# Patent

## Title
Variable impedance single pole double throw CMOS switch

## Abstract

A single pole double throw (SPDT) semiconductor switch includes a series connection of a first transmitter-side transistor and a first reception-side transistor between a transmitter node and a reception node. Each of the two first transistors is provided with a gate-side variable impedance circuit, which provides a variable impedance connection between a complementary pair of gate control signals. Further, the body of each first transistor can be connected to a body bias control signal through a body-side variable impedance circuit. In addition, the transmitter node is connected to electrical ground through a second transmitter-side transistor, and the reception node is connected to electrical ground through a second reception-side transistor. Each of the second transistors can have a body bias that is tied to the body bias control signals for the first transistors so that switched-off transistors provide enhanced electrical isolation.

## Background
BACKGROUND
The present disclosure generally relates to a semiconductor switch, and particularly to a semiconductor switch circuit including a variable impedance single pole double throw (SPDT) switch.
A complementary metal oxide semiconductor (CMOS) switch can be employed to connect a semiconductor circuit to an antenna. The antenna can be employed to broadcast a signal that the semiconductor circuit generates, or can be employed to receive a signal to be relayed to the semiconductor circuit. Depending on whether the antenna broadcasts a signal or receives a signal, different signal paths are required between the antenna and the semiconductor circuit.
A single pole double throw (SPDT) switch is typically employed between the semiconductor circuit and the two signal paths to the antenna. A first path can include a series connection of a drive amplifier and a high power amplifier. To broadcast a signal, a signal generated by a section of the semiconductor circuit configured to encode the signal passes through the drive amplifier, the high power amplifier, and the SPDT switch, and subsequently reaches the antenna, which broadcasts the signal. The node between the SPDT switch and the high power amplifier is typically referred to as a transmitter node TX. A second path can include a series connection of a limiter and a low noise amplifier. To receive a signal, a signal captured by the antenna passes the SPDT switch, and then through the limiter and the low noise amplifier, arriving at a section the semiconductor circuit configured to decode the signal. The node between the SPDT switch and the limiter is typically referred to as a reception node RX.
Referring to FIG. 1, a prior art single pole double throw (SPDT) switch configured for use with an antenna includes a serial connection of a first transmission-side transistor MT1 and a reception-side transistor MR1 between a transmission node TX and a reception node RX. An antenna is connected to a node between the drains of the first transmission-side transistor MT1 and the reception-side transistor MR1. The gate and body of the first transmission-side transistor MT1 have fixed impedances, i.e., the resistance of a gate-side resistor Rg and the resistance of the body-side resistor Rw. Likewise, the gate and body of the first reception-side transistor MR1 have fixed impedances as well.
Typically, a second transmission-side transistor MT2 is provided between the transmission node TX and electrical ground. The body of the second transmission-side transistor MT2 is grounded through a body-side resistor Rw. Likewise, a second reception-side transistor MR2 is provided between the reception node RX and electrical ground. The body of the second reception-side transistor MR2 is grounded through a body-side resistor Rw.
The first transmission-side transistor MT1 and the first reception-side transistor MR1 operate complementarily, i.e., one is on and the other is off during normal operation. Likewise, the second transmission-side transistor MT2 and the second reception-side transistor MR2 operate complementarily. During a transmission mode, the first transmission-side transistor MT1 and the second reception-side transistor MR2 are turned on, and the first reception-side transistor MR1 and the second transmission-side transistor MT2 are turned off. A signal path from the transmission node TX to the antenna is connected during the transmission mode, while the first reception-side transistor MR1 provides electrical isolation between the antenna and the reception node RX. During a reception mode, the first transmission-side transistor MT1 and the second reception-side transistor MR2 are turned off, and the first reception-side transistor MR1 and the second transmission-side transistor MT2 are turned on. A signal path from the reception node RX to the antenna is connected during the reception mode, while the first transmission-side transistor MT1 provides electrical isolation between the antenna and the transmission node TX.
The SPDT switch needs to transmit a signal through one path, while decoupling the signal in the other path in order to provide a high fidelity signal, i.e., a signal with a high signal-to-noise ratio. In order to broadcast a signal with high fidelity, an SPDT switch needs to minimize signal loss connecting to the transmitter node TX to pass signal to the antenna, while suppressing and electrically isolating the reception node RX. In order to preserve the fidelity of the signal received from the antenna, an SPDT switch needs to minimize signal loss connecting to the reception node RX to receiver the signal from the antenna, while suppressing and electrically isolating the transmitter node TX. The signal loss in a signal path due to the presence of the first transmission-side transistor MT1 or the first reception-side transistor MR1 is referred to as insertion loss. Ideally, the insertion loss should be zero decibel. The attenuation of the electrically isolated signal across the source and the drain of a turned-off first transistor, i.e., either the first transmission-side transistor MT1 or the first reception-side transistor MR1 in a turned-off state, is referred to as noise isolation. Ideally, the noise isolation should be a large negative number in decibels. An ideal SPDT switch thus needs to provide low signal loss and effective noise isolation at the same time. In the prior art SPDT switch of FIG. 1, the fixed impedance values within the circuit place a limit on the insertion loss and noise isolation.
BRIEF SUMMARY
A single pole double throw (SPDT) semiconductor switch includes a series connection of a first transmitter-side transistor and a first reception-side transistor between a transmitter node and a reception node. An antenna is attached to the node between the two first transistors. Each of the two first transistors is provided with a gate-side variable impedance circuit, which provides a variable impedance connection between a complementary pair of gate control signals. Further, the body of each first transistor can be connected to a body bias control signal through a body-side variable impedance circuit. In addition, the transmitter node is connected to electrical ground through a second transmitter-side transistor, and the reception node is connected to electrical ground through a second reception-side transistor. Each of the second transistors can have a body bias that is tied to the body bias control signals for the first transistors so that switched-off transistors provide enhanced electrical isolation.
According to another aspect of the present disclosure, a single pole double throw (SPDT) switch circuit is provided, which includes: a serial connection of a first transmission-side transistor and a first reception-side transistor between a transmission node and a reception node; an antenna connected to a node between the first transmission-side transistor and the first reception-side transistor; a first variable impedance circuit connected to a gate of the first transmission-side transistor and configured to provide a first high impedance state or a first low impedance state depending on a first impedance control voltage; and a second variable impedance circuit connected to a gate of the first reception-side transistor and configured to provide a second high impedance state or a second low impedance state depending on a second impedance control voltage.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a schematic of a circuit incorporating a prior art single pole double throw (SPDT) switch configured for use with an antenna.
FIG. 2 is a schematic of a circuit incorporating an SPDT switch according to an embodiment of the present disclosure.
FIG. 3 is a vertical cross-sectional view of an exemplary semiconductor device with a variable gate impedance and a variable body impedance and body biasing capabilities.
FIG. 4 is an equivalent circuit schematic of the circuit of FIG. 2 while a signal from a transmitter node TX is routed to an antenna and a reception node RX is electrically isolated.
FIG. 5 is an equivalent circuit schematic of the circuit of FIG. 2 while a signal from the antenna is routed to the reception node RX and the transmitter node TX is electrically isolated.
FIG. 6 is a plot of simulation results that compare the insertion loss and noise isolation of the prior art SPDT switch of FIG. 1 and the SPDT switch of FIG. 2.



DETAILED DESCRIPTION
As stated above, the present disclosure relates to a semiconductor switch circuit including a variable impedance single pole double throw (SPDT) switch, which is now described in detail with accompanying figures. It is noted that like reference numerals refer to like elements across different embodiments. The drawings are not necessarily drawn to scale. The drawings are not necessarily drawn to scale.
Referring to FIG. 2, a circuit incorporating an SPDT switch according to an embodiment of the present disclosure is shown. The SPDT switch provides an electrically conductive signal path between the antenna and one of the transmission node TX and the reception node RX. The transmission node TX is connected to a semiconductor circuit (not shown) that generates signals to be passed to the transmission node TX and then to the antenna. The reception node RX is connected to another semiconductor circuit (not shown) that receives and amplifies the signal at the reception node RX.
The SPDT switch includes a serial connection of a first transmission-side transistor MT1 and a first reception-side transistor MR1 located between the transmission node TX and the reception node RX. The source of the first transmission-side transistor MT1 can be directly connected to the transmission node TX, i.e., connected without any intervening electrical component between the source of the first transmission-side transistor MT1 and the transmission node TX. The source of the first reception-side transistor MR1 can be directly connected to the reception node RX, i.e., connected without any intervening electrical component between the source of the first reception-side transistor MR1 and the reception node RX. The antenna is connected to the node between the first transmission-side transistor MT1 and the first reception-side transistor MR1, i.e., the node between the drain of the first transmission-side transistor MT1 and the drain of the first reception-side transistor MR1. This node is referred to as an antenna node, and is directly connected to the drains of the first transmission-side transistor MT1 and the first reception-side transistor MR1.
The SPDT switch electrically connects the antenna to one of the transmission node TX and the reception node RX, while electrically isolating the antenna from the other of the transmission node TX and the reception node RX. During normal operation of the SPDT switch, one of the first transmission-side transistor MT1 and the first reception-side transistor MR1 is turned on and the other of the first transmission-side transistor MT1 and the first reception-side transistor MR1 is turned off. Specifically, during operation of the SPDT switch in a transmission mode, the first transmission-side transistor MT1 is turned on, and the first reception-side transistor MR1 is turned off. Parasitic electrical coupling through the first reception-side transistor MR1 in the turned-off state introduces noise from the reception node RX into the antenna node. Further, during operation of the SPDT switch in a reception mode, the first reception-side transistor MR1 is turned on, and the first transmission-side transistor MT1 is turned off. Parasitic electrical coupling through the first transmission-side transistor MT1 in the turned-off state introduces noise from the transmission node TX into the antenna node.
A first variable impedance circuit VIC1 is connected to the gate of the first transmission-side transistor MT1. The first variable impedance circuit VIC1 is configured to provide a first high impedance state or a first low impedance state depending on a first impedance control voltage applied to the first variable impedance circuit VIC1. A second variable impedance circuit VIC2 is connected to the gate of the first reception-side transistor MR1. The second variable impedance circuit VIC2 is configured to provide a second high impedance state or a second low impedance state depending on a second impedance control voltage applied to the second variable impedance circuit VIC2.
The first variable impedance circuit VIC1 is located between a first gate control node GC1 and the gate of the first transmission-side transistor MT1, and the second variable impedance circuit VIC2 is located between a second gate control node GC2 and the gate of the first reception-side transistor MR1. The first gate control node GC1 and second gate control node GC2 are configured to be provided with a complementary pair of gate control signals. The complementary pair of gate control signals include a first gate control signal Vctrl and a second gate control voltage signal Vctrlb.
The first transmission-side transistor MT1 and the first reception-side transistor MR1 can be field effect transistors of the same type, i.e., a pair of n-type field effect transistors or a pair of p-type field effect transistors. Thus, both the first transmission-side transistor MT1 and the first reception-side transistor MR1 are configured to be turned on or turned off by the same type of gate control voltages. Specifically, if the first transmission-side transistor MT1 and the first reception-side transistor MR1 are n-type field effect transistors, the first transmission-side transistor MT1 and the first reception-side transistor MR1 are configured to be turned on when a first voltage is applied to a gate and turned off when a second voltage is applied to the gate, in which the first voltage is more positive than the second voltage. Typically, the first voltage is a positive voltage and the second voltage is zero volt, i.e., the same as the voltage of electrical ground. Conversely, if the first transmission-side transistor MT1 and the first reception-side transistor MR1 are p-type field effect transistors, the first transmission-side transistor MT1 and the first reception-side transistor MR1 are configured to be turned on when a first voltage is applied to a gate and turned off when a second voltage is applied to the gate, in which the first voltage is more negative than the second voltage. Typically, the first voltage is zero volt and the second voltage is a positive voltage.
The first gate control signal Vctrl and a second gate control voltage signal Vctrlb are “complementary” because one of the first gate control signal Vctrl and a second gate control voltage signal Vctrlb turns on a transistor, which is one of the first transmission-side transistor MT1 and the first reception-side transistor MR1, to which the signal is applied, while the other of the first gate control signal Vctrl and a second gate control voltage signal Vctrlb turns off a transistor, which is the other of the first transmission-side transistor MT1 and the first reception-side transistor MR1, to which the signal is applied. Thus, the SPDT switch circuit is configured to alternatively provide either a combination of the first high impedance state and the second low impedance state, or a combination of the first low impedance state and the second high impedance state.
In one embodiment, the first variable impedance circuit VIC1 includes a parallel connection of a first gate-control transistor MG1 and a first gate-side resistor Rg1 between the first gate control node GC1 and the gate of the first transmission-side transistor MT1, and the second variable impedance circuit VIC2 includes a parallel connection of a second gate-control transistor MG2 and a second gate-side resistor Rg2 between the second gate-control node and the gate of the second transmission-side transistor MT2. The first variable impedance circuit VIC1 can further include a first gate-control-side resistor Rsg1 connected to the gate of the first gate-control transistor MG1, and the second variable impedance circuit VIC2 can further include a second gate-control-side resistor Rsg2 connected to the gate of the second gate-control transistor MG2. The first gate-control-side resistor Rsg1 is located between a first variable impedance control node VC1 and the gate of the first gate-control transistor MG1. The second gate-control-side resistor Rsg2 is located between a second variable impedance control node VC2 and the gate of the second gate-control transistor MG2.
In one embodiment, the first impedance control voltage applied to the first variable impedance circuit VIC1 can be the same as the second gate control signal Vctrlb, and the second impedance control voltage applied to the second variable impedance circuit VIC2 can be the same as the first gate control signal Vctrl. The first gate control node GC1 and the gate of the second gate-control transistor MG2 are provided with the first gate control signal Vctrl, and the second gate control node GC2 and the gate of the first gate-control transistor MG1 are provided with the second gate control signal Vctrlb. Thus, the pair of the first gate control signal Vctrl, and the second gate control signal Vctrlb determines not only the voltage potential at the gates of the first transmission-side transistor MT1 and the second transmission-side transistor MT2, but also the impedance at the gate of the first transmission-side transistor MT1 and impedance at the gate of the second transmission-side transistor MT2.
Specifically, the first high impedance state provides an impedance of the first gate-side resistor Rg1, and the first low impedance state provides an impedance of an on-state of the first gate-control transistor MG1. Correspondingly, the second high impedance state provides an impedance of the second gate-side resistor Rg2, and the second low impedance state provides an impedance of an on-state of the second gate-control transistor MG2. Each of the first gate-side resistor Rg1 and the second gate-side resistor Rg2 has a resistance from 1 kOhms to 10 kOhms, and typically from 2 kOhms to 20 kOhms, although lesser and greater resistances can also be employed. The impedance of the on-state of the first gate-control transistor MG1 and the impedance of the on-state of the second gate-control transistor MG2 can be from 1 Ohm to 100 Ohms, although lesser and greater impedances can also be employed. The bodies of the first gate-control transistor MG1 and the second gate-control transistor MG1 are connected to electrical ground by a well resistance Rw, which can be from 1 kOhms to 10 kOhms, although lesser and greater resistances can also be employed.
The SPDT switch can further include additional variable impedance circuits. Specifically, the SPDT switch can include a third variable impedance circuit VIC3 connected to the body of the first transmission-side transistor MT1 and a fourth variable impedance circuit VIC4 connected to the body of the first reception-side transistor MR1. The third variable impedance circuit VIC3 is configured to provide a third high impedance state or a third low impedance state depending on an impedance control voltage, which can be the same as the first impedance control voltage. In other words, the first impedance control voltage can be applied to the first variable impedance circuit VIC1 and the third variable impedance circuit VIC3. As discussed above, the first impedance control voltage can be the same as the second gate control signal Vctrlb. The fourth variable impedance circuit VIC4 is configured to provide a fourth high impedance state or a low impedance state depending on an impedance control voltage, which can be the same as the second impedance control voltage. In other words, the second impedance control voltage can be applied to the second variable impedance circuit VIC2 and the fourth variable impedance circuit VIC4. As discussed above, the second impedance control voltage can be the same as the first gate control signal Vctrl.
By cross-coupling of impedance control voltages between the first and second variable impedance circuits (VIC1 and VIC2) and the third and fourth variable impedance circuits (VIC3 and VIC4) and use of a complementary pair of voltage signals for the first gate control signal Vctrl and the second gate control signal Vctrlb, the SPDT switch circuit can be configured to alternatively provide either a combination of the first high impedance state the second low impedance state, the third high impedance state, and the fourth low impedance state, or a combination of the first low impedance state, the second high impedance state, the third low impedance state, and the fourth high impedance state.
The third variable impedance circuit VIC3 is located between a first body bias control node BBC1 and the body of the first transmission-side transistor MT1, and the fourth variable impedance circuit VIC4 is located between a second body bias control node BBC2 and the body of the first reception-side transistor MR1. The first and second body bias control nodes (BBC1 and BBC2) can be configured to be provided with a complementary pair of body bias control signals. In other words, one of the first and second body bias control nodes (BBC1 and BBC2) is provided with one of two different preset voltages, and the other of the first and second body bias control nodes (BBC1 and BBC2) is provided with the other of the two different preset voltages.
In one embodiment, the third variable impedance circuit VIC3 includes a parallel connection of a first body bias control transistor MB1 and a first body-side resistor between the first body bias control node BBC1 and the body of the first transmission-side transistor MT1. Correspondingly, the fourth variable impedance circuit VIC4 includes a parallel connection of a second body bias control transistor MB2 and a second body-side resistor between the second body bias control node BBC2 and the body of the second transmission-side transistor MT2.
The complementary pair of body bias control signals include a first body bias control signal Vb1 and a second body bias control signal Vb2. The first body bias control node BBC1 is provided with the first body bias control signal Vb1, and the second body bias control node BBC2 is provided with the second body bias control signal Vb2.
In an embodiment in which the first transmission-side transistor MT1 and the first reception-side transistor MR1 are n-type field effect transistors, the first body bias control signal Vb1 can be zero volt if the third variable impedance circuit VIC3 is in the third high impedance state, and the second body bias control signal Vb2 can be zero volt if the fourth variable impedance circuit VIC4 is in the fourth high impedance state. The third variable impedance circuit VIC3 is in the third high impedance state when the first transmission-side transistor MT1 is turned on, and is in the third low impedance state when the first transmission-side transistor MT1 is turned off. The fourth variable impedance circuit VIC4 is in the fourth high impedance state when the first reception-side transistor MR1 is turned on, and is in the fourth low impedance state when the first reception-side transistor MR1 is turned off
If the third variable impedance circuit VIC3 is in the third low impedance state and the first transmission-side transistor MT1 is turned off, the first body bias control signal Vb1 is a first non-zero voltage that reduces a source-drain leakage current of the first transmission-side transistor MT1 compared to a state in which the first body bias control signal Vb1 is zero volt. If the first transmission-side transistor MT1 is an n-type transistor, the first non-zero voltage is a negate voltage having a value between 0 V and −2 V. If the fourth variable impedance circuit VIC4 is in the fourth low impedance state and the first reception-side transistor MR1 is turned off, the second body bias control signal Vb2 is a second non-zero voltage that reduces a source-drain leakage current of the first reception-side transistor MR1 compared to a state in which the second body bias control signal Vb2 is zero volt. If the first reception-side transistor MR1 is an n-type transistor, the second non-zero voltage is a negate voltage having a value between 0 V and −2 V.
The first body bias control signal Vb1 is zero volt when the third variable impedance circuit VIC3 is in the third high impedance state, the first body bias control signal Vb1 is the first non-zero voltage when the third variable impedance circuit VIC3 is in the third low impedance state. The first non-zero voltage drives the first transmission-side transistor MT1 into a deep isolation mode, in which the voltage of the body of the first transmission-side transistor MT1 is more negative than a normal off state in which the body of the first transmission-side transistor MT1 would be at zero volt. The second body bias control signal Vb2 is zero volt when the fourth variable impedance circuit VIC4 is in the fourth high impedance state, and the second body bias control signal Vb2 is the second non-zero voltage when the fourth variable impedance circuit VIC4 is in the fourth low impedance state. The second non-zero voltage drives the first reception-side transistor MR1 into a deep isolation mode, in which the voltage of the body of the first reception-side transistor MR1 is more negative than a normal off state in which the body of the first reception-side transistor MR1 would be at zero volt.
The third variable impedance circuit VIC3 can include a parallel connection of a first body bias control transistor MB1 and a first body-side resistor Rb1 between the first body bias control node BBC1 and the body of the first transmission-side transistor MT1, and the fourth variable impedance circuit VIC4 can include a parallel connection of a second body bias control transistor MB2 and a second body-side resistor Rb2 between the second body bias control node BBC2 and the body of the second transmission-side transistor MT2. The first body-side resistor Rb1 and the second body-side resistor Rb2 can be provided in the form of a well resistance in a transistor on a triple well structure illustrated in FIG. 3.
FIG. 3 schematically illustrates an n-type transistor built on a triple well structure in a semiconductor substrate 8 with a gate bias and a body bias of the present disclosure. The semiconductor substrate includes a p-type substrate layer 10 embedding an n-type well 20. The p-type substrate layer 10 is electrically grounded, and the n-type well 20 is biased at a positive voltage VDD through an n-doped contact region 22. A p-type well 30 is embedded in the n-type well 20. A p-doped contact region 32 can be formed in the p-type well 30. A portion of the p-type well 30 forms the body of the n-type transistor. The p-type well 30 is biased with the first body bias control signal Vb1 or the second body bias control signal Vb2 through the third variable impedance circuit VIC3 or the fourth variable impedance circuit VIC4.
An n-doped source 34 and an n-doped drain 36 are formed in the p-type well 30. A gate dielectric 50 and a gate electrode 52 are formed over the channel region between the n-doped source 34 and the n-doped drain 36. The gate electrode 52 is biased with the first gate control signal Vctrl or the second gate control signal Vctrlb through the first variable impedance circuit VIC1 or the second variable impedance circuit VIC2. The n-doped source 34 is electrically connected to the source node Vs, which corresponds to the transmission node TX or the reception node RX in the circuit of FIG. 2. The n-doped drain 36 is electrically connected to the drain node Vd, which corresponds to the antenna node in the circuit of FIG. 2.
Referring back to FIG. 2, the third high impedance state can provide an impedance of the first body-side resistor Rb1, and the third low impedance state can provide an impedance of the on-state of the first body bias control transistor MB1. Further, the fourth high impedance state can provide an impedance of the second body-side resistor Rb2, and the fourth low impedance state can provide an impedance of the on-state of the second body bias control transistor MB2.
The impedance control signals for the body bias control transistors (MB1 and MB2) can be cross-coupled to the complementary gate control signals, i.e., the first gate control signal Vctrl and the second gate control signal Vctrlb. The gate of the first transmission-side transistor MT1 and the gate of the second body bias control transistor MB2 are provided with the first gate control signal Vctrl, and the gate of the second transmission-side transistor MT2 and the gate of the first body bias control transistor MB1 are provided with a second gate control signal Vctrlb.
The third variable impedance circuit VIC3 can further include a first body-control-side resistor Rbg1 connected to a gate of the first body bias control transistor MB1, and the fourth variable impedance circuit VIC4 further includes a second body-control-side resistor connected to a gate of the second body bias control transistor MB2. The first body-control-side resistor Rbg1 is located between a third variable impedance control node VC3 and the gate of the first body bias control transistor MB1. The second body-control-side resistor Rbg2 is located between a fourth variable impedance control node VC4 and the gate of the second body bias control transistor MB2.
In one embodiment, the impedance control voltage applied to the third variable impedance control node VC3 can be the same as the first impedance control voltage applied to the first variable impedance control node VC1, i.e., the second gate control signal Vctrlb that is applied to the gate of the first reception-side transistor MR1. The impedance control voltage applied to the fourth variable impedance control node VC4 can be the same as the second impedance control voltage applied to the second variable impedance control node VC2, i.e., the first gate control signal Vctrl that is applied to the gate of the first transmission-side transistor MT1. Thus, the pair of the first gate control signal Vctrl, and the second gate control signal Vctrlb determines not only the voltage potential at the gates of the first transmission-side transistor MT1 and the second transmission-side transistor MT2, but also the impedance at the body of the first transmission-side transistor MT1 and impedance at the body of the second transmission-side transistor MT2 in synchronization with the control of the impedance at the gate of the first transmission-side transistor MT1 (repetition with the red line).
Each of the first body-control-side resistor Rbg1 and the second body-control-side resistor Rbg2 has a resistance from 1 kOhms to 10 kOhms, and typically from 2 kOhms to 20 kOhms, although lesser and greater resistances can also be employed. The impedance of the on-state of the first body bias control transistor MB1 and the impedance of the on-state of the second body bias control transistor MB2 can be from 1 Ohm to 100 Ohms, although lesser and greater impedances can also be employed. The bodies of the first body bias control transistor MB1 and the second body bias control transistor MB2 are connected to electrical ground by a well resistance Rw, which can be from 1 kOhms to 10 kOhms, and typically from 2 kOhms to 20 kOhms, although lesser and greater resistances can also be employed.
The SPDT switch further includes a second transmission-side transistor MT2 connected between the transmission node and electrical ground and a second reception-side transistor MR2 connected between the reception node and electrical ground.
In one embodiment, the body of the second transmission-side transistor MT2 can be electrically connected to the second body bias control node BBC2, and the body of the second reception-side transistor MR2 can be electrically connected to the first body bias control node BBC1.
The cross-coupling of the body bias signals between the first and second body bias control transistors (MB1 and MB2) and the second transmission-side transistor MT2 and the second reception-side transistor MR2 can enhance signal isolation for transistors in the off-state. Specifically, the first body bias control node BBC1 is provided with the first body bias control signal Vb1, and the second body bias control node BBC2 is provided with the second body bias control signal Vb2. The first body bias control signal Vb1 is zero volt if the third variable impedance circuit VIC3 is in the third high impedance state, and the second body bias control signal Vb2 is zero volt if the fourth variable impedance circuit VIC4 is in the fourth high impedance state.
Referring to FIG. 4, an equivalent circuit schematic of the circuit of FIG. 2 is illustrated for a transmission mode, i.e., while a signal from a transmitter node TX is routed to an antenna and the reception node RX is electrically isolated. In the transmission mode, the first transmission-side transistor MT1, the second reception-side transistor MR2, the second gate-control transistor MG2, and the second body bias control transistor MB2 are turned on, and the first reception-side transistor MR1, the second transmission-side transistor MT2, the first gate-control transistor MG1, and the first body bias control transistor MB1 are turned off.
Since the resistance of the second gate-control transistor MG2 in the on state, and the resistance of the second body bias control transistor MB2 in the on state are negligible compared with the resistance of the second gate-side resistor Rg2 and the second body-side resistor Rb2, respectively, the second variable impedance circuit VIC2 and the fourth variable impedance circuit VIC4 can be replaced with two turned-on transistors, which are approximated by a short circuit, i.e., a direct electrical connection between the second gate control node GC2 and the gate of the first reception-side transistor MR1 and a direct electrical connection between the second body bias control node BBC2 and the body of the first reception-side transistor MR1.
Further, since the resistance of the first gate-control transistor MG1 in the off state, and the resistance of the first body bias control transistor MB1 in the off state are orders of magnitude greater than the resistance of the first gate-side resistor Rg1 and the first body-side resistor Rb1, respectively, the first variable impedance circuit VIC1 and the third variable impedance circuit VIC3 can be replaced the first gate-side resistor Rg1 and the first body-side resistor Rb1, respectively.
The large impedance at the gate and body of the first transmission-side transistor MT1, which is at least one order of magnitude greater than on-state resistance of a transistor, reduces the insertion loss of the first transmission-side transistor MT1 while the first transmission-side transistor MT1 is turned on. Further, the small impedance at the gate and body of the first reception-side transistor MR1, which are the on-state resistances of transistors, reduces coupling of spurious signals at the first reception-side transistor MR1, i.e., enhances the signal isolation at the first reception-side transistor MR1. In addition, the negative voltage bias applied from the second body bias voltage node BB2 to the body of the first reception-side transistor MR1 and the second transmission-side transistor MT2 further reduces parasitic coupling of the signals at the first reception-side transistor MR1 and the second transmission-side transistor MT2.
Referring to FIG. 5, an equivalent circuit schematic of the circuit of FIG. 2 is illustrated for a reception mode, i.e., while a signal from the antenna is routed to the reception node RX and the transmission node TX is electrically isolated. In the reception mode, the first reception-side transistor MR1, the second transmission-side transistor MT2, the first gate-control transistor MG1, and the first body bias control transistor MB1 are turned on, and the first transmission-side transistor MT1, the second reception-side transistor MR2, the second gate-control transistor MG2, and the second body bias control transistor MB2 are turned off.
Since the resistance of the first gate-control transistor MG1 in the on state, and the resistance of the first body bias control transistor MB1 in the on state are negligible compared with the resistance of the first gate-side resistor Rg1 and the first body-side resistor Rb1, respectively, the first variable impedance circuit VIC1 and the third variable impedance circuit VIC3 can be replaced with two turned-on transistors, which are approximated by a short circuit, i.e., a direct electrical connection between the first gate control node GC1 and the gate of the first transmission-side transistor MT1 and a direct electrical connection between the first body bias control node BBC1 and the body of the first transmission-side transistor MT1.
Further, since the resistance of the second gate-control transistor MG2 in the off state, and the resistance of the second body bias control transistor MB2 in the off state are orders of magnitude greater than the resistance of the second gate-side resistor Rg2 and the second body-side resistor Rb2, respectively, the second variable impedance circuit VIC2 and the fourth variable impedance circuit VIC4 can be replaced the second gate-side resistor Rg2 and the second body-side resistor Rb2, respectively.
The large impedance at the gate and body of the first reception-side transistor MR1, which is at least one order of magnitude greater than on-state resistance of a transistor, reduces the insertion loss of the first reception-side transistor MR1 while the first reception-side transistor MR1 is turned on. Further, the small impedance at the gate and body of the first transmission-side transistor MT1, which are the on-state resistances of transistors, reduces coupling of spurious signals at the first transmission-side transistor MT1, i.e., enhances the signal isolation at the first transmission-side transistor MT1. In addition, the negative voltage bias applied from the first body bias voltage node BB1 to the body of the first transmission-side transistor MT1 and the second reception-side transistor MR2 further reduces parasitic coupling of the signals at the first transmission-side transistor MT1 and the second reception-side transistor MR2.
Referring to FIG. 6, simulation results compare the insertion loss and noise isolation of the prior art SPDT switch of FIG. 1 and the SPDT switch of FIG. 2. For the purpose of simulation, all resistors were assumed to have a resistance of 5 kOhms. Transistor parameters were assigned based on specifications of typical state of the art n-type metal-oxide-semiconductor field effect transistors (MOSFETs).
A first curve 610 connects simulation data points representing the noise isolation for the prior art SPDT switch of FIG. 1. A second curve 620 connects simulation data points representing the noise isolation for the SPDT switch of the present disclosure illustrated in FIG. 2. The second curve 620 shows an enhancement in the noise isolation by at least 30 decibels in the frequency range between 2 GHz and 40 GHz, i.e., provides better noise isolation by suppressing parasitic signal couplings.
A third curve 630 connects simulation data points representing the insertion loss for the prior art SPDT switch of FIG. 1. A fourth curve 640 connects simulation data points representing the insertion loss for the SPDT switch of the present disclosure illustrated in FIG. 2. The fourth curve 640 shows an enhancement in the insertion loss by at least 0.15 decibel in the frequency range between 2 GHz and 40 GHz, i.e., provides less insertion loss during transmission of signals.
While the present disclosure has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present disclosure. It is therefore intended that the present disclosure not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.

## Claims

1. A single pole double throw (SPDT) switch circuit comprising:
a serial connection of a first transmission-side transistor and a first reception-side transistor between a transmission node and a reception node;
an antenna connected to a node between said first transmission-side transistor and said first reception-side transistor;
a first variable impedance circuit connected to a gate of said first transmission-side transistor and configured to provide a first high impedance state or a first low impedance state depending on a first impedance control voltage;
a second variable impedance circuit connected to a gate of said first reception-side transistor and configured to provide a second high impedance state or a second low impedance state depending on a second impedance control voltage;
a third variable impedance circuit connected to a body of said first transmission-side transistor and configured to provide a third high impedance state or a third low impedance state depending on said first impedance control voltage, wherein said first impedance control voltage is applied to said third variable impedance circuit; and
a fourth variable impedance circuit connected to a body of said first reception-side transistor and configured to provide a fourth high impedance state or a fourth low impedance state depending on said second impedance control voltage, wherein said second impedance control voltage is applied to said fourth variable impedance circuit,
wherein said third variable impedance circuit is located between a first body bias control node and said body of said first transmission-side transistor, and said fourth variable impedance circuit is located between a second body bias control node and said body of said first reception-side transistor, and said first and second body bias control nodes are configured to be provided with a complementary pair of body bias control signals.

2. The SPDT switch circuit of claim 1, wherein said SPDT switch circuit is configured to alternatively provide either a combination of said first high impedance state and said second low impedance state or a combination of said first low impedance state and said second high impedance state.

3. The SPDT switch circuit of claim 2, wherein said first variable impedance circuit is located between a first gate control node and said gate of said first transmission-side transistor, and said second variable impedance circuit is located between a second gate control node and said gate of said first reception-side transistor, and said first and second gate control nodes are configured to be provided with a complementary pair of gate control signals.

4. The SPDT switch circuit of claim 3, wherein said first variable impedance circuit includes a parallel connection of a first gate-control transistor (MG1) and a first gate-side resistor between said first gate control node and said gate of said first transmission-side transistor, and said second variable impedance circuit includes a parallel connection of a second gate-control transistor and a second gate-side resistor between said second gate-control node and said gate of said second transmission-side transistor.

5. The SPDT switch circuit of claim 4, wherein said complementary pair of gate control signals include a first gate control signal (Vctrl) and a second gate control signal (Vctrb), said first gate control node and a gate of said second gate-control transistor are provided with said first gate control signal (Vctrl), and said second gate control node and a gate of said first gate-control transistor are provided with said second gate control signal (Vctrlb).

6. The SPDT switch circuit of claim 4, wherein said first high impedance state provides an impedance of said first gate-side resistor, said first low impedance state provides an impedance of an on-state of said first gate-control transistor (MG1), said second high impedance state provides an impedance of said second gate-side resistor, and said second low impedance state provides an impedance of an on-state of said second gate-control transistor.

7. The SPDT switch circuit of claim 4, wherein said first variable impedance circuit further includes a first gate-control-side resistor connected to a gate of said first gate-control transistor, and said second variable impedance circuit further includes a second gate-control-side resistor connected to a gate of said second gate-control transistor.

8. The SPDT switch circuit of claim 2, wherein said SPDT switch circuit is configured to alternatively provide either a combination of said first high impedance state, said second low impedance state, said third high impedance state, and said fourth low impedance state, or a combination of said first low impedance state, said second high impedance state, said third low impedance state, and said fourth high impedance state.

9. The SPDT switch circuit of claim 8, further comprising:
a second transmission-side transistor connected between said transmission node and electrical ground; and
a second reception-side transistor connected between said reception node and electrical ground.

10. A single pole double throw (SPDT) switch circuit comprising:
a serial connection of a first transmission-side transistor and a first reception-side transistor between a transmission node and a reception node;
an antenna connected to a node between said first transmission-side transistor and said first reception-side transistor;
a first variable impedance circuit connected to a gate of said first transmission-side transistor and configured to provide a first high impedance state or a first low impedance state depending on a first impedance control voltage;
a second variable impedance circuit connected to a gate of said first reception-side transistor and configured to provide a second high impedance state or a second low impedance state depending on a second impedance control voltage;
a third variable impedance circuit connected to a body of said first transmission-side transistor and configured to provide a third high impedance state or a third low impedance state depending on said first impedance control voltage, wherein said first impedance control voltage is applied to said third variable impedance circuit; and
a fourth variable impedance circuit connected to a body of said first reception-side transistor and configured to provide a fourth high impedance state or a fourth low impedance state depending on said second impedance control voltage, wherein said second impedance control voltage is applied to said fourth variable impedance circuit,
wherein said SPDT switch circuit is configured to alternatively provide either a combination of said first high impedance state and said second low impedance state or a combination of said first low impedance state and said second high impedance state,
wherein said SPDT switch circuit is configured to alternatively provide either a combination of said first high impedance state, said second low impedance state, said third high impedance state, and said fourth low impedance state, or a combination of said first low impedance state, said second high impedance state, said third low impedance state, and said fourth high impedance state,
wherein said third variable impedance circuit is located between a first body bias control node and said body of said first transmission-side transistor, and said fourth variable impedance circuit is located between a second body bias control node and said body of said first reception-side transistor, and said first and second body bias control nodes are configured to be provided with a complementary pair of body bias control signals.

11. The SPDT switch circuit of claim 10, wherein said third variable impedance circuit includes a parallel connection of a first body bias control transistor (MB1) and a first body-side resistor between said first body bias control node and said body of said first transmission-side transistor, and said fourth variable impedance circuit includes a parallel connection of a second body bias control transistor (MB2) and a second body-side resistor between said second body bias control node and said body of said second transmission-side transistor.

12. The SPDT switch circuit of claim 11, wherein said complementary pair of body bias control signals include a first body bias control signal (Vb1) and a second body bias control signal (Vb2), said first body bias control node is provided with said first body bias control signal (Vb1), and said second body bias control node is provided with said second body bias control signal (Vb2), said first body bias control signal (Vb1) is zero volt if said third variable impedance circuit is in said third high impedance state, and said second body bias control signal (Vb2) is zero volt if said fourth variable impedance circuit is in said fourth high impedance state.

13. The SPDT switch circuit of claim 12, wherein said first body bias control signal (Vb1) is a first non-zero voltage if said third variable impedance circuit is in said third low impedance state, said second body bias control signal (Vb2) is a second non-zero voltage if said fourth variable impedance circuit is in said fourth low impedance, said first non-zero voltage applied to said first transmission-side transistor reduces a source-drain leakage current of said first transmission-side transistor compared to a state in which said first body bias control signal (Vb1) is zero volt, and said second non-zero voltage applied to said first reception-side transistor reduces a source-drain leakage current of said first reception-side transistor compared to a state in which said second body bias control signal (Vb2) is zero volt.

14. The SPDT switch circuit of claim 13, wherein said first body bias control signal (Vb1) is zero volt when said third variable impedance circuit is in said third high impedance state, said first body bias control signal (Vb1) is said first non-zero voltage when said third variable impedance circuit is in said third low impedance state, said second body bias control signal (Vb2) is zero volt when said fourth variable impedance circuit is in said fourth high impedance state, and said second body bias control signal (Vb2) is said second non-zero voltage when said fourth variable impedance circuit is in said fourth low impedance state.

15. The SPDT switch circuit of claim 12, wherein a gate of said first transmission-side transistor and a gate of said second body bias control transistor (MB2) are provided with a first gate control signal (Vctrl), and a gate of said second transmission-side transistor and a gate of said first body bias control transistor (MB1) are provided with a second gate control signal (Vctrlb), wherein said first gate control signal (Vctrl) and said second gate control signal (Vctrlb) are complementary signals.

16. The SPDT switch circuit of claim 11, wherein said third high impedance state provides an impedance of said first body-side resistor, said third low impedance state provides an impedance of an on-state of said first body bias control transistor (MB1), said fourth high impedance state provides an impedance of said second body-side resistor, and said fourth low impedance state provides an impedance of an on-state of said second body bias control transistor (MB2).

17. The SPDT switch circuit of claim 11, wherein said third variable impedance circuit further includes a first body-control-side resistor connected to a gate of said first body bias control transistor (MB1), and said fourth variable impedance circuit further includes a second body-control-side resistor connected to a gate of said second body bias control transistor (MB2).

18. A single pole double throw (SPDT) switch circuit comprising:
a serial connection of a first transmission-side transistor and a first reception-side transistor between a transmission node and a reception node;
an antenna connected to a node between said first transmission-side transistor and said first reception-side transistor;
a first variable impedance circuit connected to a gate of said first transmission-side transistor and configured to provide a first high impedance state or a first low impedance state depending on a first impedance control voltage;
a second variable impedance circuit connected to a gate of said first reception-side transistor and configured to provide a second high impedance state or a second low impedance state depending on a second impedance control voltage;
a third variable impedance circuit connected to a body of said first transmission-side transistor and configured to provide a third high impedance state or a third low impedance state depending on said first impedance control voltage, wherein said first impedance control voltage is applied to said third variable impedance circuit;
a fourth variable impedance circuit connected to a body of said first reception-side transistor and configured to provide a fourth high impedance state or a fourth low impedance state depending on said second impedance control voltage, wherein said second impedance control voltage is applied to said fourth variable impedance circuit;
a second transmission-side transistor connected between said transmission node and electrical ground; and
a second reception-side transistor connected between said reception node and electrical ground,
wherein said SPDT switch circuit is configured to alternatively provide either a combination of said first high impedance state and said second low impedance state or a combination of said first low impedance state and said second high impedance state,
wherein said SPDT switch circuit is configured to alternatively provide either a combination of said first high impedance state, said second low impedance state, said third high impedance state, and said fourth low impedance state, or a combination of said first low impedance state, said second high impedance state, said third low impedance state, and said fourth high impedance state,
wherein said third variable impedance circuit includes a parallel connection of a first body bias control transistor (MB1) and a first body-side resistor between said first body bias control node and said body of said first transmission-side transistor, and said fourth variable impedance circuit includes a parallel connection of a second body bias control transistor (MB2) and a second body-side resistor between said second body bias control node and said body of said second transmission-side transistor, a body of said second transmission-side transistor is electrically connected to said second body bias control node, and a body of said second reception-side transistor is electrically connected to said first body bias control node.

19. The SPDT switch of claim 18, wherein said first body bias control node is provided with said first body bias control signal (Vb1), and said second body bias control node is provided with said second body bias control signal (Vb2), said first body bias control signal (Vb1) is zero volt if said third variable impedance circuit is in said third high impedance state, said second body bias control signal (Vb2) is zero volt if said fourth variable impedance circuit is in said fourth high impedance state, said second body bias control signal (Vb2) is a second non-zero voltage if said fourth variable impedance circuit is in said fourth low impedance, said first non-zero voltage applied to said first transmission-side transistor reduces a source-drain leakage current of said first transmission-side transistor compared to a state in which said first body bias control signal (Vb1) is zero volt, and said second non-zero voltage applied to said first reception-side transistor reduces a source-drain leakage current of said first reception-side transistor compared to a state in which said second body bias control signal (Vb2) is zero volt.