An equal-precision digital frequency meter

Abstract

The utility model discloses a kind of equal-precision digital frequency meter, belong to the field of electronic measurement.The digital frequency meter includes: pre-processing circuit, for the signal to be measured is amplified and shaped;FPGA frequency measurement circuit, for the signal after pre-processing is frequency measurement;STM32 control display circuit, for the frequency of signal to be measured, period information is displayed.The utility model is combined with using two electronic devices of FPGA and STM32, refines time gate opening and closing time, eliminates the measurement error of positive and negative 1 cycle existing in the counting process, significantly improves the measurement accuracy of frequency meter;In broad measurement range, it maintains considerable degree of accuracy, reduces cost while accurately measuring.

Description

Technical Field

[0001] This utility model relates to the field of electronic measurement, and in particular to a digital frequency meter with equal precision. Background Technology

[0002] In recent years, with the advancement of instrument science and electronic technology, the design of modern electronic system-based measuring instruments has developed rapidly. Many industrial measurement and control systems adopt highly integrated modular designs, and industrial instruments are evolving towards digitalization and convenience. The sensitivity and accuracy of measurement signal results are two crucial indicators for the normal operation of electronic measuring instruments. Frequency is one of the most fundamental and important parameters in the field of electronic measurement. Due to its advantages such as strong anti-interference capability, large information capacity, and extremely high stability in long-distance transmission, frequency signals are widely used in aerospace, antenna broadcasting, wireless communication, geological exploration, and other fields. Wide-range, high-precision frequency measurements can drive scientific and technological progress, while scientific and technological advancements can bring new components and methods to the research of frequency measuring devices.

[0003] The measurement accuracy of traditional frequency meters based on the principle of frequency measurement changes with the frequency of the signal being measured, which has significant limitations in practical applications. Therefore, improving the accuracy of frequency measurement, expanding the range of frequency measurement, and increasing the speed of frequency measurement have become urgent problems to be solved. Utility Model Content

[0004] Purpose of the utility model: In view of the above problems, the purpose of this utility model is to provide a digital frequency meter with equal precision, which combines FPGA and STM32 electronic devices to eliminate the ±1 measurement error problem existing in the technical measurement method and broaden the frequency measurement accuracy.

[0005] Technical solution: This utility model provides a digital frequency meter with equal precision, comprising:

[0006] The preprocessing circuit is used to amplify and shape the signal to be tested;

[0007] An FPGA frequency measurement circuit is used to measure the frequency of a preprocessed signal.

[0008] The STM32 controller display circuit is used to display the frequency and period information of the signal under test.

[0009] Furthermore, the FPGA frequency measurement circuit includes an FPGA module, an active crystal oscillator, and a data storage circuit, with both the active crystal oscillator and the data storage circuit connected to the FPGA module.

[0010] Furthermore, the preprocessing circuit includes a low-noise amplifier circuit, a voltage bias circuit, and a signal rectification circuit. The output of the low-noise amplifier circuit is connected to the input of the voltage bias circuit, the output of the voltage bias circuit is connected to the input of the signal rectification circuit, and the output of the signal rectification circuit is connected to the FPGA module.

[0011] Furthermore, the voltage bias circuit includes a first resistor, a second resistor, a third resistor, and a first capacitor. One end of the first capacitor is connected to the output terminal of the low-noise amplifier circuit, and the other end of the first capacitor is connected to one end of the first resistor, one end of the second resistor, and one end of the third resistor, respectively. The other end of the first resistor is connected to a 5V voltage, the other end of the second resistor is grounded, and the other end of the third resistor serves as the output terminal of the voltage bias circuit.

[0012] Furthermore, the STM32 control display circuit includes an STM32 control circuit and a display module. The input terminal of the STM32 control circuit is connected to the FPGA module, and the output terminal of the STM32 control circuit is connected to the display module.

[0013] Furthermore, the digital frequency meter also includes a power module to power all the components contained in the digital frequency meter.

[0014] Furthermore, the power module includes a voltage conversion circuit and a power filter circuit. The output of the voltage conversion circuit is connected to the input of the power filter circuit, and the output of the power filter circuit is connected to the device that needs power.

[0015] Beneficial effects: Compared with the prior art, the significant advantages of this utility model are:

[0016] 1. Compared with the direct counting method, the present invention measures the frequency by equal precision frequency measurement method, refines the opening and closing time of the time gate, eliminates the measurement error of ±1 cycle in the counting process, and significantly improves the measurement accuracy of the frequency meter.

[0017] 2. The digital frequency meter of the present invention can accurately identify frequency measurements in a wide range of 1Hz-100MHz and maintain extremely high accuracy. The total measurement time can also be controlled within 1.5s, achieving the expected goal.

[0018] 3. The digital frequency meter of the present invention maintains constant measurement accuracy throughout the entire frequency measurement range;

[0019] 4. In terms of overall system design, this invention makes full use of the advantages of FPGA and STM32, allocating the main measurement and control functions to FPGA, which can meet the speed requirements of frequency measurement, while utilizing the excellent human-machine interface function of STM32 for real-time display and processing. Attached Figure Description

[0020] Figure 1This is a general block diagram of an equal-precision digital frequency meter;

[0021] Figure 2 This is a circuit diagram of a low-noise amplifier circuit.

[0022] Figure 3 This is a circuit diagram of a voltage bias circuit;

[0023] Figure 4 This is a circuit diagram of a signal rectifier circuit;

[0024] Figure 5 This is a schematic diagram of the equal-precision frequency measurement method.

[0025] Figure 6 This is a circuit diagram for a data storage circuit.

[0026] Figure 7 This is the circuit diagram of the STM32 control circuit.

[0027] Figure 8 This is a circuit diagram of a voltage conversion circuit;

[0028] Figure 9 This is the circuit diagram of a power supply filter circuit. Detailed Implementation

[0029] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit its scope. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the embodiments of the present invention, and not all of the structures.

[0030] In the following description, specific details such as target system architecture and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

[0031] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0032] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0033] Furthermore, in the description of this application and the appended claims, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include the target features, structures, or characteristics described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0035] Combination Figure 1 As shown in the figure, the equal precision digital frequency meter described in this embodiment includes: a preprocessing circuit, an FPGA frequency measurement circuit, and an STM32 control and display circuit. The preprocessing circuit is used to amplify and shape the signal to be measured, the FPGA frequency measurement circuit is used to measure the frequency of the preprocessed signal, and the STM32 control and display circuit is used to display the frequency and period information of the signal to be measured.

[0036] Furthermore, the preprocessing circuit includes a low-noise amplifier circuit, a voltage bias circuit, and a signal rectification circuit. The output of the low-noise amplifier circuit is connected to the input of the voltage bias circuit, the output of the voltage bias circuit is connected to the input of the signal rectification circuit, and the output of the signal rectification circuit is connected to the FPGA module.

[0037] The preprocessing circuit first amplifies the small input signal of the signal under test through a low-noise amplifier circuit, ensuring it meets the level requirements for the shaping circuit to start. Simultaneously, the low-noise amplifier circuit filters the signal, removing external noise inherent in the input signal and out-of-band noise during transmission. The signal after low-noise amplification is further processed into a square wave signal by a signal rectifier circuit for measurement. Meanwhile, the FPGA's I / O input level is limited to 0-5V; levels exceeding 5V or falling below 0V can easily damage the ports. Therefore, the shaping circuit also has a voltage limiting function, converting the input signal into a square wave signal with a low level of 0V and a high level of 3.3V.

[0038] Figure 2 This is the circuit diagram for a low-noise amplifier circuit. The circuit uses the OPA690 series chip, which maintains stable gain within a 535MHz range, meeting the design requirements. In the circuit, the input signal passes through a capacitor to filter out the DC component before entering the amplifier's inverting input. Resistor R4 is the feedback resistor. Based on the principle of virtual short and virtual open circuits, the following formula is used... Substituting the values ​​of resistors R2 and R4, we can obtain the output voltage U. OUT Approximately the input voltage U IN Twice that of the output voltage U, but in the opposite direction. OUT The output, OUT1, is obtained by passing the signal through a 50Ω load, thus realizing the input signal U. IN Extract and amplify by 2 times.

[0039] Since the signal processed by the low-noise amplifier circuit filters out the DC signal and retains only the AC signal component, this does not meet the TTL level requirements of the subsequent chip. Therefore, a suitable DC bias needs to be added. Hence, in this example, a voltage bias circuit is connected after the low-noise amplifier circuit. Because the minimum input high level in TTL is greater than or equal to 2.0V, the minimum input low level is less than or equal to 0.8V, and the noise margin is 0.4V, a bias voltage of 1.4V is chosen to be added here.

[0040] Combination Figure 3 The circuit diagram shown is for a voltage bias circuit. This circuit includes a first resistor R6, a second resistor R7, a third resistor R8, and a first capacitor C6. One end of the first capacitor C6 is connected to the output of the low-noise amplifier circuit. The other end of the first capacitor C6 is connected to one end of the first resistor R6, one end of the second resistor R7, and one end of the third resistor R8. The other end of the first resistor R6 is connected to a 5V voltage, the other end of the second resistor R7 is grounded, and the other end of the third resistor R8 serves as the output of the voltage bias circuit. The input of the voltage bias circuit is connected to the output OUT1 of the low-noise amplifier circuit. Unnecessary interference is filtered out by the first capacitor C6, and then the 5V voltage is divided by the first resistor R6 and the second resistor R7 to achieve a 1.4V bias voltage. This 1.4V bias voltage is then output through a 50Ω load, as shown in the diagram as OUT2.

[0041] Combination Figure 4 As shown, the signal rectification circuit uses the SN74LVC2G14 chip, providing two inverting buffers with Schmitt trigger inputs. This allows it to output a stable low level (0V) when the input signal is too high and a stable high level (5V) when the input signal amplitude is too low, thus converting the input frequency signal into a TTL-compliant square wave output, achieving signal shaping. The SN74LVC2G14 input can be driven by either 3.3V or 5V devices, allowing for use in mixed 3.3V and 5V environments. The input terminal of the signal rectification circuit is the output terminal OUT2 of the voltage bias circuit, and the output terminal OUT3 is connected to the FPGA module.

[0042] Furthermore, the FPGA frequency measurement circuit includes an FPGA module, an active crystal oscillator, and a data storage circuit, with both the active crystal oscillator and the data storage circuit connected to the FPGA module.

[0043] The FPGA frequency measurement circuit is the core module of the digital frequency meter. It is programmed using VHDL, replacing the traditional gate-based frequency measurement circuit. The pre-processed signal is input to the FPGA module, counted with the time base signal f0 generated by the crystal oscillator frequency divider, and the frequency value is calculated. This value is then transmitted via serial port to the STM32 control and display circuit. The data storage circuit is used to store the program, ensuring that the FPGA can still perform frequency measurement after power-on.

[0044] The equal precision frequency measurement method, also known as the multi-cycle synchronous frequency measurement method, is characterized by the synchronization of the opening and closing time of the time gate with the edge of the signal under test. Compared with the direct counting method, it refines the opening and closing time of the time gate, eliminates the ±1 cycle measurement error in the counting process, and significantly improves the measurement accuracy of the frequency meter.

[0045] The schematic diagram of the equal precision frequency measurement method is as follows: Figure 5 As shown, the measured signal After being processed by the signal rectification circuit, the signal is converted into a rectangular pulse signal, which is used as the clock input of the synchronization circuit to trigger the D flip-flop in the synchronization circuit to generate the actual gate T. This achieves synchronization between the gate opening time and the measured signal pulse. Then, the generated actual gate signal is added to the enable terminal of the counter. When the actual gate signal is valid, the counter A will count the input measured pulse, and its count value is... Simultaneously, when the actual gate is active, counter B will generate a pulse signal to the reference clock. Count, its count value .

[0046] Figure 5 The function of the logic control circuit in the system is to open and close the preset gate according to the measurement enable signal. The preset gate is generated by dividing the clock provided by the external crystal oscillator, so its error is determined by the accuracy of the crystal oscillator. The pulse is directly input to the clock terminal of the D flip-flop in the synchronization circuit. Triggered by the rising edge of the signal, an actual counting gate is generated according to a preset gate, ensuring that the start and counting of the actual counting gate are synchronized with the edge of the measured signal. With the actual gate enabled, counters A and B respectively count the input... Pulse and The pulses are counted to obtain the count value. and The measured frequency value of the signal is then fed into the arithmetic circuit to obtain the frequency measurement value of the measured signal. .

[0047] Since FPGAs lack solid-state memory, the program is lost upon power failure. Therefore, a W25Q64 FLASH chip is used as the data storage circuit to store the designed program. The circuit diagram of the data storage circuit is shown below. Figure 6 As shown, the W25Q64 is a high-capacity FLASH product launched by Winbond Corporation. It has a capacity of 64Mb and uses an SPI interface for communication. This series of devices far surpasses ordinary serial flash memory devices in terms of flexibility and performance.

[0048] The STM32 control and display circuit includes an STM32 control circuit and a display module. The input of the STM32 control circuit is connected to the FPGA module, and the output of the STM32 control circuit is connected to the display module.

[0049] Figure 7 This is a circuit diagram of the STM32 control circuit. In the STM32 control and display circuit, the STM32 microprocessor is used as the host computer to receive the frequency values ​​measured from the FPGA, obtain the period data through simple calculations, and display the frequency and period information through the display module.

[0050] To display the measurement results, the PA9 (Tx) and PA (Rx) pins of the STM32F103C8T6 are connected to the N5 (Tx) and N6 (Rx) pins of the FPGA module, respectively, and the results are displayed through the OLED display module using the SPI interface.

[0051] Furthermore, the digital frequency meter also includes a power supply module to power all the components contained in the digital frequency meter.

[0052] The power module includes a voltage conversion circuit and a power filter circuit. The output of the voltage conversion circuit is connected to the input of the power filter circuit, and the output of the power filter circuit is connected to the device that needs power.

[0053] Combination Figure 8 The circuit diagram of the voltage conversion circuit shown is required for the power supply circuit of the digital frequency meter, which needs a stable 5V, 3.3V, and -5V. Therefore, a voltage conversion chip is needed to generate the required 3.3V and -5V voltages to power different modules of the system. Figure (a) shows the 5V to 3.3V voltage conversion circuit, and Figure (b) shows the 5V to 3.3V voltage conversion circuit. This example demonstrates a voltage conversion circuit. The circuit uses the AMS1117-3.3 low-dropout regulator chip to obtain a stable 3.3V voltage. A power supply polarity inverter ICL7660, capable of outputting negative voltage, is used to achieve a stable -5V voltage. Only three external capacitors are needed to conveniently output a negative voltage with the opposite polarity to the input voltage. This circuit provides power to all components in the digital frequency meter.

[0054] Figure 9 This is a circuit diagram of a power supply filter circuit. This circuit uses two 10nF capacitors and three 0.1nF capacitors connected in parallel to filter out interference of different frequencies in the power supply. The main function of the 10nF capacitors is to filter out low-frequency interference, and the main function of the 0.1nF capacitors is to filter out high-frequency interference, thereby ensuring the stability of the power supply voltage. The circuit connection... Figure 8 The output terminal of (a) filters out interference in the power supply.

[0055] This invention describes a digital frequency meter that combines two popular electronic components, FPGA and STM32, to propose a uniform-precision digital frequency meter. This eliminates the ±1 measurement error problem inherent in traditional measurement methods, broadening the accuracy of frequency measurements and maintaining a considerable level of precision across a wide measurement range, while minimizing costs. The digital frequency meter uses an FPGA as its measurement core, matching the signal input level to construct a measurement data transmission channel, enabling fast and accurate frequency measurement. Simultaneously, it uses an STM32 as its control and display core, controlling the entire frequency meter measurement circuit and displaying information including frequency and period. This digital frequency meter can effectively measure frequencies from 1Hz to 100MHz, and the measurement error can be kept within a certain range. the following.

Claims

1. A digital frequency meter with equal precision, characterized in that, include: The preprocessing circuit is used to amplify and shape the signal to be tested; An FPGA frequency measurement circuit is used to measure the frequency of a pre-processed signal. The STM32 controller displays the frequency and period information of the signal under test.

2. The equal-precision digital frequency meter according to claim 1, characterized in that, The FPGA frequency measurement circuit includes an FPGA module, an active crystal oscillator, and a data storage circuit, both of which are connected to the FPGA module.

3. The equal-precision digital frequency meter according to claim 2, characterized in that, The preprocessing circuit includes a low-noise amplifier circuit, a voltage bias circuit, and a signal rectification circuit. The output of the low-noise amplifier circuit is connected to the input of the voltage bias circuit, the output of the voltage bias circuit is connected to the input of the signal rectification circuit, and the output of the signal rectification circuit is connected to the FPGA module.

4. The equal-precision digital frequency meter according to claim 3, characterized in that, The voltage bias circuit includes a first resistor, a second resistor, a third resistor, and a first capacitor. One end of the first capacitor is connected to the output terminal of the low-noise amplifier circuit. The other end of the first capacitor is connected to one end of the first resistor, one end of the second resistor, and one end of the third resistor, respectively. The other end of the first resistor is connected to a 5V voltage, the other end of the second resistor is grounded, and the other end of the third resistor serves as the output terminal of the voltage bias circuit.

5. A digital frequency meter with equal precision according to claim 2, characterized in that, The STM32 control display circuit includes an STM32 control circuit and a display module. The input of the STM32 control circuit is connected to the FPGA module, and the output of the STM32 control circuit is connected to the display module.

6. A digital frequency meter with equal precision according to claim 1, characterized in that, It also includes a power module to power all the components contained in the digital frequency meter.

7. A digital frequency meter with equal precision according to claim 6, characterized in that, The power module includes a voltage conversion circuit and a power filter circuit. The output of the voltage conversion circuit is connected to the input of the power filter circuit, and the output of the power filter circuit is connected to the device that needs power.

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