(1) Technical Field
This invention generally relates to electronic circuitry, and more specifically to switching devices particularly suited for use with radio frequency (RF) field effect transistors (FETs).
(2) Background
Electronic circuitry often uses FETs as electrical switches, resistors, and/or capacitors. One such usage of FETs is in integrated circuit RF switches. An RF switch is a device to route RF signals through transmission paths, such as between an antenna and multiple transceivers in a radio system; an example of such a radio system is a cellular telephone.
In operation, if selectable port RF1 is selected to be coupled to the RFC port, then an associated series switch 1021 is closed (i.e., switched “ON”) to complete the port coupling, and an associated shunt switch 1041 coupled between the selected port and circuit ground is opened (i.e., switched “OFF”). Concurrently, the associated series switches 1022-1024 for the other selectable ports RF2-RF4 are opened and their associated shunt switches 1042-1044 are closed, thereby shunting each of the open ports to ground. The various series and shunt switches are opened or closed in similar fashion to couple any other selectable port RF2-RF4 to the RFC port. All of the switches are typically implemented as FETs on an integrated circuit (IC) die or “chip”. Not shown is the conventional control circuitry for selecting and unselecting ports.
The closed shunt switches result in improved isolation of the switch 100 by shunting the open ports RF2-RF4 to ground; such a configuration results in short reflective unselected ports. However, a short reflective port RF switch 100 of the type shown in
The present invention provides greater flexibility than the prior art by providing a switch with open reflective unselected ports at radio frequencies, and which may be alternatively configured as having either open or short reflective unselected ports. Embodiments of the present invention provide for open reflective unselected ports in an RF switch while keeping such ports protected from electrostatic discharges (ESD).
Embodiments of the invention includes an RF switch circuit which may be single or multiple pole, single or multiple-throw. Radio frequency signals can be selectively coupled between a common port and at least one selectable port. In operation, if a selectable port of the switch is selected to be coupled to the common port, then an associated series switch is closed to complete the port coupling. Concurrently, the associated series switches for the remaining selectable ports are opened. Associated switches from each of the selectable ports to ground are always open, regardless of the ON or OFF state of the series switches. In a sense, the switch as a whole is “shuntless” in normal operation as an RF switch since there is no normally active connection of the selectable ports to ground, or the switch as a whole may be considered to be “shuntable” since it is capable of conducting under breakdown conditions due to a voltage overload to deal with ESD and other overvoltage events. All of the switching elements are preferably implemented as FETs on an integrated circuit (IC) die or “chip”.
An important aspect of the architecture of the inventive switch is that the shuntable switches for both the selected and unselected ports can be configured to be open at all times (i.e., switched “OFF”). This provides an open reflective termination (high impedance) for unselected ports, which is useful in impedance or aperture tuning applications. In addition, the presence of the shuntable switches provides ESD protection for all ports.
Embodiments of the present invention further allow configurability between a traditional short reflective unselected port architecture and the new open reflective unselected port architecture. Such configurability may be accomplished during integrated circuit manufacturing by applying a suitable interconnect mask, or after manufacturing by use of field configurable switch elements such as fusible links or additional active switching components.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicate like elements.
The present invention provides greater flexibility than the prior art by providing a switch with open reflective unselected ports at radio frequencies, and which may be alternatively configured as having either open or short reflective unselected ports. Embodiments of the present invention provide for open reflective unselected ports in an RF switch while keeping such ports protected from electrostatic discharges (ESD).
Embodiments of the present invention further allow configurability between a traditional short reflective unselected port architecture and the new open reflective unselected port architecture. Such configurability may be accomplished during integrated circuit manufacturing by applying a suitable interconnect mask (e.g., a metal layer mask), or after manufacturing by use of field configurable switch elements such as fusible links or additional active switching components.
In operation, if selectable port RF1 of the switch 200 is selected to be coupled to the RFC port, then an associated series switch 2021 is closed to complete the port coupling. Concurrently, the associated series switches 2022-202N for the remaining selectable ports RF2-RFN are opened. The various series switches are opened or closed in similar fashion to couple any other selectable port RF2-RFN to the RFC port (in some applications, more than one selectable port RF1-RFN may be coupled to the RFC port). However, in contrast to the prior art shown in
An important aspect of the architecture of the switch 200 is that the switches 2041-204N for both the selected and unselected ports can be configured to be open at all times (i.e., switched “OFF”). This provides an open reflective termination (high impedance) for unselected ports, which is useful in impedance or antenna aperture tuning applications. In addition, the presence of the switches 2041-204N provides ESD protection for all ports, as explained in greater detail below.
In operation, if selectable port RF1 of the switch 210 is selected to be coupled to the RFC port, then an associated series switch 2021 is closed to complete the port coupling. Concurrently, the associated series switches 2022-202N for the remaining selectable ports RF2-RFN are opened. The various series switches are opened or closed in similar fashion to couple any other selectable port RF2-RFN to the RFC port (in some applications, more than one selectable port RF1-RFN may be coupled to the RFC port). Regardless of the ON or OFF state of the series switches 2021-202N, the shuntable switch 204C between the common port and ground is always open, thus providing similar benefits (e.g., ESD protection) to the embodiment shown in
For an open reflective configuration, a bias voltage is applied to the gates of the FETs of the shuntable switch 304 so that the FETs are in a permanent OFF state. Consequently, the unselected ports of the switch 300 maintain a high impedance at all times. The bias voltage will depend on the type of FET used in the circuit, and may be optimized for RF performance.
In addition, since a shuntable switch 304 is still electrically coupled between each port (selected and unselected) and ground, even if in an OFF state, a voltage on the associated port RFx in excess of the breakdown threshold of the switch 304 (e.g., an ESD event) will cause the switch 304 to conduct and shunt the voltage to ground. Accordingly, the inventive architecture will still protect each port from an overvoltage or ESD event.
The stack height of the shuntable switch 304 can be optimized for specific applications. If designed with more FETs in series, the shuntable switch 304 breakdown voltage threshold and RF power handling capability are higher and will contribute less harmonic content to the RF signal, while still protecting the port from an ESD event and providing an open-reflective impedance.
Also of note is that the design parameters (e.g., gate width, gate length, device type, doping levels, etc.) for the FETs in a shuntable switch 304 are more flexible than in the prior art architecture for many applications because the purpose of the shuntable switch 304 need not include isolation improvement per port (isolation improvement typically requires low resistance). In particular, the FET design parameters may be optimized for ESD protection performance.
Another benefit of the inventive architecture is that a single base IC design can be configured as either a traditional short reflective unselected port architecture or the new open reflective unselected port architecture. Such configurability may be accomplished during integrated circuit manufacturing by applying a suitable interconnect mask, such that each shuntable switch 304 is permanently biased to an OFF state, or in the alternative is coupled to conventional bias and control circuitry to behave as a traditional short reflective unselected port architecture.
Alternatively, embodiments of the invention may be configured after manufacturing by use of field configurable elements such as fusible links or by adding active switching components. For example, referring to
An additional benefit of the open reflective unselected port architecture is the improvement in harmonic performance due to lower voltage across each non-linear FET. In an RF switch 200 of the type shown in
Embodiments of the invention provide flexibility and utility not available with the prior art short reflective unselected port architecture. For example,
This application requires a “shuntless” or “shuntable” architecture so that unselected ports maintain a high impedance and are not shorted to ground, as would be the case with a traditional switch of the type shown in
This configuration may be used, for example, to select different tapping points A-D across the length of a transmission line or antenna structure. The switch 500 selectively connects tapping points to ground to change the electrical behavior of the circuit; the electrical behavior may be, for example, a resonant frequency or an impedance level. This application would not work with a traditional switch because all tapping points would be shorted to ground through the switch ports regardless of the switch state.
This configuration can be used, for example, to implement a digitally tunable reactance. This application would not work with a traditional switch because the impedances of all unselected ports would be shorted to ground in such switches. Note that the values shown in the above table will differ if two or more ports are selected to be coupled to the common port. Note also that while Zoff is assumed in the table above to be the same for each selectable port of the switch 600, that need not be the case—the Zoff value for each port can be different from other ports, and may be optimized for particular applications on a port by port basis.
In the examples shown in
The example embodiments have been shown in the context of single-pole, multiple throw switches. However, the invention is similarly applicable to multiple-pole, multiple throw switches, to multiple pole, single throw switches, and to single pole, single throw switches.
In all of the examples shown in the accompanying figures, the switching and passive elements may be implemented in any suitable IC technology, including but not limited to MOSFET and IGFET semiconductor structures and micro-electromechanical systems (MEMS). Integrated circuit embodiments may be fabricated using any suitable substrates and processes, including but not limited to standard bulk silicon, silicon-on-insulator (SOI), and silicon-on-sapphire (SOS) processes. Moreover, while the embodiments above have been described in the context of switching RF signals, the inventive architecture may be used in any application in which the permanent “OFF” state of the shuntable switch structure would be useful.
Another aspect of the invention includes a method for embodying a switch having open reflective unselected ports as an integrated circuit, including the steps of:
STEP 1: fabricating at least one series switch, each series switch being coupled to a common port and to an associated selectable port such that selection of at least one series switch electrically couples the common port to the selectable port associated with the selected series switch, and decouples the common port from all unselected selectable ports;
STEP 2: fabricating, for each series switch, an associated shuntable switch, each shuntable switch being coupled between ground and the selectable port associated with such associated series switch; and
STEP 3: configuring each shuntable switch to be electrically non-conductive at all times to signals below a breakdown voltage threshold of such shuntable switch and electrically conductive to signals above such breakdown voltage threshold.
Another aspect of the invention includes a method for embodying a switch having open reflective unselected ports as an integrated circuit, including the steps of:
STEP 1: fabricating at least one series switch, each series switch being coupled to a common port and to an associated selectable port such that selection of at least one series switch electrically couples the common port to the selectable port associated with the selected series switch, and decouples the common port from all unselected selectable ports; and
STEP 2: fabricating a shuntable switch coupled between ground and the common port, wherein such shuntable switch is configured to be electrically non-conductive at all times to signals below a breakdown voltage threshold of such shuntable switch and electrically conductive to signals above such breakdown voltage threshold.
A number of embodiments of the invention have been described. It is to be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, some of the steps described above may be order independent, and thus can be performed in an order different from that described. It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the following claims, and that other embodiments are within the scope of the claims.
This application claims the benefit of priority from U.S. Provisional Patent Application No. 61/887,224, filed Oct. 4, 2013, entitled “Optimized RF Switching Device Architecture for Impedance Control Applications”, the entire disclosure of which is hereby incorporated by reference.
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Number | Date | Country | |
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61887224 | Oct 2013 | US |