Frequency measuring device for low-amplitude signal

Abstract

The utility model aims to provide a low-amplitude signal frequency measuring device which comprises an upper computer, a communication module, a single-chip microcomputer module and a signal shaping and amplifying module, a signal source to be tested is connected to the single-chip microcomputer module through the signal shaping and amplifying module, and the single-chip microcomputer module is in communication connection with the upper computer through the communication module; the signal shaping and amplifying module comprises a first operational amplifier, a second operational amplifier, a third operational amplifier, a capacitor and a resistor, and a non-inverting input end of the first operational amplifier is connected to a signal source to be tested; the inverting input end of the first operational amplifier and the output end of the first operational amplifier are connected to the non-inverting input end of the second operational amplifier through a capacitor, the output end of the second operational amplifier is connected with the non-inverting input end of the third operational amplifier, and the output end of the third operational amplifier is connected with the single-chip microcomputer module. The frequency testing device is applied to the technical field of frequency testing.

Description

TECHNICAL FIELD

[0001] The utility model relates to a technical field of frequency test, especially relate to a low amplitude signal frequency measuring device. BACKGROUND

[0002] In electronic equipment test, frequency characteristic is an important parameter index, it is not only related to electronic equipment's performance, and influence the whole system stability and efficiency's key factor. With the rapid development of electronic technology, the research and application of frequency characteristic become particularly important, the frequency stability measurement of signal source will directly influence the performance of circuit and the progress of product design and development. With the rapid development of electronic products in recent years, technology is constantly updated. The demand of long endurance is higher and higher, and the designer will choose lower voltage to maintain the stability of the system, which brings certain challenge. Therefore, the scheme of low amplitude signal frequency measurement is particularly important.

[0003] In the prior art, the measurement method mostly uses frequency counter instrument to measure, however, the frequency counter instrument has the defects of large size and high price. The current frequency measurement board card end scheme mainly calculates the number of edges in a fixed time to inversely calculate the frequency, but the IO port of the MCU end only accepts digital signals, and there is a strict setting of high and low threshold, which leads to that the low amplitude signal cannot directly enter the IO port for measurement and must be shaped. The current technology mainly amplifies the actual signal to a reasonable range, resulting in different parameters of the amplification circuit for different bias and different amplitude signals.

[0004] The existing electronic products have higher and higher requirements for function test before leaving the factory, and the demand for frequency measurement is also increasing, such as maintaining the existing frequency counter instrument measurement method. When a large number of products are produced, a large number of instruments will be occupied, which will seriously cause resource waste. When designing the existing electronic products, more and more attention will be paid to the performance of endurance, and the developer will continuously reduce the voltage of the whole system, so as to lead to that the amplitude of the signal source is lower and lower, and the bias between different products is also different, so it is difficult to realize that one amplification circuit with the same parameters completes different test requirements. Therefore, it is necessary to provide a low amplitude signal frequency measuring device, which has the advantages of low cost, small space occupation, strong practicability, flexible use, strong portability, strong operability and wide applicability. UTILITY MODEL CONTENT

[0005] The utility model solves the technical problems of the prior art, and provides a low amplitude signal frequency measuring device, which has the advantages of low cost, small space occupation, strong practicability, flexible use, strong portability, strong operability and wide applicability.

[0006] The utility model adopts the technical scheme: the utility model discloses a host computer, communication module, singlechip module, signal shaping and amplification module, the signal source of waiting for testing is accessed the singlechip module through the signal shaping and amplification module, the singlechip module is accessed the host computer through communication module, the signal shaping and amplification module includes first operational amplifier, second operational amplifier, third operational amplifier, capacitor and resistance, the same direction input end of first operational amplifier is accessed the signal source of waiting for testing, the opposite direction input end of first operational amplifier, the output of first operational amplifier is all accessed the same direction input end of second operational amplifier through capacitor, 1.8V power voltage is divided into two ways, one way is accessed the same direction input end of second operational amplifier, the node of capacitor through resistance, the output of second operational amplifier is connected with the same direction input end of third operational amplifier, the opposite direction input end of third operational amplifier is accessed 3.3V power voltage, and the output of third operational amplifier is connected with the singlechip module.

[0007] From the above scheme, the application adopts integrated circuit, occupies small space, and has strong practicability, flexible use, strong portability and low cost, and provides a high-quality scheme for the test industry;Through the ingenious shaping circuit design, the bias voltage is filtered at the same time;Using the power supply characteristics of the operational amplifier, the purpose of amplifying only the positive voltage signal is achieved, and finally a signal with fixed frequency and peak-to-peak value is outputted;The frequency measurement accuracy of the output signal by the rear-end MCU is improved to the maximum.

[0008] The application utilizes the characteristics of capacitor direct current isolation, can preliminarily process signals with different biases, and has wide applicability;Using the rail-to-rail characteristics of the operational amplifier, the amplification factor is set to be large enough, so that the output signal can be adjusted to a known signal, which is more conducive to the frequency measurement of the rear-end;The circuit is stable and reliable, and is convenient for transplantation;A first open-drain comparison circuit is added to the output circuit, and the developer can simply adjust the pull-up signal level of the rear-end to match the level of the measurement system;The ingenious cooperation of each part of the shaping and amplification circuit can support the input of signals with different amplitudes and different biases, but the final output signal is a PWM signal with fixed peak-to-peak value;Using the open-drain comparison circuit as the last stage, the developer can more easily adjust the signal output amplitude and improve the compatibility;The circuit has high integration and is convenient for transplantation;The application is applied to FCT test equipment;The application utilizes the cooperation of multiple levels such as capacitors, operational amplifiers and comparators, can convert frequency signals with different amplitudes and different biases into signals with known peak-to-peak values but fixed frequency, which greatly facilitates the design of the rear-end measurement circuit;For the selection of materials in the comparator circuit, the push-pull comparator selection is abandoned, and the open-drain comparator is used, which can reduce the cost and facilitate the modification of the user, and has strong operability.

[0009] A preferred solution is that the model of the single-chip microcomputer module is STM32F103RCT6.

[0010] A preferred solution is that the communication module comprises a USB interface and an interface conversion chip, the host computer is connected with the interface conversion chip through the USB interface, the FT232_US_N pin and the FT232_US_P pin of the USB interface are connected with corresponding pins of the interface conversion chip, and the PC_TX_TO_MCU pin and the MCU_TO_PC_RX pin of the interface conversion chip are connected with corresponding pins of the single-chip microcomputer module. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a connection block diagram of the utility model;

[0012] Figure 2 is a communication block diagram of the signal shaping and amplification module;

[0013] Figure 3 is a circuit principle diagram of the signal shaping and amplification module;

[0014] Figure 4 is a circuit principle diagram of the single-chip microcomputer module;

[0015] Figure 5 is a circuit principle diagram of the communication module;

[0016] Figure 6 is a waveform diagram of the signal shaping and amplification module. DETAILED DESCRIPTION

[0017] As Figure 1 , Figure 2 and Figure 6As shown in the utility model, in the embodiment, the utility model includes host computer 1, communication module 2, single-chip microcomputer module 3, signal shaping and amplification module 4, and the signal shaping and amplification module 4 is accessed to the single-chip microcomputer module 3, the single-chip microcomputer module 3 is communicated and connected with the host computer 1 through the communication module 2, the signal shaping and amplification module 4 includes first operational amplifier U3A, second operational amplifier U3B, third operational amplifier U4A, capacitor C8 and resistance R8, the same direction input end of the first operational amplifier U3A is accessed to the signal source 5 to be tested, the opposite direction input end of the first operational amplifier U3A, the output end of the first operational amplifier U3A is accessed to the same direction input end of the second operational amplifier U3B through the capacitor C8, 1.8V power voltage is divided into two paths, one path is accessed to the node of the same direction input end of the second operational amplifier U3B and the capacitor C8 through the resistance R8, the output end of the second operational amplifier U3B is connected with the same direction input end of the third operational amplifier U4A, the opposite direction input end of the third operational amplifier U4A is accessed to 3.3V power voltage, and the output end of the third operational amplifier U4A is connected with the single-chip microcomputer module 3.

[0018] The host computer 1 can interact with the single-chip microcomputer module 3 through serial communication tools, can issue personalized instructions to the single-chip microcomputer module 3, and can also acquire states in real time, and further calculates, analyzes, stores and displays measurement results.

[0019] The communication module 2 converts the USB communication of the host computer 1 into UART communication mode.

[0020] The single-chip microcomputer module 3 can effectively measure the frequency of the input signal by using the counting function of the single-chip microcomputer I / O port.

[0021] The signal shaping and amplification module 4 filters the bias voltage at the same time, realizes the amplification effect of only the positive voltage signal by using the power supply characteristics of the operational amplifier, finally outputs a signal with constant frequency and fixed peak-to-peak value, and better compatibility of different bias low amplitude signal frequency measurement requirements.

[0022] The communication module 2 mainly converts the UART communication interface of the single-chip microcomputer module 3 into USB, which is more convenient for the host computer 1 to control. For example, the I / O pin of PC6 / PC7 of the single-chip microcomputer module 3 is configured as a frequency counting measurement, and the signal shaping and amplification module 4 fixes the output 0-3.3V PWM wave to the measurement.

[0023] As shown in the utility model, Figure 1 、 Figure 2as well as Figure 6 As shown, in this embodiment, the first operational amplifier U3A and the second operational amplifier U3B are both OPA2192IDGKR, the third operational amplifier U4A is LM393DR, the capacitor C8 has a capacitance of 1uF, and the resistor R8 has a resistance of 10kΩ. The signal shaping and amplification module 4 can perform frequency measurement on small-amplitude signals. The specific circuit is as follows: Figure 2 As shown, the circuit is divided into 6 parts, as follows: Figure 5 The block diagram is shown below;

[0024] DC blocking by capacitor: The signal source 5 under test first flows through the OPA2192IDGKR's follower design and then into the 1uF capacitor C8 to isolate DC bias;

[0025] Fixed bias voltage: The output back end of the capacitor C8 is pulled up to 1.8V using the resistor R8, so that the output reference of the DC blocking circuit becomes 1.8V;

[0026] Amplifier circuit: Using the negative feedback design of OPA2192IDGKR, the signal is amplified 100 times with 1.8V as the reference. Since OPA2192IDGKR is a rail-to-rail operational amplifier, the amplitude of the output signal is close to VDD and VEE, that is, a PWM signal close to 5V-0V.

[0027] Comparison circuit: Design a comparator circuit using LM393DR to improve the slew rate of the output signal of the amplifier circuit and output a 3.3V-0V PWM signal to the MCU I / O port.

[0028] The actual application effect of this circuit design is as follows: Figure 6 As shown:

[0029] One channel: Input signal frequency 2.9K, amplitude 0.4V, peak value 3.1V to 3.5V;

[0030] Two-channel: Output after DC blocking and adding 1.8V bias;

[0031] Three-channel: Amplifier circuit output;

[0032] Four-channel: Comparator circuit output.

[0033] like Figure 4 As shown, in this embodiment, the microcontroller module 3 is an STM32F103RCT6. The microcontroller module 3 (STM32F103RCT6) configures the I / O pins of PC6 / PC7 for frequency counting measurement; the signal shaping and amplification module 4 outputs a fixed 0-3.3V PWM wave for measurement.

[0034] As Figures 1 to 6 shown, in the present embodiment, the communication module 2 includes a USB interface J703 and an interface conversion chip U705, the host computer 1 is connected with the interface conversion chip U705 through the USB interface J703, the FT232_US_N pin and the FT232_US_P pin of the USB interface J703 are connected with the corresponding pins of the interface conversion chip U705, the PC_TX_TO_MCU pin and the MCU_TO_PC_RX pin of the interface conversion chip U705 are connected with the corresponding pins of the single-chip microcomputer module 3. The model of the USB interface J703 is FT232; the model of the interface conversion chip U705 is FT232RL.

Claims

1. A frequency measuring device for low amplitude signals, characterized in that: It includes host computer (1), communication module (2), single-chip microcomputer module (3), signal shaping and amplification module (4), the signal source (5) to be tested is connected to the single-chip microcomputer module (3) through the signal shaping and amplification module (4), and the single-chip microcomputer module (3) is in communication connection with the host computer (1) through the communication module (2); the signal shaping and amplification module (4) includes a first operational amplifier (U3A), a second operational amplifier (U3B), a third operational amplifier (U4A), a capacitor (C8) and a resistor (R8), the same input end of the first operational amplifier (U3A) is connected to the signal source (5) to be tested, the opposite input end of the first operational amplifier (U3A) and the output end of the first operational amplifier (U3A) are connected to the same input end of the second operational amplifier (U3B) through the capacitor (C8), 1.8V power voltage is divided into two paths, one path is connected to the node of the same input end of the second operational amplifier (U3B) and the capacitor (C8) through the resistor (R8), the output end of the second operational amplifier (U3B) is connected with the same input end of the third operational amplifier (U4A), the opposite input end of the third operational amplifier (U4A) is connected with 3.3V power voltage, and the output end of the third operational amplifier (U4A) is connected with the single-chip microcomputer module (3).

2. A device for frequency measurement of a low amplitude signal as claimed in claim 1, characterized in that: The model of the single-chip microcomputer module (3) is STM32F103RCT6.

3. A device for frequency measurement of low amplitude signals as claimed in claim 1 wherein: The communication module (2) includes a USB interface (J703) and an interface conversion chip (U705), the host computer (1) is connected with the interface conversion chip (U705) through the USB interface (J703), the FT232_US_N pin and the FT232_US_P pin of the USB interface (J703) are connected with the corresponding pins of the interface conversion chip (U705), and the PC_TX_TO_MCU pin and the MCU_TO_PC_RX pin of the interface conversion chip (U705) are connected with the corresponding pins of the single-chip microcomputer module (3).

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