High-power switching circuit

Abstract

In order to overcome the defects in the prior art, a radio frequency circuit and a driving circuit of the PIN tube switch are redesigned, and the PIN tube switch comprises a PIN diode pair and a half-bridge NMOS driving circuit which are connected back to back. Each PIN diode in the PIN diode pair bears a half of input voltage, and secondary harmonics generated by the two back-to-back diodes are offset. The driving circuit only charges and discharges the gate capacitor during switching of the switch, and the driving circuit has no high-voltage quiescent current, so that the power consumption of the driving circuit is reduced. Compared with the prior art, the power divider has the advantages of high bearing power, small second harmonic, low power consumption and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave antennas, and in particular relates to a high-power switching circuit. Background Art

[0002] Microwave switches based on PIN diodes have the characteristics of fast response, low loss and high power capacity, and are widely used in radar, communication and electronic countermeasure systems. However, the existing RF switches still have the following problems that need to be solved urgently. The RF voltage is borne by a single PIN diode, which is not conducive to the increase of peak power. The PIN drive circuit resistor works at a high voltage and has a large static power consumption. The high-voltage PNP (or PMOS) transistor devices required for the drive module have few application scenarios and poor electrical performance. The PIN switch has no second harmonic cancellation mechanism, and a complex filter needs to be added to suppress the second harmonic. At the same time, the DC blocking capacitor needs to withstand high DC voltage. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention proposes a high-power switching circuit, which makes significant improvements to the RF circuit and driving circuit of the PIN tube switch, so as to obtain the advantages of second harmonic cancellation, doubling of RF withstand voltage, improvement of isolation, reduction of drive circuit power consumption and reduction of DC blocking capacitor withstand voltage, thereby greatly improving the performance of the PIN tube switch.

[0004] The high-power switch circuit of the present invention is composed of a radio frequency circuit module and a drive circuit module; the internal switch element of the radio frequency circuit module is two PIN diode pairs connected back to back, the PIN diode pair is composed of two diodes whose cathodes are connected together and connected to pin 3, the anode of the first diode is connected to pin 1, the anode of the second diode is connected to pin 2, and the two diodes are packaged in the same tube shell; the radio frequency circuit module, the DC blocking capacitor and the circuit distributed inductor form an LC resonant circuit, and the resonant frequency is within the working frequency band; the drive circuit module is composed of a MOS drive circuit and an NMOS transistor.

[0005] Furthermore, the PIN diode pair can also be composed of the same number of PIN diodes connected in parallel, with the positive electrodes of each group of PIN diodes connected together as the positive electrode, and the negative electrodes of each group connected together as the negative electrode. Multiple diodes connected in parallel can increase the power handling capacity of the switch.

[0006] Furthermore, the PIN diode can also be connected in reverse to the internal diode, with the anodes of the two diodes connected together, the cathodes of the two diodes connected to pins 1 and 3 of the pipe shell respectively, and pin 2 connected to the control input.

[0007] The PIN diode pair has an airtight structure. The internal pressure of the tube shell remains unchanged under low-pressure working conditions, which does not affect the withstand voltage of the PIN diode pair under low-pressure working conditions. The PIN diode pair is filled with inert gas to reduce the risk of internal gas breakdown.

[0008] In the reverse bias state, the two PIN diodes bear the RF voltage together, and the voltage of a single diode is half of the voltage of the tube pair; in the forward bias state, the current passing through each PIN diode is the same as that of a single tube. Under the same device conditions, the PIN tube pair has a higher withstand voltage and the same carrying current as a single tube, and has a greater power handling capacity than a switch composed of a single tube.

[0009] The two PIN diodes in the same package come from adjacent locations on the same wafer, and the electrical performance deviation can be controlled within ±1%. The even harmonics generated by the two diodes cancel each other out, reducing the technical difficulty of the harmonic suppression filter.

[0010] PIN diode switches use a series-parallel topology, with one PIN diode pair connected in series on the transmission line connecting the input and output, and another PIN diode pair connected in parallel between the transmission line and ground.

[0011] The parallel PIN diode pair, the ground decoupling capacitor and the diode pair distributed inductance LS designed in the present invention work in a series resonance mode, and the resonance frequency is designed to be the center frequency, thereby avoiding the isolation reduction phenomenon caused by the lead inductance.

[0012] The maximum DC voltage that all DC blocking capacitors in RF circuits can withstand does not exceed 5V. DC blocking capacitors do not need to withstand high-voltage driving voltages, so there is no need to use high-voltage DC blocking capacitors, thereby reducing device costs.

[0013] The switch drive circuit uses a more cost-effective NMOS half-bridge circuit and integrated MOS driver, and only charges and discharges the gate capacitance during the switch switching state. There is no high-voltage current when the switch is not switching, which reduces the power consumption of the drive circuit.

[0014] Second harmonic cancellation principle:

[0015] When the switch circuit module is working, the output corresponding to the signal input of the two frequencies F1 F2 includes not only the F1 F2 frequency, but also the F1 F2 combination frequency F1+F2, F1-F2, 2F1-F2, 2F2-F1, 2F1, 2F2, 3F1, 3F2, mF1+nF2. These frequencies are mainly due to the intermodulation caused by the nonlinear response of semiconductor devices. PIN diodes are typical semiconductor devices, and the intermodulation index can be expressed by the 2nd order intercept point and the 3rd order intercept point.

[0016]

[0017] Qnc =I m Aτ μs …………………………………………………………(3)

[0018] Second harmonic output:

[0019] P2dBm=2PidBm-IP2dBm……………………………………(4)

[0020] Third harmonic output:

[0021] P3dBm=3PidBm-2IP3dBm……………………………………(5)

[0022] From equation (1), it can be concluded that the second harmonic decreases with the increase of stored charge and increases with the increase of input power. The response of a single PIN diode to the positive and negative half-cycles of the RF is different, and second harmonics must exist. According to the law of Fourier analysis, the even harmonics of a periodic odd function are zero. The device can be changed to a symmetrical device to achieve the electrical characteristics of the odd function and thus eliminate the even harmonics. By connecting two diodes with the same electrical properties in reverse series, the responses of the PIN diodes formed by them to the positive and negative half-cycles are equal in magnitude and opposite in sign, and the even harmonics output by them are zero, thus achieving even harmonic cancellation. The effect of the cancellation depends on the consistency of the electrical parameters of the two diodes.

[0023] The two PIN diodes in the same package come from adjacent positions on the same wafer and have excellent consistency. The two diodes installed back to back have ideal odd function characteristics, so they have a good cancellation effect. The specific cancellation effect is affected not only by the consistency of the device, but also by the distribution parameters. The cancellation effect of the circuit of the present invention varies slightly with different operating frequencies. For details, see Figure 8 .

[0024] Withstand voltage multiplication principle:

[0025] The equivalent DC circuit of the PIN diode is shown in Fig. 6A When pin 3 is connected to a high positive voltage, the AC equivalent circuit is as follows: Fig.9A ; When the 3rd pin is grounded, the AC equivalent circuit is shown in Fig. 9B . Because the electrical parameters of the two tubes in the PIN diode pair are the same, the applied DC voltage is the same as the voltage at each PIN diode terminal. The applied AC voltage is twice the voltage at each PIN diode terminal, and the current passing through the two PIN diodes is the same. Therefore, the parameters of the PIN diode pair are that the junction capacitance is halved, the withstand voltage is doubled, and the series resistance is doubled. Without considering the mutual influence of the two tubes, the dissipated power of the tube pair is the sum of the two diodes, that is, the dissipated power is also doubled.

[0026] Resonance isolation improvement principle:

[0027] The isolation of the switch when it is off can be expressed as:

[0028]

[0029] The distributed inductance of the PIN diode lead and the distributed inductance of the external circuit are combined into Ls. The series equivalent resistance RF of the high-power PIN diode is usually less than 1Ω. The reactance of the series inductance LS and the decoupling capacitor C1 cannot be ignored compared with RF, and the impact on isolation is usually greater than 6dB. It can be concluded from formula (6) that the reactance of the distributed inductance and the decoupling capacitor C1 can cancel each other. When the reactance of C1 and the reactance of LS are equal, the two form a series resonance, and its reactance term is zero, thereby improving the isolation. The resonant frequency is calculated by (7). Cancellation has an ideal effect only near the resonant frequency, and the isolation deteriorates as the bandwidth widens. Fig.11 Demonstrates the isolation effect achieved using a resonant design.

[0030] Working principle of driving circuit:

[0031] See the driver module using NMOS transistors and MOS drivers. Figure 4 , MOS drive internal circuit see Fig.10 . The MOS driver is typically referred to as NSD1624, whose inputs HI and LI are two inverting logic signals. When Hi input is low level and Li input is high level, the driver HO outputs low level, NMOS transistor S1 is cut off, NMOS transistor S4 is turned on, and the circuit outputs low level; when Hi input is high level and Li input is low level, the driver HO outputs high level, NMOS transistor S1 is turned on, NMOS transistor S4 is cut off, and the circuit outputs high level. When the output is low level, diode D1 is turned on, and the low-voltage power supply charges the bootstrap capacitor CB1 through diode D1. When the output is high level, diode D1 is cut off, and CB1 supplies power to the MOS driver HO part of the circuit. Because the mobility of electrons in semiconductors is faster than that of holes, the electrical performance is reflected in small on-resistance, fast speed, small die and low price. NMOS tubes have a wide range of application scenarios and have a higher cost performance.

[0032] Principle of voltage reduction of RF DC blocking capacitors:

[0033] From the circuit Figure 3 It can be seen that one end of the DC blocking capacitor C1 is connected to +5V through resistors R1 and L1, and the other end is the circuit output end. There is no DC high voltage at both ends of capacitor C1. The working conditions of C2 and C3 are the same as C1, so the DC blocking capacitor does not need to withstand a higher DC voltage, which greatly reduces the withstand voltage requirements of the RF DC blocking capacitor.

[0034] The beneficial effects of the present invention are

[0035] Compared with the prior art, the present invention has the advantages of high power bearing capacity, small second harmonic, low power consumption and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of a PIN switch radio frequency module in the prior art.

[0037] Figure 2 This is a schematic diagram of a PIN switch drive module in the prior art.

[0038] Figure 3 This is a schematic diagram of a radio frequency module according to Embodiment 1 of the present invention.

[0039] Figure 4 This is a schematic diagram of a driving module according to Embodiment 1 of the present invention.

[0040] Figure 5 This is a schematic diagram of a radio frequency module according to Embodiment 2 of the present invention.

[0041] Fig. 6A This is a schematic diagram of the packaged PIN diode pair used in Example 1 of the present invention.

[0042] Figure 6B This is the schematic diagram of another packaged PIN diode pair.

[0043] Figure 6C This is the schematic diagram of another higher power package PIN diode pair.

[0044] Figure 7 This is a diode pair embodiment of the present invention.

[0045] Figure 8 This is the second harmonic improvement curve of the present invention.

[0046] Fig.9A This is a reverse biased AC equivalent circuit diagram of the PIN diode of the present invention.

[0047] Fig. 9B This is the forward biased AC equivalent circuit diagram of the PIN diode of the present invention.

[0048] Fig.10 for Figure 4 MOS driver internal circuit diagram.

[0049] Fig.11 Isolation curve for a switching circuit using a resonant design.

[0050] Fig.12 Isolation curve for a switching circuit without using resonance design. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] The principle of the radio frequency module of the embodiment 1 of the present invention is shown in Figure 3 , driver module see Figure 4 Each switch consists of 1 RF module and 4 driver modules. The outputs of the 4 driver modules are connected to K1A, K1B, K2A, and K2B respectively. The driver is connected to the appropriate input to make K1A and K2B at a low level. When K1B and K2A are at a high level, the two PIN diodes of GD1 are cut off and the two PIN diodes of GD2 are turned on. The bias voltage makes the equivalent circuit of GD1 Fig.9A , GD2 equivalent circuit Fig. 9B , JX-1 port is connected to JX-0; similarly, the two PIN diodes of GD3 are cut off, and the two PIN diodes of GD4 are turned on. The bias voltage makes the equivalent circuit of GD3 Fig.9A , GD4 equivalent circuit Fig. 9B , JX-2 is disconnected from JX-0.

[0053] When the drivers K1A and K2B are high and K1B and K2A are low, the two PIN diodes of GD1 are turned on and the two PIN diodes of GD2 are turned off. The bias voltage makes the equivalent circuit of GD1 Fig. 9B , GD2 equivalent circuit Fig.9A , JX-1 port and JX-0 are turned off; similarly, the two PIN diodes of GD3 are turned on, and the two PIN diodes of GD4 are turned off. The bias voltage makes the equivalent circuit of GD3 Fig. 9B , GD4 equivalent circuit Fig.9A , JX-2 is connected with JX-0.

[0054] Another embodiment of the present invention is shown in Figure 5 , the switch adds GD5, GD6 and corresponding RC components. When the driver K1A, K2B, K3B is at a low level and K1B, K2A, K3A is at a high level, JX-1 and JX-0 are turned on, JX-2, JX-3 and JX-0 are turned off; when the driver K1B, K2A, K3B is at a low level and K1A, K2B, K3A is at a high level, JX-2 and JX-0 are turned on, JX-1, JX-3 and JX-0 are turned off; when the driver K1B, K2B, K3A is at a low level and K1A, K2A, K3B is at a high level, JX-3 and JX-0 are turned on, JX-1, JX-2 and JX-0 are turned off.

[0055] The present invention is not limited to the above specific implementations, and the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the above implementations based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-frequency, high-power PIN switch circuit, characterized in that: It is composed of a radio frequency circuit module and a driving circuit module; the internal switching element of the radio frequency circuit module is two PIN diode pairs connected back to back, the PIN diode pair is composed of two diodes with cathodes connected together and connected to pin 3, the anode of the first diode connected to pin 1, the anode of the second diode connected to pin 2, and the two diodes are packaged in the same tube shell; the radio frequency circuit module, the DC blocking capacitor and the circuit distributed inductance form an LC resonant circuit, and the resonant frequency is within the working frequency band; the driving circuit module is composed of a MOS driving circuit and an NMOS transistor.

2. A low-frequency, high-power PIN switch circuit according to claim 1, characterized in that: The PIN diode pair can also be composed of the same number of PIN diodes connected in parallel, with the positive electrodes of each group of PIN diodes connected together as the positive electrode, and the negative electrodes of each group connected together as the negative electrode. Multiple diodes connected in parallel can increase the power resistance of the switch.

3. A low-frequency, high-power PIN switch circuit according to claim 1, characterized in that: The PIN diode can also be connected in reverse to the internal diode, with the positive electrodes of the two diodes connected together, the negative electrodes of the two diodes connected to pins 1 and 3 of the pipe shell respectively, and pin 2 connected to the control input.

4. A low-frequency, high-power PIN switch circuit according to any one of claims 1 to 3, characterized in that: The PIN diode pair tube shell is an airtight structure, and the air pressure inside the tube shell remains unchanged under a low-pressure working environment, which does not affect the withstand voltage of the PIN diode pair under the low-pressure working condition.

5. A low-frequency, high-power PIN switch circuit according to claim 4, characterized in that: The PIN diode is filled with an inert gas to reduce the risk of internal gas breakdown.

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