Switching circuit for broadband signals
The present invention relates to a switching circuit for broadband signals. It applies notably to radiocommunications systems, in particular power systems.
The receive circuit and the transmit circuit of a radiocommunications system sometimes use the same antenna, in particular when a compact system is desired. It is then necessary to place a switch between the antenna and said circuits, the switch allowing the circuits to share the antenna by alternately connecting the antenna with the transmitter circuit and the receiver circuit. The signals processed by the radiocommunications system may be high-power signals, for example with a power of the order of 1000 W, and spread over a broad band of frequencies, for example from 1 MHz to 1 GHz.
To be able to transmit a radiofrequency signal, a switch may be produced with a mechanical relay. However, this type of switch is relatively slow, the switching period generally being at the minimum of the order of 20 ms. Furthermore, its lifetime is limited by the number of switchings performed.
Switches in the form of electrical circuits comprising active components such as diodes or transistors have also been proposed. These active components are conventionally biased with the aid of DC voltage sources isolated from the radiofrequency circuit by inductances. However, the inductances exhibit stray capacitances causing short-circuits at the high frequencies and thus limiting the operating frequency band of the switch.
An aim of the invention is to propose a device able to switch a power signal over a broad band of frequencies. For this purpose, the subject of the invention is a switching circuit for controlling the passage of a radiofrequency signal between a first input-output and a second input-output, said circuit comprising at least one diode between said inputs-outputs, said circuit being characterized in that said diode is biased by a DC voltage source by way of at least two crossed transmission lines interconnecting said diode with said DC voltage source.
According to one embodiment of the switching circuit according to the invention each of the transmission lines comprises at least two conductors, said bias voltage source being linked to the first end of the second conductor of the first line, said diode being placed between the first end of the first conductor of the second line and an input-output of said circuit, said lines being mutually crossed so that the second end of the first conductor of the first line is linked to the second end of the second conductor of the second line and that the second end of the second conductor of the first line is linked to the second end of the first conductor of the second line, the first end of the first conductor of the first line being linked to the input-output.
The switching circuit according to the invention is open or closed to the passage of the radiofrequency signal according to the bias which is applied to the diode. In contradistinction to a conventional circuit whose operation is band-limited because of the presence of inductances, the switching circuit according to the invention makes it possible to bias the diode without bringing about undesirable resonance and thus to switch power signals over very broad bands of frequencies, for example of the order of 30 octaves, 1 MHz up to 1 GHz.
The switching circuit according to the invention is suitable for switching signals of high power, of power at least equal to 1000 Watts. Preferably, a PIN diode is used, this type of diode being very suited to the switching of high-power signals.
According to one embodiment of the switching circuit according to the invention, each of the transmission lines is a coaxial cable whose core forms one of the conductors of the line and whose braid forms the other conductor of said line.
Each of the transmission lines may be surrounded by a material of magnetic permeability greater than 1, so as to extend their electrical length. For example, a ferromagnetic torus may be placed around the lines.
According to one embodiment of the switching circuit according to the invention, the first end of the second conductor of the second line is linked to a terminal of said circuit, which terminal is connected to an electrical ground.
According to one embodiment of the switching circuit according to the invention, the first input-output of said circuit is linked to the first end of the first conductor of the first line, the diode linked to the second transmission line via a first terminal being connected via its second terminal to the second input-output of said circuit. The terminal of the diode linked to the second input-output is either the anode, or the cathode, depending on the direction in which the radiofrequency signal is transmitted.
According to another embodiment of the switching circuit according to the invention, the first input-output of said circuit is linked to the first end of the first conductor of the second line and to the first terminal of the diode, which diode is connected via its second terminal to an electrical ground, said circuit comprising a second input-output linked to the first end of the first conductor of the first line. A capacitor may be placed between the first input-output of said circuit and the first end of the core of the first transmission line.
The switching circuit according to the invention can comprise a capacitor placed between the voltage source and the electrical ground.
According to one embodiment of the switching circuit according to the invention, a second diode (D1) is linked to the first end (111a) of the first conductor of the first line (110) and controlled by a second voltage source (Vdd) linked to the first end of the second conductor (122) of the second line (120), the diodes (D1, D2) being placed by choice as follows:
- the anode of the first diode (D2) and the cathode of the second diode (D1) are each linked to a different input-output (101, 105),
- or the cathode of the first diode (D2) and the anode of the second diode (D1) are each linked to a different input-output (101, 105).
The switching circuit can comprise a capacitor placed between the voltage source and the electrical ground.
The subject of the invention is also a device for routing between several inputs-outputs and an access a power signal, for example a broadband signal, provided on one of said inputs-outputs, said device comprising a junction point biased by a voltage source, said device being characterized in that it comprises between each of said inputs-outputs and said junction point a switching circuit such as described above, the first input-output of each of said circuits being linked to a different input-output of said
device, the second input-output of each of said circuits being linked together at the junction point.
According to one embodiment of the routing device, a biasing module is placed between the access of the routing device and the junction point, said module comprising two transmission lines, the access of the device being linked to the first end of the first conductor of the first line, the junction point being connected to the first end of the first conductor of the second line, a bias voltage being applied to the second conductor of said first line, said lines being mutually crossed by connecting the second end of the first conductor of the first line with the second conductor of the second line and by connecting the second conductor of the first line with the second end of the first conductor of the second line.
Other characteristics will become apparent on reading the following nonlimiting detailed description given by way of example in regard to appended drawings which represent:
- Figure 1, an illustration of the function fulfilled by the switching circuit according to the invention;
- Figure 2a, a first embodiment of a switching circuit according to the invention;
- Figure 2b, a second embodiment of a switching circuit according to the invention;
- Figure 2c, a third embodiment of a switching circuit according to the invention;
- Figure 2d, a fourth embodiment of a switching circuit according to the invention;
- Figure 2e, a fifth embodiment of a switching circuit according to the invention;
- Figure 2f, a sixth embodiment of a switching circuit according to the invention;
- Figure 3, an exemplary arrangement of the switching circuits according to the invention for producing a routing device,
- Figure 4a, a first exemplary routing device comprising switching circuits according to the invention;
- Figure 4b, a second exemplary routing device comprising switching circuits according to the invention;
- Figure 5, a third exemplary routing device comprising switching circuits according to the invention.
With a view to clarity in the description, the same references in different figures designate the same elements.
Figure 1 illustrates the function fulfilled by the switching circuit according to the invention. The switching circuit 100 comprises an input-output 101, a terminal 103 and a second input-output 105. In the examples presented, the first input-output 101 plays the role of input and the second input-output 105 plays the role of output but these two roles may be swapped. A radiofrequency signal received by the input 101 is directed either toward the terminal 103 which is connected to an electrical ground 130 in the example, or toward the second output 105 depending on a control 104.
Figure 2a presents a first embodiment of a switching circuit according to the invention. The switching circuit 100 of Figure 2a comprises two active components - in the example, two diodes D1, D2 —, two transmission lines — in the example, two coaxial cables 110, 120 —. The expression "transmission line" is understood to mean a set of one (in reality two if the ground is considered), of two or more conductors conveying in unison an electrical signal from a source to a load. In the example, the braid 112, 122 and the core 111, 121 of each coaxial cable 110, 120 are the two conductors conveying the current. Other elements may be used in place of the coaxial cables 110, 120 to produce the transmission lines, for example bifilar pairs or twisted pairs. In the case of a printed circuit, a transmission line can take the form of a printed line.
According to the first embodiment, the anode 106a of the first diode D1 is linked to the input 101 of the switching circuit 100, the cathode 106b of this same diode D1 being linked to the terminal 103 of said circuit 100. The cathode 108b of the second diode D2 is linked to the second output 105 of the switching circuit 100. The anode 106a of the first diode D1 and the input 101 of the circuit 100 are connected to a first end 111a of the core of the first coaxial cable 110, while the anode 108a of the second diode D2 is connected to the first end 121a of the core of the second coaxial cable 120.
The coaxial cables 110, 120 are linked together in a crossed manner. The second end 111b of the core of the first coaxial cable 110 is connected to the braid 122 of the second coaxial cable 120, the second end 121b of the core of the second coaxial cable 120 being connected to the braid 112 of the first cable 110. The crossover makes it possible to invert the states of DC and radiofrequency current. Advantageously, each coaxial cable 110, 120 is surrounded by an element 115, 125 of magnetic permeability at least equal to 1. In the example, the element 115, 125 is a ferromagnetic torus 115, 125 (represented truncated in Figure 2a). The torus 115, 125 consists for example of ferrite, an inexpensive material having a high magnetic permeability. Although not indispensable, each of these tori 115, 125 makes it possible to extend the electrical length of the transmission line consisting of the cable 110, 120, and thus to operate the switching circuit 100 at lower frequencies and consequently to increase the operating band of this circuit.
Furthermore, the anode 106a of the first diode D1 is biased with a DC voltage source Vdc1 connected to the braid 122 of the second coaxial cable 120, the anode 108a of the second diode D2 being biased with a voltage source Vdc2 connected to the braid 112 of the first coaxial cable 110. The voltage sources Vdc1 and Vdc2 play the role of the control 104 presented in Figure 1. In the example, a capacitor CIN is placed between the input 101 of the switching circuit and the diode D1 so as to isolate the latter from the radiofrequency current at input 101. Moreover, a first capacitor C1 is placed between the braid 112 of the first coaxial cable 110 and an electrical ground 130 and a second capacitor C2 is placed between the braid 122 of the second coaxial cable 120 and the electrical ground 130, so as to isolate the braids 112, 122 from the radiofrequency current. According to another embodiment, the switching circuit 100 does not comprise the first capacitor C1 and the second capacitor C2.
The bias voltages Vdc1, Vdc2 are applied so that when the first diode D1 is on, the second diode D2 is off and that when the first diode D1 is off, the second diode D2 is on. For example, if a zero voltage is applied to the second output 105, the terminal 103 being linked to the electrical ground 130, then a first negative voltage Vdc1 combined with a second positive voltage Vdc2 makes it possible to direct an incoming signal 101 toward the second
output 105. On the contrary, if a zero voltage is applied to the second output 105, the terminal 103 being linked to the electrical ground 130, then a first positive voltage Vdc1 combined with a second negative voltage Vdc2 makes it possible to direct an incoming signal 101 toward the terminal 103.
All types of diodes may be used in the guise of active components D1, D2. For example, Schottky diodes or PIN diodes may be employed, PIN diodes being preferred for high-power signals.
In the case where the input 101 and the second output 105 are swapped, then each diode D1, D2 may be reversed with respect to the direction presented in Figure 2a, so that the cathode 106b of the first diode D1 is connected to the core of the first cable 110, its anode being connected to terminal 103, and that the cathode of the second diode D2 is connected to the core of the second cable 120, its anode being connected to the second output 105.
Figure 2b presents a second embodiment of a switching circuit according to the invention. Like the first embodiment of Figure 2a, the switching circuit 200 of Figure 2a comprises two diodes D1, D2 and two coaxial cables 110, 120. However, relative to this first embodiment, the biases are reversed at the level of the braid and the core of the cables 110, 120.
More precisely, the cathode 106b of the first diode D1 is linked to the input 101 of the switching circuit 200, the anode 106a of this same diode D1 being linked to the terminal 103 of said circuit 100, which is linked to the electrical ground 130. The cathode 108b of the second diode D2 is linked to the second output 105 of the switching circuit 200. The cathode 106b of the first diode D1 and the input 101 of the circuit 200 are connected to the braid 112 of the first coaxial cable 110, while the anode 108a of the second diode D2 is connected to the braid 122 of the second coaxial cable 120.
The coaxial cables 110, 120 are linked together in a crossed manner. The second end 111b of the core of the first coaxial cable 110 is connected to the braid 122 of the second coaxial cable 120, the second end 121b of the core of the second coaxial cable 120 being connected to the braid 112 of the first cable 110. As in the first embodiment, each coaxial cable 110, 120 is advantageously surrounded by an element of magnetic
permeability at least equal to 1, said element not being represented in the figure for the sake of simplification.
Furthermore, the cathode 106b of the first diode D1 is biased with a DC voltage source Vdc1 connected to the first end 121a of the core of the second coaxial cable 120, the anode 108a of the second diode D2 being biased with a voltage source Vdc2 connected to the first end 111a of the core of the first coaxial cable 110. In the example, a capacitor CIN is placed between the input 101 of the switching circuit and the diode D1 so as to isolate the latter from the radiofrequency current at input 101. Moreover, a first capacitor C1 is placed between the first end 111a of the core of the first coaxial cable 110 and the electrical ground 130 and a second capacitor C2 is placed between the first end 121a of the core of the second coaxial cable 120 and the electrical ground 130.
Figure 2c presents a third embodiment of a switching circuit according to the invention. Relative to the first embodiment of Figure 2a, the switching circuit 202 does not comprise any diode D1. Stated otherwise, the switching circuit 202 of Figure 2c comprises a diode D2 and two coaxial cables 110, 120.
The cathode 108b of the second diode D2 is linked to the second output 105 of the switching circuit 100. The input 101 of the circuit 100 is connected to the first end 111 a of the core of the first coaxial cable 110, while the anode 108a of the second diode D2 is connected to the first end 121a of the core of the second coaxial cable 120.
The coaxial cables 110, 120 are linked together in a crossed manner. The second end 111 b of the core of the first coaxial cable 110 is connected to the braid 122 of the second coaxial cable 120, the second end 121b of the core of the second coaxial cable 120 being connected to the braid 112 of the first cable 110.
Furthermore, the anode 108a of the second diode D2 is biased with a voltage source Vdc2 connected to the braid 112 of the first coaxial cable 110. No capacitor CIN is necessary at the input 101 of the switching circuit since there is no diode to be isolated from the radiofrequency current at input 101. Moreover, a first capacitor C1 is placed between the braid 112 of the first coaxial cable 110 and the electrical ground 130.
Although the embodiment of Figure 2c does not allow switching of as good quality as that of the first embodiment presented in Figure 2a, it makes it possible to dispense with a bias source Vdc1 and a capacitor CIN, this being worthwhile, notably, when seeking to reduce the size of a circuit.
Figure 2d presents a fourth embodiment of a switching circuit according to the invention. Relative to the first embodiment of Figure 2a, the switching circuit 204 does not comprise any diode D2. Stated otherwise, the switching circuit 204 of Figure 2d comprises a diode D1 and two coaxial cables 110, 120. Although the embodiment of Figure 2d does not allow switching of as good quality as that of the first embodiment presented in Figure 2a, it makes it possible to dispense with a bias source Vdc2.
Figure 2e presents a fifth embodiment of a switching circuit according to the invention. Relative to the second embodiment of Figure 2b, the switching circuit 206 does not comprise any diode D1. Stated otherwise, the switching circuit 206 of Figure 2e comprises a diode D2 and two coaxial cables 110, 120.
Figure 2f presents a sixth embodiment of a switching circuit according to the invention. Relative to the second embodiment of Figure 2b, the switching circuit 208 does not comprise any diode D2. Stated otherwise, the switching circuit 204 of Figure 2d comprises a diode D1 and two coaxial cables 110, 120. Although the embodiment of Figure 2d does not allow switching of as good quality as that of the first embodiment presented in Figure 2a, it makes it possible to dispense with a bias source Vdc2.
Figure 3 presents an exemplary arrangement of the switching circuits according to the invention for producing a routing device without inductance. The routing device 300 of Figure 3 comprises two inputs RF1, RF2 and an output COM. Signals are received on the two inputs RF1, RF2 and the routing device makes it possible to steer one or the other of these signals toward the single output COM.
The routing device 300 comprises two switching circuits 100, 100' according to the invention. The input 101 of the first switching circuit 100 is linked to the input RF1 of the routing device 300. The input 101' of the second switching circuit 100' is linked to the second input 101' of the device 300. The terminals 103, 103' of each switching circuit 100, 100' are joined to an electrical ground 130 and the second outputs 105, 105' of each switching
circuit 100, 100' are joined together at a junction point 301. Furthermore, the junction point 301 is biased by a DC voltage delivered by a block 305 placed between the output COM of the device 300 and the junction point 301.
The switching circuits 100, 100' are controlled in an alternated manner, so that when one circuit transmits the signal that it receives on its input to the junction point 301 and therefore to the output COM, the other switching circuit transmits the signal that it receives to the electrical ground 130.
Figure 4a presents a first exemplary routing device comprising switching circuits according to the invention. The routing device of Figure 4a corresponds to the schematic layout presented in Figure 3.
The block 305 making it possible to bias the junction point 301 comprises two transmission lines 310, 320 and a DC voltage source VdcO. In the example, the two transmission lines 310, 320 are coaxial cables 310, 320. The first end 311a of the core of the first cable 310 is linked to the output COM of the routing device 300 and the first end 321a of the core of the second cable 320 is linked to the junction point 301.
The coaxial cables 310, 320 are linked together in a crossed manner. The second end 311b of the core of the first coaxial cable 310 is connected to the braid 322 of the second coaxial cable 320, the second end 321b of the core of the second coaxial cable 320 being connected to the braid 312 of the first cable 310. In the example, each coaxial cable 110, 120 is surrounded by a ferromagnetic torus 315, 325 (the tori are represented truncated in Figure 4a). The DC voltage source VdcO is applied to the braid 312 of the first coaxial cable 310, so as to bias the junction point 301 via the two coaxial cables 310, 320. In the example, the voltage VdcO applied is zero.
Moreover, the voltages Vdc1, Vdc3 and Vdc2, Vdc4 for biasing the diodes of the switching circuits are controlled in a synchronized manner. Stated otherwise, the first voltage Vdc1 of the first switching circuit 100 and the second voltage Vdc3 of the second switching circuit 100' are positive when the second voltage Vdc2 of the first switching circuit 100 and the first voltage Vdc4 of the second switching circuit 100' are negative. Likewise, the first voltage Vdc1 of the first switching circuit 100 and the second voltage Vdc3 of the second switching circuit 100' are negative when the second
voltage Vdc2 of the first switching circuit 100 and the first voltage Vdc4 of the second switching circuit 100' are positive.
Figure 4b presents a second exemplary routing device comprising switching circuits according to the invention. The device of Figure 4b comprises an identical arrangement of the switching circuits to that of Figure 4a, but each of these circuits 200, 200' is a switching circuit according to the second embodiment presented in Figure 2b.
Figure 5 presents a third exemplary routing device comprising switching circuits according to the invention. The routing device of Figure 5 is a generalization of the device of Figures 3 and 4. It comprises N inputs RF1, RF2, RFN and one output COM. Signals are received on the N inputs RF1, RF2, RFN and the routing device makes it possible to steer one or other of these signals toward the single output COM.
In the device 500 of Figure 5, a number N of switching circuits are used. The input 101, 101', 101" of each switching circuit 100, 100", 100" is linked to the input RF1 of the routing device 300. The input 101' of the second switching circuit 100' is linked to the second input 101' of the device 300. The terminals 103, 103' of each switching circuit 100, 100' are joined to an electrical ground 130 and the second outputs 105, 105' of each switching circuit 100, 100' are joined together at a voltage-biased junction point 301.
The switching circuit according to the invention may be employed in radiocommunications systems, for example for selecting multiple transmitters to multiple antennas or for selecting multiple antennas to multiple receivers. According to another implementation, the switching circuit according to the invention may be used for selecting a frequency sub-band filter from among several thereof downstream of a single transmitter and to a single transmitter.
In contradistinction to the switches of the prior art which were passband-limited, they being able to operate for example for high-power signals spread over a few octaves, for example over a frequency band of from 20 to 100 MHz, the switch according to the invention can operate for signals of high power, for example 1000 W, and spread over 20 or 30 octaves, for example from 1 MHz to 1 GHz.

CLAIMS
1. A switching circuit (202) for controlling the passage of a radiofrequency signal between a first input-output (101) and a second input-output (105), said circuit comprising at least one diode (D2) between said inputs-outputs (101, 105), said circuit being characterized in that said diode (D2) is biased by a DC voltage source (Vdc2) by way of at least two crossed transmission lines (110, 120) interconnecting said diode (D2) with said DC voltage source (Vdc2).
2. The switching circuit (202) as claimed in claim 1, each of said lines (110, 120) comprising at least two conductors (111, 121, 112, 122), said circuit being characterized in that the bias voltage source (Vdc2) is linked to the first end of the second conductor (112) of the first line (110), said diode (D2) being placed between the first end (121a) of the first conductor of the second line (120) and an input-output (101, 105) of said circuit, said lines (110, 120) being mutually crossed so that the second end (111b) of the first conductor of the first line (110) is linked to the second end of the second conductor (122) of the second line (120) and that the second end of the second conductor (112) of the first line (110) is linked to the second end (121b) of the first conductor of the second line (120), the first end (111a) of the first conductor of the first line (110) being linked to the input-output (101, 105).
3. The switching circuit as claimed in claim 1 or 2, characterized in that each of the transmission lines (110, 120) is a coaxial cable whose core (111, 121) forms one of the conductors of the line and whose braid (112, 122) forms the other conductor of said line.
4. The switching circuit as claimed in one of claims 1 to 3, characterized in that each of the transmission lines (110, 120) is surrounded by a material of magnetic permeability greater than 1 (315, 325).
5. The switching circuit as claimed in any one of claims 2 to 4, characterized in that the first end of the second conductor (122) of the
second line (120) is linked to a terminal (103) of said circuit, which terminal (103) is connected to an electrical ground (130).
6. The switching circuit as claimed in any one of claims 2 to 5, characterized in that the first input-output (101) of said circuit is linked to the first end (111a) of the first conductor of the first line (110), the diode (D2) linked to the second transmission line (120) via a first terminal (108a) being connected via its second terminal (108b) to the second input-output (105) of said circuit.
7. The switching circuit as claimed in any one of claims 2 to 4, characterized in that the first input-output (101) of said circuit is linked to the first end (121a) of the first conductor of the second line (120) and to the first terminal (108a) of the diode (D2), which diode (D2) is connected via its second terminal (108b) to an electrical ground (130), said circuit comprising a second input-output (105) linked to the first end (111a) of the first conductor of the first line (110).
8. The switching circuit as claimed in claim 7, characterized in that a capacitor (CIN) is placed between the first input-output (101) of said circuit and the first end (111a) of the core of the first transmission line (110).
9. The switching circuit as claimed in any one of the preceding claims, characterized in that it comprises a capacitor (C1) placed between the voltage source (Vdc2) and the electrical ground (130).
10. The switching circuit as claimed in any one of claims 2 to 9, characterized in that it comprises a second diode (D1) linked to the first end (111a) of the first conductor of the first line (110) and controlled by a second voltage source (Vdc1) linked to the first end of the second conductor (122) of the second line (120), the diodes (D1, D2) being placed by choice as follows:
- the anode of the first diode (D2) and the cathode of the second diode (D1) are each linked to a different input-output (101, 105),
- or the cathode of the first diode (D2) and the anode of the second diode (D1) are each linked to a different input-output (101, 105).
11. The switching circuit as claimed in claim 10, characterized in that it
comprises a capacitor (C2) placed between the voltage source (Vdc1)
and the electrical ground (130).
12. A device for routing between several inputs-outputs (RF1, RF2) and an
access (COM) a power signal provided on one of said inputs-outputs
(RF1, RF2), said device comprising a junction point (301) biased by a
voltage source (VdcO), said device being characterized in that it
comprises between each of said inputs-outputs (RF1, RF2) and said
junction point (301) a switching circuit (100, 100') according to one of the
preceding claims, the first input-output (101, 101') of each of said circuits
(100, 100*) being linked to a different input-output (RF1, RF2) of said
device, the second input-output (105, 105') of each of said circuits being
linked together at the junction point (301).
13. The routing device as claimed in claim 12, characterized in that a biasing
module (305) is placed between the access (COM) of the routing device
and the junction point (301), said module comprising two transmission
lines (310, 320), the access (COM) of the device being linked to the first
end (311a) of the first conductor of the first line (310), the junction point
(301) being connected to the first end (321a) of the first conductor of the
second line (320), a bias voltage (VdcO) being applied to the second
conductor (312) of said, first line (320), said lines (310, 320) being
mutually crossed by connecting the second end (311b) of the first
conductor of the first line (310) with the second conductor (322) of the
second line (320) and by connecting the second conductor (312) of the
first line (310) with the second end (321b) of the first conductor of the
second line (320).