propagation through Ti indiffused LiNb03 waveguides and directional couplers. The data for refractive index profile required as the input for running the computer program implementing the matrix method were obtained from the above computer-aided analysis. The computed results of Ti-concentration, refractive index profiles and the critical coupling length of directional couplers were validated with available experimental data. Due attention has also been paid to reduce the radiation loss from waveguide bends and to incorporate the polarization dependence in the design of directional couplers. The electrode structure and its placement on Ti:LiNb03 waveguides have been optimized for a 5V switching voltage. The effects of buffer layer and I/O fiber-to-waveguide coupling have also been considered to estimate the total loss. Necessary data generation in appropriate format for electron beam masks for Ti-waveguides and electrode patterns has been completed, and the fabrication of masks is now in progress. A simplistic design of 8x8 switch matrix has also been included.

Integrated optics switch matrices are expected to play an important role in optical space switching systems due to their ability to route information practically irrespective of its bandwidth and coding format (” code and frequency transparency”), in marked contrast to electronic switching networks. The integrated optics switches also offer the advantage of integration, as opposed to mechanical optical switches. Accordingly a number of integrated optics matrices have been reported1,2,3. However , all of these have been polarization sensitive, requiring interfacing to non-standard polarization holding fibers, and this can be considered a major factor in complicating systems applications. Ref4describes a polarization independent 1×16 switch in the tree structure employed below, however with strict fabrication tolerance on the switches. One reason for staying with polarization sensitive matrices has been the difficulty to combine integratability (reasonably low voltage -length product) with high yield for low crosstalk switch points. Here we report a matrix based on a switch point which combines these features by electronic tuning of its switching characteristics, relaxing fabrication tolerances5. The switch points are further arranged in a tree structure6,7which combines the capability for communicative as well as distributive switching with relaxed requirements on the crosstalk of each switching point. This is achieved at the expense of the number of switches: The 4×4 matrix reported in this paper (Fig 1) comprises 24 switches as opposed to the 16 switches of a crossbar structure, but the number of cascaded levels is only 4, as opposed to 7 in the crossbar case.

A scalable pulsewidth control approach with 7-bit resolution for thermal control of optical ring resonator switch matrices in 0.16- $\mu\text{m}$ Bipolar-CMOS-DMOS (BCD) with a cell size of $79\ast 105 \mu\text{m}^2$ is introduced. One Gray counter at up to 1.2-GHz clock and pulsewidth modulation generation in each matrix cell leads to an electrical power consumption of 330 mW for all electronic control circuits of an optical 1000-switch-node matrix, resulting in a reduction of 11.1% of the power needed by a constant-voltage control approach.

A maximum likelihood estimator of the zero-order switching matrix

High-speed low-drive power guided-wave optical matrix switches should perform various functions in future wideband multichannel integrated and fiber optic systems. An integrated optical switching matrix (network) was first described by Taylor(1) and a 4x4 switching network was later realized in a LiNbO3 substrate using five stepped Δβ reversal directional-coupler switches(2) by Schmidt.(3) In this paper we will report on an electrooptical channel waveguide matrix switch which utilizes total internal reflection (TIR) in a Y-cut LiNbO3 substrate. We will first present the performance characteristics of a basic channel waveguide TIR switch which is an improved version of the one we reported earlier.(4) We will then describe the design, fabrication, measurement technique, and the performance characteristics of a 3x3 and a 4x4 integrated switching matrices consisting of such basic TIR switches.

Functionally partitioned module-based programmable architecture for wireless base-band processing

The objective of this paper is to investigate novel configurations of planar multiport radio-frequency (RF) microelectromechanical systems (MEMS) C-type and R-type switches and redundancy switch matrices for satellite communications. An in-house monolithic fabrication process dedicated to electrostatic multiport RF MEMS switches and switch matrices is developed and fine tuned. The proposed C-type switch is a four-port device with two operational states. This switch exhibits an insertion loss of less than 0.3 dB and isolation of about 25 dB at satellite C-band frequency range. The novel R-type switch is also a four-port device with an additional operational state. The measured results show an insertion loss of better than 0.4 dB and an isolation of better than 25 dB at C-band. This is the first time that an R-type RF MEMS switch is ever reported. Several of these switches are integrated in the form of redundancy switch matrices, and two novel monolithic five to seven redundancy switch matrices are developed, fabricated, and tested. It is shown that the additional operating state of the R-type switch not only decreases the number of elements by 50% but also reduces the size drastically

We have developed a fully operational remotely controlled reconfigurable microwave switch matrix for applications in upcoming satellite-based multimedia communication systems. The robust and compact modular setup includes appropriate microwave oscillators, power detectors, and diode drivers. The individual modules take full advantage of the low temperature co-fired ceramics technology (LTCC). The experiment will be controlled by a field-programmable gate array (FPGA), to verify, control, and monitor the operation of the switch matrix during an on-orbit verification in a one-year-period following the expected launch in 2010. Present activities aim at a complete space qualification and the timely integration into the payload of the satellite. The switch matrix is laid out for Ka-band frequencies using a single-pole multiple-throw architecture and incorporates integrated PIN-diode switch circuits. We have achieved very promising values for input matching, insertion loss, and path isolation over the entire passband width of 5GHz, which meet realistic specifications. The electrical control of the switch matrix module is realized by the use of diode drivers, which enable a fully digital control of the path configuration.

We investigate the improvement of an insertion loss in silicon arrayed waveguide grating (AWG), by analyzing the multimode generation due to the field-mismatching effect. 8 channel silicon AWGs on a 6” SOI wafer are fabricated with an ultra-shallow etching structure and various aperture size of arrayed WGs. Our experimental results demonstrate the improved insertion loss and crosstalk characteristics. The fabricated AWG shows an insertion loss less than 1 dB with a crosstalk of -23.2 ~ -25.6 dB, exhibiting ~2.5 dB improvement of insertion loss and ~5 dB improvement of crosstalk, compared to our reported result.