Broadband amplitude limiting module with low reflection after overvoltage

Abstract

The invention discloses a broadband amplitude limiting module with low reflection after overvoltage. The broadband amplitude limiting module comprises an impedance matching circuit, a high-input impedance amplifying circuit and a low-frequency gain control circuit, wherein the impedance matching circuit is used for performing 50 omega termination matching between an input signal and the high input impedance amplification circuit, and in the high input impedance amplification circuit, a low and medium frequency signal fed back by the low frequency gain control circuit and a high frequency signal coupled by the high frequency coupling capacitor are synthesized and then input to the differential operation amplification circuit; therefore, the problem of reflection caused by overvoltage in the circuit is solved, and the waveform quality of a signal path is ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electronic testing, and more particularly relates to a wideband limiting module with low reflection after overvoltage. BACKGROUND

[0002] Limiting circuits are widely used in electronic systems to protect electronic devices from overvoltage. Specifically, when the input signal amplitude is within the limiting range, the output voltage of the limiting circuit is equal to the input voltage, but when the input signal amplitude exceeds the limiting range, the output of the limiting circuit is limited to the set limiting voltage.

[0003] In the field of electronic testing, in order to accurately capture a single sporadic signal (the signal amplitude is unknown, which can be as high as tens or hundreds of volts, or as low as only a few tens of millivolts) at one time, the common method is to divide the signal into several paths for simultaneous acquisition through a multi-way power divider, and the input range of the front stage of each acquisition path is different, and finally the signal path waveform data with the smallest distortion is obtained. In order to protect the small range path when a large signal comes, a clamping protection circuit needs to be added in front of the small range path, but when the traditional clamping diode limiting circuit appears overvoltage limiting, the input impedance will change suddenly, the signal will be reflected, and the signal of other signal paths will be affected, resulting in signal distortion.

[0004] A typical diode limiting circuit is shown in Figure 1 , which can limit the input signal between V1 and V2. When the signal amplitude is within the limiting range, Vout = Vin, and when the signal exceeds the limiting voltage, Vout is limited to V2 or V1. However, for a multi-way power division measurement system, the conduction of the diode when the signal exceeds the limiting voltage will cause the input impedance of the path to change suddenly, resulting in reflection, affecting the signal integrity of other power division paths, and causing measurement waveform distortion.

[0005] A two-way power division measurement system is shown in Figure 2 , the signal is divided into two paths through a power divider and sent to two high-speed acquisition modules, and the high-speed acquisition modules receive the signal in a matched manner. The input ranges of the two acquisition modules are different (corresponding to different signal front-end gains G1 and G2), and the required limiting voltages (limiting voltages V 1_1 and V 1_2 correspond to V 2_1 and V 2_2) are also different, for small range, the required limiting voltage is low, for large range, the required limiting voltage is high, and even no limiting. In each measurement process, the isolation degree between each signal output by the power divider needs to be high, and they do not affect each other, which requires that the output end of each power divider has good matching. For the traditional diode limiting circuit, if the signal is within the limiting range, the clamping diode is not conductive, the input impedance of the high-speed acquisition module is standard 50Ω, the circuit matching is good, and the signal integrity is good, as shown in (a) and (b) of Figure 3 ; but if the signal amplitude exceeds the limiting voltage, the clamping diode in the small range limiting circuit is conductive, the input impedance of this path changes suddenly, reflection occurs, and the waveforms of other signal acquisition paths of the power divider are distorted, as shown in (c) and (d) of Figure 3 . In (c) of Figure 3 , the dashed pulse waveform is the waveform without limiting circuit after the power divider, when the input signal exceeds the limiting voltage V1_1, the waveform of Vin1 is limited (solid line), the amplitude is low, at this time the input path impedance changes suddenly, the reflection phenomenon of pulse signal occurs; the reflected signal affects Vin2 through the power divider, and the reflection phenomenon occurs on the pulse waveform of Vin2, as shown in (d), which causes waveform distortion and affects the integrity test of the normal signal path. Figure 3

[0006] Therefore, the present application designs a special overvoltage low reflection wideband limiting module for the above problems. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, provide an overvoltage low reflection wideband limiting module, solve the reflection problem caused by the overvoltage condition in the signal path after the traditional clamping diode limiting circuit in the power divider, and ensure the waveform quality of the signal path.

[0008] In order to achieve the above-mentioned purpose of the application, an overvoltage low reflection wideband limiting module, characterized in that it comprises: an impedance matching circuit, a high input impedance amplification circuit and a low frequency gain control circuit.

[0009] The impedance matching circuit is used for 50Ω termination matching between the input signal and the high input impedance amplification circuit.

[0010] The high input impedance amplification circuit is used for receiving the input signal after impedance matching, then performing 0dB gain output on the input signal within the limiting voltage, and performing limiting output on the input signal outside the limiting voltage, so as to realize the buffer isolation between the output signal and the input signal port, and protect the subsequent circuit; in addition, the high input impedance amplification circuit can present an input impedance much larger than 50Ω within the dynamic voltage input range required by the scene.

[0011] ​The low-frequency gain control circuit is used for receiving a feedback signal output by the high input impedance amplification circuit, and generating a low-frequency adjustment signal, and then feeding back the low-frequency adjustment signal to the high input impedance amplification circuit, so as to adjust the high input impedance amplification circuit, reduce the leakage current and the offset voltage of the high input impedance amplification circuit, and ensure the stable performance of the entire wideband limiting module.

[0012] The application object of the application is achieved as follows:

[0013] The wideband limiting module with low reflection after overvoltage of the application comprises an impedance matching circuit, a high input impedance amplification circuit and a low-frequency gain control circuit, wherein the impedance matching circuit is used for 50Ω termination matching between an input signal and the high input impedance amplification circuit, in the high input impedance amplification circuit, a middle-low frequency signal fed back by the low-frequency gain control circuit is combined with a high frequency signal coupled through a high frequency coupling capacitor, and then input to a differential operational amplifier circuit, and then amplified by a high-speed operational amplifier circuit and output, so as to solve the reflection problem caused by overvoltage in the circuit and ensure the waveform quality of the signal path.

[0014] Meanwhile, the wideband limiting module with low reflection after overvoltage also has the following beneficial effects:

[0015] (1) The application proposes a wideband limiting module with low reflection after overvoltage, aiming at the reflection problem caused by overvoltage in the signal path after the traditional clamping diode limiting circuit, which is based on a high input impedance wideband amplification circuit, on the one hand, ensures that the signal with the amplitude within the limiting voltage is output without distortion with 0dB gain, and on the other hand, ensures that the reflection caused by the input signal amplitude exceeding the limiting voltage is small enough (the input impedance change is small), so as to hardly affect the waveform quality of other signal paths.

[0016] (2) Since there is leakage current, offset voltage and the like in the amplifier of the high input impedance amplification circuit, the low-frequency gain control circuit is introduced to process the output of the high input impedance amplification circuit as a feedback signal, generate a low-frequency adjustment signal and act on the front stage of the high input impedance amplification circuit, so as to ensure that the circuit has stable low-frequency gain and small offset voltage.

[0017] (3) The gain of the wideband limiting module designed by the application is 0dB, and the limiting voltage range is determined by the linear range of the operational amplifier, which can ensure that the input voltage amplitude of the rear-stage acquisition circuit is within the safe voltage range, and if it is necessary to increase the limiting voltage range, a linear attenuation module can be added at the front end of the circuit to expand the use occasions. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a traditional typical diode limiting circuit diagram.

[0019] Figure 2 This is a schematic diagram of the acquisition principle of a traditional dual-channel power divider measurement system;

[0020] Figure 3 This is a schematic diagram comparing the reflections before and after the limiting circuit is applied;

[0021] Figure 4 This is a structural diagram of a broadband limiting module with low reflection after overvoltage according to the present invention;

[0022] Figure 5 This is a circuit diagram of a broadband limiting module with low reflection after overvoltage according to the present invention;

[0023] Figure 6 This is the input impedance variation curve of the DC-1GHz broadband limiting module; Detailed Implementation

[0024] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0025] Example

[0026] In this embodiment, as Figure 4 As shown, the present invention provides a broadband limiting module with low reflection after overvoltage, comprising: an impedance matching circuit, a high input impedance amplifier circuit, and a low-frequency gain control circuit.

[0027] In this embodiment, as Figure 5 As shown, the impedance matching circuit consists of resistors R1 and R2 and inductor L1. Resistors R1 and R2 are connected in series, and inductor L1 is connected in parallel across resistor R2. The other end of resistor R1 is connected to the input signal, and the other end of resistor R2 is grounded. The impedance matching circuit is used to perform 50Ω termination matching between the input signal and the high input impedance amplifier circuit.

[0028] In this embodiment, R1 is a 50Ω resistor, R2 is a small resistor of a few ohms (2Ω in this embodiment), and L1 is an nH-level inductor. The high input impedance amplifier circuit acts as the "load" of the impedance matching circuit and should be considered when taking into account the input impedance of the entire limiting module. Therefore, the expression for the input impedance Z1 of the limiting module is:

[0029] Z1=(R1+(R2 / / Z L1 )) / / Z2

[0030] Where Z2 is the input impedance of the high input impedance amplifier circuit, Z L1 The impedance is the inductor.

[0031] When the input signal is DC, Z L1 = 0, Z2>>R1, so the input impedance is R1=50Ω. R2 and L1 are used to compensate the effect of Z2 as the frequency increases. When the input signal frequency increases, Z2 decreases, which will reduce the input resistance to some extent, and due to the existence of inductor L1, the impedance of L1 increases as the frequency increases, which can offset the effect of Z2 change to some extent. The input impedance changes with frequency as shown by the solid line in Figure 6 , the input impedance of the wideband limiting amplitude module can be maintained at about 50Ω from DC to 200MHz.

[0032] In this embodiment, as shown in Figure 5 , the high input impedance amplification circuit includes a high frequency coupling capacitor, a differential operational amplifier circuit and a high speed operational amplifier circuit;

[0033] The differential operational amplifier circuit is composed of operational amplifier U1, frequency compensation capacitors C1, C2, C3, C4 and resistors R3, R4, R5, R6, R7, R8, R9, R 10 ;

[0034] Among them, the two ends of resistors R3, R4, R9, R 10 are connected in parallel with frequency compensation capacitors C1, C2, C3, C4 in turn, the frequency compensation capacitors are used to adjust the high frequency signal gain to ensure that the circuit has good flatness; resistors R3 and R7 are connected in series, and the positive input end of differential operational amplifier U1 is connected; the other end of resistor R3 is connected with high frequency coupling capacitor C6; one end of resistor R5 is grounded, and the other end is connected with the connection point of resistors R3 and R7; resistors R4 and R8 are connected in series, and the inverting input end of differential operational amplifier U1 is connected; the other end of resistor R4 is grounded; one end of resistor R6 is grounded, and the other end is connected with the connection point of resistors R4 and R8; resistor R9 is connected in parallel between the inverting output end and the positive input end of differential operational amplifier U1 as a feedback path; resistor R 10 is connected in parallel between the positive output end and the inverting input end of differential operational amplifier U1 as another feedback path; the gain of differential operational amplifier circuit is determined by resistors R3, R4, R7, R8, R9 and R 10 ;

[0035] The high speed operational amplifier circuit is composed of operational amplifier U2 and resistors R 11 , R 12 , R 13 , R 14 , R 15 ;

[0036] Among them, the inverting output end and the positive output end of differential operational amplifier U1 are respectively connected with resistors R 11 , R12 The inverting input end and the non-inverting input end of the high-speed operational amplifier U2 are connected in series; one end of the resistor R 14 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R 13 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R 12 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R 14 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R 11 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R 13 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R 15 is grounded, and the other end is connected to the non-inverting input end of the high-speed operational amplifier U2; one end of the resistor R

[0037] C6 realizes the function of isolating direct current, preventing the influence of the static voltage of the input end due to the existence of the leakage current of U1 (the normal situation should be zero, but if there is no C6, the leakage current will form a small voltage through R1 and L1, affecting the normal input).

[0038] C1, C2, C3, and C4 are used to realize compensation for high-frequency signals; R3, R4, R9, and R 10 are kΩ order resistors, such as 5.6kΩ, which are used to determine the gain of the amplification circuit composed of the differential operational amplifier U1; R7 and R8 are small resistors of tens of ohms, which are used to realize the adjustment of the flatness of the high-frequency signal response; R5 and R6 are used to compensate for the influence of the leakage current of U1, ensuring that the static voltage of the input end of U1 is about 0V; the operational amplifier U2 is used to convert the differential signal into a single-ended signal, ensuring that the entire limiting amplitude circuit has a higher output voltage range. In addition, the amplification multiple can be adjusted according to the specific use occasion (such as amplifying the signal by N times) by adjusting R 12 , R 14 , R 11 , and R 13 ; R 15 is an output resistor, which is set to 50Ω, and is used for matching to the subsequent acquisition circuit.

[0039] Therefore, it can be seen that the high input impedance amplification circuit is used to receive the impedance matched input signal, and then outputs the input signal within the limiting amplitude voltage with 0dB gain and limits the output of the input signal outside the limiting amplitude voltage, so as to realize the buffer isolation between the output signal and the input signal port, and protect the subsequent circuit; in addition, the high input impedance amplification circuit can present an input impedance much greater than 50Ω within the dynamic voltage input range required by the scene;

[0040] In this embodiment, the high input impedance amplifier circuit, when faced with large signals, experiences a very small current flowing into the amplifier's input port due to its high input impedance. The amplifier is not easily damaged by large signals, and the input impedance Z2 does not change drastically with large signals. This characteristic reduces the impact of the input impedance Z2 on the impedance matching circuit, avoiding the impedance abrupt changes caused by traditional clamping diode limiting circuits. When faced with large voltage signals, the input impedance change of the broadband limiting module is as follows: Figure 6 As shown by the dashed lines, the dashed lines represent the input impedance changes of the broadband limiting module when a large signal is input (the amplitude of the input signal is already greater than the limiting voltage), while the solid lines represent the input impedance changes of the broadband limiting module when a small signal is input. It can be seen that the input impedance changes of the two are basically the same within 200MHz. Moreover, when a large signal is input, the input impedance of the broadband limiting module can still be maintained at around 50Ω. There is no sudden change in input impedance, the reflected energy is extremely low, and it will not cause waveform distortion in other paths, ensuring signal integrity testing.

[0041] In this embodiment, as Figure 5 As shown, the low-frequency gain control circuit consists of operational amplifier U3 and gain resistor R. 16 R 17 R 18 R 19 R 20 R 21 It consists of a feedback capacitor C5;

[0042] The feedback signal output from the high input impedance amplifier circuit is passed through a series resistor R. 18 R 19 Voltage divider, in resistor R 18 R 19 The connection introduces the feedback signal to the inverting input of operational amplifier U3, and resistor R... 19 The other end is grounded;

[0043] The input signal passes through a series resistor R 16 R 17 Voltage divider, in resistor R 16 R 17 The connection point introduces the input signal to the non-inverting input of operational amplifier U3, and resistor R... 17 The other end is grounded to achieve stable control of low-frequency signals;

[0044] Series resistor R 20 R 21 Together with feedback capacitor C5, they form a local feedback network, and resistor R... 20 The other end is connected to the output of operational amplifier U3, and resistor R 21The other end is grounded. One end of the feedback capacitor C5 is connected to the inverting input of the operational amplifier U3, and the other end is connected to the resistor R. 20 and R 21 The connection terminal; used to adjust the signal gain in the mid-frequency band to ensure good circuit flatness;

[0045] The output of operational amplifier U3 is connected to resistor R. 22 The output is a low-to-medium frequency signal used for low-frequency adjustment and fed back to the high input impedance amplifier circuit.

[0046] Therefore, the low-frequency gain control circuit is used to receive the feedback signal output by the high input impedance amplifier circuit and generate a low-frequency adjustment signal. The low-frequency adjustment signal is then fed back to the high input impedance amplifier circuit for feedback adjustment, reducing the leakage current and offset voltage of the high input impedance amplifier circuit, and ensuring the stable performance of the entire broadband limiting module.

[0047] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A broadband limiting module with low reflection after overvoltage, characterized in that, include: Impedance matching circuit, high input impedance amplifier circuit, and low frequency gain control circuit; The impedance matching circuit is used to perform 50Ω termination matching between the input signal and the high input impedance amplifier circuit. The high input impedance amplifier circuit is used to receive the input signal after impedance matching, and then output a 0dB gain for the input signal within the limiting voltage, and limit the output signal outside the limiting voltage, thereby achieving buffer isolation between the output signal and the input signal port and protecting the subsequent circuits; in addition, the high input impedance amplifier circuit can present an input impedance much greater than 50Ω within the dynamic voltage input range required by the scenario. The low-frequency gain control circuit is used to receive the feedback signal output by the high input impedance amplifier circuit and generate a low-frequency adjustment signal. The low-frequency adjustment signal is then fed back to the high input impedance amplifier circuit for feedback adjustment, reducing the leakage current and offset voltage of the high input impedance amplifier circuit, and ensuring the stable performance of the entire broadband limiting module.

2. The broadband limiting module with low reflection after overvoltage as described in claim 1, characterized in that, The impedance matching circuit consists of resistors R1 and R2 and inductor L1. Resistors R1 and R2 are connected in series, inductor L1 is connected in parallel across resistor R2, the other end of resistor R1 is connected to the input signal, and the other end of resistor R2 is grounded.

3. A broadband limiting module with low reflection after overvoltage as described in claim 1, characterized in that, The high input impedance amplifier circuit includes: a high-frequency coupling capacitor, a differential operational amplifier circuit, and a high-speed operational amplifier circuit; The differential operational amplifier circuit consists of operational amplifier U1, frequency compensation capacitors C1, C2, C3, and C4, and resistors R3, R4, R5, R6, R7, R8, R9, and R1. 10 composition; Among them, resistors R3, R4, R9, and R 10 Frequency compensation capacitors C1, C2, C3, and C4 are connected in parallel across the two ends of the differential operational amplifier U1. These capacitors are used to adjust the gain of high-frequency signals and ensure good circuit flatness. Resistors R3 and R7 are connected in series to the non-inverting input of the differential operational amplifier U1, with the other end of resistor R3 connected to the high-frequency coupling capacitor C6. One end of resistor R5 is grounded, and the other end is connected to the junction of resistors R3 and R7. Resistors R4 and R8 are connected in series to the inverting input of the differential operational amplifier U1, with the other end of resistor R4 grounded. One end of resistor R6 is grounded, and the other end is connected to the junction of resistors R4 and R8. Resistor R9 is connected in parallel as a feedback path between the inverting output and non-inverting input of the differential operational amplifier U1. 10 As another feedback path, it is connected in parallel between the non-inverting output and the inverting input of the differential operational amplifier U1; the gain of the differential operational amplifier circuit is determined by resistors R3, R4, R7, R8, R9, and R 10 Joint decision; The high-speed operational amplifier circuit consists of operational amplifier U2 and resistor R. 11 R 12 R 13 R 14 R 15 composition; Among them, the inverting output terminal and the non-inverting output terminal of the differential operational amplifier U1 are respectively connected to resistor R. 11 R 12 After being connected in series, it is connected to the inverting input and non-inverting input of the high-speed operational amplifier U2; resistor R 14 One end of the resistor is grounded, and the other end is connected to the non-inverting input of the high-speed operational amplifier U2; resistor R 13 It is connected in parallel between the inverting input and output of the high-speed operational amplifier U2 as a feedback path; resistor R 12 With R 14 The ratio and R 11 With R 13 The ratio of these two factors together determines the gain of the high-speed operational amplifier circuit; resistor R 15 Connected in series at the output of the high-speed operational amplifier U2, it ultimately converts the differential signal output by the differential operational amplifier circuit into a single-ended signal output.

4. A broadband limiting module with low reflection after overvoltage as described in claim 1, characterized in that, The low-frequency gain control circuit consists of operational amplifier U3 and gain resistor R. 16 R 17 R 18 R 19 R 20 R 21 It consists of a feedback capacitor C5; The feedback signal output from the high input impedance amplifier circuit is passed through a series resistor R. 18 R 19 Voltage divider, in resistor R 18 R 19 The connection introduces the feedback signal to the inverting input of operational amplifier U3, and resistor R... 19 The other end is grounded; The input signal passes through a series resistor R 16 R 17 Voltage divider, in resistor R 16 R 17 The connection point introduces the input signal to the non-inverting input of operational amplifier U3, and resistor R... 17 The other end is grounded to achieve stable control of low-frequency signals; Series resistor R 20 R 21 Together with feedback capacitor C5, they form a local feedback network, and resistor R... 20 The other end is connected to the output of operational amplifier U3, and resistor R 21 The other end is grounded. One end of the feedback capacitor C5 is connected to the inverting input of the operational amplifier U3, and the other end is connected to the resistor R. 20 and R 21 The connection terminal; used to adjust the signal gain in the mid-frequency band to ensure good circuit flatness; The output of operational amplifier U3 is connected to resistor R. 22 The output is a low-to-medium frequency signal used for low-frequency adjustment and fed back to the high input impedance amplifier circuit.

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