Impedance detection circuit and method for a radio frequency power supply

Abstract

The application discloses an impedance detection circuit and method of a radio frequency power supply, wherein the input end of a directional coupler is connected with the output end of the radio frequency power supply, the output end is connected with an impedance matcher, the output end of the impedance matcher is connected with a plasma load, the coupling end and the isolation end of the directional coupler are coupled with a vector voltage signal respectively; a first voltage measurement module is connected with the coupling end of the directional coupler; a second voltage measurement module is connected with the isolation end of the directional coupler; an analog-digital conversion module is connected with the first voltage measurement module and the second voltage measurement module; a processor is connected with the analog-digital conversion module, and the converted first and second voltage digital signals are analyzed and processed to determine the load impedance, the radio frequency power supply output power and the load power. The circuit structure of the application is simpler, has an advantage in cost, realizes real-time monitoring of the plasma load change, and provides effective technical support for realizing more complex processes.

Description

Technical Field

[0001] This invention relates to the field of radio frequency technology, and in particular to an impedance detection circuit and method for radio frequency power supplies. Background Technology

[0002] Radio frequency (RF) power supplies are core components of plasma processing, serving as the primary devices for igniting and sustaining plasma discharges. As circuit integration increases, controllable, high-precision RF power supplies are needed to generate different forms of plasma to meet process requirements. Furthermore, because plasma impedance constantly changes, an automatic impedance matching device is required to match the varying load impedance with the RF output impedance in order to maximize the output power of the RF power supply into the plasma generator. Some complex plasma processing techniques demand high precision and speed in matching, necessitating real-time tracking of load changes. This requires rapid and accurate acquisition of the RF power supply output signal to provide the necessary data for impedance matching.

[0003] Currently, there are two main methods for measuring the output signal of RF power supplies. One method uses a directional coupler as a sensor to measure the output power of the power supply. However, this method does not provide a way to measure the load impedance, thus failing to meet the application requirements of real-time detection and analysis of load changes. The other method involves acquiring the incident and reflected voltage wave signals coupled from the directional coupler and performing addition and subtraction operations on the two signals in the circuit to obtain the changes in load voltage and current. This allows for the detection of voltage and current, enabling the calculation of plasma load based on real-time current and voltage data. This method overcomes the shortcomings of the first method, but because it requires accurate acquisition of the incident and reflected voltage wave signals, it places high demands on the directionality of the directional coupler. Furthermore, the voltage and current signal detection circuit requires numerous computational modules, resulting in a certain degree of circuit complexity. Summary of the Invention

[0004] In view of the above problems, an impedance detection circuit and method for RF power supplies are proposed. This method calculates the load impedance based on the S-parameters of a four-port directional coupler and the two coupling voltages. This method can quickly and accurately calculate the load impedance to achieve real-time tracking of load changes. Furthermore, embodiments of this invention are presented to provide a simple and efficient impedance detection circuit.

[0005] This invention discloses an RF power supply impedance detection circuit for connection to an RF power supply. The impedance detection circuit includes a signal acquisition circuit, a processor, an impedance matching circuit, and a plasma load.

[0006] The signal acquisition circuit includes: a directional coupler, a first voltage measurement module, a second voltage measurement module, and an analog-to-digital conversion module.

[0007] The input terminal of the directional coupler is connected to the output terminal of the radio frequency power supply, the output terminal of the directional coupler is connected to the input terminal of the impedance matching device, the output terminal of the impedance matching device is connected to the plasma load, and the coupling terminal and the isolation terminal of the directional coupler respectively couple out vector voltage signals.

[0008] The input terminal of the first voltage measurement module is connected to the coupling terminal of the directional coupler, and is used to acquire the first vector voltage signal output by the coupling terminal.

[0009] The input terminal of the second voltage measurement module is connected to the isolation terminal of the directional coupler, and is used to acquire the second vector voltage signal output by the isolation terminal.

[0010] The input terminal of the analog-to-digital converter module is connected to the output terminal of the first voltage measurement module and the output terminal of the second voltage measurement module, and converts the two sets of differential voltage analog signals, the first vector voltage signal and the second vector voltage signal, into the first voltage digital signal and the second voltage digital signal, respectively.

[0011] The processor input terminal is connected to the output terminal of the analog-to-digital converter module, and is used to analyze and process the converted first voltage digital signal and second voltage digital signal to determine the plasma load impedance, RF power supply output power and load power.

[0012] The first voltage measurement module and the second voltage measurement module are completely identical in circuit structure, and will be referred to as voltage measurement module from now on.

[0013] The voltage measurement module includes: a first low-pass filter circuit, a single-ended to differential circuit, a differential amplifier circuit, and a second low-pass filter circuit.

[0014] The first low-pass filter circuit includes a first low-pass filter and a first Π-type attenuator connected in series. The first low-pass filter is used to filter the signal coupled out by the directional coupler; the first Π-type attenuator is used to attenuate the signal by 20dB and perform impedance matching.

[0015] The input terminal of the single-ended to differential circuit is connected to the output terminal of the first low-pass filter circuit, and is used to convert the previous single-ended voltage signal into a differential signal.

[0016] The input terminal of the differential amplifier circuit is connected to the output terminal of the single-ended to differential circuit, and is used to amplify the differential signal.

[0017] The input terminal of the second low-pass filter circuit is connected to the output terminal of the differential amplifier circuit, and is used to filter the differential amplifier signal.

[0018] This invention also discloses an impedance detection method for an RF power supply, comprising the following steps:

[0019] Step 1: First, the two sets of differential voltage analog signals of the RF power supply are acquired through the directional coupler, the first voltage measurement module and the second voltage measurement module in the signal acquisition circuit.

[0020] Step 2: The analog-to-digital converter module in the signal acquisition circuit converts the two sets of differential voltage analog signals into two sets of corresponding voltage digital signals and provides them to the processor.

[0021] Step 3: The processor combines the S-parameters of the RF power supply output signal frequency, the vector voltage data, and the impedance matching network parameters to calculate the impedance value of the plasma load, as well as the RF power supply output power and the load received power.

[0022] The present invention has the following advantages:

[0023] This invention comprises an impedance detection circuit for an RF power supply, consisting of a directional coupler, a voltage measurement module, an analog-to-digital converter, and a processor. Compared to methods that calculate the load voltage and current by detecting the incident and reflected voltage signals coupled from the directional coupler to obtain the load impedance, this invention has a simpler circuit structure and does not have strict requirements on the directionality of the directional coupler, resulting in a cost advantage. The impedance detection method proposed in this invention can quickly and accurately obtain the load impedance, RF power supply output power, and load received power, enabling real-time monitoring of plasma load changes and providing effective technical support for more complex processes. Attached Figure Description

[0024] Figure 1 This is a block diagram of an RF power supply impedance detection circuit according to an example of the present invention;

[0025] Figure 2 This is a circuit block diagram of a voltage measurement module according to an example of the present invention;

[0026] Figure 3 This is a circuit diagram of the first low-pass filter in an example of the present invention;

[0027] Figure 4 This is a circuit diagram of the first Π-type attenuator in an example of the present invention;

[0028] Figure 5 This is a circuit diagram of a single-ended to differential circuit in an example of the present invention;

[0029] Figure 6 This is a circuit diagram of the differential amplifier circuit in an example of the present invention;

[0030] Figure 7This is a circuit diagram of the second low-pass filter in an example of the present invention;

[0031] Figure 8 This is a network port diagram of a four-port directional coupler, as exemplified by this invention. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Reference Figure 1 The diagram illustrates a block diagram of an RF power supply impedance detection circuit according to an embodiment of the present invention. The RF power supply signal acquisition circuit is used to connect to the RF power supply and includes an RF power supply signal acquisition circuit, a processor, an impedance matching circuit, and a plasma load.

[0034] The radio frequency power signal acquisition circuit includes: a directional coupler, a first voltage measurement module, a second voltage measurement module, and an analog-to-digital conversion module.

[0035] The directional coupler connects the output terminal of the RF power supply and the input terminal of the impedance matching device, and is used to acquire the RF power supply output signal and output two vector voltage signals at the coupling terminal and the isolation terminal of the directional coupler.

[0036] The input terminal of the first voltage measurement module is connected to the coupling terminal of the directional coupler, and is used to acquire the first vector voltage signal output by the coupling terminal.

[0037] The input terminal of the second voltage measurement module is connected to the isolation terminal of the directional coupler, and is used to acquire the second vector voltage signal output by the isolation terminal.

[0038] The input terminal of the analog-to-digital converter module is connected to the output terminals of the first voltage measurement module and the second voltage measurement module, and is used to convert the analog voltage signals obtained by the two voltage measurement modules into digital voltage signals.

[0039] The processor input terminal is connected to the analog-to-digital converter output terminal, and is used to process digital voltage signals and calculate the impedance of the plasma load, the output power of the radio frequency power supply, and the received power of the load according to the impedance detection method.

[0040] The first voltage measurement module and the second voltage measurement module are completely identical in circuit structure, and their structures can both be derived from... Figure 2 This will be referred to as the voltage measurement module from now on.

[0041] The voltage measurement module includes: a first low-pass filter circuit, a first Π-type attenuation circuit, a single-ended to differential circuit, a differential amplifier circuit, and a second low-pass filter circuit.

[0042] The first low-pass filter circuit includes a first low-pass filter and a first Π-type attenuation circuit connected in series. The first low-pass filter is as follows: Figure 3 As shown, it is connected to a directional coupler and is used to filter the input voltage signal.

[0043] The first Π-type attenuation circuit is as follows Figure 4 As shown, it is connected to the first low-pass filter to attenuate the preceding signal by 20dB and to provide impedance matching.

[0044] The single-ended differential circuit is as follows: Figure 5 As shown, it is connected to the first Π-type attenuation circuit and is used to convert the single-ended voltage signal of the preceding stage into a differential signal.

[0045] The differential amplifier circuit is as follows: Figure 6 As shown, it is connected to a single-ended to differential circuit for amplifying differential signals.

[0046] The second low-pass filter circuit is as follows Figure 7 As shown, it is connected to a differential amplifier circuit and used to filter the differential amplified signal.

[0047] An impedance detection method for an radio frequency power supply, used in the circuit according to any one of claims 1 to 4, characterized in that it includes the following steps:

[0048] Step 1: First, the two sets of differential voltage analog signals of the RF power supply are acquired through the directional coupler, the first voltage measurement module and the second voltage measurement module in the signal acquisition circuit.

[0049] Step 2: The analog-to-digital converter module in the signal acquisition circuit converts the two sets of differential voltage analog signals into two sets of corresponding voltage digital signals and provides them to the processor.

[0050] Step 3: The processor combines the S-parameters of the RF power supply output signal frequency, the vector voltage data, and the impedance matching network parameters to calculate the impedance value of the plasma load, as well as the RF power supply output power and the load received power.

[0051] Figures 3-7 The diagram below shows the circuit diagrams of each sub-module in the voltage measurement module. For a clearer explanation of the circuit principle of the voltage measurement module, please refer to [reference needed]. Figures 3-7 The circuit of the voltage measurement module will be illustrated as an example.

[0052] The first low-pass filter circuit includes a first low-pass filter and a first Π-type attenuator. The first low-pass filter includes capacitors C1, C2, and C3, and inductors L1 and L2. The directional coupler's coupling voltage output terminal is connected to one end of capacitor C1 and inductor L1, and the other end of capacitor C1 is grounded. The other end of inductor L1 is connected to one end of capacitor C2 and inductor L2, and the other end of capacitor C2 is grounded. The other end of inductor L2 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to ground. The first low-pass filter is connected to the first Π-type attenuator. The first Π-type attenuator circuit provides 20dB attenuation and impedance matching. The first Π-type attenuator circuit includes resistors R1, R2, R3, R4, R5, and R6. One end of resistors R1, R2, R3, and R4 are connected together, and the other end is grounded, forming a parallel circuit. The non-grounded end of the parallel circuit is connected to one end of resistor R5. The other end of R5 is connected to one end of resistor R6 and to the next stage single-ended to differential circuit. The other end of R6 is grounded.

[0053] The single-ended to differential circuit includes capacitor C4, resistors R7, R8, and R9, transformer T1, resistors R10, R11, R12, R13, R14, R15, and R16, and capacitors C5 and C6. One end of capacitor C4 is connected to the first low-pass filter circuit in the preceding stage, and the other end is connected to one end of resistors R7 and R8. The other end of resistor R7 is grounded. The other end of resistor R8 is connected to one end of resistor R9, and the other end of resistor R9 is grounded. One end of resistor R10 is grounded. Pin 1 of transformer T1 is connected to the non-grounded ends of resistors R9 and R10. On one end, pin 3 of transformer T1 is connected to one end of resistors R11 and R12, and the other ends of resistors R11 and R12 are grounded. Pin 4 of transformer T1 is connected to one end of capacitor C6. Pin 6 of transformer T1 is connected to one end of capacitor C5. Pin 5 of transformer T1 is connected to one end of resistor R13, and the other end of resistor R13 is grounded. The other end of capacitor C5 is connected to one end of resistor R14. The other end of capacitor C6 is connected to one end of resistor R15. The other end of resistor R15, the other end of resistor R14, and one end of resistor R16 are connected, and the other end of resistor R16 is grounded.

[0054] The differential amplifier module includes a differential amplifier chip U1, resistors R17, R18, R19, R20, R21, R22, capacitors C16, C17, C7, and C8. One end of resistor R17 is connected to one end of capacitor C5 in the preamplifier circuit, and the other end is connected to pin 6 of chip U1, as well as one end of resistor R19 and capacitor C7. The other end of resistor R19 and capacitor C7 is connected to pin 7 of chip U1 and one end of resistor R21. One end of resistor R18 is connected to... One end of C6 is connected to pin 2 of chip U1, and the other end is connected to one end of resistor R20 and capacitor C8. The other end of resistor R20 and capacitor C8 is connected to pin 1 of chip U1 and one end of resistor R22. Pins 3, 4 and 9 of chip U1 are connected to the drive power supply. Pin 5 of chip U1 is connected to capacitors C16 and C17 and the common-mode voltage port of the analog-to-digital converter chip. The other ends of capacitors C16 and C17 are grounded. Pins 8, 10 and 11 of chip U1 are grounded.

[0055] The second low-pass filter circuit includes capacitors C9, C10, C11, C12, C13, C14, C15, and C18; inductors L3, L4, L5, and L6; and resistors R23 and R24. One end of capacitor C9 is connected to one end of resistor R21, capacitor C10, and inductor L3 in the pre-amplifier module circuit. The other end of capacitor C9 is connected to one end of resistor R22, capacitor C11, and inductor L4 in the pre-amplifier circuit. The other ends of capacitors C10 and L3 are connected to capacitors C12, C13, and L6. One end of L5 is connected, the other ends of capacitor C11 and inductor L4 are connected to the other end of capacitor C12 and one end of capacitor C14 and inductor L6, the other ends of capacitor C13 and inductor L5 are connected to capacitor C15 and one end of resistor R23 and serve as one differential signal output terminal, the other ends of capacitor C14 and inductor L6 are connected to capacitor C15 and one end of resistor R24 ​​and serve as another differential signal output terminal, the other ends of resistor R23 and resistor R24 ​​are connected to one end of capacitor C18 and connected to the common mode voltage port of analog-to-digital converter chip, and the other end of capacitor C18 is grounded.

[0056] The voltage measurement module is applicable to both the first voltage measurement module and the second voltage measurement module. Since there is a certain difference in the amplitude range of the two voltages, the amplification gain in the differential amplifier circuit can be adjusted appropriately to achieve the best measurement effect.

[0057] To better illustrate the impedance detection method, the following is the calculation formula for this method:

[0058] The processor pre-stores the S-parameter data of the directional coupler at a specific frequency point of the RF power supply. Let the S-parameter matrix of the directional coupler be:

[0059]

[0060] The four-port directional coupler end is as follows Figure 8 As shown, a1, a2, a3, and a4 are the normalized incident waves at the four ports, and b1, b2, b3, and b4 are the normalized reflected waves at the four ports. The normalized impedance is Z0. Port 1 of the directional coupler is connected to the RF power supply output, and port 2 is connected to the load Z. L Ports 3 and 4 are connected to the RF power signal measurement circuit.

[0061] The vector voltages at the coupling and isolation terminals of the directional coupler obtained by the RF power signal measurement circuit are V3 and V4, respectively. Therefore, the values ​​of b3 and b4 can be derived as follows:

[0062]

[0063] By combining the pre-stored S-parameter data and the two measured vector voltage values, the normalized incident wave and normalized reflected wave values ​​at port 2 of the directional coupler can be calculated, thereby obtaining the load impedance Z. L The reflection coefficient is:

[0064]

[0065] From the reflection coefficient Γ L The input impedance Z of the impedance matching circuit can be obtained from the characteristic impedance Z0. in for:

[0066]

[0067] Depending on the structure and specific device parameters of different impedance matching circuits, it can be determined through Z... in The load impedance Z is calculated. L .

[0068] Furthermore, the load power P can be calculated based on the normalized reflected and incident waves from ports 1 and 2 of the directional coupler. L and RF power output power P out :

[0069]

[0070]

Claims

1. An impedance detection circuit for an RF power supply, characterized in that, Includes signal acquisition circuitry, processor, impedance matching circuit, and plasma load; The signal acquisition circuit includes: a directional coupler, a first voltage measurement module, a second voltage measurement module, and an analog-to-digital conversion module; The input terminal of the directional coupler is connected to the output terminal of the radio frequency power supply, the output terminal of the directional coupler is connected to the input terminal of the impedance matching device, the output terminal of the impedance matching device is connected to the plasma load, and the coupling terminal and the isolation terminal of the directional coupler respectively couple out vector voltage signals. The input terminal of the first voltage measurement module is connected to the coupling terminal of the directional coupler to acquire the first vector voltage signal output from the coupling terminal; The input terminal of the second voltage measurement module is connected to the isolation terminal of the directional coupler to acquire the second vector voltage signal output from the isolation terminal; The input terminal of the analog-to-digital conversion module is connected to the output terminal of the first voltage measurement module and the output terminal of the second voltage measurement module, and converts the two sets of differential voltage analog signals, the first vector voltage signal and the second vector voltage signal, into the first voltage digital signal and the second voltage digital signal, respectively. The processor input is connected to the analog-to-digital converter output to analyze and process the converted first and second voltage digital signals to determine the plasma load impedance, RF power output power, and load power.

2. The impedance detection circuit for the radio frequency power supply according to claim 1, characterized in that, The first voltage measurement module includes: a first low-pass filter circuit, a single-ended to differential circuit, a differential amplifier circuit, and a second low-pass filter circuit; The input terminal of the single-ended to differential circuit is connected to the output terminal of the first low-pass filter circuit to convert the previous single-ended voltage signal into a differential signal. The input terminal of the differential amplifier circuit is connected to the output terminal of the single-ended to differential circuit to amplify the differential signal. The input terminal of the second low-pass filter circuit is connected to the output terminal of the differential amplifier circuit to filter the differential amplifier signal.

3. The impedance detection circuit for the radio frequency power supply according to claim 2, characterized in that, The first low-pass filter circuit includes a first low-pass filter and a first Π-type attenuator connected in series. The first low-pass filter filters the signal coupled out by the directional coupler, and the first Π-type attenuator attenuates the signal by 20dB and performs impedance matching.

4. The impedance detection circuit for the radio frequency power supply according to claim 3, characterized in that, The first voltage measurement module and the second voltage measurement module are identical in circuit structure.

5. An impedance detection method for an RF power supply, used in the circuit described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: First, the two sets of differential voltage analog signals of the RF power supply are acquired through the directional coupler, the first voltage measurement module and the second voltage measurement module in the signal acquisition circuit; Step 2: The analog-to-digital converter module in the signal acquisition circuit converts the two sets of differential voltage analog signals into two sets of corresponding voltage digital signals and provides them to the processor. Step 3: The processor combines the S-parameters of the RF power supply output signal frequency, the vector voltage data, and the impedance matching network parameters to calculate the impedance value of the plasma load, as well as the RF power supply output power and the load received power.

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