Radio frequency switch

This application is related to U.S. patent application Ser. No. 15/494,605, filed Apr. 24, 2017, now U.S. Pat. No. 10,181,478, titled ELECTRONIC COMPONENT HAVING FIELD EFFECT TRANSISTOR CELLS, which claims priority to U.S. provisional application Ser. No. 62/443,047, filed Jan. 6, 2017, the disclosures of which are hereby incorporated herein by reference in their entireties.

Embodiments of the present disclosure relate to radio frequency switching circuitry.

An important electronic component of a radio frequency (RF) transceiver is a field-effect transistor (FET) that makes up stacked FET-type RF switches. An RF switch that is FET based typically needs linearity compensation to prevent generation of harmonic distortion when transmit signals are applied to the RF switch while the RF switch is in an off-state. The RF switch is effectively open while in the off-state, and the transmit signals are prevented from passing through the RF switch. However, while the RF switch is open, undesirable harmonics are generated from the transmit signals in part due to non-linear capacitance inherent to the RF switch. The undesirable harmonics pass from the RF switch and interfere with the RF transceiver's receiver circuitry.

A traditional off-state linearization network is placed in parallel with the RF switch to reduce the undesirable harmonics. While the traditional off-state linearization network does reduce the harmonic distortion when transmit signals are applied to the RF switch in the off-state, the traditional off-state linearization network takes up valuable circuit real estate because it requires external bias circuitry. What is needed to regain valuable real estate are off-state linearization networks that do not require external bias circuitry.

A radio frequency switch having a first node, a second node, and a plurality of switch cells that are coupled in series between the first node and the second node is disclosed. Each of the plurality of switch cells includes a field-effect transistor having a drain terminal, a source terminal, a field-effect transistor gate terminal, and a body terminal and an off-state linearization network. The off-state linearization network includes varactors coupled to the drain terminal and the source terminal of the field-effect transistor.

Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

FIG. 1 is a schematic depicting an embodiment of an inversion-mode varactor version of a radio frequency (RF) switch cell structured in accordance with the present disclosure.

FIG. 2 is a schematic depicting another embodiment of the RF switch cell that includes a body resistor that provides increased linearization at some power levels.

FIG. 3 is a schematic depicting an accumulation-mode varactor version of an RF switch cell.

FIG. 4 is an embodiment of a hybrid RF switch cell that combines the inversion-mode varactor-based linearization network ( FIGS. 1 and 2 ) with the accumulation-mode varactor-based linearization network ( FIG. 3 ) to yield a hybrid linearization network.

FIG. 5 is an embodiment of a hybrid RF switch cell that includes the hybrid linearization network of FIG. 4 and the body resistor.

FIG. 6 is a schematic of an inversion-mode varactor version of an RF switch made up of a plurality of the RF switch cells depicted in FIG. 1 .

FIG. 7 is a schematic of an inversion-mode varactor version of an RF switch made up of a plurality of the RF switch cells depicted in FIG. 2 .

FIG. 8 is a schematic of an accumulation-mode varactor version of an RF switch made up of a plurality of the RF switch cells depicted in FIG. 3 .

FIG. 9 is a schematic of a hybrid version of an RF switch made up of a plurality of the RF switch cells depicted in FIG. 4 .

FIG. 10 is a schematic of a hybrid version of an RF switch made up of a plurality of the RF switch cells depicted in FIG. 5 .

FIG. 11 is a graph of peak harmonic distortion versus signal amplitude comparing an RF switch having no off-state linearization with an RF switch having accumulation-mode varactor off-state linearization and an RF switch having inversion-mode varactor off-state linearization.

FIG. 12 is a graph of peak harmonic distortion versus signal amplitude comparing off-state linearization performance of different sizes of inversion-mode varactors.

FIG. 13 is a graph of peak harmonic distortion versus signal amplitude comparing off-state linearization performance of having no off-state linearization, inversion-varactors that share a body diffusion, and inversion varactors coupled to the body terminal through an isolation resistance.

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The present disclosure includes embodiments of a radio frequency switch that uses either accumulation-mode varactors or inversion-mode varactors or combinations of both to reduce undesired harmonics generated by the radio frequency switch when a radio frequency signal is applied across the radio frequency switch in an off-state. Exemplary embodiments of the accumulation-mode varactors and inversion-mode varactors are fabricated with negative metal oxide semiconductor (NMOS) structures. A structural difference between an NMOS-type accumulation-mode varactor and an NMOS-type inversion-mode varactor is an N-well in the channel between the source and the drain of the NMOS-type accumulation-mode varactor. NMOS-type inversion-mode varactors do not have the N-well and in some exemplary embodiments can be fabricated to share body diffusions of field-effect transistors making up the RF switch. Behaviorally, a total capacitance of an accumulation-mode varactor generally transitions from a smaller value to a larger value as tuning voltage is transitioned from a more positive voltage region to a more negative voltage region. In contrast, the total capacitance of an inversion-mode varactor generally transitions from a larger value to a smaller value as tuning voltage is transitioned from the more positive voltage region to the more negative voltage region.

FIG. 1 is a schematic depicting a first embodiment of a radio frequency (RF) switch cell 10 structured in accordance with the present disclosure. The RF switch cell 10 includes a field-effect transistor (FET) 12 having a drain terminal D 1 , a source terminal S 1 , a FET gate terminal GF 1 , and a body terminal B 1 . The RF switch cell 10 further includes an off-state linearization network 14 that reduces undesirable harmonics that are generated from RF signals applied across the RF switch cell 10 when the FET 12 is in an off-state that blocks the RF signals from passing between the drain terminal D 1 and the source terminal S 1 . The undesirable harmonics are generated in part due to parasitic non-linear capacitances inherent in the RF switch cell 10 . The parasitic non-linear capacitances are attributable at least in part to drain-body and source-body diodes (not shown) of the FET 12 .

In FIG. 1 , the parasitic non-linear capacitances are symbolically represented in dashed line as a drain-to-body capacitor C DB and a source-to-body capacitor C SB . The off-state linearization network 14 includes a first inversion-mode varactor 16 to counter undesirable harmonics due to the drain-to-body capacitor C DB . The first inversion-mode varactor 16 has a first varactor gate terminal GI 1 coupled to the drain terminal D 1 and a first tuning terminal TI 1 coupled to the body terminal B 1 . A second inversion-mode varactor 18 is included to counter undesirable harmonics due to the source-to-body capacitor C SB . The second inversion-mode varactor 18 has a second varactor gate terminal GI 2 coupled to the source terminal S 1 and a second tuning terminal TI 2 coupled to the body terminal B 1 .

The letter “I” in the varactor symbols representing the first inversion-mode varactor 16 and the second inversion-mode varactor 18 signifies inversion-mode operation that allows the first inversion-mode varactor 16 and the second inversion-mode varactor 18 to be tuned without need of an external bias network. Instead, the first inversion-mode varactor 16 and the second inversion-mode varactor 18 are tuned by gate voltage VG that places the FET 12 in the off-state. The gate voltage VG is applied to the gate of the FET 12 at a first control terminal SC 1 . A gate resistor RG 1 may be coupled between the first control terminal SC 1 and the FET gate terminal GF 1 .

The gate voltage VG is applied to the body terminal B 1 , the first tuning terminal TI 1 , and the second tuning terminal TI 2 through a gate-body switch SW 1 that is coupled between FET gate terminal GF 1 and the body terminal B 1 . A second control terminal SC 2 for control of the gate-body switch SW 1 is coupled to the first control terminal SC 1 . The gate-body switch SW 1 is configured to close when the gate voltage VG is at a level that maintains the FET 12 in the off-state and open when the gate voltage VG is at a level that maintains the FET 12 in an on-state that passes RF signals between the drain terminal D 1 and the source terminal S 1 . An exemplary voltage level for VG to maintain the FET 12 in the off-state is −2.5 V. The FET 12 of FIG. 1 is depicted in the off-state. As such, the gate voltage VG is shown as being negative with respect to ground, and the gate-body switch SW 1 is depicted in its closed state to apply the gate voltage VG at a negative level to the body terminal B 1 , the first tuning terminal TI 1 , and the second tuning terminal TI 2 . Therefore, FIG. 1 depicts an instant configuration for the RF switch cell 10 in which the first inversion-mode varactor 16 counters undesirable harmonics due to the drain-to-body capacitor C DB and the second inversion-mode varactor 18 counters undesirable harmonics due to the source-to-body capacitor C SB . In the exemplary embodiment of FIG. 1 , the first inversion-mode varactor 16 and the second inversion-mode varactor 18 are fabricated such that they share a body diffusion 20 with the FET 12 . The body diffusion 20 is represented symbolically with a dashed rectangle with rounded edges.

FIG. 2 is a schematic depicting a second embodiment of an RF switch cell 22 that includes a body resistor RB 1 coupled between the body terminal B 1 and the first tuning terminal TI 1 and the second tuning terminal TI 2 . The body resistor RB 1 provides an isolation resistance and increased linearization. As shown in FIG. 2 , the body resistor RB 1 can share the body diffusion 20 .

FIG. 3 is a schematic of an RF switch cell 24 that includes an off-state linearization network 26 that in accordance with the present disclosure is structured differently than the off-state linearization network 14 of FIGS. 1 and 2 . In this case, the off-state linearization network 26 includes a first accumulation-mode varactor 28 and a second accumulation-mode varactor 30 that are arranged in an anti-parallel configuration. The letter “A” in the varactor symbols representing the first accumulation-mode varactor 28 and the second accumulation-mode varactor 30 signifies accumulation-mode operation.

In greater detail, the first accumulation-mode varactor 28 has a first varactor gate terminal GA 1 coupled to the drain terminal D 1 and a first tuning terminal TA 1 coupled to the source terminal S 1 . The second accumulation-mode varactor 30 has a second varactor gate terminal GA 2 coupled to the source terminal S 1 and a second tuning terminal TA 2 coupled to the drain terminal D 1 . Similar to the operation of the embodiments of FIG. 1 and FIG. 2 , the gate-body switch SW 1 is configured to automatically open when the FET 12 transitions to an on-state that passes an RF signal between the drain terminal D 1 and the source terminal S 1 and is further configured to automatically close when the FET 12 transitions to an off-state that blocks passage of the RF signal between the drain terminal D 1 and the source terminal S 1 .

The first accumulation-mode varactor 28 and the second accumulation-mode varactor 30 are each a tenth of the size of traditional accumulation-mode varactors used to linearize RF switches in the off-state. As such, no figure of merit for an RF switch constructed of a plurality of RF switch cells 24 is negatively affected. For comparison, a traditional off-state linearization network causes an 8% to 10% degradation in figure of merit. An exemplary size for first accumulation-mode varactor 28 and the second accumulation-mode varactor 30 is 2 microns square.

FIG. 4 is an embodiment of an RF switch cell 32 that combines the inversion-mode varactor-based version of the off-state linearization network 14 ( FIGS. 1 and 2 ) with the accumulation-mode varactor-based version of the off-state linearization network 26 ( FIG. 3 ) to yield a hybrid linearization network 34 . In this exemplary embodiment, the first inversion-mode varactor 16 and the second inversion-mode varactor 18 are fabricated such that they share the body diffusion 20 with the FET 12 , whereas the first accumulation-mode varactor 28 and the second accumulation-mode varactor 30 do not share the body diffusion 20 .

FIG. 5 is an embodiment of an RF switch cell 36 that includes the hybrid linearization network 34 along with the body resistor RB 1 . In this exemplary embodiment, the body resistor RB 1 shares the body diffusion 20 with the FET 12 and the first inversion-mode varactor 16 and the second inversion-mode varactor 18 . The body resistor RB 1 provides an isolation resistance and increased linearization. An exemplary resistance value for the body resistor RB 1 is 10,000Ω.

FIG. 6 is a schematic of an inversion-mode varactor version of an RF switch 38 having a first node RF 1 , a second node RF 2 , and a plurality of the RF switch cells 10 depicted in FIG. 1 . The RF switch cells 10 are coupled in series from the source terminal S 1 to the drain terminal D 1 between the first node RF 1 and the second node RF 2 . A gate control terminal receives the gate voltage VG ( FIGS. 1-5 ) to transition and/or maintain the RF switch 38 between the on-state and the off-state.

FIG. 7 is a schematic of an inversion-mode varactor version of an RF switch 40 made up of a plurality of the RF switch cells 22 depicted in FIG. 2 . The RF switch cells 22 are coupled in series from the source terminal S 1 to the drain terminal D 1 between the first node RF 1 and the second node RF 2 . A difference between the RF switch 38 and the RF switch 40 is the body resistor RB 1 that is included with each of the RF switch cells 22 .

FIG. 8 is a schematic of an accumulation-mode varactor version of an RF switch 42 made up of a plurality of the RF switch cells 24 depicted in FIG. 3 . The RF switch cells 24 are coupled in series from the source terminal S 1 to the drain terminal D 1 between the first node RF 1 and the second node RF 2 .

FIG. 9 is a schematic of a hybrid version of an RF switch 44 made up of a plurality of the RF switch cells 32 depicted in FIG. 4 . In this exemplary embodiment, the RF switch cells 32 combine attributes of inversion-mode varactor operation and accumulation-mode varactor operation for increased linearization of the RF switch 44 over the previous embodiments for particular RF signal amplitude ranges. The RF switch cells 32 are coupled in series from the source terminal S 1 to the drain terminal D 1 between the first node RF 1 and the second node RF 2 .

FIG. 10 is a schematic of a hybrid version of an RF switch 46 made up of a plurality of the RF switch cells 36 depicted in FIG. 5 . A difference between the RF switch 46 and the RF switch 38 is the body resistor RB 1 that is included with each of the RF switch cells 36 .

FIG. 11 is a graph of peak harmonic distortion versus signal amplitude comparing an RF switch having no off-state linearization with an RF switch having accumulation-mode varactor off-state linearization and an RF switch having inversion-mode varactor off-state linearization. Performance of the RF switch 42 ( FIG. 8 ) having accumulation-mode off-state linearization only is plotted in dashed line. The accumulation-mode off-state linearization of the RF switch 42 is superior over a traditional RF switch with no off-state linearization with the exception of a higher voltage region after a notch at which maximum linearization occurs.

Performance of the RF switch 44 ( FIG. 9 ) having inversion-mode off-state linearization only is plotted in dot-dash line. The inversion-mode off-state linearization of the RF switch 44 is superior over a traditional RF switch with no off-state linearization over a larger signal voltage range than that of the RF switch 42 . Even after a notch at which maximum linearization occurs, the inversion-mode off-state linearization of the RF switch 44 is superior over a traditional RF switch. However, it is to be understood that the performance depicted in FIG. 11 is exemplary and that greater linearization performance is envisioned for RF switches having different dimensions and fabrication processes. In this regard, FIG. 12 is a graph of peak harmonic distortion versus signal amplitude comparing off-state linearization performance of different sizes of inversion-mode varactors.

FIG. 13 is a graph of peak harmonic distortion versus signal amplitude comparing off-state linearization performance of having no off-state linearization, inversion-varactors that share a body diffusion, and tuning terminals of varactors are coupled to a body terminal through an isolation resistance. In particular, the graph of FIG. 13 illustrates enhanced linearization of the RF switch cell 10 of FIG. 1 and even greater linearization provided by the RF switch cell 22 of FIG. 2 . The isolation of 10 kΩ is provided by the body resistor RB 1 ( FIG. 2 ), which can be a well-type resistor.

Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.