CN114826230B - Ultra-wideband single-pole multi-throw radio frequency switch applying reconfigurable filter network - Google Patents

Abstract

The purpose of the present invention is to provide an ultra-wideband single-pole multi-throw radio frequency switch using a reconfigurable filter network, which belongs to the technical field of radio frequency switches. The present invention is based on the idea of designing an ultra-wideband switch based on frequency band division, introduces a filter network into the single-pole multi-throw switch, and divides the working bandwidth of the switch into two frequency bands, low-pass and high-pass, and the corresponding branches are low-pass and high-pass. A number of single-pole single-throw units are connected after each branch; at the same time, combined with a reconfigurable filter network, the components connected to the filter network are switched through switching transistors when working in different frequency bands, so that the insertion loss of each branch in its operating frequency band is better than The traditional single-pole multi-throw switch has twice the operating frequency band.

Description

An ultra-wideband single-pole multi-throw radio frequency switch using a reconfigurable filter network

technical field

The invention belongs to the technical field of radio frequency switches, and in particular relates to an ultra-wideband single-pole multi-throw radio frequency switch using a reconfigurable filter network.

Background technique

Switches are a crucial part of radio frequency integrated circuits, and single-pole multi-throw switches composed of field effect transistors are widely used in wireless communication systems. The principle of the field effect transistor as a switch is very simple. Its gate is connected to the control voltage V _G . When V _G is greater than the threshold voltage of the field effect transistor, the field effect transistor is turned on. At this time, the path is equivalent to a small resistance, and the switch is turned on. ; When V _G is less than the threshold voltage of the field effect transistor, the field effect transistor is cut off, and the cut-off path is equivalent to a capacitor, and the switch is turned off.

SPMT switching circuits generally consist of multiple SPST units. Among the single-pole single-throw units, the most widely used is the series-parallel structure; that is, the single-pole single-throw unit is composed of a field effect transistor connected in series and a field effect transistor connected in parallel to the ground, and the control levels of the gates of the two are opposite. When the field effect transistors connected in series are turned on and the field effect transistors connected in parallel to the ground are turned off, the SPST unit is turned on; when the field effect transistors connected in series are turned off and the field effect transistors connected in parallel to the ground are turned on, the SPST unit is turned off At this time, the field effect transistor connected in parallel to the ground can reduce signal leakage and improve the isolation between SPST units.

With the continuous development of communication technology, the functions of RF front-end circuits are becoming more and more complex, and the application of multiple-input multiple-output technology is increasing, and the performance and bandwidth requirements of single-pole multiple-throw switches are getting higher and higher. However, since the transistor is not an ideal switch, there are parasitic effects and resistance, so when the number of throws is high and the frequency is high, the signal will leak from the parasitic capacitance of the turn-off branch transistor, which will cause the insertion loss and isolation of the switch to deteriorate .

Therefore, how to reduce the signal leakage of multi-throw switches at high frequencies and achieve ultra-wide operating frequency bands is a research focus.

Contents of the invention

In view of the problems existing in the background technology, the purpose of the present invention is to provide an ultra-wideband single-pole multi-throw radio frequency switch using a reconfigurable filter network. The switch provides a brand-new structure, so that different branches of the switch work in two frequency bands of low-pass and high-pass respectively, and each branch can realize very low insertion loss in the frequency band where it is located. .

To achieve the above object, the technical scheme of the present invention is as follows:

An ultra-wideband single-pole multi-throw radio frequency switch using a reconfigurable filter network, including several single-pole single-throw switch (SPST) units and a reconfigurable filter network, the reconfigurable filter network includes a switch transistor _ST , a An inductor L and a capacitor C;

The common port of the switch is connected to one end of the inductance L and one end of the capacitor C; the other end of the inductance L is connected to the drain of the transistor ST and the common end of several parallel _SPST units; the source of the transistor _ST is grounded, and the gate The pole is connected to the control voltage; the other end of the capacitor C is connected to several parallel SPST units; the other end of all SPST units is the output port of the SPMT switch;

The common port of the switch is connected with two branches in parallel, the branch where the inductor L is located is a low-pass branch, and the branch where the capacitor C is located is a high-pass branch.

Further, when any single-pole single-throw unit connected in parallel with the drain of the switching transistor _ST is turned on, and the switching transistor _ST and all other SPST units are disconnected, the low-pass branch works at this time, and the switching transistor _ST The parasitic capacitor, capacitor C and inductor L form a low-pass filter network; when any single-pole single-throw unit connected in parallel with one end of the capacitor and the switching transistor _ST are turned on, and all other single-pole single-throw units are turned off, the high-pass branch works at this time , Capacitor C and inductor L form a high-pass filter network.

Further, the switching transistor _ST should be a large-sized switching transistor to obtain a larger parasitic capacitance, so that the parasitic capacitance in the off state becomes a part of the filter network.

Further, the capacitance of the capacitor C and the inductance of the inductor L are comprehensively determined by the frequency band division range of the switch and the parasitic capacitance of the switch transistor _ST .

Further, the single-pole single-throw unit is a series-parallel structure composed of two transistors; wherein the drain of the first transistor is the input port of the single-pole single-throw switch unit, and the source is respectively connected to the drain of the second transistor, and at the same time It is the output port of the single-pole single-throw switch unit, the gate is connected to the first control level; the source of the second transistor is grounded, and the gate is connected to the second control level; the first control level and the second control level are opposite to ensure The two transistors are turned on and off respectively.

In summary, owing to adopting above-mentioned technical scheme, the beneficial effect of the present invention is:

1. The scheme of the present invention is based on the idea of designing an ultra-wideband switch based on frequency band division, and divides the working frequency bands of the two branches of the single-pole multi-throw switch into low-pass and high-pass two sections, and simultaneously introduces a filter network into the branches of the single-pole multi-throw switch. The insertion loss of each branch in its working frequency band is better than that of a traditional single-pole multi-throw switch, and the working frequency band is expanded twice. The traditional single-pole multi-throw switch can only realize the insertion loss less than 1dB in DC-9GHz, and the present invention extends to DC-18GHz.

2. The present invention jointly designs a reconfigurable filter network through an inductor, a capacitor, and a switching transistor, combined with the parasitic capacitance of the single-pole single-throw unit. The switching transistor cleverly introduces itself and the parasitic capacitance of the single-pole single-throw unit into the filter network, thereby reducing the influence of the parasitic capacitance of different frequency band branches on the working frequency band branch. The single-pole multi-throw switch of the present invention has an insertion loss of less than 1dB and a return loss of more than 15dB in the DC-18GHz full-frequency working frequency band.

Description of drawings

FIG. 1 is a schematic structural diagram of a traditional series-parallel single-pole multi-throw switch.

Fig. 2 is a schematic structural diagram of the single-pole multi-throw switch of the present invention.

Fig. 3 is the working principle and equivalent circuit diagram of the single-pole multi-throw switch circuit of the present invention.

Among them, (a) is a low-pass working path and its equivalent circuit diagram, and (b) is a high-pass working path and its equivalent circuit diagram.

Fig. 4 is a circuit structure diagram of a SPDT switch according to Embodiment 1 of the present invention.

FIG. 5 is a circuit structure diagram of a SPDT switch in Comparative Example 1. FIG.

FIG. 6 is a working principle and an equivalent circuit diagram of the SPDT switch of Comparative Example 1. FIG.

Among them, (a) is a low-pass working path and its equivalent circuit diagram, and (b) is a high-pass working path and its equivalent circuit diagram.

Fig. 7 is a circuit structure diagram of the SPDT switch of Comparative Example 2.

Fig. 8 is a performance comparison diagram of the SPDT switch of Embodiment 1 of the present invention, its Comparative Example 1 and Comparative Example 2;

Among them, (a) is the insertion loss, (b) is the return loss.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the implementation methods and accompanying drawings.

Figure 1 is a schematic structural diagram of a traditional SPMT switch. Each branch is a series-parallel SPST unit. The circuit will have an impact, which will increase the insertion loss, and the more branches and the higher the frequency, the more obvious the leakage; these shortcomings greatly limit the use of switches and the development of radio frequency integrated circuits.

In order to solve these problems, the present invention provides an ultra-wideband single-pole multi-throw radio frequency switch using a reconfigurable filter network, which can realize wide-band operation, reduce the mutual influence between branches of different frequency bands, and achieve low insertion Loss; the structure schematic diagram of single-pole multi-throw radio frequency switch of the present invention is as shown in Figure 2, comprises several single-pole single-throw switch (SPST) units and reconfigurable filtering network, and described reconfigurable filtering network comprises a switching transistor _ST , An inductor L and a capacitor C;

The common port of the switch is connected to one end of the inductance L and one end of the capacitor C; the other end of the inductance L is connected to the drain of the transistor ST and the common end of several parallel _SPST units; the source of the transistor _ST is grounded, and the gate The pole is connected to the control voltage VGH; the other end of the capacitor C is connected to several parallel SPST units; the other end of all SPST units is the output port of the SPMT switch;

The common port of the switch is connected with two branches in parallel, the branch where the inductor L is located is a low-pass branch, and the branch where the capacitor C is located is a high-pass branch.

Fig. 3 is the working principle and equivalent circuit diagram of the single-pole multi-throw switch of the present invention. As shown in figure (a), when a single-pole single-throw unit S _Ln in the low-pass branch is turned on, and all other SPST units are turned off and the transistor _ST is turned off, the low-pass branch works, and the inductance L and The capacitor C, the total parasitic capacitance C _ef1 of the m transistors whose high-pass branch is turned off, and the parasitic capacitance C _M1 of the switching transistor _ST jointly form a third-order low-pass filter network. When a single-pole single-throw unit S _Hm of the high-pass branch is turned on, and all other single-pole single-throw units are turned off and the transistor _ST is turned on, the high-pass branch works, and the capacitor C and the inductor L together form a second-order high-pass filter network. The transistor The _ST isolates all the low-pass branches connected to its back end, reducing the influence of the parasitic capacitance of the low-pass branch transistor on the turned-on high-pass branch.

The filter network order is determined by the number of capacitors and inductors in the filter network. The higher the filter network order, the smaller the signal attenuation within the cutoff frequency, and the faster the signal attenuation outside the cutoff frequency, the better the filter performance.

Example 1

A single-pole double-throw radio frequency switch using a reconfigurable filter network, its circuit structure diagram as shown in Figure 4, including two single-pole single-throw switch (SPST) units and a reconfigurable filter network;

The drain of the switching tube _ST is connected to one end of the inductor L and the drain of the switching tube S1 respectively, the source of the switching tube _ST is connected to the ground, and the gate is connected to the control signal VGH; the source of the switching tube S1 is connected to the terminal of the switching tube S2 The drain is also the low-pass port of the SPDT RF switch. The gate of the switch S1 is connected to the control signal VGL; the source of the switch S2 is connected to the ground, and the gate is connected to the control signal VGH; the drain of the switch S3 is connected to One end of the capacitor C, the source is connected to the drain of the switch tube S4, which is the high-pass port of the single-pole double-throw RF switch, the gate of the switch tube S3 is connected to the control signal VGH; the source of the switch tube S4 is connected to the ground, and the gate is connected to the control signal VGH. Signal VGL; the common port is connected to two branches, one is connected to the other end of the inductor L, and the other is connected to the other end of the capacitor C;

The control signals VGH and VGL have opposite levels. When VGH is high and VGL is low, the high-pass branch works; when VGH is low and VGL is high, the low-pass branch works.

Among them, inductance L=0.97nH, capacitance C=9.2pF.

The operating bandwidth of the SPDT radio frequency switch in this embodiment is in the frequency range of DC-18GHz, wherein the low-pass frequency band is DC-9GHz, and the high-pass frequency band is 9-18GHz.

Comparative example 1

A non-reconfigurable single-pole double-throw radio frequency switch, its circuit structure diagram is shown in Figure 5, its main structure is similar to Embodiment 1, except that the filter network does not contain a switching transistor _ST ; that is, the common terminals of the single-pole double-throw switch are respectively Connect one end of the inductor L to one end of the capacitor C, the other end of the inductor is connected to a series-parallel structure SPST, which is a low-pass branch; the other end of the capacitor is connected to a series-parallel structure SPST, this branch is Qualcomm branch.

Fig. 6 is the working principle and equivalent circuit diagram of the SPDT switch of the comparative example. As shown in figure (a), when the single-pole single-throw unit of the low-pass branch is turned on and the other SPST is turned off, the low-pass branch works. At this time, the inductance L, capacitor C and high-pass branch turn off the parasitic capacitance of the transistor C _ef2 together form a second-order low-pass filter, which can pass low-frequency signals. When one SPST unit of the high-pass branch is turned on and the other SPST is turned off, the high-pass branch works, and the high-pass filter network consists of a capacitor C and a parallel band-pass filter; where the band-pass filter consists of an inductor L It is formed in series with the parasitic capacitance C _ef3 when the low-pass branch is turned off; this band-pass filter will cause the intermediate frequency signal between low frequency and high frequency to leak to the ground, thereby increasing the insertion loss of the high-pass branch.

Comparative example 2

The circuit structure diagram of a traditional single-pole double-throw switch is shown in Figure 7. The common end of the single-pole double-throw switch is connected to two series-parallel SPSTs, and the output ports of the two SPSTs are the two output ends of the single-pole double-throw switch.

Fig. 8 is a performance comparison chart of SPDT switches of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention, wherein (a) is insertion loss, and (b) is return loss. It can be seen from Figure (a) that the insertion loss of Example 1 is less than 1dB and the return loss is higher than 15dB in the DC-18GHz full frequency band; the insertion loss of Comparative Example 1 exceeds 1dB at the overlap of the spectrum, and the return loss is all The frequency band is higher than 10dB; in comparison example 2, the insertion loss in the DC-9GHz frequency band is less than 1dB, and the insertion loss increases significantly in the 9-18GHz frequency band. When the frequency is higher than 12GHz, the return loss is lower than 10dB. Compared with Comparative Example 2, the present invention reduces the signal leakage of the single-pole multi-throw switch at high frequencies, reduces the insertion loss at high frequencies, thereby expanding the working bandwidth by two times; compared with Comparative Example 1, it can be reconfigured The design of the filter network reduces the leakage of signals at the overlapping frequency bands.

The above is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All method or process steps may be combined in any way, except for mutually exclusive features and/or steps.

Claims (4)

1. An ultra-wideband single-pole multi-throw radio frequency switch applying a reconfigurable filter network is characterized by comprising a plurality of single-pole single-throw switch units and the reconfigurable filter network;

the reconfigurable filter network comprises a switching transistor S _T An inductance L and a capacitance C; the public port of the ultra-wideband single-pole multi-throw radio frequency switch is connected with one end of the inductor L and one end of the capacitor C; the other end of the inductor L and the transistor S _T The drain electrodes of the single-pole single-throw units are connected in parallel; transistor S _T The source electrode of the transistor is grounded, and the grid electrode is connected with the control voltage; the other end of the capacitor C is connected with a plurality of single-pole single-throw units which are connected in parallel; the other ends of all the single-pole single-throw units are output ports of the single-pole multi-throw switch;

the common port of the ultra-wideband single-pole multi-throw radio frequency switch is connected with two branches in parallel, the branch where the inductor L is located is a low-pass branch, and the branch where the capacitor C is located is a high-pass branch; when switching transistor S _T Any single-pole single-throw unit connected in parallel with the drain electrode of the transistor S is turned on _T When all the other single-pole single-throw units are disconnected, the low-pass branch circuit works, and the switch transistor S _T The parasitic capacitance, the capacitance C and the inductance L form a low-pass filter network; any single-pole single-throw unit and switch transistor S connected in parallel when one end of capacitor _T When all the other single-pole single-throw units are disconnected, the high-pass branch circuit works, and the capacitor C and the inductor L form a high-pass filter network; when a single pole single throw unit S in a low pass branch _Ln On, all other single pole single throw units are off and transistor S _T When cut-off, the low-pass branch works, the inductor L and the capacitor C and the high-pass branchTotal parasitic capacitance C of m transistors with off-state _ef1 Switching transistor S _T Parasitic capacitance C of (2) _M1 Forming a third-order low-pass filter network together; when a single-pole single-throw unit S of a high-pass branch is used _Hm On, all other single pole single throw units are off and transistor S _T When the high-pass branch is conducted, the capacitor C and the inductor L jointly form a second-order high-pass filter network, and the transistor S _T The low-pass branches connected with the rear end are all isolated, so that the influence of parasitic capacitance of the transistor of the low-pass branch on the conducted high-pass branch is reduced.

2. The ultra-wideband single pole multiple throw radio frequency switch of claim 1, wherein switching transistor S _T The switching transistor should be selected to be large in size to obtain a large parasitic capacitance, so that the parasitic capacitance in its off-state becomes part of the filter network.

3. The ultra-wideband single pole multiple throw RF switch as claimed in claim 1, wherein the capacitance of the capacitor C and the inductance of the inductor L are divided by the frequency band of the switch and the switching transistor S _T Is determined comprehensively.

4. The ultra-wideband single pole, multi-throw radio frequency switch of claim 1, wherein the single pole, single throw unit is a series-parallel structure comprised of two transistors; the drain electrode of the first transistor is an input port of the single-pole single-throw switch unit, the source electrodes of the first transistor and the second transistor are respectively connected with the drain electrode of the second transistor, the drain electrode of the first transistor is an output port of the single-pole single-throw switch unit, and the grid electrode of the first transistor is connected with a first control level; the source electrode of the second transistor is grounded, and the grid electrode of the second transistor is connected with a second control level; the first control level is opposite to the second control level to ensure that the two transistors are turned on and off, respectively.

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