Patent Application
20120286846
Various aspects of the present invention are directed to switches, and more particularly to switching circuits including mechanically-actuated switches.
Electronic devices, and in particular mobile electronic devices, have grown dramatically in functionality and needs with respect to power and data connectivity, while the demand for such devices and high data rates and bandwidth therewith continues to rise. In particular, the data rate of standards for the transmission of digital signals has been continually increasing. For instance, recent versions of the PCI Express bus (e.g., 3.0) require a transmission rate of 8 Gb/s. The USB 3.0 standard supports 5 Gb/s. Such standards are pushing towards (and beyond) 10 Gb/s, and are expected to continue to increase.
While the demands upon communication speed have been increasing, circuits used to terminate and switch communication lines have experienced difficulties in meeting bandwidth, loss and other characteristics pertaining to these communications. Most broad frequency bandwidth switches, such as transistor-based switches, behave as a resistor when closed, and as a capacitor when open. Low resistance and capacitance can be desirable, but can be limited due to the voltage levels of signals that are passed via the transistor-based switches. It has been challenging to reduce both closed/on resistance and open/off capacitance while achieving desirable voltage signal values. For example, increasing the area of a transistor can reduce its resistance, but increase its capacitance such that the product of resistance and capacitance remains roughly constant. Other approaches to reducing this resistance-capacitance product can adversely affect achievable signal voltage. Further, many approaches are susceptible to non-linear behavior.
In addition, many mobile devices require separate connectors for high data rate signals (e.g., for communications), and for high-current signals (e.g., for power). Certain devices combine both high data rate and high-current connectors in one, often employ rather large connectors to suit this need. Space requirements and design constraints associated with such larger connectors can be undesirable. Other approaches, such as those involving the separation of data and power types of signals using LCR filtering can be subject to undesirable resonances and distortion.
Accordingly, providing connectivity for devices in a variety of applications, and particularly for high-bandwidth and power applications, continues to be challenging.
Various example embodiments are directed to MEMS switching circuits for a variety of applications and addressing various challenges, including those discussed above.
In connection with an example embodiment, a switching circuit for an electronic device includes a communication port, a plurality of MEMS switch circuits and a sensing control circuit. Each of the plurality of MEMS switch circuits is respectively configured to electrically couple the communication port to one or more of different circuits in the electronic device. At least one MEMS switch circuit couples power between the communication port and an internal circuit in the electronic device, and at least one MEMS switch circuit couples data between the communication port and an internal circuit in the electronic device. In various embodiments, one of the MEMS switch circuits couples both power and data between the communication port and an internal circuit. The sensing control circuit configured to sense a type of connection at the communication port and, based upon the sensed type of connection, actuate at least one of the MEMS switch circuits between an open position in which the communication port is not electrically coupled via the at least one of the MEMS switch circuits, and a closed position in which the communication port is electrically coupled via the at least one of the MEMS switch circuits to at least one of the internal circuits.
Another example embodiment is directed to a method for switching a connection between a communication port and a plurality of different circuits in an electronic device, in which the different circuits include circuits using power and/or data. A type of connection is sensed at the communication port and, based upon the sensed type of connection, at least one of a plurality of MEMS switch circuits is actuated between an open position in which the communication port is not electrically coupled via the at least one of the MEMS switch circuits, and a closed position in which the communication port is electrically coupled via the at least one of the MEMS switch circuits to at least one of the power and data circuits.
Another example embodiment is directed to a switching circuit for an electronic device, the switching circuit including a communication port and a dynamic switch circuit. The dynamic switch circuit includes a plurality of switches respectively configured to selectively electrically couple the communication port to different circuits in the electronic device responsive to a type of connection detected at the communication port. Each of the switches operates at an on resistance Ron and off capacitance Coff having a product Ron* Coff<300 fs. At least one of the switches is configured to couple power between the communication port and an internal circuit in the electronic device, and at least one of the switches is configured to couple data between the communication port and an internal circuit in the electronic device.
The above discussion is not intended to describe each embodiment or every implementation of the present disclosure. The figures and following description also exemplify various embodiments.
Various example embodiments may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention including aspects defined in the claims. Furthermore, the term “example” as used throughout this document is by way of illustration, and not limitation.
The present invention is believed to be applicable to a variety of different types of circuits, devices and arrangements involving switches or switching components, including MEMS-based switching circuits that switch different types of signals on a common communications line. While the present invention is not necessarily limited in this context, various aspects of the invention may be appreciated through a discussion of related examples.
In accordance with various example embodiments, a microelectromechanical systems (MEMS)-based switching circuit includes a plurality of MEMS switches that operate to couple different types of signals passed through a common interface. The switching circuit passes high-speed signals, such as those associated with high radio frequency (RF) signals and high-speed serial data streams, to data circuits appropriate for the signals. The switching circuit also passes low frequency (LF), high current signals in the same signal path. In many embodiments, such as for audio communications (e.g., a speaker), or data communications having power associated therewith, power and data are passed via the same switch.
In various implementations, the MEMS switches are configured to operate with an RC value, corresponding to the product of resistance and capacitance values respectively in the on and off states, that is several orders of magnitude lower that such products with various transistor-based circuits. Accordingly, ohmic-type MEMS switches can be implemented using this approach, to achieve low on resistances and low off capacitances. This approach facilitates the use of a relatively large contact area in the MEMS switches to handle relatively large current while maintaining desirable RF (high frequency) characteristics. For general information regarding membranes and MEMS switches, and for specific information regarding MEMS switches that may be implemented in connection with one or more example embodiments herein, reference may be made to Wunnicke et al., “Small, low-ohmic RF MEMS switches with thin-film package,” Proc. IEEE MEMS 2011, Jan. 23-27 2011, page 793 (2011), which is fully incorporated herein by reference.
In accordance with another example embodiment, a switching circuit includes MEMS switches for coupling different types of connectors to circuitry in an electronic device. A communication port (e.g., an input/output port) communicates (receives and/or sends) different types of inputs and outputs, including power and data and combinations of power and data. Both AC and DC may be passed using these approaches, to pass (communicate) power between the communication port and an internal circuit. In addition, the switch may pass information in a bidirectional manner, such as for data communications.
For each of the different types of inputs/outputs to be served by the switching circuit, a MEMS switch couples the communication port to a circuit in the mobile device. Accordingly, at least one MEMS switch couples power to a power circuit in the mobile device, and at least another MEMS switch couples data to a data circuit in the mobile device. A sensing control circuit senses a type of connection made to the communication port and then, based upon the sensed type of connection, actuates at least one of the MEMS switches to move between open and closed positions for coupling the communication port with at least one of the power and data circuits in the device.
In some implementations, each MEMS switch includes a substrate having a substrate contact electrode and a bias circuit, and a suspended membrane including a membrane contact electrode and another bias circuit. The membrane being moves between an open position and a closed position for respectively engaging and disengaging the contact electrodes to pass and block signals between the communication port and the circuit in the mobile device to which the MEMS switch is connected.
In some embodiments, the MEMS switches are actuated via a voltage bias applied by a controller to selectively control the state (open/closed) of each MEMS switch. This voltage bias can be applied, for example, to effect an electrostatic or piezoelectric bias to move a membrane having an electrode (or electrodes) therein, to bring the electrode in contact with another electrode and/or to move break contact of the electrodes.
The MEMS-based switches are implemented using one or more of a variety of components, generally involving an ohmic or metal-contact material to achieve wide bandwidth. In various contexts, the switches are configured to achieve a resistance in the on/closed state that is less than 3 Ohms, and an insertion loss of less than about 2 dB. In the off/open state, the switches are configured to achieve an isolation between electrodes of at least 25 dB. These characteristics can be achieved for signals in a frequency range from 0 Hz to above 10 GHz. This approach may be implemented to facilitate connection to cables carrying high data rate digital signals, such as for PCI Express, DisplayPort, HDMI, eSATA, or USB 3.0. Such a data rate may include, for example, a rate higher than 2 Gb/s, higher than 5 Gb/s, or higher than 10 Gb/s. In some implementations, each channel is designed to operate as a 50 Ohm transmission line between the frequencies 100 kHz and 10 GHz when a corresponding MEMS switch is closed. In accordance with these implementations, it has been discovered that the implementation of MEMS-based switches with membranes as discussed herein (e.g., at exhibited distances of separation), can be used to achieve such data rates, signal loss and other transmission characteristics as described above.
A variety of different types of inputs can be switched using MEMS-based switching circuits as discussed herein. For example, both single-ended and differential signals can be passed, with single-ended signals carrying a signal voltage on one line and holds the other line at ground, and with differential signals using pairs of switches to pass signals of opposite polarity. The switches may pass digital binary signals composed of arbitrary sequences of two voltage levels (e.g., 3V=1 and 0 V=0), direct current (DC) signals, radio frequency (RF) signals, and bi-directional signals as well. Analog input/output signals, RF signals, digital signals and modulated digital signals can all be passed using these approaches. In connection with various embodiments, MEMS-based switches having a resistance that depends very little on the amplitude or sign of the signal voltage are used to achieve desirable linearity, maintain the shape of the electrical waveform, permit negative voltages to pass through the switch and simplify differential signal circuit designs.
In some implementations, a shared electrical conductor connects a communication port and a plurality of MEMS switch circuits as discussed herein. The MEMS switch circuits respectively couple the communication port to different circuits in the electronic device using the shared electrical conductor to provide connections between the communication port and MEMS switch circuits for electrically coupling both power and data between the communication port and the MEMS switch circuit.
Turning now to the Figures,
The switching arrangement 100 includes MEMS switches 110, with five switches shown and controlled by a connection-type sensor/controller 120 that senses a type of connection made at a communication port 130 (e.g., an I/O port). The type of connection may be sensed, for example, by detecting a type of data passed via the communication port 130, detecting a frequency (e.g., with low frequency signals corresponding to power, and higher frequency signals corresponding to data), detecting a voltage level, detecting signals characteristic of an input type, detecting a power source (e.g., based on an amount of current that can be drawn from the source to which I/O port is connected), using information in a data stream identifying a type of source, or in other manners. A dedicated line in the communication port 130 can also be used to communicate a signal type, or a shape of a connector and/or a mechanical switch coupled at the communication port can be used to detect a signal type.
By way of example, the five switches are shown for coupling the communication port 130 to HDMI, USB, battery charger (power), audio and auxiliary (aux.) circuits 140. All signals (as also applicable to power connections) see the sum of the off-capacitance of all switches. The sensor/controller 120 applies a voltage to an appropriate switch or combination of switches to make a connection between the communication port 130 and one of the circuits 140. Further, while one switch is represented for each of the circuits 140 in
In some embodiments, MEMS switches 110 are configured to switch audio signals while injecting little or no charge into the audio signal path. The switches 110 are thus configured to mitigate or eliminate capacitance charging or discharging, which can cause audible clicks. Accordingly, audible clicks are mitigated or otherwise not generated during the actuation of the switch (e.g., while changing the input source of an audio amplifier).
The sensor/controller 120 can be implemented using one or more of a variety of different types of sensors, to suit various embodiments. In one embodiment, sensor/controller 120 includes a MEMS switch that connects the sensor/controller to the communication port 130 for detecting an input type thereat, and disconnects the sensor/controller from the communication port thereafter. This approach can be used, for example, to ensure that the sensor/controller 120 does not add capacitance to the communication port after a proper connection is made via the MEMS switches 110.
In a particular embodiment, the communication port 130 is connected to a multipurpose antenna that receives different types of signals including signals providing at least one of data and power. The sensor/controller 120 detects a type of signal received via the multipurpose antenna and controls the MEMS switches 110 to electrically couple the multipurpose antenna to different internal circuits based upon the detected type of signal received via the multipurpose antenna.
By way of example (and similar to
Other embodiments involve the use of additional MEMS switches, which can be used to connect switches, and to form a multiplexed connection with the communication port 230. For example, a M to N multiplexer can be implemented using M parallel (1 to N) multiplexers. Multiplexers can also be cascaded to provide a few low capacitance inputs, and communication standards with lower data rates (e.g., USB 1, RS 232) can be multiplexed with conventional transistors (or also MEMS switches) after the first MEMS switch.
The switching arrangement 200 also includes a MEMS connector switch 224 that is configured to selectively connect the sensor/controller 220 with the communication port 230 for detecting a type of input thereat. Once an input type is detected, the MEMS connector switch 224 disconnects the sensor/controller 220 from the communication port 230.
In some embodiments, the switching arrangement 200 includes an electrostatic discharge (ESD) protection circuit 222, which shunts ESD pulses to ground to protect the sensor/controller 220 or the MEMS switches 210. In certain implementations, the switching arrangement 200 is configured to maintain the MEMS switches 210 in an open position to electrically isolate the MEMS switches 210 from the communication port 230 until a signal is present, thus decoupling ESD pulses, such as may occur during connection/disconnection of the communication port 230, from the circuits 240.
In certain embodiments, the switching arrangement 200 also includes a connection detector circuit 226 that detects a connection condition of the communication port 230, such as by detecting the connection or disconnection of a cable to the communication port. The detection may, for example, involve a physical detection (e.g., depression or release of a switch via the connection of a cable), an electrical detection at the communication port, or both. The connection detector circuit 226 provides an output to the sensor/controller 220, which operates the connector switch 224 based upon the received output. For example, the connector switch 224 can be closed upon the detection of a connector being coupled to the communication port 230, or in response to detecting the disconnection of a connector from the communication port 230 (such that the sensor/controller 220 is coupled and ready for detecting a new connection to the communication port).
In some implementations, one or both of the sensor/controller 220 and the connection detector 226 operate to monitor the communication port 230 to detect the connection of an external connector thereto. In response to detecting the connection of an external connector to the communication port 230, the connector switch 224 is closed to electrically couple the sensor/controller 220 to the communication port to detect an input type at the communication port. After the input type has been detected, the connector switch 224 is opened to electrically decouple the sensor/controller 220 from the communication port 230 (e.g., by opening a MEMS switch to electrically insulate/isolate internal circuits from the communication port).
In various embodiments, the MEMS switches as shown in
In some implementations, the type of the input connector is detected by successively connecting controllers (e.g., as attached to 140, 240, 350 in
Based on the indicated input type, the switch controller 332 applies a voltage to actuate one or more MEMS switches in the MEMS switching circuit 320, to electrically couple the I/O port 310 with an internal circuit appropriate for the detected signal type. For example, when the detected input type is a power input, an appropriate MEMS switch is actuated to couple the I/O port 310 to a power circuit 340, such as for charging a battery 342. In certain implementations, the power circuit 340 is omitted and the MEMS switching circuit 320 is coupled directly to the battery 342 (e.g., to terminals to which a battery is connected, such as in a mobile electronic device). When the detected input type is a data input, an appropriate MEMS switch is actuated to couple the I/O port 310 to a data circuit 350 (e.g., to a video circuit for receiving and/or sending video data via an HDMI type of communication link).
In other embodiments, the switch controller (332) is connected to the internal circuits (340, 350) via another communication link (shown dashed), for detecting or otherwise responding to characteristics at these internal circuits for controlling the MEMS switching circuit 320. For example, in response to detecting that the battery 342 has been fully charged, via the power circuit 340, the switch controller 332 can actuate one or more MEMS switches in the MEMS switching circuit 320 for disconnecting the power circuit 340 from power supplied via the I/O port 310.
The switching arrangement 400 also includes a controller 412, which may be implemented in a manner similar to that of controllers 120 and 220 in
The size of the switch 405 can be set to suit particular applications and communication needs. For example, the membrane 410 can be implemented at a diameter of between about 25 μm and 90 μm, or larger or smaller to suit applications. The switch 405 can be implemented on a variety of different types of substrates, and using a variety of different types of materials. For example, silicon, glass, ceramic, alumina, sapphire, GaAs, GaN, SiC, ceramics such as LTCC and HTCC, and other substrates can be used alone or in combination to suit particular applications. Various embodiments directed to semiconductors substrates may be implemented with one or more components in the substrate. In various implementations, the switch 405 is located on an area of a semiconductor substrate that is at least 100 μm2 and less than 10000 μm2. The membrane 410 is also arranged relative to the substrate to suit applications, and in some implementations, is arranged such that a gap size between the electrodes 420 and 422 is about 300 nm. In other implementations, the membrane 410 is arranged to position the contact 426 and underlying contact for the electrodes 420 and 422 at a distance of at least 100 nm and less than 200 nm, to achieve desirable on/off circuit characteristics in connection with a limited switch size.
Based upon the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein. For example, a variety of different combinations of MEMS-based switches can be made, to suit various connectivity needs for particular applications. In addition, the MEMS-based switches as shown and/or described may be implemented with different types of switches, such as with a GaN switch, a pHEMT (pseudomorphic high electron mobility transistor) switch, or another switch that operates at an on resistance Ron and off capacitance Coff having a product Ron* Coff<300 fs. Such modifications do not depart from the true spirit and scope of the present invention, including that set forth in the following claims.
