CN115395941A

CN115395941A - Gallium nitride radio frequency switch with positive bias voltage

Info

Publication number: CN115395941A
Application number: CN202210951274.3A
Authority: CN
Inventors: 何日青; 许明伟; 樊晓兵
Original assignee: Shenzhen Huixin Communication Technology Co ltd
Current assignee: Shenzhen Huixin Communication Technology Co ltd
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2022-11-25

Abstract

The invention discloses a gallium nitride radio frequency switch with positive bias voltage. The gallium nitride radio frequency switch is a single-pole N-throw switch and is provided with N branches; each branch circuit is provided with a series transistor and a parallel transistor which are gallium nitride switching tubes; for the ith branch, the series transistor means that the source and the drain of the transistor are connected in series in the branch, and the grid is connected with the bias voltage Vi1; the parallel transistors are that the drain electrodes of the transistors are connected to the branch circuits, the source electrodes of the transistors are grounded, and the grid electrodes of the transistors are connected with bias voltage Vi2; when Vi1 is a proper positive voltage and Vi2 is 0V, the ith branch is in a conducting state; when Vi1 is 0V and Vi2 is a proper positive voltage, the ith branch is in an off state; the proper positive voltage refers to a bias voltage greater than or equal to a critical voltage value, and the critical voltage value refers to a voltage value which enables a transistor connected with the bias voltage in the branch to be just turned off. The radio frequency switch is switched on and off under positive bias voltage by the depletion type GaN switching tube.

Description

Gallium nitride radio frequency switch with positive bias voltage

Technical Field

The invention relates to a depletion mode GaN (gallium nitride) radio frequency switch.

Background

GaN is a latest generation of wide bandgap semiconductor material. Most of GaN devices in the current market are depletion type devices, and the grid opening voltage is negative voltage due to the characteristics of materials. The lower the negative voltage of the grid electrode (namely the larger the absolute value), the more thoroughly the channel between the drain and the source is cut off; the closer the gate negative voltage is to 0V (i.e., the smaller the absolute value), the more thoroughly the channel between the drain and the source is opened. Therefore, the depletion mode GaN rf switch is usually applied with a negative gate bias voltage.

In the current depletion type GaN radio frequency switch circuit, two bias levels are usually switched on and off in a reciprocal (interchangeable) manner. In order to realize better loss index when the grid is conducted, the grid bias voltage is mostly 0V; when turned off, the gate bias voltage is a negative voltage lower than the gate turn-on voltage. Therefore, a circuit capable of generating negative voltage is required in an application circuit of the depletion-type GaN radio frequency switch, and the negative voltage circuit has the defects of difficulty in implementing ESD (Electrostatic Discharge) protection, poor power supply ripple and the like. Therefore, it is highly desirable to design a depletion mode GaN rf switch circuit with a positive bias voltage.

Disclosure of Invention

The invention aims to provide a depletion type GaN radio frequency switch capable of realizing on and off under a positive bias voltage.

In order to solve the technical problem, the invention discloses a gallium nitride radio frequency switch with positive bias voltage. The gallium nitride radio frequency switch is a single-pole N-throw switch, and N is a positive integer; the single-pole N-throw switch is provided with a single radio frequency input port and N radio frequency output ports; from the radio frequency input port to the radio frequency output port i, the ith branch is called i =1,2, \8230;, N; each branch circuit is provided with a series transistor and a parallel transistor which are gallium nitride switching tubes; for the ith branch, the series transistor means that the source and the drain of the transistor are connected in series in the branch, and the grid is connected with the bias voltage Vi1; the parallel transistors are that the drain electrodes of the transistors are connected to the branch circuits, the source electrodes of the transistors are grounded, and the grid electrodes of the transistors are connected with bias voltage Vi2; when Vi1 is a proper positive voltage and Vi2 is 0V, the ith branch is in a conducting state; when Vi1 is 0V and Vi2 is a proper positive voltage, the ith branch is in an off state; the proper positive voltage refers to a bias voltage greater than or equal to a critical voltage value, and the critical voltage value refers to a voltage value which enables a transistor connected with the bias voltage in the branch to be just turned off.

Further, the single-pole N-throw switch is controlled by 2N bias voltages; but the single pole double throw switch when N =2 is controlled by four or two bias voltages.

Further, to realize that the ith branch is in an on state and the other branches are in off states, the single-pole N-throw switch requires: vi1 is a suitable positive voltage and Vi2 is 0V and Vj1 is 0V and Vj2 is a suitable positive voltage, j =1,2, \8230;, N, and j ≠ i.

Preferably, the gallium nitride switching tube is a depletion type gallium nitride high electron mobility transistor HEMT or a depletion type gallium nitride pseudo high electron mobility transistor PHEMT.

Furthermore, a blocking capacitor is arranged at the radio frequency input port and each radio frequency output port.

Further, the source of each parallel transistor is grounded through a grounded capacitor.

Further, a leakage resistor is connected between the source electrode and the drain electrode of each transistor.

Optionally, the gate of each transistor is connected to a bias voltage through a bias resistor.

Furthermore, in each branch circuit, the series transistor and the parallel transistor form a self-bias circuit, and each branch circuit forms the self-bias circuit through the voltage difference between two bias voltages and the leakage current between the grid electrode and the drain electrode of each transistor.

Preferably, a single pole single throw switch when N =1, has a single branch and two bias voltages. When the first bias voltage is a proper positive voltage and the second bias voltage is 0V, the only branch is conducted. When the first bias voltage is 0V and the second bias voltage is a proper positive voltage or 0V, the only branch is turned off.

Preferably, a single pole double throw switch when N =2, has two branches and two bias voltages. When the first bias voltage is a proper positive voltage and the second bias voltage is 0V, the first branch is switched on, and the second branch is switched off. When the first bias voltage is 0V and the second bias voltage is a proper positive voltage, the first branch is switched off, and the second branch is switched on. When the two bias voltages are both 0V, the first branch circuit and the second branch circuit are both switched off.

Preferably, there are three legs and six bias voltages for a single pole, triple throw switch when N = 3. When the first bias voltage, the fourth bias voltage and the sixth bias voltage are proper positive voltages, and the second bias voltage, the third bias voltage and the fifth bias voltage are 0V, the first branch circuit is switched on, and the second branch circuit and the third branch circuit are switched off. When the third bias voltage, the second bias voltage and the sixth bias voltage are proper positive voltages and the fourth bias voltage, the first bias voltage and the fifth bias voltage are 0V, the second branch circuit is switched on, and the first branch circuit and the third branch circuit are switched off. When the bias voltage five, the bias voltage two and the bias voltage four are proper positive voltages and the bias voltage six, the bias voltage one and the bias voltage three are 0V, the third branch circuit is conducted, and the first branch circuit and the second branch circuit are disconnected. When the bias voltage II, the bias voltage IV and the bias voltage VI are proper positive voltages or 0V, and the bias voltage I, the bias voltage III and the bias voltage V are 0V, all three branches are turned off.

The invention has the technical effects that: first, a radio frequency switch that can be turned on and off under a positive bias voltage is realized by a depletion mode GaN switching tube. Second, a single pole N-throw switch can be formed by controlling the bias voltage, N being a positive integer.

Drawings

Fig. 1 is a specific circuit diagram of a first embodiment (single-pole double-throw switch) of the present invention.

Fig. 2 is a functional block diagram according to a first embodiment of the present invention.

Fig. 3 is a specific circuit diagram of a second embodiment (single pole single throw switch) of the present invention.

Fig. 4 is a functional block diagram of a second embodiment of the present invention.

Fig. 5 is a specific circuit diagram of a third embodiment (single pole, three throw switch) of the present invention.

Fig. 6 is a functional block diagram of a third embodiment of the present invention.

Detailed Description

Please refer to fig. 1, which illustrates a single-pole double-throw switch implemented by a gan rf switch with a positive bias voltage according to a first embodiment of the present application. The single-pole double-throw switch has a single radio frequency input port RFIN and has two radio frequency output ports RFOUT1 and RFOUT2. The first branch is called from the rf input port RFIN to the rf output port RFOUT 1. The path from the rf input port RFIN to the rf output port two RFOUT2 is referred to as a second branch. The switching tubes D1, D2, D3, D4 are depletion-mode GaN HEMTs (High-Electron-Mobility transistors), depletion-mode gaas phemt (pseudo High-Electron-Mobility transistors), or other depletion-mode GaN switching transistors. A switching tube D1 is connected in series with the first branch circuit, and a switching tube three D3 is connected in parallel with the first branch circuit. The second switching tube D2 is connected in series with the second branch circuit, and the fourth switching tube D4 is connected in parallel with the second branch circuit. C1, C2 and C3 are blocking capacitors, and C4 and C5 are grounding capacitors. R1, R2, R5 and R6 are leakage resistors and are respectively connected between the source electrode and the drain electrode of the switching tubes D1, D2, D3 and D4. R3, R4, R7 and R8 are bias resistors and are respectively connected between the grids of the switching tubes D1, D2, D3 and D4 and bias voltage V1 or V2. In the specific circuit shown in fig. 1, functions realized by the respective elements are abstracted into individual functional blocks, as shown in fig. 2.

In fig. 1, all the bias resistors R3, R4, R7, and R8 (i.e., all the bias circuits in fig. 2) may be omitted, and these bias resistors affect the magnitude of the current in the entire switch circuit and do not affect the implementation of the function of the entire switch circuit. If bias resistors R3, R4, R7 and R8 are arranged, the size of leakage current in the whole switch circuit can be reduced, and the service life of the GaN transistor is prolonged.

In the first embodiment shown in fig. 1 and fig. 2, the first switch tube D1 and the third switch tube D3 form a first self-bias circuit, and by applying a suitable positive bias voltage, the first branch can be turned on and off. In any transistor, due to parasitics, there is leakage current and resistance between the gate and the drain. The whole switch circuit of the invention is formed into a self-bias circuit through the voltage difference between the bias voltage I V1 and the bias voltage II V2 and the leakage current between the grid electrode and the drain electrode of each transistor. Taking the first branch as an example, when a voltage difference exists between the first bias voltage V1 and the second bias voltage V2, a current will be formed in the first branch, and due to the resistance between the gates and the drains of the switching tubes D1 and D3 and the leakage current, a voltage difference exists between the gate and the drain of the switching tube D1 and a voltage difference also exists between the gate and the drain of the switching tube D3, and the voltage differences are their respective gate bias voltages, that is, they bias themselves through the leakage current and the inter-electrode resistance. Based on the same principle, the second switching tube D2 and the fourth switching tube D4 form a second self-bias circuit, and the second branch circuit can be switched on and off by applying proper positive bias voltage.

In the first embodiment shown in fig. 1 and fig. 2, a single-pole double-throw switch can be formed by controlling two bias voltages V1 and V2, which is implemented as follows.

When the first bias voltage V1 is a proper positive voltage and the second bias voltage V2 is 0V, the first branch is turned on and the second branch is turned off. When V1 is a positive voltage and V2 is 0V, V1 > V2. When V1 > V2, the direction of the leakage current in the first branch is V1 → R3 → D1 gate → D1 drain → D3 gate → R7 → V2. For the first switch tube D1, the current flows from the gate to the drain, the voltage difference between the gate and the drain is positive, i.e., the gate bias voltage is a positive voltage, and the first switch tube D1 is in an on state. For the three switching tubes D3, the current flows from the drain to the gate, the voltage difference between the gate and the drain is negative, i.e., the gate bias voltage is a negative voltage, and the three switching tubes D3 are in an off state. Similarly, in the second branch, D2 is in an off state, and D4 is in an on state. The radio frequency signal can go from RFIN to RFOUT1, and can not go from RFIN to RFOUT2, i.e. the first branch is on, and the second branch is off.

When the first bias voltage V1 is 0V and the second bias voltage V2 is a proper positive voltage, the first branch is turned off and the second branch is turned on. When V2 is a positive voltage and V1 is 0V, V2 > V1. When V2 > V1, the direction of the leakage current in the first branch is V2 → R7 → D3 gate → D3 drain → D1 gate → R3 → V1. For the first switching tube D1, the current flows from the drain to the gate, the voltage difference between the gate and the drain is negative, i.e., the gate bias voltage is a negative voltage, and the first switching tube D1 is in an off state. For the three switching tubes D3, the current flows from the gate to the drain, the voltage difference between the gate and the drain is positive, i.e., the gate bias voltage is a positive voltage, and the three switching tubes D3 are in an on state. Similarly, in the second branch, D2 is in the on state, and D4 is in the off state. The radio frequency signal cannot go from RFIN to RFOUT1 and can go from RFIN to RFOUT2, i.e. the first branch is off and the second branch is on.

And when the first bias voltage V1 and the second bias voltage V2 are both 0V, the first branch circuit and the second branch circuit are both switched off. When V1 and V2 are both 0V, there is no leakage current in the first branch and the second branch, the voltage difference between the gate and the drain of any transistor is 0V, i.e. the gate bias is 0V, and the transistor is in the on state. The radio frequency signal can be from RFIN → D1 → D3 → C4 → ground, and from RFIN → D2 → D4 → C5 → ground, i.e. the radio frequency signal is short to ground, and both the first and second branches are off.

The appropriate positive voltage is dependent on the transistor used. The leakage current, the inter-electrode resistance and the turn-on voltage vary from transistor to transistor. When a certain bias voltage of a certain branch is at a certain voltage value, the drain current in the branch enables the voltage difference of the grid and the drain of the transistor connected with the bias voltage in the branch to be just equal to the turn-on voltage, and the transistor connected with the bias voltage in the branch is just turned off. The suitable positive voltage is greater than or equal to the threshold voltage value.

It can be known from the specific implementation process of the single-pole double-throw switch, the whole switch circuit of the invention does not need to provide negative bias voltage, and the positive bias and the negative bias of the grid voltage can be realized only by ensuring that the two bias voltages are different, namely V1 is not equal to V2 (V1 and V2 can be both positive), and leakage current exists in the whole switch circuit.

Please refer to fig. 3, which illustrates a single-pole single-throw switch implemented by a gallium nitride rf switch with a positive bias voltage according to a second embodiment of the present application. The single-pole single-throw switch has only one radio frequency input port RFIN and only one radio frequency output port RFOUT. The path from the rf input port RFIN to the rf output port RFOUT is referred to as a unique leg. The switching tubes D1 and D2 are depletion type GaN HEMTs, depletion type gaasp HEMTs or other depletion type gallium nitride switching transistors. The first switch tube D1 is connected in series with the only branch, and the third switch tube D2 is connected in parallel with the only branch. C1 and C2 are blocking capacitors, and C3 is a grounding capacitor. R1 and R3 are leakage resistors and are respectively connected between the source and the drain of the switching tubes D1 and D2. R2 and R4 are bias resistors and are respectively connected between the grid electrodes of the switching tubes D1 and D2 and bias voltage V1 or V2. In the specific circuit shown in fig. 3, functions realized by the respective elements are abstracted into individual functional modules, which are shown in fig. 4. In fig. 3, all the bias resistors R2 and R4 (i.e., all the bias circuits in fig. 4) may be omitted, which is the same as the first embodiment.

In the second embodiment shown in fig. 3 and 4, the first switching tube D1 and the second switching tube D2 form a self-bias circuit, and by applying a proper positive bias voltage, the on and off of the only branch can be realized. Therefore, a single-pole single-throw switch can be formed by controlling the two bias voltages V1 and V2, and the specific implementation process is as follows. (1) When the bias voltage one V1 is a proper positive voltage and the bias voltage two V2 is 0V, the only branch is conducted. (2) When the first bias voltage V1 is 0V and the second bias voltage V2 is a proper positive voltage or 0V, the only branch is switched off. The suitable positive voltage is greater than or equal to the threshold voltage value of "leakage current causes the voltage difference of the gate drain of the GaN transistor to be just equal to the turn-on voltage".

Please refer to fig. 5, which shows a single-pole-triple-throw switch implemented by a positive-bias gan rf switch according to a third embodiment of the present application. The single-pole-three-throw switch has a single radio frequency input port RFIN and three radio frequency output ports RFOUT1, RFOUT2 and RFOUT3. The path from the rf input port RFIN to the rf output port RFOUT1 is referred to as a first branch. The second branch is called from the rf input port RFIN to the rf output port two RFOUT2. The path from the rf input port RFIN to the rf output port three RFOUT3 is referred to as a third branch. The switching tubes D1, D2, D3, D4, D5, D6 are depletion mode GaN HEMTs, depletion mode gaasphemts or other depletion mode gallium nitride switching transistors. A switching tube D1 is connected in series with the first branch circuit, and a switching tube D4 is connected in parallel with the first branch circuit. The second switching tube D2 is connected in series with the second branch circuit, and the fifth switching tube D5 is connected in parallel with the second branch circuit. And the three D3 switch tubes are connected in series with the third branch, and the six D6 switch tubes are connected in parallel with the third branch. C1, C2, C3 and C4 are blocking capacitors, and C5, C6 and C7 are grounding capacitors. R1, R2, R3, R7, R8 and R9 are leakage resistors and are respectively connected between the source and the drain of the switching tubes D1, D2, D3, D4, D5 and D6. R4, R5, R6, R10, R11 and R12 are bias resistors and are respectively connected between the grids of the switching tubes D1, D2, D3, D4, D5 and D6 and bias voltage V1 or V2. In the specific circuit shown in fig. 5, the functions realized by the respective elements are abstracted into individual functional blocks, as shown in fig. 6. In fig. 5, all the bias resistors R4, R5, R6, R10, R11, and R12 (i.e., all the bias circuits in fig. 6) may be omitted, which is the same as the first embodiment.

In the third embodiment shown in fig. 5 and 6, the first switch tube D1 and the fourth switch tube D4 form a first self-bias circuit, and by applying a suitable positive bias voltage, the first branch can be turned on and off. The second switching tube D2 and the fifth switching tube D5 form a second self-bias circuit, and the second branch circuit can be switched on and off by applying proper positive bias voltage. And the third switching tube D3 and the sixth switching tube D6 form a third self-bias circuit, and the third branch circuit can be switched on and off by applying proper positive bias voltage. Therefore, the single-pole-three-throw switch can be formed by controlling six bias voltages V11, V12, V21, V22, V31 and V32, and the specific implementation process is as follows. (1) When the bias voltage I V11, the bias voltage IV 22 and the bias voltage IV 32 are proper positive voltages and the bias voltage II V12, the bias voltage III V21 and the bias voltage V31 are 0V, the first branch is conducted, and the second branch and the third branch are disconnected. (2) When the bias voltage three V21, the bias voltage two V12 and the bias voltage six V32 are proper positive voltages, and the bias voltage four V22, the bias voltage one V11 and the bias voltage five V31 are 0V, the second branch circuit is conducted, and the first branch circuit and the third branch circuit are disconnected. (3) When the bias voltage five V31, the bias voltage two V12 and the bias voltage four V22 are proper positive voltages and the bias voltage six V32, the bias voltage one V11 and the bias voltage three V21 are 0V, the third branch is conducted, and the first branch and the second branch are disconnected. (4) When the bias voltage two V12, the bias voltage four V22 and the bias voltage six V32 are proper positive voltages or 0V, and the bias voltage one V11, the bias voltage three V21 and the bias voltage five V31 are 0V, all three branches are turned off.

From the above three embodiments, the depletion-mode gan switching transistor with positive bias voltage provided by the present invention can realize a single-pole N-throw switch, where N is a positive integer. Single pole N-throw switches require 2N bias voltages. The single-pole double-throw switch with N =2 is a special case, and may be controlled by four bias voltages or two bias voltages (as shown in embodiment two). The single-pole N-throw switch has a single radio frequency input port RFIN with N radio frequency output ports RFOUT1, RFOUT2, \ 8230 \ 8230;, RFOUTN. The first branch is called from the rf input port RFIN to the rf output port RFOUT 1. The path from the rf input port RFIN to the rf output port two RFOUT2 is referred to as a second branch. 8230a branch from the rf input port RFIN to the rf output port NRFOUTN is called the nth branch. Each branch circuit is provided with a series transistor and a parallel transistor which are GaN switching tubes. For the ith (i =1,2, \8230;. N) branch of the single-pole N-throw switch, a series transistor means that the source and drain of the transistor are connected in series in the branch, and the gate is connected with a bias voltage Vi1; the parallel transistor is characterized in that the drain electrode of the transistor is connected into the branch, the source electrode of the transistor is grounded through a grounded capacitor, and the grid electrode of the transistor is connected with a bias voltage Vi2. With reference to the previous analysis: when Vi1 is a proper positive voltage and Vi2 is 0V, the ith branch is in a conducting state; when Vi1 is 0V and Vi2 is a suitable positive voltage, the ith branch is in an off state. Therefore, to realize that the ith branch is in an on state and the other branches are in an off state, it is required that: vi1 is a suitable positive voltage, vi2 is 0V, and Vj1 is 0V, vj2 is a suitable positive voltage (j =1,2, \8230: \8230;, N, and j ≠ i).

Compared with the prior art, the single-pole N-throw radio frequency switch realized by the depletion type GaN switch tube provided by the invention does not need a circuit for generating negative voltage, all bias voltages (control voltages) are positive voltages or 0V, and the whole radio frequency switch can be switched on or off, so that the ESD protection is simpler to realize, and the power supply ripple is improved.

The above are merely preferred embodiments of the present invention, and are not intended to limit the present invention. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A gallium nitride radio frequency switch with positive bias voltage is characterized in that the gallium nitride radio frequency switch is a single-pole N-throw switch, and N is a positive integer; the single-pole N-throw switch is provided with a single radio frequency input port and N radio frequency output ports; from the radio frequency input port to the radio frequency output port i, the ith branch is called i =1,2, \8230;, N; each branch circuit is provided with a series transistor and a parallel transistor which are gallium nitride switching tubes; for the ith branch, the series transistor means that the source and the drain of the transistor are connected in series in the branch, and the grid is connected with the bias voltage Vi1; the parallel transistors are that the drain electrodes of the transistors are connected to the branch circuits, the source electrodes of the transistors are grounded, and the grid electrodes of the transistors are connected with bias voltage Vi2; when Vi1 is a proper positive voltage and Vi2 is 0V, the ith branch is in a conducting state; when Vi1 is 0V and Vi2 is a proper positive voltage, the ith branch is in an off state; the proper positive voltage refers to a bias voltage greater than or equal to a critical voltage value, and the critical voltage value refers to a voltage value which enables a transistor connected with the bias voltage in the branch to be just turned off.

2. The positive bias voltage gan rf switch of claim 1, wherein the single-pole N-throw switch is controlled by 2N bias voltages; but the single pole double throw switch when N =2 is controlled by four or two bias voltages.

3. The positive bias voltage gan rf switch of claim 1, wherein the single-pole N-throw switch requires that the ith branch is turned on and the other branches are turned off: vi1 is a suitable positive voltage and Vi2 is 0V and Vj1 is 0V and Vj2 is a suitable positive voltage, j =1,2, \8230;, N, and j ≠ i.

4. The positive bias voltage gan rf switch of claim 1, wherein the gan switch is a depletion mode gan HEMT or a depletion mode gan pseudo HEMT.

5. The positive bias voltage gan rf switch of claim 1, wherein a dc blocking capacitor is provided at the rf input port and each rf output port.

6. The positive bias voltage gan rf switch of claim 1, wherein the source of each of the shunt transistors is grounded through a grounded capacitor.

7. The positive bias voltage gan rf switch of claim 1, wherein a bleed-through resistor is connected between the source and drain of each transistor.

8. The positive bias voltage gan rf switch of claim 1, wherein the gate of each transistor is connected to a bias voltage through a bias resistor.

9. The forward biased gan rf switch of claim 1, wherein the transistors in series and in parallel form a self-biasing circuit in each branch, and wherein each branch is self-biased by the voltage difference between the two bias voltages and the leakage current between the gate and drain of each transistor.

10. The positive bias voltage gan rf switch of claim 1, wherein the single-pole single-throw switch with N =1 has only one branch and two bias voltages;

when the bias voltage I is a proper positive voltage and the bias voltage II is 0V, the only branch circuit is conducted;

when the first bias voltage is 0V and the second bias voltage is a proper positive voltage or 0V, the only branch is switched off.

11. The positive bias voltage gan rf switch of claim 1, wherein the single-pole double-throw switch when N =2 has two branches and two bias voltages;

when the first bias voltage is a proper positive voltage and the second bias voltage is 0V, the first branch is conducted, and the second branch is disconnected;

when the first bias voltage is 0V and the second bias voltage is a proper positive voltage, the first branch is switched off, and the second branch is switched on;

when the two bias voltages are both 0V, the first branch circuit and the second branch circuit are both switched off.

12. The positive bias voltage gan rf switch of claim 1, wherein the single-pole-triple-throw switch when N =3 has three branches and six bias voltages;

when the first bias voltage, the fourth bias voltage and the sixth bias voltage are proper positive voltages and the second bias voltage, the third bias voltage and the fifth bias voltage are 0V, the first branch is conducted, and the second branch and the third branch are disconnected;

when the bias voltage I, the bias voltage II and the bias voltage II are proper positive voltages and the bias voltage II, the bias voltage I and the bias voltage V are 0V, the second branch circuit is switched on, and the first branch circuit and the third branch circuit are switched off;

when the bias voltage V, the bias voltage II and the bias voltage IV are proper positive voltages and the bias voltage VI, the bias voltage I and the bias voltage III are 0V, the third branch circuit is switched on, and the first branch circuit and the second branch circuit are switched off;

when the bias voltage II, the bias voltage IV and the bias voltage VI are proper positive voltages or 0V, and the bias voltage I, the bias voltage III and the bias voltage V are 0V, all three branches are turned off.