Filter circuit and test machine

Abstract

The utility model relates to a filter circuit and a test machine, and the filter circuit comprises an input impedance adjustment unit which is connected with a signal receiving end and is used for adjusting the input impedance of a filtering unit; the filtering unit is connected with the input impedance adjusting unit and is used for filtering the input signal; and the output impedance adjusting unit is connected with the filtering unit and the signal output end and is used for adjusting the output impedance of the filtering unit. The input impedance and the output impedance of the filtering unit can be changed through the input impedance adjusting unit and the output impedance adjusting unit according to actual requirements so as to be suitable for scenes with different input and output impedance requirements, and the use convenience is improved.

Description

Technical Field

[0001] The present application relates to the technical field of signal processing, and particularly to a filter circuit and a testing machine. Background Art

[0002] A filter is an electronic component used to remove noise and interference in a signal. It can selectively pass signals of specific frequencies to filter out unwanted frequencies. The impedance matching of a filter refers to matching the filter with a circuit or system to achieve optimal signal transmission. Impedance matching is very important in electronic engineering and can ensure signal integrity and system stability. In traditional filter circuits, the input impedance and output impedance of the filter are fixedly set and cannot be applied to scenarios with different input and output impedance requirements, having the disadvantage of low usability. Summary of the Utility Model

[0003] Based on this, it is necessary to provide a filter circuit and a testing machine that can improve usability in view of the above problems.

[0004] The first aspect of the present application provides a filter circuit, including:

[0005] An input impedance adjustment unit, connected to a signal receiving end, for adjusting the input impedance of the filtering unit;

[0006] A filtering unit, connected to the input impedance adjustment unit, for filtering the input signal;

[0007] An output impedance adjustment unit, connected to the filtering unit and a signal output end, for adjusting the output impedance of the filtering unit.

[0008] In one embodiment, the filtering unit includes two or more filtering components, and the filtering components are connected in sequence. The filtering component at the head end is connected to the input impedance adjustment unit, and the filtering component at the tail end is connected to the output impedance adjustment unit.

[0009] In one embodiment, the filtering component includes a filtering inductor, and the filtering inductors in the filtering components are connected in sequence. The filtering inductor at the head end is connected to the input impedance adjustment unit, and the filtering inductor at the tail end is connected to the output impedance adjustment unit.

[0010] In one embodiment, the filtering component further includes a grounding capacitor. The first end of the filtering inductor in each filtering component is connected to the second end of the filtering inductor in the previous-level filtering component. The first end of the filtering inductor at the head end is connected to the input impedance adjustment unit, and the second end of the filtering inductor at the tail end is connected to the output impedance adjustment unit; the first end of the grounding capacitor in each filtering component is connected to the first end of the corresponding filtering inductor, and the second end of the grounding capacitor is grounded.

[0011] In one embodiment, the filter circuit further includes a first amplifier and a second amplifier. The input impedance adjustment unit is connected to the signal receiving end through the first amplifier, and the output impedance adjustment unit is connected to the signal output end through the second amplifier. The first amplifier and the second amplifier are used for impedance conversion.

[0012] In one embodiment, the input impedance adjustment unit includes a resistor R2, and the output impedance adjustment unit includes a resistor R3. The input end of the first amplifier is connected to the signal receiving end, the output end of the first amplifier is connected to the first end of the resistor R2, the second end of the resistor R2 is connected to the filtering unit, the first end of the resistor R3 is connected to the input end of the second amplifier and the filtering unit, the second end of the resistor R3 is grounded, and the output end of the second amplifier is connected to the signal output end.

[0013] In one embodiment, the filter circuit further includes an input adjustment unit and an output adjustment unit. The input adjustment unit is connected to the input end of the first amplifier and the signal receiving end, and the output end of the second amplifier is connected to the signal output end through the output adjustment unit.

[0014] In one embodiment, the input adjustment unit includes a resistor R1 and a switch K1. The first end of the switch K1 is connected to the input end of the first amplifier and the signal receiving end, the second end of the switch K1 is connected to the first end of the resistor R1, and the second end of the resistor R1 is grounded.

[0015] In one embodiment, the output adjustment unit includes a resistor R4 and a switch K2. The first end of the resistor R4 is connected to the output end of the second amplifier, the second end of the resistor R4 is connected to the signal output end, and the switch K2 is connected in parallel with the resistor R4.

[0016] The second aspect of the present application provides a testing machine, including the above-mentioned filter circuit.

[0017] For the above-mentioned filter circuit and testing machine, the input impedance adjustment unit is connected to the signal receiving end and is used to adjust the input impedance of the filtering unit; the filtering unit is connected to the input impedance adjustment unit and is used to filter the input signal; the output impedance adjustment unit is connected to the filtering unit and the signal output end and is used to adjust the output impedance of the filtering unit. According to actual needs, the input impedance and the output impedance of the filtering unit can be changed through the input impedance adjustment unit and the output impedance adjustment unit to be applicable to scenarios with different input and output impedance requirements, improving the convenience of use. Description of the Drawings

[0018] Figure 1It is a structural block diagram of a filter circuit in an embodiment;

[0019] Figure 2 It is a structural schematic diagram of a filter circuit in an embodiment;

[0020] Figure 3 It is a simulation schematic diagram of a filter circuit in an embodiment;

[0021] Figure 4 It is a test framework diagram of a filter circuit in an embodiment;

[0022] Figure 5 It is a test result schematic diagram of a filter circuit in an embodiment;

[0023] Figure 6 It is a simulation schematic diagram of the signal input and output magnitudes of a filter circuit in an embodiment;

[0024] Figure 7 It is a simulation schematic diagram of the signal input and output magnitudes of a filter circuit with its impedance matched to 50R (ohms) in an embodiment. Detailed implementation manners

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0027] It can be understood that the terms "first", "second", etc. used in this application can be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, the first resistor can be called the second resistor, and similarly, the second resistor can be called the first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0028] It can be understood that "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if there is an electrical signal or data transfer between the connected circuits, modules, units, etc.

[0029] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprises / comprising", "has / including", etc. specify the presence of the stated features, integers, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, components, parts, or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the related listed items.

[0030] In one embodiment, as Figure 1 shown, a filter circuit is provided, including: an input impedance adjustment unit 110, a filtering unit 120, and an output impedance adjustment unit 130. The input impedance adjustment unit 110 is connected to a signal receiving end and is used to adjust the input impedance of the filtering unit; the filtering unit 120 is connected to the input impedance adjustment unit 110 and is used to filter the input signal; the output impedance adjustment unit 130 is connected to the filtering unit 120 and a signal output end and is used to adjust the output impedance of the filtering unit. Among them, the signal Vin accessed by the signal receiving end is delivered to the filtering unit 120 through the input impedance adjustment unit 110 for filtering, and the filtered signal passes through the output impedance adjustment unit 130 and finally outputs the signal Vout through the signal output end.

[0031] The filtering unit 120 may adopt an LC (inductor-capacitor) filtering structure. The input impedance adjustment unit 110 and the output impedance adjustment unit 130 may be a single resistor or multiple resistors. When the input impedance adjustment unit 110 and the output impedance adjustment unit 130 adopt a single resistor, it may be using a variable resistor for impedance adjustment or a resistor with a fixed resistance value. For example, by connecting the connection terminals to relevant devices in the circuit, the impedance adjustment is achieved by replacing the resistor between the connection terminals; when the input impedance adjustment unit 110 and the output impedance adjustment unit 130 adopt multiple resistors, it may be connecting multiple resistors in series, parallel, or in a combination of series and parallel, and the impedance adjustment is performed by changing the resistor connection relationship through the internal switch of the unit. The multiple resistors used may be resistors with fixed resistance values or variable resistors. According to actual needs, the input impedance and output impedance of the filtering unit 120 can be changed through the input impedance adjustment unit 110 and the output impedance adjustment unit 130. After the input impedance and output impedance are determined, the parameters of the inductor and capacitor in the filtering unit 120 are determined to ensure the filtering effect of the filter circuit.

[0032] In one embodiment, as Figure 2As shown, the filtering unit 120 includes more than two filtering components 122, and the filtering components 122 are connected in sequence. The filtering component 122 at the head end is connected to the input impedance adjusting unit 110, and the filtering component 122 at the tail end is connected to the output impedance adjusting unit 130. The number of the filtering components 122 may be two or more. Specifically, the filtering component 122 may include a filtering inductor, and the filtering inductors in each filtering component 122 are connected in sequence. The filtering inductor at the head end is connected to the input impedance adjusting unit 110, and the filtering inductor at the tail end is connected to the output impedance adjusting unit 130. Further, the filtering component 122 further includes a grounding capacitor. The first end of the filtering inductor in each filtering component 122 is connected to the second end of the filtering inductor in the previous-stage filtering component 122. The first end of the filtering inductor at the head end is connected to the input impedance adjusting unit 110, and the second end of the filtering inductor at the tail end is connected to the output impedance adjusting unit 130. The first end of the grounding capacitor in each filtering component 122 is connected to the first end of the corresponding filtering inductor, and the second end of the grounding capacitor is grounded.

[0033] As Figure 2 shown, taking the number of the filtering components 122 being 4 as an example, the filtering inductors include a filtering inductor L1, a filtering inductor L2, a filtering inductor L3, and a filtering inductor L4, and the grounding capacitors include a grounding capacitor C1, a grounding capacitor C2, a grounding capacitor C3, and a grounding capacitor C4. The first end of the filtering inductor L1 is connected to the input impedance adjusting unit 110, the second end of the filtering inductor L1 is connected to the first end of the filtering inductor L2, the second end of the filtering inductor L2 is connected to the first end of the filtering inductor L3, the second end of the filtering inductor L3 is connected to the first end of the filtering inductor L4, the second end of the filtering inductor L4 is connected to the output impedance adjusting unit 130, the first end of the grounding capacitor C1 is connected to the first end of the filtering inductor L1, the second end of the grounding capacitor C1 is grounded, the first end of the grounding capacitor C2 is connected to the first end of the filtering inductor L2, the second end of the grounding capacitor C2 is grounded, the first end of the grounding capacitor C3 is connected to the first end of the filtering inductor L3, the second end of the grounding capacitor C3 is grounded, the first end of the grounding capacitor C4 is connected to the first end of the filtering inductor L4, and the second end of the grounding capacitor C4 is grounded.

[0034] In one embodiment, the filter circuit further includes a first amplifier OPA1 and a second amplifier OPA2. The input impedance adjusting unit 110 is connected to the signal receiving end through the first amplifier OPA1, and the output impedance adjusting unit 130 is connected to the signal output end through the second amplifier OPA2. Among them, the first amplifier OPA1 and the second amplifier OPA2 may specifically adopt operational amplifiers, and the first amplifier OPA1 and the second amplifier OPA2 are used for impedance conversion.

[0035] Further, the input impedance adjustment unit 110 includes a resistor R2, and the output impedance adjustment unit 120 includes a resistor R3. The input terminal of the first amplifier OPA1 is connected to the signal receiving terminal, the output terminal of the first amplifier OPA1 is connected to the first end of the resistor R2, the second end of the resistor R2 is connected to the filtering unit 120, specifically to the first end of the filtering inductor L1. The first end of the resistor R3 is connected to the input terminal of the second amplifier OPA2 and the filtering unit 120, specifically to the second end of the filtering inductor L4. The second end of the resistor R3 is grounded, and the output terminal of the second amplifier OPA2 is connected to the signal output terminal. In this embodiment, the resistors R2 and R3 are fixed-value resistors to ensure stable signal filtering. The input impedance and output impedance can be adjusted by replacing the resistors. In other embodiments, the resistors R2 and R3 can also be variable resistors, and the input impedance and output impedance can be adjusted without replacing components.

[0036] In one embodiment, with continued reference to Figure 2 , the filter circuit further includes an input adjustment unit 140 and an output adjustment unit 150. The input adjustment unit 140 is connected to the input terminal of the first amplifier OPA1 and the signal receiving terminal, and the output terminal of the second amplifier OPA2 is connected to the signal output terminal through the output adjustment unit 150. Among them, the filter circuit can include a filtering mode and a test mode. The filter circuit can be mode-adjusted through the input adjustment unit 140 and the output adjustment unit 150, so that the filter circuit can be used to filter signals in the filtering mode, or the filter circuit can be tested by an external test device in the test mode.

[0037] Among them, the input adjustment unit 140 can include a resistor R1 and a switch K1. The first end of the switch K1 is connected to the input terminal of the first amplifier OPA1 and the signal receiving terminal, the second end of the switch K1 is connected to the first end of the resistor R1, and the second end of the resistor R1 is grounded. Further, the output adjustment unit 150 can include a resistor R4 and a switch K2. The first end of the resistor R4 is connected to the output terminal of the second amplifier OPA2, the second end of the resistor R4 is connected to the signal output terminal, and the switch K2 is connected in parallel with the resistor R4. In addition, the output adjustment unit 150 can further include a resistor R5. The switch K2 is connected in series with the resistor R5 and then connected in parallel with the resistor R4. The resistance value of the resistor R5 can be selected as 0R, and the switches K1 and K2 can be relay switches or other control switches. When the switch K1 is open and the switch K2 is closed, the filter circuit is in the filtering mode and filters the input signal. When the switch K1 is closed and the switch K2 is open, the filter circuit is in the test mode, and an external test device can be connected to the signal receiving terminal and the signal output terminal to test the filter circuit.

[0038] In one embodiment, a testing machine is further provided, including the above-mentioned filter circuit. Among them, the testing machine can be a digital-analog hybrid testing machine, a radio frequency testing machine, etc. The number of filter circuits can be more than two, supporting multi-channel signal filtering.

[0039] For current high-speed digital signal transmission circuits and radio frequency circuits, the input and output impedances of the filter are both fixed at 50R. For common related test instruments, including network analyzers, spectrum signal analyzers, vector signal sources, etc., the input and output impedances are also 50R. The filter is designed with fixed input and output impedances and cannot be applied to scenarios with different input and output impedance requirements. In addition, taking the Butterworth low-pass filter as an example, its matched source impedance (input impedance) and load impedance (output impedance) are both 50R. In the passband range of 0 - 30MHz, although there is no energy loss due to impedance mismatch, half of the energy is still lost due to the voltage division of the source impedance and the load impedance.

[0040] The above-mentioned filter circuit provided by this application can be a conventional filter, that is, both the source impedance and the load impedance are 50R; it can also be a new type of filter with "non-standard" impedance, that is, both the source impedance and the load impedance are non-50R and can be arbitrarily matched. As Figure 2 shown, when designing the filter, the 50R matching scheme is no longer used. The source impedance matching is designed as resistor R2, and the load impedance matching is designed as resistor R3. For example, when designing a filter circuit with a source impedance matched to 125R and a load impedance matched to 650R, the resistance values of resistor R1, resistor R2, resistor R3, resistor R4, and resistor R5 are respectively R1 = 50R, R2 = 125R, R3 = 650R, R4 = 50R, R5 = 0R. Disconnect switch K1 and close switch K2. The filter circuit is in the filtering mode, and the input and output impedances are fixed. Substitute the design values into the simulation tool for simulation debugging. The simulation calculation results are as Figure 3 shown. The passband of this filter is 70M, with small in-band fluctuations and good stopband suppression.

[0041] After building the circuit structure, it is also necessary to use test equipment to debug the state of the filter circuit to achieve the best performance before it can be applied to the actual circuit. For current test equipment, such as the vector network analyzer VNA, the input and output impedances are designed according to 50R. At this time, if the filter circuit designed with "non-standard" impedance is directly used for performance testing with the vector network analyzer VNA, due to impedance mismatch, the data obtained from the test will not be the true performance of the filter. Therefore, it is necessary to match the impedance of the filter circuit with "non-standard" impedance with the vector network analyzer VNA.

[0042] Specifically, as Figure 4As shown, keep the target input impedance (resistor R2) = 125R and the target output impedance (resistor R3) = 650R unchanged. Close switch K1 and open switch K2, and conduct physical debugging on the circuit according to the design values:

[0043] (1) A resistor R1 = 50R is connected in parallel to the ground at the input terminal of the first amplifier OPA1, and a resistor R2 = 125R is connected in series at the output terminal of the first amplifier OPA1. The first amplifier OPA1 plays a role in impedance transformation here, transforming the impedance of 50R at the input terminal of the first amplifier OPA1 to the impedance of 125R at the output terminal of the first amplifier OPA1. At this time, ensure that the input terminal of the first amplifier OPA1 is matched to 50R;

[0044] (2) A resistor R3 = 650R is connected in parallel to the ground at the input terminal of the second amplifier OPA2, and a resistor R4 = 50R is connected in series at the output terminal of the second amplifier OPA2. The second amplifier OPA2 plays a role in impedance transformation here, transforming the impedance of 650R at the input terminal of the second amplifier OPA2 to the impedance of 50R at the output terminal of the second amplifier OPA2. At this time, ensure that the output terminal of the second amplifier OPA1 is matched to 50R;

[0045] Those skilled in the art know that the characteristics of an operational amplifier are high input impedance (such as an input impedance of 1 MΩ) and low output impedance (such as an output impedance of 1 Ω). Therefore, a resistor R1 = 50R is connected in parallel at the input terminal of the first amplifier OPA1, resulting in an impedance of 50R at the input terminal of the first amplifier OPA1. Similarly, a resistor R4 = 50R is connected in series at the output terminal of the second amplifier OPA2. Therefore, the output terminal of the second amplifier OPA1 is matched to 50R.

[0046] Combining (1) and (2), the input terminal of the entire circuit is 50R when viewed from the left side, and the output terminal is 50R, achieving impedance matching with the ports of the vector network analyzer VNA, and achieving the purpose of testing the "non-standard" impedance new filter. Through the Figure 4 connection block diagram shown, establish a circuit debugging environment. According to the actual circuit requirements, debug the capacitance values of capacitors C1, C2, C3, C4, C5, C6, C7, and the inductance values of inductors L1, L2, L3, L4, so that the performance of the filter circuit meets the design expectations. The test results are as follows Figure 5 As shown, the actual measurement is consistent with the design expectations.

[0047] In the actual circuit application of the above "non-standard" impedance filter circuit, when switch K1 is opened and switch K2 is closed, a circuit matching an input impedance of 125R and an output impedance of 650R is obtained. Assuming that the in-band insertion loss of the filtering unit 120 is very small, then the magnitude of the signal energy passing through this filter circuit is the voltage division magnitude between resistor R2 and resistor R3.

[0048] The filter circuit proposed in this application supports arbitrary impedance matching. According to the actual circuit requirements, the resistance values of resistor R2 and resistor R3 can be adjusted to match the target impedance, providing more design options. It is no longer restricted to having to match 50 ohms. Therefore, when the link signal passes through this circuit, there is no situation where the amplitude is reduced by half. For example, if the input and output impedances of the filter circuit are 125R and 650R respectively, at this time, the signal energy of the "non-standard" impedance new filter of this application is 5 dB higher than that of the conventionally agreed 50R impedance matching. This can improve the SNR (signal-to-noise ratio) and the signal quality under certain conditions. Moreover, the input end of the entire filter circuit is 50R and the output end is 50R, achieving impedance matching with the ports of conventional test instruments such as the vector network analyzer VNA, thus achieving the purpose of testing the "non-standard" impedance new filter.

[0049] Taking the "non-standard" arbitrary impedance filter circuit with an input impedance of 125R and an output impedance of 650R as an example, from Figure 6 the shown simulation results, it can be seen that the output signal of the filter circuit is Vout = 0.84Vin, and the energy is lost by 1.5 dB relative to the input. Figure 7 For the simulation results of the filter circuit with an input and output impedance of 50R by convention, it can be seen that the magnitude of the output signal of the output filter circuit is Vout = 0.5Vin, and the energy is lost by 6 dB relative to the input. In summary, the magnitude of the output signal of the "non-standard" arbitrary impedance filter circuit is 4.5 dB higher than that of the filter with the conventionally agreed 50R impedance matching. This can improve the SNR by about 4.5 dB under certain conditions, thus improving the signal quality.

[0050] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0051] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the utility model patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A filter circuit, characterized in that: include: An input impedance adjustment unit, connected to the signal receiving end, for adjusting the input impedance of the filter unit; A filtering unit, connected to the input impedance adjustment unit, for filtering the input signal; The output impedance adjustment unit is connected to the filter unit and the signal output end, and is used to adjust the output impedance of the filter unit.

2. The filter circuit according to claim 1, characterized in that: The filter unit includes more than two filter components, and the filter components are connected in sequence. The filter component located at the head end is connected to the input impedance adjustment unit, and the filter component located at the end end is connected to the output impedance adjustment unit.

3. The filter circuit according to claim 2, characterized in that: The filter assembly includes a filter inductor. The filter inductors in each of the filter assemblies are connected in sequence. The filter inductor at the head end is connected to the input impedance adjustment unit, and the filter inductor at the end end is connected to the output impedance adjustment unit.

4. The filter circuit according to claim 3, characterized in that: The filter component also includes a grounding capacitor, the first end of the filter inductor in each of the filter components is connected to the second end of the filter inductor in the previous level filter component, the first end of the filter inductor located at the head end is connected to the input impedance adjustment unit, and the second end of the filter inductor located at the end is connected to the output impedance adjustment unit; the first end of the grounding capacitor in each of the filter components is connected to the first end of the corresponding filter inductor, and the second end of the grounding capacitor is grounded.

5. The filter circuit according to any one of claims 1 to 4, characterized in that: It also includes a first amplifier and a second amplifier, the input impedance adjustment unit is connected to the signal receiving end through the first amplifier, the output impedance adjustment unit is connected to the signal output end through the second amplifier, and the first amplifier and the second amplifier are used for impedance conversion.

6. The filter circuit according to claim 5, characterized in that: The input impedance adjustment unit includes a resistor R2, and the output impedance adjustment unit includes a resistor R3; the input end of the first amplifier is connected to the signal receiving end, the output end of the first amplifier is connected to the first end of the resistor R2, the second end of the resistor R2 is connected to the filtering unit, the first end of the resistor R3 is connected to the input end of the second amplifier and the filtering unit, the second end of the resistor R3 is grounded, and the output end of the second amplifier is connected to the signal output end.

7. The filter circuit according to claim 6, characterized in that: It also includes an input adjustment unit and an output adjustment unit, wherein the input adjustment unit is connected to the input end of the first amplifier and the signal receiving end, and the output end of the second amplifier is connected to the signal output end through the output adjustment unit.

8. The filter circuit according to claim 7, characterized in that: The input adjustment unit includes a resistor R1 and a switch K1, a first end of the switch K1 is connected to the input end of the first amplifier and the signal receiving end, a second end of the switch K1 is connected to the first end of the resistor R1, and a second end of the resistor R1 is grounded.

9. The filter circuit according to claim 7, characterized in that: The output adjustment unit includes a resistor R4 and a switch K2. The first end of the resistor R4 is connected to the output end of the second amplifier, the second end of the resistor R4 is connected to the signal output end, and the switch K2 is connected in parallel with the resistor R4.

10. A testing machine, characterized in that: A filter circuit comprising any one of claims 1 to 9.

Images