Handheld digital oscilloscope

Abstract

The invention discloses a handheld digital oscilloscope which comprises a main control chip. The attenuation circuit is provided with four input resistors, and each parallel compensation capacitor and the adjustable capacitor form a resistor-capacitor pair; the in-phase input end of a first operational amplifier is connected with the attenuation circuit, and a feedback resistor is arranged between the anti-phase input end and the output end of the first operational amplifier; the first adder circuit and the second operational amplifier eliminate direct current bias of the alternating current signal; the second adder circuit and the third operational amplifier perform direct current lifting on the signal and then input the signal into the main control chip; the fourth operational amplifier is connected with the second adder circuit, and the inverted input end of the fourth operational amplifier is connected with three feedback resistors in parallel; the high-speed comparator circuit outputs TTL level signals; the key circuit and the keyboard management chip are connected with the main control chip; the power circuit supplies power. Therefore, the device has the advantages of high measurement precision, good sampling performance, rich and practical functions, convenient man-machine interaction and the like.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a handheld digital oscilloscope. Background Art

[0002] In the field of power electronics technology, the oscilloscope is an important instrument for observing and measuring electrical signals. With the development of science and technology, higher requirements are placed on the performance, portability and functional diversity of oscilloscopes. Traditional oscilloscopes have certain limitations in terms of measurement range, sampling rate, portability, etc. For example, the measurement frequency range is limited, low-amplitude and small signals cannot be accurately measured, the sampling rate is not high, resulting in inaccurate measurement of high-frequency signals, and the size is large and not portable. In actual work, such as electronic equipment research and development, field signal detection and other scenarios, an oscilloscope that can accurately measure signals with a wide frequency range and a large amplitude range, has a high sampling rate, is easy to carry and simple to operate is needed. Therefore, the development of a handheld digital oscilloscope to meet the growing needs of field testing and mobile applications has become a problem that needs to be solved urgently by technicians in this field. Summary of the invention

[0003] The present invention aims to solve the technical problems in the above-mentioned technology at least to some extent.

[0004] To this end, the present invention discloses a handheld digital oscilloscope, comprising:

[0005] Main control chip;

[0006] An attenuation circuit is provided with four input resistors, each of which is connected in parallel with a compensation capacitor to form four resistor-capacitor pairs, the time constants of the four resistor-capacitor pairs are the same, and each of the compensation capacitors is connected in parallel with an adjustable capacitor;

[0007] A follower circuit is provided with a first operational amplifier, wherein a non-inverting input terminal of the first operational amplifier is electrically connected to the attenuation circuit, and a feedback resistor is provided between an inverting input terminal and an output terminal of the first operational amplifier;

[0008] a first adder circuit, provided with a second operational amplifier, wherein the second operational amplifier is used to eliminate a DC bias voltage of an AC signal output by the first operational amplifier;

[0009] a second adder circuit, which is provided with a third operational amplifier, and the third operational amplifier is used to DC-boost the AC signal after the DC bias voltage is eliminated, provide a preset DC bias voltage, and input the AC signal after the DC boost into the ADC module of the main control chip;

[0010] an amplifier circuit, wherein a fourth operational amplifier is provided, the fourth operational amplifier is electrically connected to the second adder circuit, an inverting input terminal of the fourth operational amplifier is connected in parallel to three other feedback resistors, the three feedback resistors are electrically connected to a switch chip respectively, and each of the switch chips is electrically connected to the main control chip;

[0011] A high-speed comparator circuit, which is provided with a high-speed comparator, the high-speed comparator is electrically connected to the amplification circuit, and the high-speed comparator is used to output a TTL level signal;

[0012] A key circuit is provided with a keyboard management chip, and the keyboard management chip is electrically connected to the main control chip;

[0013] A power supply circuit is used to supply power to the main control chip, the attenuation circuit, the follower circuit, the first adder circuit, the second adder circuit, the amplifier circuit, the high-speed comparator circuit and the key circuit.

[0014] In addition, the handheld digital oscilloscope disclosed in the present invention may also have the following additional technical features:

[0015] Furthermore, the resistance values ​​of the four input resistors in the attenuation circuit are 900 kΩ, 300 kΩ, 180 kΩ and 120 kΩ respectively.

[0016] Furthermore, the resistance of the feedback resistor in the follower circuit is 200Ω.

[0017] Furthermore, the second operational amplifier in the first adder circuit is used to eliminate the mV-level DC bias voltage of the AC signal output by the first operational amplifier.

[0018] Furthermore, the third operational amplifier in the second adder circuit is used to perform a DC boost on the AC signal after the DC bias voltage is eliminated, thereby providing a DC bias voltage of 1.6V.

[0019] Furthermore, the resistance values ​​of the three feedback resistors in the amplifying circuit are 1 kΩ, 2 kΩ and 4 kΩ respectively.

[0020] Furthermore, the high-speed comparator in the high-speed comparator circuit is used to perform waveform shaping on the input wide voltage range periodic signal and output a TTL level signal.

[0021] Furthermore, the keyboard management chip in the key circuit is provided with a de-jitter circuit, and is provided with a low-level effective output and a low-level pulse output.

[0022] As shown in the following table, the function of each key in the key circuit is:

[0023] Key1 Vertical Sensitivity - Increased Key8 Automatic measurement Key2 Vertical Sensitivity - Reduced Key9 Waveform moves up Key3 Horizontal Sensitivity - Increased Key10 Waveform moves down Key4 Horizontal Sensitivity - Reduced Key11 storage Key5 Trigger Level - Increase Key12 Call Out Key6 Trigger Level - Reduction Key13 Return to the initial position Key7 Trigger polarity reversal Key14 Coupling mode changes

[0024] Table 1 As shown in the following table, the input signal frequency range test of the handheld digital oscilloscope is:

[0025]

[0026] Table 2 As shown in the following table, the input signal amplitude measurement range of this handheld digital oscilloscope is:

[0027]

[0028] Table 3

[0029] As shown in the table below, a single frequency Vpp=1V sinusoidal signal is generated by a signal generator. By changing the signal frequency, the measured signal waveform of the handheld digital oscilloscope is displayed as follows:

[0030]

[0031] Table 4 As shown in the following table, the comprehensive performance of this handheld digital oscilloscope is:

[0032]

[0033]

[0034] Table 5

[0035] The handheld digital oscilloscope disclosed in the present invention has the following beneficial effects:

[0036] (1) High measurement accuracy. The present invention uses an external clock counting method to measure the signal frequency. The accuracy is high at both high and low frequencies, and the frequency measurement error is less than 5%. For amplitude measurement, a reasonable signal conditioning scheme is used to reduce the measurement error. For example, at different frequencies and amplitudes, the input signal amplitude measurement error is within a certain range, ensuring the accuracy of the measurement.

[0037] (2) Good sampling performance and high sampling rate. The maximum real-time sampling rate is 1MSa / s, and the equivalent sampling rate is 200MSa / s, which can meet the sampling requirements of signals of different frequencies. It also supports multiple vertical sensitivity and scanning speed gears, such as eight gears of vertical sensitivity and sixteen gears of scanning speed, which can better adapt to different signal characteristics and ensure the measurement effect;

[0038] (3) It is rich in functions and practical, with adjustable trigger mode and trigger level, and can display the measurement results in real time without obvious waveform distortion. It also has storage and call-out functions, which facilitates users to manage and review the measurement data. In addition, it has additional functions such as triangle wave, square wave display and adjustable coupling mode, which is suitable for a variety of signal analysis scenarios;

[0039] (4) The human-computer interaction is convenient, and the button module has rich functions, including vertical sensitivity, horizontal sensitivity, trigger level, trigger polarity, waveform movement, storage / recall, automatic measurement, return to initial position, coupling mode change and other function buttons. It is easy to operate and easy to use, which can effectively meet the needs of users in different measurement scenarios and improve the user experience.

[0040] Additional contents and advantages of the present invention will be given in the following description or may be understood through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The technical solutions and beneficial effects of the present invention will become apparent and easily understood from the following contents in conjunction with the accompanying drawings, wherein:

[0042] Figure 1 An attenuation circuit diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0043] Figure 2 A follower circuit diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0044] Figure 3 A first adder circuit diagram and a second adder circuit diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0045] Figure 4 An amplifying circuit diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0046] Figure 5 A high-speed comparator circuit diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0047] Figure 6 A key circuit diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0048] Figure 7 A timing diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0049] Figure 8 A real-time sampling diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0050] Fig. 9 An equivalent sampling diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0051] Fig.10 A system block diagram of an embodiment of a handheld digital oscilloscope of the present invention;

[0052] Fig.11 The software flow chart of one embodiment of the handheld digital oscilloscope of the present invention is shown in FIG. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0054] The handheld digital oscilloscope disclosed in the present invention will be described below with reference to the accompanying drawings.

[0055] A handheld digital oscilloscope, comprising:

[0056] The main control chip can be selected from STM32F407 microcontroller;

[0057] like Figure 1 As shown, the attenuation circuit is provided with four input resistors, each input resistor is connected in parallel with a compensation capacitor to form four resistor-capacitor pairs, the time constants of the four resistor-capacitor pairs are the same, each compensation capacitor is connected in parallel with an adjustable capacitor, and the four input resistors and the corresponding compensation capacitors and adjustable capacitors are packaged in 0805;

[0058] The resistance values ​​of the four input resistors in the attenuation circuit are 900kΩ, 300kΩ, 180kΩ and 120kΩ, respectively, so that four gears can be realized, namely ×1 gear, ×0.4 gear, ×0.2 gear and ×0.08 gear, which can meet the input range of 100mVpp~20Vpp as a whole, and the input frequency of 1Hz~10MHz at the same time;

[0059] like Figure 2 As shown, the follower circuit is provided with a first operational amplifier, and the first operational amplifier can be selected from THS4001 chip, which has a bandwidth of 270MHz, a conversion rate of more than 400V / μs, and a settling time of less than 30ns, a gain error of 0.04%, a phase error of 0.15°, and a gain flatness of 0.1dB (up to 60MHz). In an application with a frequency of 1MHz, its total harmonic distortion is as low as 72dBc, which is very suitable for the handheld digital oscilloscope;

[0060] The non-inverting input terminal of the first operational amplifier is electrically connected to the attenuation circuit, and a feedback resistor is provided between the inverting input terminal and the output terminal of the first operational amplifier;

[0061] The resistance of the feedback resistor in the follower circuit is 200Ω;

[0062] like Figure 3 As shown, a first adder circuit is provided with a second operational amplifier, and the second operational amplifier is used to eliminate the DC bias voltage of the AC signal output by the first operational amplifier;

[0063] The second operational amplifier in the first adder circuit is used to eliminate the mV level DC bias voltage of the AC signal output by the first operational amplifier;

[0064] like Figure 3 As shown, the second adder circuit is provided with a third operational amplifier, which is used to DC-boost the AC signal after the DC bias voltage is eliminated, provide a 1.6V DC bias voltage, ensure that the range of the AC signal is between 0 and 3.3V, and input the AC signal after DC boost into the ADC module of the main control chip;

[0065] In order to solve the problem that the signal frequency is too high, resulting in large sampling errors in the ADC module of the STM32F407 microcontroller, a sample-and-hold circuit with the OPA615 chip as the core can be added;

[0066] The OPA615 chip is a broadband DC recovery chip with a propagation delay time of only 1.9ns. It contains an operational amplifier (OTA) inside. Its self-biased structure ensures low input bias current and a bandwidth of 710Mhz. The chip also contains a fast and accurate sampling OTA (SOTA) with a bandwidth of 730Mhz. It has two identical high-impedance input terminals and a current source output terminal, with the characteristics of low input bias current and offset voltage, and plays the role of a comparator and buffer. The use of the OPA615 chip can ensure that the handheld digital oscilloscope is suitable for use in sample-and-hold circuits, high-speed integrators or nanosecond pulse peak detectors.

[0067] The third operational amplifier in the second adder circuit is used to DC-boost the AC signal after the DC bias voltage is eliminated, and provide a DC bias voltage of 1.6V;

[0068] It should be noted that the second operational amplifier and the third operational amplifier may also both adopt THS4001 chips;

[0069] like Figure 4As shown, the amplification circuit is provided with a fourth operational amplifier. The fourth operational amplifier can use an OPA847 chip. The OPA847 chip has extremely low input voltage and current noise, and a gain bandwidth of up to 3.9 GHz. In the handheld digital oscilloscope, it is used as a voltage gain stage. The OPA847 has a flat frequency response at a gain of +20V, and can stably work to a gain as low as +12V. At the same time, the external compensation technology of the OPA 847 chip itself enables the handheld digital oscilloscope to achieve excellent frequency response control;

[0070] The fourth operational amplifier is electrically connected to the second adder circuit, the inverting input terminal of the fourth operational amplifier is connected in parallel with three other feedback resistors, the three feedback resistors are electrically connected to a switch chip respectively, and each switch chip is electrically connected to the main control chip;

[0071] It should be noted that the switch chip can be SGM3157, which is a bidirectional, SPDT (single pole / double throw), CMOS analog switch with low on-resistance, low voltage and high bandwidth.

[0072] The resistance values ​​of the three feedback resistors in the amplifier circuit are 1 kΩ, 2 kΩ and 4 kΩ, respectively, thereby achieving three gears, namely ×10, ×20 and ×40;

[0073] like Figure 5 As shown, the high-speed comparator circuit is provided with a high-speed comparator, and the high-speed comparator can use the TLV3501 chip;

[0074] The high-speed comparator is electrically connected to the amplifier circuit, and the high-speed comparator is used to output a TTL level signal;

[0075] The high-speed comparator in the high-speed comparator circuit is used to shape the waveform of the input wide voltage range periodic signal and output a TTL level signal;

[0076] like Figure 6 As shown, the key circuit is provided with a keyboard management chip, and the keyboard management chip can be a CH452 chip;

[0077] The keyboard management chip is electrically connected to the main control chip;

[0078] The keyboard management chip in the key circuit is provided with a de-jitter circuit, and is provided with a low-level effective output and a low-level pulse output;

[0079] A power supply circuit, which is used to supply power to the main control chip, the attenuation circuit, the follower circuit, the first adder circuit, the second adder circuit, the amplifier circuit, the high-speed comparator circuit and the key circuit;

[0080] It should be noted that the power supply circuit can use the TPS5430 chip. The handheld digital oscilloscope uses ±5V to power the front-stage circuit. When using the power supply circuit based on the TPS5430 chip, 3A current can be output. At the same time, the power supply circuit has overcurrent protection and thermal shutdown functions. In the off state, there is only 17uA quiescent current.

[0081] In addition, due to the existence of multiple gears of the handheld digital oscilloscope, a 74HC4052 chip is added for data selection to facilitate circuit management.

[0082] Specifically, if Figure 7 As shown in the figure, the frequency measurement scheme of the handheld digital oscilloscope is to compare and reshape the signal into an equal-frequency square wave, and then send it to the STM32F407 microcontroller for frequency measurement. Within the determined gate time, the counter is used to record the number of pulses of the signal to be measured, so as to calculate the frequency of the signal to be measured. The measurement principle is shown in the figure. Within the timing time, every falling edge of the external signal signal, the count value count+1;

[0083] It should be noted that in actual measurement, using TIM3 timing (84Mhz frequency division, i.e. timing for one second), at low frequency (frequency less than 65535), T=1s, then, at high frequency (frequency greater than 65535), since the maximum capacity of the timer is 65535, the timer will overflow and the count will be reset to zero and count again, and the number of times the count value overflows N needs to be recorded in the interrupt;

[0084] Specifically, the signal acquisition and conditioning solution of the handheld digital oscilloscope, because the amplitude range of the input signal is 100mVpp~20Vpp, and the measurement range of the ADC module of the STM32F407 microcontroller is 0~3.3V, it cannot measure excessively high voltages and the acquisition accuracy is very low at lower voltages. Therefore, the signal needs to be conditioned before it can be sent to the microcontroller for sampling;

[0085] The ADC module of the TM32F407 microcontroller samples multiple points in one cycle to detect the amplitude range of the signal. The microcontroller selects different channels of the analog switch according to the peak value and performs amplification with different gains. This solution can well solve the problem of input signal conditioning with a wide amplitude range.

[0086] Specifically, if Figure 8 As shown, the sampling scheme of the handheld digital oscilloscope is real-time sampling. The sampling points of each acquisition cycle can express a waveform by simply arranging them in time sequence. Since this method requires sampling many points in a signal cycle to restore the waveform, real-time sampling is used when the signal frequency is less than 100kHz.

[0087] Specifically, if Fig. 9 As shown, the sampling scheme of the handheld digital oscilloscope is equivalent sampling, in which only one sample point is taken on the waveform in each sampling cycle, and each time it is delayed by a known Δt time;

[0088] The interval between two samples is set to mT+Δt, that is, the waveform under test samples one point every m cycles. The sampling time interval needs to be accurately set to Δt, and the equivalent sampling rate depends on Δt. If the equivalent sampling rate is required to be 200MSa / s, then Δt=0.005us. This method is used to sample high-frequency signals in this question.

[0089] Specifically, the system block diagram of the handheld digital oscilloscope is as follows: Fig.10 As shown;

[0090] Specifically, if Fig.11 As shown, the software part of the handheld digital oscilloscope is completed by the STM32F407 single-chip microcomputer, which completes the processing of the human-computer interaction part and the control of the system, the measurement of the frequency and amplitude, and the display function;

[0091] It should be noted that modular programming can be performed for the software part of the handheld digital oscilloscope. Each module has a certain degree of independence and portability. It is easier to find program loopholes during debugging. When modifying the program, it will not affect the implementation of other modules. In addition, the limited resources inside the microcontroller can be fully utilized to improve the efficiency of program operation and finally improve the readability of the program, especially the naming of variables and functions to reflect their functions and make the program logic clear. Comments in the program are also indispensable, which is of great significance for the debugging and maintenance of the system.

[0092] In addition, it should be noted that, on the one hand, in order to prevent the digital signal of the handheld digital oscilloscope from coupling with the analog signal and causing interference, the specific reason is that the handheld digital oscilloscope is a hybrid system composed of a digital system and an analog system interconnected, and because the distribution of analog signals and digital signals in the frequency domain is different, digital signals are more likely to enter circuits that do not belong to them and cause interference. Therefore, relevant staff can make the routing of digital signals as far away from the routing of analog signals as possible. If the routing of digital signals and the routing of analog signals have to cross, the routing of digital signals and the routing of analog signals should be crossed at 90° as much as possible, and a shielding layer should be set between the routing of digital signals and the routing of analog signals;

[0093] On the other hand, since the STM32F407 microcontroller and some interface circuits are digital circuits, a large peak current will be generated in the power supply circuit. The power supply is the main channel for external instantaneous pulses to enter the system, and necessary anti-interference measures must be taken. Relevant staff can use a 0.01~0.1uF capacitor between the power line and the ground line as a bypass capacitor to filter out ripples. At the power input of the digital chip, a 0.1uF ceramic capacitor and a 220uF electrolytic capacitor are connected in parallel to form a charge pool grounding, which effectively suppresses the influence of the digital chip on the power supply. The capacitor connection is close to the power supply end and as short as possible, and is directly connected with solder.

[0094] In summary, the handheld digital oscilloscope disclosed in the present invention has high measurement accuracy on the one hand. The present invention adopts an external clock counting method to measure the signal frequency. The accuracy is high at both high and low frequencies, and the frequency measurement error is less than 5%. For amplitude measurement, a reasonable signal conditioning scheme is used to make the measurement error smaller. For example, at different frequencies and amplitudes, the input signal amplitude measurement error is within a certain range, which ensures the accuracy of the measurement. On the other hand, it has good sampling performance and a high sampling rate. The maximum real-time sampling rate is 1MSa / s, and the equivalent sampling rate is 200MSa / s, which can meet the sampling requirements of signals of different frequencies. It also supports a variety of vertical sensitivity and scanning speed gears, such as eight gears of vertical sensitivity and sixteen gears of scanning speed, which can better adapt to different signal characteristics and ensure the measurement effect. In addition, it is rich in functions and practical, and the trigger mode and trigger level are adjustable. The measurement results can be displayed in real time, and the waveform has no obvious distortion. It also has storage and call-out functions, which is convenient for users to manage and review the measurement data. In addition, it has additional functions such as triangle wave, square wave display and adjustable coupling mode, which is suitable for a variety of signal analysis scenarios. Finally, it has convenient human-computer interaction and the button module has rich functions, including vertical sensitivity, horizontal sensitivity, trigger level, trigger polarity, waveform movement, storage / recall, automatic measurement, return to initial position, coupling mode change and other function buttons. It is easy to operate and easy to use. It can effectively meet the needs of users in different measurement scenarios and improve the user experience.

[0095] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A handheld digital oscilloscope, characterized in that: include: Main control chip; An attenuation circuit is provided with four input resistors, each of which is connected in parallel with a compensation capacitor to form four resistor-capacitor pairs, the time constants of the four resistor-capacitor pairs are the same, and each of the compensation capacitors is connected in parallel with an adjustable capacitor; A follower circuit is provided with a first operational amplifier, wherein a non-inverting input terminal of the first operational amplifier is electrically connected to the attenuation circuit, and a feedback resistor is provided between an inverting input terminal and an output terminal of the first operational amplifier; a first adder circuit, provided with a second operational amplifier, wherein the second operational amplifier is used to eliminate a DC bias voltage of an AC signal output by the first operational amplifier; a second adder circuit, which is provided with a third operational amplifier, and the third operational amplifier is used to DC-boost the AC signal after the DC bias voltage is eliminated, provide a preset DC bias voltage, and input the AC signal after the DC boost into the ADC module of the main control chip; an amplifier circuit, wherein a fourth operational amplifier is provided, the fourth operational amplifier is electrically connected to the second adder circuit, an inverting input terminal of the fourth operational amplifier is connected in parallel to three other feedback resistors, the three feedback resistors are electrically connected to a switch chip respectively, and each of the switch chips is electrically connected to the main control chip; A high-speed comparator circuit, which is provided with a high-speed comparator, the high-speed comparator is electrically connected to the amplification circuit, and the high-speed comparator is used to output a TTL level signal; A key circuit is provided with a keyboard management chip, and the keyboard management chip is electrically connected to the main control chip; A power supply circuit is used to supply power to the main control chip, the attenuation circuit, the follower circuit, the first adder circuit, the second adder circuit, the amplifier circuit, the high-speed comparator circuit and the key circuit.

2. The handheld digital oscilloscope according to claim 1, characterized in that: The resistance values ​​of the four input resistors in the attenuation circuit are 900 kΩ, 300 kΩ, 180 kΩ and 120 kΩ respectively.

3. The handheld digital oscilloscope according to claim 1, characterized in that: The resistance of the feedback resistor in the follower circuit is 200Ω.

4. The handheld digital oscilloscope according to claim 1, characterized in that: The second operational amplifier in the first adder circuit is used to eliminate the mV-level DC bias voltage of the AC signal output by the first operational amplifier.

5. The handheld digital oscilloscope according to claim 1, characterized in that: The third operational amplifier in the second adder circuit is used to perform DC boost on the AC signal after the DC bias voltage is eliminated, and provide a DC bias voltage of 1.6V.

6. The handheld digital oscilloscope according to claim 1, characterized in that: The resistance values ​​of the three feedback resistors in the amplifying circuit are 1 kΩ, 2 kΩ and 4 kΩ respectively.

7. The handheld digital oscilloscope according to claim 1, characterized in that: The high-speed comparator in the high-speed comparator circuit is used to perform waveform shaping on an input wide voltage range periodic signal and output a TTL level signal.

8. The handheld digital oscilloscope according to claim 1, characterized in that: The keyboard management chip in the key circuit is provided with a de-jitter circuit, and is provided with a low-level effective output and a low-level pulse output.

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