阅读说明：本技术 一种基于二极管的宽频射频开关及边沿优化方法 (Broadband radio frequency switch based on diode and edge optimization method ) 是由 姚守权 徐俊成 蒋瑜 宋一桥 沈明 胡炳文 于 2020-12-11 设计创作，主要内容包括：本发明涉及一种基于二极管的宽频射频开关,包括基于二极管的开关电路部分和偏置电路,所述偏置电路与所述开关电路部分相连,所述开关电路部分的射频输入端与第一阻交流电感的一端相连,所述第一阻交流电感的另一端接地；所述开关电路部分的射频输出端与第二阻交流电感的一端相连,所述第二阻交流电感的另一端接地。本发明还涉及一种基于二极管的宽频射频开关的边沿优化方法。本发明解决了射频开关状态切换时由于二极管管压降而造成的直流电平跳变过大问题。(The invention relates to a broadband radio frequency switch based on a diode, which comprises a switch circuit part based on the diode and a bias circuit, wherein the bias circuit is connected with the switch circuit part; the radio frequency output end of the switch circuit part is connected with one end of a second alternating current resistance inductor, and the other end of the second alternating current resistance inductor is grounded. The invention also relates to an edge optimization method of the diode-based broadband radio frequency switch. The invention solves the problem of overlarge direct current level jump caused by the voltage drop of the diode when the state of the radio frequency switch is switched.)

1. A broadband radio frequency switch based on a diode comprises a switch circuit part based on the diode and a bias circuit, wherein the bias circuit is connected with the switch circuit part; the radio frequency output end of the switch circuit part is connected with one end of a second alternating current resistance inductor, and the other end of the second alternating current resistance inductor is grounded.

2. The diode-based wideband radio frequency switch of claim 1, wherein freewheeling diodes are connected in parallel to both ends of the first and second ac blocking inductors.

3. The diode-based wideband radio frequency switch of claim 1, wherein a dump diode is connected in parallel to both ends of the first and second ac blocking inductors.

4. The diode-based wideband radio frequency switch of claim 1, wherein the switch circuit portion comprises an even number of diodes connected in reverse symmetrical series.

5. The diode-based wideband radio frequency switch of claim 1, wherein the bias circuit is an inductor and a current limiting resistor connected in series with each other.

6. The diode-based wideband radio frequency switch of claim 1, wherein the diode is a PIN diode or a switch diode.

7. An edge optimization method for a diode-based wideband radio frequency switch, characterized in that, the diode-based wideband radio frequency switch as claimed in any one of claims 1 to 6 is adopted, during the on period of the radio frequency switch, the current of the bias circuit is reduced under the condition of ensuring that the insertion loss of the radio frequency switch meets the requirement, so that the voltages of the first resistance alternating current inductor and the second resistance alternating current inductor approach to zero; during the disconnection and the conduction of the radio frequency switch, the first resistance alternating current inductor and the second resistance alternating current inductor are grounded through self resistors.

Technical Field

The invention relates to the technical field of radio frequency switches, in particular to a diode-based broadband radio frequency switch and an edge optimization method.

Background

The radio frequency switch is used for connecting or disconnecting one or more paths of radio frequency signals through control logic so as to realize switching of different signal paths, including switching of receiving and transmitting, switching between different time and different frequency bands and the like. The radio frequency switch is used as a switch unit, and can form switches in various forms such as single-pole single-throw, single-pole double-throw and double-pole double-throw through different combinations.

Currently, radio frequency switches can be generally classified into mechanical switches and solid state switches according to implementation modes. The mechanical radio frequency switch is realized based on contact, and the on-off of the contact is controlled by a magnetic field generated by a current driving coil. Such switches are generally suitable for scenarios where transmission power is high, isolation requirements are high, but switching speed is slow. The solid-state radio frequency switch is generally implemented by using a transistor or a diode, and the impedance value of the devices is changed by an electric signal to switch on and off the radio frequency signal, so that the radio frequency switch can realize very fast switching (for example, less than 100 nanoseconds) to be applied to a use scene with a high requirement on the switching speed. For example, in radar systems and magnetic resonance systems, a transmit/receive (T/R) switch is used as a key component for channel switching, and the main function of the T/R switch is to switch a radio frequency transmit channel and a signal receive channel.

PIN diodes are currently widely used as switching devices in the design of T/R switches and actively tuned coils. The PIN diode incorporates a low-doped Intrinsic (Intrinsic) semiconductor layer between the P and N semiconductor materials, so that it behaves, for radio frequency signals, as a variable resistance controlled by a dc power supply: when a positive bias current is applied, the radio frequency signal presents low impedance, and the impedance is smaller when the current is larger in a certain range; when a reverse bias voltage is applied, the impedance state is high. Compared with a radio frequency switch formed by a field effect transistor (MOSFET) or a triode (BJT), the PIN diode switch has lower insertion loss, smaller junction capacitance and more excellent noise coefficient, and can realize faster switching speed.

With the development of magnetic resonance spectroscopy and imaging systems, the requirements on transmission power, transmit-receive switching time and received signal-to-noise ratio are continuously increased, so as to realize rapid and accurate measurement. When the magnetic resonance system works, a radio frequency signal with larger power is firstly emitted to excite a sample, and then the magnetic resonance signal generated by the sample is detected. The high-power radio-frequency excitation signal belongs to a transmitting channel, and the detection of the magnetic resonance signal belongs to a receiving channel. The function of the T/R switch is to switch the two channels in the shortest possible time according to the measurement requirement. Therefore, it is required that: 1. the smaller the insertion loss and noise of the T/R switch, the higher the signal-to-noise ratio of the detected magnetic resonance signal upon entering the preamplifier. 2. The higher the isolation of the T/R switch is, the less high-power radio-frequency signals for exciting the sample through the magnetic resonance coil enter the receiving channel during the transmission of the magnetic resonance system, so that the saturation or damage of a preamplifier in the receiving channel caused by the overlarge amplitude of the input signals can be avoided. 3. When a magnetic resonance system acquires certain signals, the faster the switching time of the magnetic resonance system, the larger the amplitude of the acquired signals, and the switching time of a T/R switch generally used for the magnetic resonance system is about a few microseconds. Based on the above requirements for T/R switches, diodes, in particular PIN diodes, are very suitable for the design of radio frequency switches. Compared with a PN junction diode, when the PIN diode is conducted in the forward direction, two carriers, namely a P layer hole carrier and an N layer electron carrier, are stored in the I layer in a large quantity, so that the conduction resistance is reduced, and the PIN diode can bear large high-frequency current; when the diode is in reverse cut-off, the I layer space charge region expands along with the increase of an electric field, so that the impedance is improved, and meanwhile, the PIN diode can bear higher voltage. The switching speed of the PIN diode is related to the thickness of the I layer and the service life of a current carrier, and the switching time of the PIN diode with the thin thickness of the I layer and the short service life of the current carrier can be shortened to be within 1 mu s.

However, the following problems still exist when the radio frequency switch is designed by using the diode: 1. when the diode is conducted, a forward biased direct current path is needed to be provided for the diode, and after the diode is conducted, a forward biased voltage drop of about 0.7V is generated. At the same time, the diode needs to be supplied with a reverse bias voltage when it is turned off. The on and off characteristics of the diodes cause level jump when the state is switched, and the amplitude of the level jump of the output end increases along with the increase of the number of the diodes. When a plurality of diodes are connected in series or in parallel in a radio frequency path, a level jump when the state of the diode is switched can be coupled to an output end, and if the level jump is too large, the normal operation of a subsequent stage circuit can be influenced. 2. Because the forward bias current and the radio frequency signal flow through the diode simultaneously when the switch is turned on, the bias circuit must be able to realize the characteristics of AC resistance and DC resistance in order to ensure that the radio frequency signal does not flow into the DC bias circuit to generate attenuation. In a narrow-band system, the isolation of the radio frequency signal of a specific frequency is generally realized by a resonant circuit. In a broadband system, to ensure that radio frequency and dc signals can be separated in a wider frequency band, a large inductor or rf choke is generally connected in series in a bias circuit. When the radio frequency switch needs to work in a lower frequency band, in order to ensure the isolation of an alternating current signal, the inductance value of the alternating current resistance inductance of the radio frequency switch is generally larger. Although the large inductor or choke coil can isolate the alternating current signal, when the radio frequency switch is switched between the on state and the off state, because the current in the inductor cannot be changed rapidly, a switch burr with large amplitude is generated at two ends of the inductor or the radio frequency choke coil, and the amplitude of the switch burr is increased along with the increase of the inductance value of the alternating current resistor. The problem that arises is that, in addition to reducing the switching speed of the switch, an oscillating overshoot signal with a longer duration and a larger amplitude is generated on the rf path, and when the amplitude of the oscillating signal is too large, the subsequent circuit is saturated or even damaged. 3. The switching characteristics of the diode require that its diode for the switching function be in a reverse biased state when the radio frequency switch is off. However, the radio frequency power used by the magnetic resonance system is generally large, and when the radio frequency power enters the radio frequency switch, if the reverse bias voltage of the diode is not enough to meet the cut-off condition of the diode, that is, the voltage amplitude of the high-power radio frequency signal input by the radio frequency switch is enough to make the diode conduct in the forward direction, the radio frequency switch enters the conducting state, so that the high-power signal part leaks to the rear-stage circuit through the radio frequency switch.

Disclosure of Invention

The invention provides a diode-based broadband radio frequency switch and an edge optimization method, which solve the problem of overlarge direct current level jump caused by the voltage drop of a diode when the state of the radio frequency switch is switched.

The technical scheme adopted by the invention for solving the technical problems is as follows: the broadband radio frequency switch based on the diode comprises a switch circuit part based on the diode and a bias circuit, wherein the bias circuit is connected with the switch circuit part, the radio frequency input end of the switch circuit part is connected with one end of a first alternating current resistance inductor, and the other end of the first alternating current resistance inductor is grounded; the radio frequency output end of the switch circuit part is connected with one end of a second alternating current resistance inductor, and the other end of the second alternating current resistance inductor is grounded.

And two ends of the first resistance alternating current inductor and the second resistance alternating current inductor are connected with a freewheeling diode in parallel.

And energy discharge diodes are connected in parallel at two ends of the first resistance alternating current inductor and the second resistance alternating current inductor.

The switching circuit part includes an even number of diodes connected in series in reverse symmetry.

The bias circuit is composed of an inductor and a current-limiting resistor which are connected in series.

The diode is a PIN diode or a switch diode.

The technical scheme adopted by the invention for solving the technical problems is as follows: the edge optimization method of the broadband radio frequency switch based on the diode is adopted, and during the conduction period of the radio frequency switch, the current of the bias circuit is reduced under the condition that the insertion loss of the radio frequency switch meets the requirement, so that the voltages of the first resistance alternating current inductor and the second resistance alternating current inductor approach to zero; during the disconnection and the conduction of the radio frequency switch, the first resistance alternating current inductor and the second resistance alternating current inductor are grounded through self resistors.

Advantageous effects

Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects: the invention solves the problem of overlarge direct current level jump caused by the voltage drop of the diode when the state of the radio frequency switch is switched by connecting the input end and the output end in parallel with the single-ended grounding inductor. The invention adds a freewheeling diode and an energy-leakage diode after the output end is connected with the ground inductor to solve the problem that the current in the inductor can not change suddenly. The invention adopts a symmetrical design that the homonymous ends of the diodes are connected, and solves the problem that the radio frequency switch is passively conducted due to overlarge input signals. Through reasonable circuit design, the invention reduces the direct current level change of the diode during switching, inhibits the edge burr during switching of the switch and enhances the isolation of high-power signals. Meanwhile, the radio frequency switch structure has wider bandwidth, lower insertion loss and smaller noise coefficient.

Drawings

Fig. 1 is a schematic diagram of an embodiment of the present invention.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

The embodiment of the invention relates to a diode-based broadband radio frequency switch, which comprises a diode-based switch circuit part and a bias circuit, wherein the bias circuit is connected with the switch circuit part, as shown in figure 1.

As shown IN fig. 1, IN is a radio frequency input terminal, OUT is a radio frequency output terminal, and DRV port is an input port of the bias circuit, and when the port is a negative voltage, the diode of the switch circuit portion is IN a forward bias state, and the switch is IN a conducting state. When the port is at a positive voltage, the diode of the switching circuit portion is in a reverse bias state and the switch is in an off state. D1-D6 are diodes, and it is noted that the number of diodes in the present invention is not less than one to realize the function of the rf switch, and the present embodiment takes 6 diodes as an example to illustrate the structure and principle. D7 and D10 are diodes for inductor freewheeling, and D8 and D9 are diodes for inductor energy leakage. C1 and C2 are DC blocking capacitors connected in series at the input and output ends. L1 and L2 are resistance alternating current inductors, L3 is an inductor in the bias circuit, and the resistance alternating current inductors L1, the resistance alternating current inductors L2 and the bias circuit form a bias loop. R1 is a current limiting resistor. The diodes D1-D6 are divided into two groups, the first group is diodes D1-D3, and the directions of the diodes are the same; the second group is diodes D4-D6, the directions of the diodes are the same, the two groups of diodes are connected in series in an inverted mode, the negative ends of the diodes are connected with each other, the positive end of the diode of the first group is connected with a capacitor C1, and the positive end of the diode of the second group is connected with a capacitor C2. A capacitor C1 and a capacitor C2 are connected in series in the switch circuit portion of the radio frequency path, the capacitor C1 is connected to the input terminal, and the capacitor C2 is connected to the output terminal. A resistance alternating current inductor L1, a resistance alternating current inductor L2 and an inductor L3 are connected in series in a bias loop of the diode, wherein one end of the resistance alternating current inductor L1 is connected to the back of the positive end of the diode D1, and the other end of the resistance alternating current inductor L1 is grounded; one end of an alternating current resistance inductor L2 is connected behind the positive end of the diode D6, and the other end of the alternating current resistance inductor L2 is grounded; one end of the inductor L3 is connected between the two groups of diodes, and the other end is connected with the current limiting resistor R1. The negative end of the diode D7 is connected to the positive end of the diode D1, and the positive end is grounded; the positive end of the diode D8 is connected to the positive end of the diode D1, and the negative end is grounded; the positive end of the diode D9 is connected to the positive end of the diode D1, and the negative end is grounded; the diode D10 has its negative terminal connected to the positive terminal of the diode D1 and its positive terminal connected to ground. One end of the current limiting resistor R1 is connected with the inductor L3, and the other end is connected with the DRV port.

In this embodiment, the diodes D1 to D6 may be PIN diodes or switch diodes, and all of them may function as a broadband rf switch. The switch diode is a nonlinear device in a radio frequency band, the frequency response is not good enough, and the insertion loss and the isolation of the switch diode are not good as those of a PIN diode. In order to ensure broadband performance, a PIN diode is optimally used.

In the embodiment, the switching circuit part takes 6 diodes connected in series as an example, the number of the diodes is not necessarily 6, and the radio frequency switching function can be realized by using not less than 1 diode. If the isolation degree of the radio frequency switch is required to be increased, the number of diodes is increased; conversely, reducing the number of diodes can reduce the insertion loss of the radio frequency switch. It should be noted that although 1 diode can also be used to implement the rf switching function, a reverse symmetric serial design of diodes cannot be formed, that is, the problem of passive conduction of diodes caused by high-power signals cannot be effectively solved, and a minimum of 2 diodes are required to implement the high-power signal suppression function.

IN order to solve the problem of instantaneous level jump of diode switching, a diode bias loop is reasonably designed, and a structure that one end of an AC resistance inductance L1 and an AC resistance inductance L2 is grounded and the other end of the AC resistance inductance L is connected to a radio frequency input end IN and a radio frequency output end OUT IN parallel is formed. During the on period of the radio frequency switch, the resistance alternating current inductor L1 and the resistance alternating current inductor L2 provide a loop for the diode bias current, and the current flowing through the inductor is I₀. The self DC resistances of the AC resistance inductance L1 and the AC resistance inductance L2 are both R_LThen the voltage across the AC-resistance inductance L1 and the AC-resistance inductance L2 is the same as U_L1＝U_L2＝I₀R_L. When a constant voltage source is used to drive the diode switch, the current can be regulated by varying the value of the current limiting resistor R1. Reducing the current I under the condition of ensuring that the insertion loss of the radio frequency switch meets the design requirement₀And using a DC impedance R_LAfter the smaller inductance is used as the first resistance alternating current inductance and the second resistance alternating current inductance, the voltage U on the resistance alternating current inductance L1 and the resistance alternating current inductance L2_L1And U_L2Are all close to 0V. During the disconnection period of the radio frequency switch, the resistance alternating current inductor L1 and the resistance alternating current inductor L2 are grounded through self resistors, and the voltage U is_L1And U_L2Also approaching 0V. Therefore, the design can effectively reduce the level jump of the input end and the output end of the radio frequency switch when the states are switched.

The invention has the advantages that through reasonable design of the bias loop, the resistance alternating current inductor is arranged at the tail end of the diode bias loop, so that the resistance alternating current inductor is grounded in a single point, the voltage is pulled to be close to 0V through the resistance of the resistance alternating current inductor, and the problem of level jump when the state of the diode radio frequency switch is switched is optimized.

When the diode radio frequency switch is conducted, forward bias needs to be applied, the diode is conducted in the forward direction, and the conducting impedance of the diode is inversely proportional to the magnitude of bias current; when the diode is cut off, a reverse bias is applied, the diode is cut off in a reverse direction, and no current flows in the diode. However, the current in the inductor cannot change suddenly rapidly, and at the moment when the radio frequency switch is turned on, the alternating current resistance inductor L1 and the alternating current resistance inductor L2 in fig. 1 cannot provide a loop for the bias current, which may cause the turn-on speed of the radio frequency switch to become slow; at the moment that the radio frequency switch is turned off, the currents in the ac resistance inductance L1 and the ac resistance inductance L2 cannot be immediately released, but at the moment, the diodes D1 to D6 are all in a cut-off state, and then the currents in the ac resistance inductance L1 and the ac resistance inductance L2 generate an oscillation overshoot with a long time and a large amplitude on a radio frequency path. This overshoot may cause saturation and even burn out of subsequent circuits. If the frequency of the rf signal in the rf switch is low, in order to ensure that the rf signal is not coupled to the ground through the bias loop, an ac resistance inductance with a large inductance value is required, which further slows down the switching time of the rf switch and aggravates the overshoot of the switch.

In the embodiment, the freewheeling diode D7 is connected in parallel to the alternating current resistance inductor L1, the freewheeling diode D10 is connected in parallel to the alternating current resistance inductor L2, and a loop is provided for the bias current of the diode instead of the alternating current resistance inductor at the moment of turning on the radio frequency switch; a leakage energy diode D8 is connected in parallel to the side of the alternating current resistance inductor L1, a leakage energy diode D9 is connected in parallel to the side of the alternating current resistance inductor L2, and a leakage energy loop is provided for current in the alternating current resistance inductor at the moment that the radio frequency switch is turned off. Taking the ac resistance inductor L1 as an example, at the moment when the rf switch is turned on, the voltage at the DRV port changes from positive to negative, the voltage at the positive terminal of the diode D1-diode D3 is greater than the voltage at the negative terminal, the bias current should flow through the ac resistance inductor L1, but the current suddenly increases at the moment of switching, the ac resistance inductor L1 presents a high resistance to the sudden current, and the impedance of the ac resistance inductor L1 is inversely proportional to the current sudden change time. The diode D7 can replace the ac resistance inductor L1 to provide a freewheeling circuit for the diodes D1 to D3. When the current switching is finished and the bias current is direct current, the AC resistance inductor L1 is low-resistance, and the bias loop of the diode D1-the diode D3 flows current again through the AC resistance inductor L1. At the moment when the radio frequency switch is switched off, the voltage of the DRV port is changed from negative to positive, the voltage of the positive end of the diode D1-the voltage of the positive end of the diode D3 is smaller than the voltage of the negative end, and the diode D1-the voltage of the positive end of the diode D3 are in a cut-off state. However, current remains in the ac resistance inductor L1, and the diode D8 can provide a release current loop for the ac resistance inductor L1, so that the release of current in the ac resistance inductor L1 is accelerated, and the coupling of oscillation overshoot into the rf loop is reduced. The operating principles of the freewheeling diode D10 and the energy-discharging diode D9 of the ac resistance inductor L2 are the same as those of the ac resistance inductor L1, and are not described herein again.

Therefore, the direct current loop is provided at the moment when the radio frequency switch of the diode is conducted by a method of connecting the freewheeling diode and the energy leakage diode in parallel beside the resistance alternating current inductor; the energy leakage loop is provided for the alternating current resistance inductance at the moment of disconnection, the switching time of the diode radio frequency switch is shortened, and the switch oscillation is reduced.

In the present embodiment, the diodes D1 to D6 are divided into two groups, and the directions of the diodes D1 to D3 are the same; the directions of the diodes D4-D6 are the same, and the two groups of diodes are reversely connected in series with the negative terminal. When the radio frequency switch is IN an off state, the DRV port should be a positive voltage, and if a high-power signal is input to the radio frequency input terminal IN at this time, and the forward voltage of the high-power signal is higher than the sum of the DRV port voltage and the conduction voltages of the three diodes, the positive end voltages of the diodes D1-D3 are higher than the negative end, and the diodes D1-D3 are turned on. However, the voltage at the negative end of the diode D4-the diode D6 is still higher than the voltage at the positive end, and the diode D4-the diode D6 are kept cut off; when the negative voltage is higher, the diodes D1-D3 still keep cut-off. The clamping of the high-power input signal cannot be completely guaranteed only by connecting the clamping diode in parallel at the input end, because the diode needs time to be conducted. When the frequency of the high-power signal is high, a part of the high-power signal leaks into the radio frequency switch before the clamping diode is completely conducted. In the embodiment, the diodes are divided into two groups, and the two groups of diodes are connected in series in a reverse symmetrical mode, so that the two groups of diodes cannot be conducted by a high-power signal at the same time, and the problem of passive conduction of the diodes caused by the high-power signal is effectively solved.

The direction of the diodes D1-D6 may be opposite to that described in the present embodiment, and the same function can be achieved by changing the DRV port to a positive voltage to turn on the rf switch and a negative voltage to turn off the rf switch. However, the positive voltage driving can cause the rf switch to output a positive voltage overshoot at the moment of turning on, and the negative voltage driving in this embodiment outputs a negative voltage overshoot at the moment of turning on the rf switch. The radio frequency switch post-stage circuit is generally an amplifier, the positive voltage overshoot can saturate the post-stage amplifier, and the negative voltage overshoot can cut off the post-stage amplifier. The time for the amplifier to return from the off state to the on state is generally shorter than the time for the amplifier to return from the saturation state. The mode that the radio frequency switch is driven to be conducted by the negative voltage can enable the post-stage amplifier to enter a working state more quickly after the switch is conducted.

Through reasonable circuit design, the invention reduces the direct current level change of the diode during switching, inhibits the edge burr during switching of the switch and enhances the isolation of high-power signals. Meanwhile, the radio frequency switch structure has wider bandwidth, lower insertion loss and smaller noise coefficient.