WO2008095708A1

WO2008095708A1 - Directional coupler

Info

Publication number: WO2008095708A1
Application number: PCT/EP2008/000944
Authority: WO
Inventors: Ekkehard Mann; Christoph Gerhardt; Chistian Thome; Christian Wangler; Daniel Krause; Stephan Günther; Rolf Weber
Original assignee: Hüttinger Elektronik Gmbh + Co. Kg
Priority date: 2007-02-08
Filing date: 2008-02-07
Publication date: 2008-08-14

Abstract

In a directional coupler (10, 20) with a. coupling loss in the forward direction cf = cf ejφcf; b. coupling loss in the rearward direction cr = cr ejφcr; c. decoupling in the forward direction If = If ejφif; d. decoupling in the rearward direction Ir = Ir ejφIr, the absolute value of Δφ = φCr + φCf - (φIr + φlf ) is ≤ 20°. As a result, phase-independent power measurement can take place.

Description

DESCRIPTION

directional coupler

The invention relates to a directional coupler with an a. Coupling loss in the forward direction C _f = C _f - e ^1Ψcι ;

b. Coupling loss in reverse direction C. = C _r - e ^JΨCr ;

c. Decoupling in forward direction I _f - l _f - e ^{) ψ} ";

d. Decoupling in reverse direction I _r = I _r - e ^jφ ' ^r .

RF generators are used to generate and deliver RF power to a load. As a load, for example, plasma processes, such as plasma coatings and plasma etching in question. Since the impedance of the load may change, and thus, mismatch may result in (partial) reflection of the power supplied by the RF generator, often not all of the power delivered by the RF generator is absorbed in the load (the plasma) , In order to accurately adjust or regulate the RF power delivered to the load, it is desirable to determine the power absorbed in the load.

BESTATIGUNGSKOPIE It is known to use a directional coupler to measure / determine the RF power absorbed in a load, the absorbed RF power resulting from the difference in power produced by the RF generator and the reflected power. This makes it possible to regulate the RF generator so that the power absorbed in the load can be set with high precision and kept constant.

The measurement of the power supplied to a load (incident power, forward power) by a directional coupler or by a reflectometer and the measurement of the reflected power (reflected power) is due to the finite directivity (directivity) (also directivity) of the directional coupler but faulty. The measurement of the power absorbed in the load is thus also faulty. In the prior art, a phase measurement between the traveling and the returning wave (load delivered power and load reflected power) is known. With the help of this measurement, the error can be calculated out.

Another way to accurately measure the power delivered to the load is to measure the current and voltage. However, a very good decoupling of the voltage and the current sensor must be achieved here. You also need a very accurate phase measurement between the voltage and the current.

Fig. Ia shows a high-frequency system 11 according to the prior art with a high-frequency generator 100 as a source, a coupler arrangement 12 with a designed as a directional coupler coupler 200 and a load 300 as a sink. The coupler has a main line 290 with a first and second port 1, 3 and a secondary line 291 with secondary line ports 2, 4, which are terminated with impedances 205, 206 corresponding to the nominal impedance Z _{0 of} the high-frequency system 11 or at least that of the coupler 200. At Port 2, a proportion of the incoming wave at the corresponding port 1 of the main line 290 can be observed with a measuring device 207; Correspondingly, a portion of the wave reflected by the load and entering at the corresponding port 3 of the main line can be observed with a measuring device 208 at the port 4. The size of the share depends on the coupling factor. In the case of an ideal coupler, the directivity is infinitely large, and no portion of the incoming wave at port 3 and no portion of the incoming wave at port 1 will be observed at port 2.

FIG. 1b likewise shows a high-frequency system 10. The coupler 240 has two secondary lines 291, 292. At port 2 of the first secondary line 291, a portion of the input to the port 1 of the main line 290 is measured at the port 4 of the second secondary line 292, a proportion of the input to the port 3 of the main line 290 wave. The ports 223, 4 of the second sub-line 292 are terminated by the impedances 225, 226, which correspond to the nominal impedance Z ₀ .

For the description of multiple ports, such as a directional coupler, it is common to consider wave amplitudes or wave strengths instead of the voltage sources at the ports. In this case, the wave strength of an incident wave at the port i is usually designated by aj and the wave strength of the outgoing wave at the port i by bj. Furthermore, it is customary to link the outgoing and incoming waves via a scattering matrix.

A directional coupler can be regarded as a four-port, whose transmission behavior due to the complex sizes coupling damping (coupling) and decoupling (isolation) can be described. In FIG. 1 b, the directional coupler 10 is shown as a fourth gate with coupling lines 291, 292, which are arranged on both sides of the main line 290. It is

C _f = C _f -e ^{JΨc /} the coupling loss in the forward direction, ie from port 1 to

Port 2. The coupling loss in the reverse direction is C _r = C _r • e ^3Ψcr , ie from

Port 3 to port 4. Accordingly, I _f = I _f - e ^jφ ' ^{f is} the decoupling in

Forward direction (port 1 to port 4) and I _r = I _r - e ^jφ ' ^r the decoupling in

Reverse direction (port 3 to port 2). The quantities C _f , C _r , I _f , I _r are in this case the inverse of the scattering parameters of the scattering matrix. It holds on the condition that l << λ:

b _λ = Y - a _λ

where r is the reflection factor.

The object of the present invention is to provide a directional coupler with which the forward power delivered by an RF generator into a load and / or the reverse power reflected by the load can be measured more accurately.

This object is achieved by a directional coupler of the type mentioned, in which Δφ = φ _Cr + φ _Cf - {φ _lr + φ _lf ) ≤ 20 °, preferably

<10 °, more preferably <5 °, most preferably <1 °.

This object is also achieved if Aφ = φ _Cr + φ _Cf - (φ _lr + φ, _f ) ≥ -20 °. In summary, the problem is solved if the magnitude of Δφ is <20 °, that is | Δφ | <20 °, preferably <10 °, more preferably <5 °, most preferably <1 °.

A directional coupler designed in this way minimizes the measurement error in the measurement of the power delivered to and reflected from the load, and thus the RF power absorbed in the load. The above criterion has not been considered in the production of directional couplers. A directional coupler is usually applied to printed circuit board material FR4 or on ceramic in the form of printed conductors. However, this quite precise production method still results in small inaccuracies and thus errors in such orders of magnitude that a phase error | Δφ | <20 ° neither deliberately nor accidentally can be achieved. Only by using simulation tools and state-of-the-art manufacturing technology can values | Δφ | <20 ° can be achieved. With the help of rework and especially sophisticated manufacturing technology, values of less than 10 °, less than 5 ° or even less than 1 ° can be achieved. Ideally, Δφ = 0 °. this means

Alternatively or additionally, the directional coupler according to the invention can be so

be configured that AT = 1.6, preferably <1.2, especially

C _f I _{f is} preferably <1.1. This means that in the ideal case - corresponds to - about. Of the

Error in the measurement of the power absorbed in the load is then neither dependent on the magnitude nor on the phase of the load reflection factor. Thus, the error in the measurement is load-independent, both by amount and by phase of the load. Therefore, the error may look like a systematic error out of the measured value and thus completely compensated. A phase measurement between the outgoing wave (power delivered to the load) and the returning wave (power reflected by the load) is therefore superfluous. Thus, costs for the components of the phase measurement can be saved. It should be noted that, according to the above criterion, it is not even necessary for the unwanted couplings (I _f , I ₁ -) to disappear due to lack of attenuation, but their ratio need only be as great as that of C _f and C ₁ -.

It is particularly preferred if the directional coupler is reciprocal and applies: C _f = C _r and I _f = I ₁ -.

The above condition is realized according to a development in a particularly simple manner by a directional coupler, in which φ _Cr = -φ _Cf + k and φ _lr = -φ _ιf + k, where k can take any values. In the simplest case, k assumes the value 0, so that φ _Cr = -φ _Cf and

φ, _r = -φ, _f ^■

Further advantages result if I _f and / or I _r > C _f and / or C _n This means, in particular, that the values I _f and / or I _r should be as large as possible. Under these conditions, a very accurate value for the power remaining (absorbed) in the load can be determined.

The measurement of the power delivered to the load at port 2 of the sub-line is P _ml =

and the measurement of the power reflected by the load at port 4 of the sub-line is P _mr = Ib ₄ ² . The measurement of the remaining power in the load to the Secondary lines of a non-optimized, so erroneously measuring

Directional coupler amounts

1 r ² Γ ² 1 2rcos (^ _{/ r} -φ _Cf -φ _r ) 2 rcos (^ _Cr - φ _lf - φ _r )

ΔP _mea s = P _m , - P _mr = h _/ ^ 2 + -; r +

C C J J C J J C

The actual power consumed in the load is obtained under the

1 r

_Measurement condition ΔP _meorap , = U

C ² C

An optimal directional coupler that measures without errors, and thus the power actually absorbed in the load, is thus obtained taking into account the following conditions:

1) I _f , I ₁ -: as large as possible, and / or

2) -L = -L, and / or C _r I _r 3) φ _Cr + φ _cf = φ _Ir + φ _If

In fulfilling these conditions, ΔP _meas = ΔP _measopl ; ie the load-dependent error in the power measurement is minimized.

The directivity during operation (not the directivity in the strict definition at nominal impedance) is almost independent of the load (neither magnitude nor phase of the load reflection factor). An embodiment of the invention is characterized in that the directional coupler has two coupling lines, which are arranged at least partially parallel to each other. As a result, they can also be arranged parallel to a main line, via which the power to be measured is transmitted. With the one coupling line, the power delivered in the direction of load can be determined and with the other coupling line, the power reflected by the load can be determined. Preferably, the coupling lines are arranged on opposite sides of a main line.

The wiring of at least one port of the directional coupler can be designed so that it consists of a variable impedance arrangement whose impedance can be changed by electronic control signals. For a directional coupler used for measuring purposes, the secondary line port not occupied by the measuring device can be used for this purpose.

Due to the particular electronically variable impedance of the impedance arrangement Auskoppelfaktor and directivity of the directional coupler can be optimized. The impedance arrangement may comprise one or more elements, wherein the impedance of the entire arrangement or at least one element of the arrangement is variable by the control signal. A variable impedance impedance device may be connected not only to a port but to (at least) one secondary line somewhere.

Of course, if only the impedance of a single element or a group of elements is changed by the control signal, the total impedance of the impedance arrangement is also changed. The termination, ie the impedance arrangement, may consist of a real resistor and a capacitance diode. A control voltage as an electrical control signal on the capacitance diode can change its capacity.

The impedance arrangement may alternatively or additionally have an inductance. An electronically controllable or controllable inductance and thus controllable impedance can be achieved, for example, that the permeability of the coil core of the inductance is reduced by an additional magnetic DC field, which is generated by a DC-flow-through auxiliary winding, the magnetic flux against the Saturation limit of the core material is driven. For example, a PIN diode can be used as an electronically changeable, ie by an electronic control signal variable real resistance.

To be able to set both real and imaginary resistance values for the impedance arrangement connected to a port, the impedance arrangement can have at least two influenceable impedances which are connected to the port, which do not act collinearly on the complex resistance level. This means that the pointers or vectors describing the impedances in the resistance plane are not linearly dependent. Such an impedance arrangement can be, for example, a circuit consisting of a capacitance diode and a PIN diode.

The electronically variable impedance may vary depending on the

Operating frequency of the system in which the coupler is integrated, for example, the fundamental frequency of an RF power generator, depending on the impedance of at least one of the coupler connected source or sink and / or depending on the real characteristics of the coupler produced.

For more complex tasks, such as the compensation of impedances connected to two main ports of a directional coupler, which deviate from the system impedance, both ports of the secondary line of this directional coupler or corresponding one port or both ports of two secondary lines to impedance arrangements with controllable by an electronic signal Impedances are connected.

When dimensioning the variation ranges of the controllable variable impedances, the characteristic of the directional coupler in the intended operating frequency range as well as the range of the possible impedance variation of the connected sources and sinks can be taken into account.

The control voltages for at least one electronically variable impedance can come from an electronic circuit which indicates the current operating state of the device and thus the connected impedances at at least one port of the main line, the current operating frequency and the frequency-dependent behavior and / or the real characteristic given by the production of the at least one inserted coupler knows.

The circuit may be analog or digital and also include a microprocessor. The circuit may include memory or may access memory that sets the parameters for particular ones

Impedance values at a port of the secondary line, for the compensation, for the frequency dependent behavior or for the individual characteristic of the

Coupler or for other operating conditions of the high frequency system includes. The memory may be a permanent memory that is described during production and / or installed in the device. Alternatively or additionally, the memory may be a writable memory that is rewritten, for example, during a calibration process.

The calibration process may be performed by means of a control circuit which measures the signals on at least one port of the coupler while controlling the control voltages for the electronically variable impedances. In this case, the above-mentioned circuit can be used as a control circuit.

The electronic circuit can also work as a permanent control. In a first step, all parameters can be set or the control can be operated so that an optimal behavior of the directional coupler occurs, so for example, a very high directivity. The control loop should now have a low-pass characteristic whose cut-off frequency is lower than the expected change in the impedances of the connected sources and sinks connected to the coupler. If the ratios of the impedances of the sources or sinks change, then the regulation will not be able to follow so quickly, so that the directional coupler arrangement can very accurately reproduce the impedance changes due to the high directivity. The coupling variances can be designed in accordance with the impedance arrangements. In particular, they can be embodied as fixed, for example fixed design impedances, manually adjustable or electronically adjustable impedances. Furthermore, the use of PIN diodes, coils with adjustable saturation, capacitance diodes and the interconnection of several such elements for the coupling variances is conceivable. Between at least one coupling line and the main line can be arranged a coupling variance. In this case, the coupling variance can be changed in their resistance. Alternatively or additionally, the coupling variance in its position between the coupling line and the main line can be changed. Several of these additional coupling variances between the main and each secondary line can be used.

The scope of the invention also includes a method for setting or designing a directional coupler according to claim 20. Method variants are specified in the dependent claims. A method according to claim 26 is also within the scope of the invention.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

Preferred embodiments of the invention are shown schematically in the drawing and are explained below with reference to the figures of the drawing. It shows:

Fig. Ia, Ib each have a high-frequency system with directional coupler;

FIG. 2 shows a schematic illustration of a high-frequency system with a coupler arrangement and an impedance arrangement; FIG.

3 shows an embodiment of an impedance arrangement; and 4 shows a directional coupler with coupling variances.

In the figures, the same reference numerals are used for corresponding components.

2 shows a high-frequency system 20 with a high-frequency generator 100 as the source, a coupler arrangement 30 with a coupler 240 designed as a directional coupler and a load 300 as sink. The coupler 240 has a main line 290 with a first and second port 1, 3 (main line ports) and a secondary line 291 with auxiliary power ports 2, 204. The port 2 is terminated with a resistor 205, the nominal impedance Z _{0 of} the radio frequency system 20 or at least the of the coupler 240 corresponds. At port 2, a proportion of the incoming wave at the corresponding port 1 of the main line 290 can be observed with a measuring device 207.

Furthermore, the coupler 240 has a second secondary line 292 with secondary line ports 223, 4. At the port 4 of the second secondary line 292, a proportion of the input to the port 3 of the main line 290 wave is measured. For this purpose, a measuring device 228 is connected to the port 4. The port 4 of the second secondary line 292 is terminated by the resistor 226, which corresponds to the nominal impedance Z ₀ .

The measuring devices 207, 228 shown in the figures can each be voltmeters, oscilloscopes, diodes / demodulators or the like, or analog or digital evaluation circuits with or without prior rectification of the shaft. Furthermore, the input impedances of the measuring devices can replace the terminating impedances attached to the same port or, together with these, form the impedance present at the port. In Fig. 2 there is connected to the port 204 according to the invention

Impedance arrangement 210 of two electronically controllable impedances

211, 212 which are non-collinear in the complex resistance plane. By supplying a control voltage from the electronic

Circuit 250, these two impedances 211, 212 are tuned, whereby the port 204 is completed with a certain set complex resistance. This means that through the

Circuit 250, the total impedance of the impedance arrangement 210 can be set, which is composed of the impedances 211, 212.

Symmetrically with the port 204, port 223 is terminated with an impedance arrangement 230 consisting of two impedances 231, 232, which are also driven by the electronic circuit 250.

The electronic circuit 250 obtains further information, such as the frequency-dependent behavior of the coupler 240, the current operating frequency of the generator 100, the frequency-dependent complex internal resistance of the generator 100 and the frequency-dependent impedance of the load 300. The static quantities, such as the frequency-dependent behavior of the coupler 240 or the frequency-dependent impedance of the generator 100 or an antenna as a load 300 may be stored in a memory. This can be done in digital or analog form. The memory may be permanent or rewritable. The memory may be included in the circuit 250 or located externally. In the exemplary embodiment shown, the memory 251 is arranged in the circuit 250.

In one embodiment of the invention, the coupler assembly 30 or the coupler is calibrated with associated impedance arrangements 210, 220. These are the measuring devices 207, 228 with the electronic circuit 250 connected, which has a low-pass filter 252. At a frequency of the generator 100 or over a certain frequency range and under certain external conditions, for example in the case of a defined ohmic resistance or a faultless antenna as the load 300, the impedances 211, 212, 231, 232 are respectively controlled such that the desired measured values are applied to the Ports 2 and 4 are present. These drive values are stored in the memory 251 and used during normal operation. If the working conditions deviate from the specification, the measured values at ports 2 and 4 will be very sensitive to it.

In an embodiment of the invention not shown, only one sub-line of the coupler 240 is provided with the variable impedances, i. An impedance arrangement 210, 230 is only connected to a secondary line. However, in each case an impedance arrangement 210, 230 can be connected to both ports of the secondary line.

In one embodiment of the invention, a coupler 200 may be provided with only one secondary line 291. In this case, an impedance arrangement 210, 230 can be connected to both ports of the secondary line 291 in each case. However, it is also possible to connect an impedance arrangement 210, 230 to only one port.

Fig. 3 shows an embodiment for the impedance arrangement 210. At the port 204 of the sub-line 291, a pair 213 of two is antiserially arranged

Capacitance diodes 217, 218 connected to ground, which in response to the coming of the electronic circuit 250

Control voltage applied to the central point or connection point of the

Pair 213 is placed to represent a more or less large capacity. Via an inductor 214, another pair 215 is antiserial Capacitance diodes 219, 220 and a real resistor 216 connected to the port 204, the second pole is connected to ground. By a

Control voltage at the central point of the diode pair 215, which also comes from the electronic circuit 250, the capacitance of this pair 215 can be influenced. The inductor 214, the variable capacitance of the diode pair 215, and the capacitance-parallel real resistor 216 together form an impedance that is not collinear with the capacitance of the diode pair 213 in the complex resistance plane. It follows that the impedances of an impedance arrangement can each be made up of a plurality of components.

In the exemplary embodiment of FIG. 4, the directional coupler 240 additionally has coupling variances 310, 320 between the main line 290 and a secondary line 291, in each case. Coupling variants 310, 320 may be designed as variable impedances. In particular, they may be formed in the same way as the impedance arrangements 210, 230 of Figure 2, e.g. a PIN diode as a resistor, a coil with adjustable saturation, a capacitance diode or combinations thereof. In addition, it can be provided that the coupling variants 310, 320 are adjustable in their position along the main line 290 or the coupling lines 291, 292. The adjustment can be done during the design or later. As a result, even better coordination and design of the directional coupler 240 is possible.

Claims

1. directional coupler (10, 20) with an a. Coupling loss in the forward direction C _f - C _f - e ^{J c /} ;

b. Coupling loss in reverse direction C _r = C _r -e ^JΨcr ;

c. Decoupling in forward direction I _f = I _f -e ^jφ '^f;

d. Decoupling in reverse direction l _r = l _r -e ^{) φ} ";

characterized in that the amount of Aφ = φ _Cr + φ _{c /} - (φ, _r + φ _If ) ≤20 ° preferably <10 °, more preferably <5 °, most preferably <1 ° and / or preferably <1 , 2,

more preferably <1.1.

2. Directional coupler according to claim 1, characterized in that Q = C _n and I _f = I _r .

3. directional coupler according to claim 1 or 2, characterized in that

Ψcr = - <PC / + ^{k and} Ψlr = - <Plf + * ^•

4. Directional coupler according to one of the preceding claims, characterized in that i> and / or I _r > C _f and / or C _Λ .

5. Directional coupler according to one of the preceding claims, characterized in that the directional coupler (10, 20) two Coupling lines (290, 291, 292), which are arranged at least partially parallel to each other.

6. Directional coupler according to one of the preceding claims, characterized in that at least one secondary line (291, 292) an impedance arrangement (210, 230) is connected with variable impedance, in particular at least one port (3, 4) of a secondary line (291, 292 ) is terminated with a variable impedance impedance arrangement (210, 230).

7. Directional coupler according to one of the preceding claims, characterized in that between at least one coupling line (291, 292) and the main line (290) a coupling variance (310, 320) is arranged.

8. directional coupler according to claim 7, characterized in that the coupling variance (310, 320) is variable in their resistance.

9. directional coupler according to claim 7 or 8, characterized in that the coupling variance in position between the coupling line (291,

292) and the main line (290) is variable.

10. Directional coupler according to one of the preceding claims 6 to 9, characterized in that the impedance of the impedance arrangement (210, 230) by an electronic

Control signal is changeable.

11. Directional coupler according to one of the preceding claims 6 to 10, characterized in that an electronic circuit (250) is provided for controlling the impedance arrangement (210, 230).

12. Directional coupler according to claim 11, characterized in that the electronic circuit (250) is designed as a control circuit.

13. Directional coupler according to one of the preceding claims 11 or 12, characterized in that the control circuit comprises a low-pass filter (252).

14. Directional coupler according to one of the preceding claims 6 to 13, characterized in that the impedance arrangement (210, 230) has at least two impedances (211, 212, 231, 232).

15. Directional coupler according to claim 14, characterized in that the impedance arrangement (210, 230) has at least two variable impedances (211, 212, 231, 232) which are not collinear in the complex resistance plane.

16. Directional coupler according to one of the preceding claims 6 to 15, characterized in that the impedance arrangement (210, 230) comprises a resistor (216) and a capacitance diode (217-220).

17. Directional coupler according to one of the preceding claims 6 to 16, characterized in that the impedance arrangement (210, 230) has an inductance with a core and an auxiliary winding.

18. Directional coupler arrangement according to one of the preceding claims 6 to 17, characterized in that the impedance arrangement (210, 230) has a controllable resistance.

19. Directional coupler according to one of the preceding claims, characterized in that at a plurality of ports (2, 204, 3, 223) of the coupler (200, 240) an adjustable by an electronic control signal impedance arrangement (210, 230) is connected.

20. Method for setting a directional coupler with an a. Coupling loss in forward direction C _f = C _f - e ^JΨcj ;

b. Coupling loss in reverse direction C _r = C _r -e ^JΨcr ;

c. Decoupling in forward direction I _f = I _f - e ^{} ψ} ";

d. Decoupling in reverse direction I _r - I _r - e ^jφ '^r;

characterized in that the directional coupler is set such that at least one of the conditions:

Δφ = φ _Cr + φ _cf - (φ _lr + φ _If ) ≤ 20 °, preferably <10 °, more preferably <5 °, most preferably <1 °

C _f I

• K = - ^J - * - ≤ \, 6, preferably <1.2, more preferably <1.1.

C _r I _f • I _f and / or I ₁ -> C _f and / or C ₁ - is satisfied.

21. The method according to claim 20, characterized in that a

Impedance arrangement (210, 230) to at least one secondary port (2, 204, 3, 223) and / or a coupling variance (310, 320) between

Main line (290) and a secondary line (291, 292) is connected and the value of the impedance and / or coupling variance (310, 320) is changed until at least one of the conditions is met.

22. The method according to any one of the preceding claims 20 or 21, that the impedance arrangement (210, 230) for changing the

Impedance value is driven with a control voltage.

23. The method according to any one of the preceding claims 20 to 22, characterized in that at least two by at least one electronic control signal variable impedances (211, 212,

231, 232) are connected to at least one port (204, 223) and the impedances (211, 212, 231, 232) are adjusted.

24. The method according to any one of the preceding claims 20 to 23, characterized in that a calibration process is performed by signals on at least one port (203, 224) of the coupler (200, 240) are measured while the control signal (s) for the Impedance (s) are controlled so that the desired behavior of the coupler (200, 240) occurs.

25. The method according to any one of the preceding claims 20 to 24, characterized in that a frequency-dependent calibration curve is generated.

26. Method in which a directional coupler according to one of claims 1 to 19 is used in a power supply or between the power supply of a plasma process and a plasma load for determining the power consumed in the plasma load.