A high voltage SOI CMOS RF switch

Abstract

The present invention relates to the technical field of radio frequency switches, and discloses a capacitance-compensated SOI CMOS radio frequency switch, comprising a fixed end and at least one selection end, wherein a channel is formed between each selection end and the fixed end, wherein the main path of each channel is M cascaded switch tubes, wherein the gate of the switch tube of each channel is connected to the same control voltage, and a resistor is connected between the source and the drain of each switch tube, and each channel selects N consecutive switch tubes from the fixed end, wherein capacitors are respectively connected between the source and the drain of the N consecutive switch tubes, and the capacitor between the source and the drain of the switch tube is connected in parallel with the resistor between the drain and the source of the switch tube. In actual use, the capacitor between the source and the drain of the N consecutive switch tubes can make the radio frequency signal evenly distributed on the switch tube on the closed channel, thereby ensuring that the switch tube on the closed channel will not be broken down due to uneven voltage distribution, thereby improving the power carrying capacity of the entire radio frequency switch.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency switches, and in particular to a high-voltage SOI CMOS radio frequency switch. Background Art

[0002] In the field of mobile communication technology, in order to support different mobile communication standards and different operating frequency bands of one or more mobile communication standards, a mobile terminal is often provided with multiple RF power amplifiers inside the mobile terminal. Each RF power amplifier can only be used for signal amplification of one frequency band or multiple frequency bands with similar frequency ranges, and an RF switch is used to switch the required RF power amplifier to the corresponding path for use.

[0003] Reference Figure 1 , Figure 1 The RF switch shown includes a transmitting channel and a receiving channel. The main path of the transmitting channel is from terminal 2 S2 through the three cascaded switch tubes T1 to T3 to terminal 1 S1, and the transmitting signal TX follows this path to reach the antenna. The main path of the receiving channel is from terminal 1 S1 through the three cascaded switch tubes T4 to T6 to terminal 3 S3, and the receiving signal RX follows this path to leave the antenna.

[0004] During the use of the RF switch, when the RF signal enters the S2 terminal, since T4 / T5 / T6 is turned off at this time, and the S3 terminal is grounded through the resistor R22. Then the RF power signal will form a certain voltage difference between the source and drain of T4 / T5 / T6, and theoretically it will be evenly distributed between the source and drain of these three switch tubes. But in fact, since each switch tube has a parasitic capacitance to the ground at the physical level, it will cause the voltage between the source and drain at the RF power signal entry end to be greater than that of other switch tubes. And a trend of smaller and smaller voltage distribution from top to bottom is formed. Specifically, when the RF power signal enters from the S2 terminal and passes through T1 / T2 / T3 to reach the S1 terminal. At this time, T4 / T5 / T6 is turned off. Then the voltage formed by the RF power signal is distributed on T4 / T5 / T6. And the voltage between the source and drain of the T4 tube is greater than the voltage between the source and drain of the T5 tube; the voltage between the source and drain of the T5 tube is greater than the voltage between the source and drain of the T6 tube. Under this trend, when the RF signal power level of the S2 port continues to increase, the T4 switch tube will reach its source-drain voltage carrying limit before T5 and T6, that is, the T4 tube will be broken down. Summary of the invention

[0005] In view of the shortcomings of the background technology, the present invention provides a high-voltage SOI CMOS radio frequency switch, and the technical problem to be solved is that the power carrying capacity of the existing radio frequency switch is insufficient.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: a high-voltage SOI CMOS radio frequency switch, comprising a fixed end and at least one selection end, a channel is formed between each selection end and the fixed end, the main path of each channel is M cascaded switch tubes, the gate of the switch tube of each channel is connected to the same control voltage, a resistor is connected between the source and the drain of each switch tube, each channel selects N consecutive switch tubes starting from the fixed end, capacitors are respectively connected between the source and the drain of the N consecutive switch tubes, the capacitance of the capacitor between the source and the drain of the N consecutive switch tubes gradually decreases in the direction away from the fixed end, the capacitor between the source and the drain of the switch tube is connected in parallel with the resistor between the drain and the source of the switch tube, M and N are both integers, and N is less than M.

[0007] As a further technical solution, the radio frequency switch includes a fixed terminal and n selection terminals, forming a single-pole n-throw switch.

[0008] As a further technical solution, m of the single-pole n-throw switches are stacked in parallel, and these m single-pole n-throw switches are single-pole n1 throw switch, single-pole n2 throw switch, ..., single-pole nm throw switch, forming an m-pole (n1+n2+...+nm) throw switch.

[0009] As a further technical solution, the number of switch tubes selected on each channel, that is, the size of N, depends on the power level that the RF switch needs to withstand.

[0010] As a further technical solution, each channel includes three cascaded switch tubes, and each channel selects a switch tube at the fixed end, and a capacitor is connected between the source and drain of the switch tube.

[0011] As a further technical solution, each channel includes three cascaded switch tubes, and each channel selects two switch tubes at the fixed end, and capacitors are respectively connected between the source and drain of the two switch tubes.

[0012] As a further technical solution, the switch tube is a SOI CMOS transistor or a plurality of SOI CMOS transistors connected in series.

[0013] Compared with the prior art, the present invention has the following beneficial effects: by selecting a number of switch tubes at the fixed end of each channel and connecting a capacitor between the source and drain of the selected switch tube, when the radio frequency signal enters the channel from the fixed end, the radio frequency signal can be evenly distributed on the switch tube on the closed channel through the capacitor between the source and drain of the switch tube, ensuring that the switch tube on the closed channel will not be broken down due to uneven voltage distribution, thereby improving the power carrying capacity of the entire radio frequency switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention has the following accompanying drawings:

[0015] Figure 1 is a circuit diagram of an existing radio frequency switch;

[0016] Figure 2 is a circuit diagram of the present invention in Embodiment 1;

[0017] Figure 3 is a circuit diagram of the present invention in Embodiment 2;

[0018] Figure 4 is a circuit diagram of the present invention in Embodiment 3;

[0019] Figure 5 This is a circuit diagram of the present invention in Embodiment 4. DETAILED DESCRIPTION

[0020] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0021] Embodiment 1

[0022] like Figure 2 As shown, the RF switch in this embodiment includes a transmitting channel and a receiving channel. The main path of the transmitting channel is from terminal two S2 through three cascaded switch tubes T1 to T3 to terminal one S1, and the transmitting signal TX follows this path to reach the antenna. The main path of the receiving channel is from terminal one S1 through three cascaded switch tubes T4 to T6 to terminal three S3, and the receiving signal RX leaves the antenna along this path. The switch tubes T1 to T6 are all implemented using SOI CMOS technology, for example, NMOS devices. A resistor R1, a resistor R2, a compensation capacitor C2 and a resistor R3, a compensation capacitor C1 and a resistor R4, a resistor R5, and a resistor R6 are connected between the source and drain of the switch tubes T1 to T6, respectively. The gates of the switch tubes T1 to T3 on the main path of the transmitting channel are respectively connected to the control voltage one VT through a resistor R11 to R13. The gates of the switch tubes T4 to T6 on the main path of the receiving channel are respectively connected to the control voltage two VR through a resistor R14 to R16.

[0023] Figure 2 In the RF switch shown, only one of the two control signals VT and VR is a positive voltage at any time, and the other is a negative voltage. At any time, only one of the transmitting channel and the receiving channel is closed and the other is open, realizing a single-pole double-throw RF switch. At the same time, due to the existence of compensation capacitors C1 / C2 / , the power capacity of the RF switch is greatly enhanced compared with similar designs.

[0024] In actual use, a compensation capacitor C1 is connected in parallel between the source and drain of the switch tube T4. As mentioned above, due to the influence of the parasitic capacitance characteristics of the switch tubes T4 / T5 / T6 to the ground, the voltage difference between the source and drain of the switch tube T4 is larger than that of T5 / T6, which means that it is more likely to be broken down. Then adding compensation capacitor C1 at both ends of the T4 switch tube can alleviate this situation, so that the voltage can be more evenly distributed on T4 / T5 / T6.

[0025] Embodiment 2

[0026] Figure 2 When the RF switch in the circuit is used for a long time, if the RF signal power level of the S2 port is increased, the T5 switch tube T5 will reach its source-drain voltage carrying limit before the T6 tube, and the switch tube T5 will be broken down first. Figure 3 As shown, the RF switch in this embodiment includes a transmitting channel and a receiving channel. The main path of the transmitting channel is from terminal two S2 through three cascaded switch tubes T1 to T3 to terminal one S1, and the transmitting signal TX follows this path to reach the antenna. The main path of the receiving channel is from terminal one S1 through three cascaded switch tubes T4 to T6 to terminal three S3, and the receiving signal RX leaves the antenna along this path. The switch tubes T1 to T6 are all implemented using SOI CMOS technology, such as NMOS devices. A resistor R1, a compensation capacitor C4 and a resistor R2, a compensation capacitor C2 and a resistor R3, a compensation capacitor C1 and a resistor R4, a compensation capacitor C3 and a resistor R5, and a resistor R6 are connected between the source and drain of the switch tubes T1 to T6, respectively. Since the original voltage distribution shows a trend of getting smaller and smaller from T4-T6, the value of the compensation capacitor C3 connected in parallel to the source and drain of the switch tube T5 is smaller than the compensation capacitor C1 connected in parallel to the source and drain of the switch tube T4. The gates of the switches T1 to T3 on the main path of the transmitting channel are connected to the control voltage 1 VT through a resistor R11 to R13 respectively. The gates of the switches T4 to T6 on the main path of the receiving channel are connected to the control voltage 2 VR through a resistor R14 to R16 respectively.

[0027] Figure 3 In the RF switch shown, only one of the two control signals VT and VR is a positive voltage at any time, and the other is a negative voltage. At any time, only one of the transmitting channel and the receiving channel is closed and the other is open, realizing a single-pole double-throw RF switch. At the same time, due to the presence of compensation capacitors C1 / C2 / C3 / C4, the power capacity of the RF switch is greatly enhanced compared with similar designs.

[0028] In actual use, compensation capacitors need to be added to the source and drain ends of the initial several switch tubes from the S2 end, that is, the RF entry port to the RF ground (S3 port), until the voltage swing between the source and drain of each switch tube is evenly distributed when the RF signal enters.

[0029] Embodiment 3

[0030] The RF switch in the first and second embodiments can be used not only to switch the transmitting channel and the receiving channel, but also to switch any two channels. Figure 4 This is a variation of the second embodiment, schematically used to switch radio frequency signals TX1 and TX2 of two different transmission channels. Figure 4 The RF switch shown includes channel 1 and channel 2. The main path of channel 1 is from terminal 2 S2 through three cascaded switch tubes T1 to T3 to terminal 1 S1, and signal 1 TX follows this path to reach the antenna. The main path of channel 2 is from terminal 3 S3 through three cascaded switch tubes T4 to T6 to terminal 1 S1, and signal 2 TX2 follows this path to reach the antenna. Figure 4 The implementation principle of the RF switch shown is similar to Figure 3 The RF switches shown are the same and will not be described in detail.

[0031] In embodiments one to three, only three switch tubes are cascaded in the main path of each channel. Optionally, the number of switch tubes cascaded in each channel may be between 3 and 15. The main factors that determine the number of switch tubes cascaded in the main path of each channel are the size of the RF power that the RF switch needs to withstand and the RF power that each switch tube can withstand. Assuming that the RF power that a single switch tube can withstand remains unchanged, if the RF switch needs to withstand a larger RF power, then a larger number of switch tubes need to be cascaded in the main path of each channel; vice versa, if the RF switch only needs to withstand a smaller RF power, then only a smaller number of switch tubes need to be cascaded in the main path of each channel. At the same time, the use of compensation capacitors in the present invention also makes the voltage values ​​​​on switches with different numbers of layers as uniform as possible, thereby achieving the effect of improving power carrying capacity.

[0032] Embodiment 4

[0033] like Figure 5As shown, the RF switch in this embodiment includes three channels. The main path of channel one is from terminal two S2 through three cascaded switch tubes T1 to T3 to terminal one S1, and signal one TX1 follows this path to reach the antenna. The main path of channel two is from terminal three S3 through three cascaded switch tubes T4 to T6 to terminal one S1, and signal two TX2 follows this path to reach the antenna. The main path of channel three is from terminal four S4 through three cascaded switch tubes T7 to T9 to terminal one S1, and signal three TX3 follows this path to reach the antenna. Switch tubes T1 to T9 are all implemented using SOI CMOS technology, for example, NMOS devices. A resistor R1, a compensation capacitor C4 and a resistor R2, a compensation capacitor C1 and a resistor R3, a resistor R4, a compensation capacitor C5 and a resistor R5, a compensation capacitor C2 and a resistor R6, a resistor R7, a compensation capacitor C6 and a resistor R8, a compensation capacitor C3 and a resistor R9 are connected between the source and drain of the switch tubes T1 to T9, respectively. The gates of the switch tubes T1 to T3 on the main path of channel 1 are connected to the control voltage 1 VT through a resistor R11 to R13 respectively. The gates of the switch tubes T4 to T6 on the main path of channel 2 are connected to the control voltage 2 VR through a resistor R14 to R16 respectively. The gates of the switch tubes T7 to T9 on the main path of channel 3 are connected to the control voltage 3 VQ through a resistor R17 to R19 respectively.

[0034] Figure 5 In the RF switch shown, only one of the three control signals VT, VR and VQ is a positive voltage at any time, and the other two are negative voltages. The channel of the control signal with a positive voltage input will be closed, and the channel of the control signal with a negative voltage input will be disconnected. At any time, only one of the three channels is closed and the other two are disconnected, realizing a single-pole three-throw RF switch.

[0035] in addition, Figure 5 The RF switch in the embodiment can be used not only to switch three transmission channels, but also to switch any three channels.

[0036] In summary, in combination with embodiments one to four, the present invention includes a fixed end and at least one selection end, a channel is formed between each selection end and the fixed end, the main path of each channel is M cascaded switching tubes, the gate of the switching tube of each channel is connected to the same control voltage, a resistor is connected between the source and the drain of each switching tube, each channel selects N consecutive switching tubes starting from the fixed end, capacitors are respectively connected between the source and the drain of the N consecutive switching tubes, the capacitor between the source and the drain of the switching tube is connected in parallel with the resistor between the drain and the source of the switching tube, M and N are both integers, and N is less than M.

[0037] In actual use, the control method of the present invention has not changed. At the same time, there is no need to adjust any other parameters of the overall RF switch. It is only necessary to add parallel compensation capacitors on several switch tubes at the RF power signal input port. The capacitance value is generally proportional to the size of the RF switch tube, and the magnitude ranges from 0.5 to 3pF. And it has a tendency to gradually decrease from the RF power signal entry end to the bottom. In addition, in actual design, the capacitor can be stacked on the RF switch tube on the layout, and there is no need to expand the original chip layout area. However, a higher power carrying capacity can be achieved. From another point of view, if the traditional design is adopted, in order to achieve the same power carrying capacity, it is necessary to expand the area of ​​a single switch tube and increase the number of switches in series. In comparison, the present invention has the advantage of a small area.

[0038] The above is based on the present invention as an inspiration. Through the above description, relevant staff can make various changes and modifications without departing from the technical idea of ​​this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A high withstand voltage SOI CMOS radio frequency switch, characterized in that: The invention comprises a fixed end and at least one selection end, wherein a channel is formed between each selection end and the fixed end, wherein the main path of each channel is M cascaded switch tubes, wherein the gate of the switch tube of each channel is connected to the same control voltage, and a resistor is connected between the source and the drain of each switch tube, and each channel selects N consecutive switch tubes starting from the fixed end, wherein capacitors are respectively connected between the source and the drain of the N consecutive switch tubes, and the capacitance of the capacitor between the source and the drain of the N consecutive switch tubes gradually decreases in the direction away from the fixed end, and the capacitor between the source and the drain of the switch tube is connected in parallel with the resistor between the drain and the source of the switch tube, and M and N are both integers, and N is less than M.

2. The high withstand voltage SOI CMOS RF switch according to claim 1, characterized in that: The radio frequency switch comprises a fixed terminal and n selection terminals, forming a single-pole n-throw switch.

3. The high withstand voltage SOI CMOS RF switch according to claim 2, characterized in that: m single-pole n-throw switches are stacked in parallel, and the m single-pole n-throw switches are single-pole n1 throw switch, single-pole n2 throw switch, ..., single-pole nm throw switch, forming an m-pole (n1+n2+...+nm) throw switch.

4. The high withstand voltage SOI CMOS RF switch according to claim 1, characterized in that: The size of N depends on the power level that the RF switch needs to withstand.

5. The high withstand voltage SOI CMOS RF switch according to claim 1, characterized in that: Each channel includes three cascaded switch tubes. Each channel selects a switch tube at the fixed end, and a capacitor is connected between the source and drain of the switch tube.

6. The high withstand voltage SOI CMOS RF switch according to claim 1, characterized in that: Each channel includes three cascaded switch tubes. Each channel selects two switch tubes at the fixed end. Capacitors are respectively connected between the source and drain of the two switch tubes.

7. The high withstand voltage SOI CMOS RF switch according to claim 1, characterized in that: The switch tube is a SOI CMOS transistor or a plurality of SOI CMOS transistors connected in series.

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