An automatic level adjustment system and method for pulse signals
By using an automatic level adjustment system to detect and adjust the gain of the receiving device in real time, the problems of test errors and equipment damage when the receiving device is faced with unknown pulse signals are solved, and fast and accurate signal measurement and equipment protection are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA ELECTRONIS TECH INSTR CO LTD
- Filing Date
- 2026-02-12
- Publication Date
- 2026-06-05
AI Technical Summary
Existing receiving equipment cannot automatically and quickly adjust the receiving channel gain when faced with pulse signals of unknown power, resulting in large errors in test results and potentially damaging the equipment.
An automatic level adjustment system is adopted, which uses an RF signal processing channel, a gain detection and comparison path, and a control processing unit to detect the signal gain in real time and dynamically adjust the state of the attenuator and low-noise amplifier to ensure that the signal is within the linear operating range.
It enables rapid and accurate testing of receiving equipment when faced with unknown power pulse signals, avoiding equipment overload damage and improving testing accuracy and equipment safety.
Smart Images
Figure CN122159839A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electronic measurement technology, specifically relating to an automatic level adjustment system and method for pulse signals. Background Technology
[0002] With increasingly stringent requirements for electromagnetic compatibility (EMC) and electromagnetic interference (EMI) testing, higher challenges are being placed on the performance of test receiving equipment.
[0003] For electromagnetic interference (EMI) testing, the most commonly used receiving devices are spectrum analyzers and receivers. Spectrum analyzers are general-purpose electromagnetic signal measuring devices, capable of testing various signal types such as continuous wave signals and pulse signals, and are widely used in the electronics and communications industries. Receivers are specialized instruments used to detect and analyze EMI in electronic equipment, primarily used in professional EMI testing fields. Depending on the testing scenario, receivers come in various styles; for example, EMI testing receivers are used for EMI testing and disturbance power testing in EMC testing, measurement receivers are specifically used for metrological testing of signal generators, and monitoring receivers are used for wireless signal search, monitoring, and location. Whether using a spectrum analyzer or a receiver, key performance indicators for testing EMI signals include sensitivity and linear operating range.
[0004] This article mainly uses EMI test receivers, which are frequently subjected to electromagnetic interference testing, as an example for detailed description.
[0005] Receiver sensitivity is a core indicator of a receiver's ability to detect weak signals, representing the minimum signal level that can be reliably identified under specific conditions. In EMI testing, high sensitivity directly determines whether the equipment can capture weak electromagnetic interference signals.
[0006] The formula for sensitivity is expressed as follows: S (dBm) = -174 + 10log( BW Hz )+ NF Rx + SNR min in, S Represents receiver sensitivity. BW Hz Represents receiver bandwidth in Hz. NF Rx This represents the overall noise figure of the receiver. SNR min This represents the minimum required signal-to-noise ratio.
[0007] The noise figure of a system is often the total noise figure after multiple stages of devices are cascaded. The expression for the cascaded noise figure is as follows: It can be seen that when the noise figure of the preceding stage amplifier remains constant, the higher the gain, the lower the system noise figure, and thus the higher the system sensitivity. When the gain remains constant, the lower the noise figure of a single stage, the lower the overall system noise figure, and the higher the sensitivity. The closer the high-gain, low-noise-figure amplifier is to the beginning of the system, the more significant the improvement in the overall system noise figure. Therefore, to significantly improve the overall sensitivity of the receiver, a low-noise amplifier is often added after the receiver input port.
[0008] A preamplifier (low-noise amplifier) can amplify small signals; however, when amplified, signals with slightly higher power may exceed the linear operating range of the amplifier or subsequent mixer, causing signal distortion or even damaging components. The linear operating range of an amplifier is often quantized using a 1dB compression point or a third-order intercept point. The linear operating range of the receiver as a whole is also limited by the linear operating range of the amplifier or mixer. Therefore, to ensure undistorted signal reception, the receiver adds an adjustable attenuator between the input port and the amplifier. By adjusting the attenuation value of the attenuator, the signal can be kept within the linear operating range of the amplifier and mixer.
[0009] However, the attenuation of the attenuator directly worsens the noise figure, thus leading to a contradiction for the receiver: when the test signal contains both small and large signals, it is necessary to balance the attenuation and the amplifier gain to ensure that as many accurate signals as possible are received. The ability to receive both small and large signals at the same time is the receiver's dynamic range.
[0010] Receivers or spectrum analyzers typically rely on software settings to manually adjust attenuation via a reference level and enhance sensitivity by manually activating amplifiers. This means they cannot automatically adjust dynamic range based on signal power. When testing unknown electromagnetic signals, the signal strength must be estimated beforehand, and a suitable reference level must be established for accurate testing. Incorrect estimations require manual adjustments or yielding incorrect test results.
[0011] The existing method for receivers or spectrum analyzers is to use a reference level to link with the attenuator. For example, according to the principle of the maximum mixer level setting value, (reference level - mechanical attenuator value + preamplifier gain - reference level offset) must be less than or equal to the maximum mixer level setting value. Under the above conditions, the mechanical attenuator takes the minimum value.
[0012] The existing methods described above can effectively ensure that the receiver can operate within a suitable dynamic range when the approximate power of the signal being tested is known. However, they lack flexibility when testing unknown signals. When the power of the signal being tested is outside the receiver's dynamic range, or when the power difference between signals in different frequency ranges within the scanning band is large, the test results obtained by the existing methods will have large errors.
[0013] With the widespread adoption of automated testing, system software directly controls the receiver for testing. The system software often only sets the frequency sweep range and reference level of the receiver once, without adjusting the receiver settings based on the signal test results. Without human intervention, incorrect results are obtained, posing potential risks to mass production.
[0014] Current automatic leveling methods are mostly used in signal generation equipment to correct signal power and achieve amplitude stabilization. In the signal link, it is only necessary to detect whether the signal power reaches the specified power. If it does not reach the specified power, the output power is ensured to be accurate by adjusting the gain adjustable amplifier and attenuator. There is no need to pay attention to the signal frequency information, nor is there any special processing for pulse signals.
[0015] Therefore, there is an urgent need for a technical solution that can be integrated into the signal receiving device, automatically and quickly identify the power of the input signal (especially the pulse signal), and optimize the gain of the receiving channel in real time to ensure that it can operate within the linear range throughout the entire frequency band. Summary of the Invention
[0016] The purpose of this invention is to overcome the shortcomings of the prior art and provide an automatic level adjustment system and method for pulse signals, so that when the receiving device faces unknown power, especially sudden high-power pulse signals, it can automatically and quickly adjust the receiving channel gain to the optimal linear operating point, thereby ensuring the accuracy of test results, expanding the effective dynamic range, and preventing the device from being damaged due to overload.
[0017] To achieve the above objectives, the present invention adopts the following technical solution: An automatic level adjustment system for pulse signals, applied in a receiving device, includes: The radio frequency signal processing channel includes an attenuator, a low-noise amplifier, a preselector, and a mixer connected sequentially along the signal flow direction, used to attenuate, amplify, filter, and downconvert the radio frequency input signal. A gain detection and comparison path is used to detect and evaluate the gain status of the RF signal processing channel in real time. The path includes a power divider, a detector, and a subtraction circuit. The input of the power divider is connected between the output of the preselector and the input of the mixer, and is used to split the RF signal output by the preselector into a path to the detector. The detector is used to convert the input RF signal into a detection voltage characterizing its power. The first input of the subtraction circuit is connected to the output of the detector to receive the detection voltage, and its second input is connected to a reference voltage source to receive a preset reference voltage. The subtraction circuit is used to output the difference signal between the detection voltage and the reference voltage. A control processing unit is configured to dynamically adjust the gain of the radio frequency signal processing channel based on the difference signal; the control processing unit includes: The acquisition and logic judgment module has its input terminal connected to the output terminal of the subtraction circuit. It is used to acquire and latch the difference signal, and generate a gain adjustment request signal based on whether the latched difference signal exceeds a preset range. The central processing unit, which is communicatively connected to the acquisition and logic judgment module, is used to respond to the gain adjustment request signal, generate control commands according to preset adjustment rules, and output them to the attenuator and the low-noise amplifier to adjust the attenuation amount or the on / off state of the amplifier.
[0018] Preferably, the reference voltage source is a numerically controlled reference source, and the reference voltage value output by the central processing unit is set by querying a preset reference voltage mapping table based on the current operating frequency of the receiving device, the current attenuation level of the attenuator, and the current switching state of the low-noise amplifier.
[0019] Preferably, the reference voltage mapping table is established through the following calibration steps: For a specific frequency point, under the condition that the attenuator is set to a first predetermined attenuation value and a standard power signal is input, the initial value of the reference voltage at that frequency point is determined; Based on the initial value of the reference voltage, the attenuation level of the attenuator and the switching state of the low-noise amplifier are changed respectively, and the corresponding reference voltage compensation values are measured and recorded.
[0020] Preferably, the acquisition and logic judgment module is a field-programmable gate array (FPGA), which is configured as follows: Receive an enable control signal from the central processing unit, the enable control signal being used to mask the response to the difference signal under specific conditions; When the enable control signal is valid, the difference signal that lasts for more than a predetermined time width is latched to obtain the latched difference signal; The latch difference signal is compared with preset upper and lower thresholds. If it exceeds the threshold range, a valid gain adjustment request signal is generated.
[0021] Preferably, the preset adjustment rule executed by the central processing unit is: with the goal of minimizing the absolute value of the difference signal output by the subtraction circuit, the attenuation level of the attenuator is adjusted in steps, and the low-noise amplifier is controlled to be turned on or off, so that the total gain of the radio frequency signal processing channel is adjusted to a predetermined linear operating range.
[0022] Furthermore, this invention also mentions an automatic level adjustment method for pulse signals, employing the automatic level adjustment system for pulse signals as described above, specifically including the following steps: Step 1: Signal detection and comparison: A power detection channel is separated from the radio frequency signal filtered by the preselector to obtain the detected voltage; the detected voltage is compared with a reference voltage preset according to the current device status to obtain the difference signal; Step 2: Gain Status Determination: Determine whether the difference signal is within the preset voltage range that characterizes the RF signal processing channel operating in the linear region; Step 3: Automatic gain adjustment: If the difference signal exceeds the preset voltage range, the attenuation of the attenuator and / or the switching state of the low noise amplifier are adjusted according to the amplitude and polarity of the difference signal and a predetermined logic. Step 4: Iterative convergence: Repeat steps 1 to 3 until the difference signal falls within the preset voltage range or reaches the preset maximum number of adjustments.
[0023] Preferably, in step 2, the determination is performed by the field-programmable gate array, specifically including: latching the difference signal in the gain adjustment enabled state; determining whether the latched signal exceeds a preset threshold, and setting the gain adjustment interrupt flag accordingly; the central processing unit triggers step 3 by querying the interrupt flag.
[0024] Preferably, the predetermined logic in step 3 includes: If the difference signal indicates that the current signal power is higher than the upper limit of the linear operating region, then the attenuation of the attenuator is increased; if the attenuator has reached the maximum attenuation and still does not meet the requirements, then the low-noise amplifier is turned off. If the difference signal indicates that the current signal power is below the lower limit of the linear operating region, the attenuation of the attenuator is reduced; if the attenuator has reached the minimum attenuation but still does not meet the requirements, the low-noise amplifier is turned on.
[0025] Preferably, after each adjustment operation of the attenuator or the low-noise amplifier in step 3, a preset stabilization delay is waited before the next step 1 is executed to obtain a new difference signal.
[0026] Preferably, the method is automatically executed at each scanning frequency point or when switching to a new frequency band during frequency scanning by the receiving device, so as to achieve dynamic gain management of unknown pulse signals throughout the scanning process.
[0027] The beneficial technical effects of this invention are as follows: 1. Fully automated: No manual estimation or setting of reference levels is required, simplifying the operation process and making it particularly suitable for automated testing systems, thus improving testing efficiency.
[0028] 2. High reliability and safety: It can respond to sudden high-power pulse signals in real time, quickly reduce the gain, and effectively avoid overload, distortion or even hardware damage to the receiving channel.
[0029] 3. High testing accuracy: By automatically adjusting the signal power to the receiver's optimal linear range, it ensures that signals of different power can be accurately measured throughout the scanning process.
[0030] 4. High versatility: The system is based on a general superheterodyne architecture, requires minimal hardware modifications, and can be widely used in various devices that need to receive and analyze electromagnetic signals.
[0031] 5. Highly targeted: It specifically considers the transient characteristics of pulse signals and sets up a fast response and adjustment mechanism in the control logic to ensure the accuracy of pulse signal capture and measurement. Attached Figure Description
[0032] Figure 1 This is a schematic diagram of the hardware circuit architecture of an embodiment of the present invention.
[0033] Figure 2 This is a software control flowchart of an embodiment of the present invention. Detailed Implementation
[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Overall Design Overview: This invention comprises a collaborative design of three parts: hardware circuitry, scanning logic, and software control, specifically designed to meet the automatic level adjustment requirements of receiving devices for processing pulse signals.
[0035] 1. Hardware circuit design; Hardware architecture: such as Figure 1As shown, the automatic level adjustment system of this invention is integrated into a superheterodyne EMI test receiver. The RF input signal first passes through a programmable attenuator and then enters a switchable low-noise amplifier. The amplified signal is bandpass filtered by a preselector to suppress out-of-band interference. The filtered signal is then fed into a mixer to mix with the local oscillator signal and down-converted to an intermediate frequency signal for subsequent processing; on the other hand, a small portion of the power is split off by a power divider.
[0036] One of the output signals is fed into a detector, which linearly converts the RF power into a DC detector voltage V_det. This detector voltage is then fed into the positive input of a subtraction circuit. The negative input of the subtraction circuit is connected to a reference voltage source consisting of a high-precision digital-to-analog converter (DAC), providing a programmable reference voltage V_ref. The subtraction circuit outputs the difference signal between the two: ΔV = V_det - V_ref.
[0037] The difference signal ΔV is sent to the FPGA on the acquisition board.
[0038] Reference Voltage Determination: The reference voltage REF (i.e., V_ref) is generated by a high-precision DAC. Its value needs to be calibrated and determined during the production stage: For each operating frequency, under the reference conditions of attenuator set to 10dB and input of a -20dBm standard signal, the DAC is adjusted to make ΔV≈0, and this DAC value is recorded as the baseline value for that frequency. Subsequently, at the same frequency, the attenuator settings and LNA switch states are changed, and the DAC is fine-tuned to bring ΔV back to zero. The DAC offset values under each state are recorded to form a complete frequency-state-reference voltage mapping table.
[0039] Response mechanism: After the radio frequency signal is detected and compared by subtraction, the L signal reflects the deviation between the instantaneous power and the expected value. This signal is acquired in real time and used for control decisions.
[0040] 2. Scanning logic design (FPGA implementation); To coordinate automatic level adjustment and receiver scanning, the FPGA design is as follows: Parameter settings: The CPU sets parameters for the FPGA, including the enable signal L_En (1 = enable detection), the single-shot shield signal L_Single, and the scan start pulse Start_Step.
[0041] Signal processing: When L_En=1, the FPGA synchronously latches the L signal with a duration >10ns to obtain L_reg.
[0042] Compare L_reg with the software-preset threshold. If it exceeds the range, set the gain adjustment interrupt flag Gain_Int=1; otherwise, set Gain_Int=0.
[0043] L_reg and Gain_Int can be cleared by a timer or by a specific event.
[0044] 3. Software control design; Software control flow such as Figure 2 As shown, the core steps are as follows: Initialization and Enabling: The user or upper-layer system sets Emi_Adjust_En to always be enabled. When Emi_Adjust_En=1, the software decides whether to set L_En=1 based on the current attenuator status, etc. (For example, adjustment may be disabled when attenuation is at its maximum).
[0045] Status query and interrupt response: Software timer or event-driven query of Gain_Int and L_reg in FPGA.
[0046] Gain adjustment decision and execution: If Gain_Int=1, the adjustment direction (increase / decrease attenuation, or switch LNA on / off) is determined based on the L_reg value. Adjustments are made step by step according to the principle of "adjust attenuation first, then switch LNA", and stability is waited after each adjustment.
[0047] Iteration and Termination: After adjustment, the L signal is re-detected, and the adjustment is repeated until Gain_Int=0 (L enters the allowable range) or the maximum number of adjustments M is reached. After the adjustment is completed, a Start_Step pulse is emitted, and the receiver continues or begins normal scanning measurement.
[0048] Inter-scan coordination: During receiver frequency sweeping, this adjustment process can be automatically invoked during the dwell time at each frequency point or when switching to a new frequency band, to achieve adaptive gain optimization across the entire frequency sweep range.
[0049] Brief description of working principle: During system operation, the RF signal power in the channel is monitored in real time (represented by the detection voltage V_det) and compared with the expected reference voltage V_ref under the current operating conditions. The difference ΔV directly reflects whether the input signal power allows the channel to operate in the linear region. An excessively large ΔV (positive or negative) indicates improper gain setting. The control system automatically adjusts the attenuator and LNA through closed-loop feedback to bring ΔV close to zero, thereby dynamically maintaining the signal power near the center of the receiving channel's linear range. For pulse signals, fast detection and FPGA response ensure that adjustment decisions can be made throughout the signal duration.
[0050] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.
Claims
1. An automatic level adjustment system for pulse signals, applied to a receiving device, characterized in that, include: The radio frequency signal processing channel includes an attenuator, a low-noise amplifier, a preselector, and a mixer connected sequentially along the signal flow direction, used to attenuate, amplify, filter, and downconvert the radio frequency input signal. A gain detection and comparison path is used to detect and evaluate the gain status of the RF signal processing channel in real time; the path includes a power divider, a detector, and a subtraction circuit; the input of the power divider is connected between the output of the preselector and the input of the mixer, and is used to split the RF signal output by the preselector into one path to the detector; The detector is used to convert the input radio frequency signal into a detection voltage that characterizes its power; the first input terminal of the subtraction circuit is connected to the output terminal of the detector to receive the detection voltage, and its second input terminal is connected to a reference voltage source to receive a preset reference voltage; the subtraction circuit is used to output the difference signal between the detection voltage and the reference voltage. A control processing unit is used to dynamically adjust the gain of the radio frequency signal processing channel based on the difference signal; The control processing unit includes: The acquisition and logic judgment module has its input terminal connected to the output terminal of the subtraction circuit. It is used to acquire and latch the difference signal, and generate a gain adjustment request signal based on whether the latched difference signal exceeds a preset range. The central processing unit, which is communicatively connected to the acquisition and logic judgment module, is used to respond to the gain adjustment request signal, generate control commands according to preset adjustment rules, and output them to the attenuator and the low-noise amplifier to adjust the attenuation amount or the on / off state of the amplifier.
2. The automatic level adjustment system for pulse signals according to claim 1, characterized in that, The reference voltage source is a numerically controlled reference source, and its output reference voltage value is set by the central processing unit by querying a preset reference voltage mapping table based on the current operating frequency of the receiving device, the current attenuation level of the attenuator, and the current switching state of the low noise amplifier.
3. The automatic level adjustment system for pulse signals according to claim 2, characterized in that, The reference voltage mapping table is established through the following calibration steps: For a specific frequency point, under the condition that the attenuator is set to a first predetermined attenuation value and a standard power signal is input, the initial value of the reference voltage at that frequency point is determined; Based on the initial value of the reference voltage, the attenuation level of the attenuator and the switching state of the low-noise amplifier are changed respectively, and the corresponding reference voltage compensation values are measured and recorded.
4. The automatic level adjustment system for pulse signals according to claim 1, characterized in that, The data acquisition and logic judgment module is a field-programmable gate array (FPGA), which is configured as follows: Receive an enable control signal from the central processing unit, the enable control signal being used to mask the response to the difference signal under specific conditions; When the enable control signal is valid, the difference signal that lasts for more than a predetermined time width is latched to obtain the latched difference signal; The latch difference signal is compared with preset upper and lower thresholds. If it exceeds the threshold range, a valid gain adjustment request signal is generated.
5. The automatic level adjustment system for pulse signals according to claim 1, characterized in that, The preset adjustment rule executed by the central processing unit is: with the goal of minimizing the absolute value of the difference signal output by the subtraction circuit, the attenuation level of the attenuator is adjusted in steps, and the low-noise amplifier is controlled to be turned on or off, so that the total gain of the radio frequency signal processing channel is adjusted to a predetermined linear operating range.
6. An automatic level adjustment method for pulse signals, characterized in that, The automatic level adjustment system for pulse signals as described in claim 1 specifically includes the following steps: Step 1: Signal detection and comparison: A power detection channel is separated from the radio frequency signal filtered by the preselector to obtain the detected voltage; the detected voltage is compared with a reference voltage preset according to the current device status to obtain the difference signal; Step 2: Gain Status Determination: Determine whether the difference signal is within the preset voltage range that characterizes the RF signal processing channel operating in the linear region; Step 3: Automatic gain adjustment: If the difference signal exceeds the preset voltage range, the attenuation of the attenuator and / or the switching state of the low noise amplifier are adjusted according to the amplitude and polarity of the difference signal and a predetermined logic. Step 4: Iterative convergence: Repeat steps 1 to 3 until the difference signal falls within the preset voltage range or reaches the preset maximum number of adjustments.
7. The automatic level adjustment method for pulse signals according to claim 6, characterized in that, In step 2, the determination is performed by the field-programmable gate array, specifically including: latching the difference signal in the gain adjustment enabled state; determining whether the latched signal exceeds a preset threshold, and setting the gain adjustment interrupt flag accordingly; the central processing unit triggers step 3 by querying the interrupt flag.
8. The automatic level adjustment method for pulse signals according to claim 6, characterized in that, The predetermined logic in step 3 includes: If the difference signal indicates that the current signal power is higher than the upper limit of the linear operating region, the attenuation of the attenuator is increased; if the attenuator has reached its maximum attenuation and still does not meet the requirements, the low-noise amplifier is turned off. If the difference signal indicates that the current signal power is below the lower limit of the linear operating region, the attenuation of the attenuator is reduced; if the attenuator has reached the minimum attenuation but still does not meet the requirements, the low-noise amplifier is turned on.
9. The automatic level adjustment method for pulse signals according to claim 6, characterized in that, In step 3, after each adjustment operation of the attenuator or the low-noise amplifier, a preset stabilization delay is waited before the next step 1 is executed to obtain a new difference signal.
10. The automatic level adjustment method for pulse signals according to claim 6, characterized in that, The method is automatically executed at each scanning frequency point or when switching to a new frequency band during frequency scanning by the receiving device, so as to achieve dynamic gain management of unknown pulse signals throughout the scanning process.