What is the difference between active and passive filters?

I don't know about signal filters. I specialize in power filters. The main function of power filters is to filter out harmonics other than the fundamental current (50HZ) in the power system. There are mainly third harmonic, 150HZ, fifth harmonic, 250HZ, seventh harmonic, 350HZ signal filter. According to the brother upstairs, it should be similar to the power filter. It retains useful signals or currents and filters out useless ones. Waveform display, according to the principle of oscilloscope, when a DC voltage is added to a pair of deflector plates, the point of light will produce a fixed displacement on the fluorescent screen, which is proportional to the DC voltage added. If two DC voltages are applied to both vertical and horizontal deflectors, the position of the spot on the phosphor screen will be determined by the displacement in both directions. If a sinusoidal AC voltage is applied to a pair of deflector plates, the spot will move in response to the change in voltage on the phosphor screen. When a sinusoidal AC voltage is applied to the vertical deflector plates, the voltage is Vo (zero value) at the instant t=0, and the position of the spot of light on the screen is at coordinate origin 0. At the instant time t=1, the voltage is V1 (positive value), and the position of the spot of light on the screen is at a point 1 above the origin of the coordinate 0, with a displacement proportional to the voltage V1. At the instant of time t=2, the voltage is V2 (very positive value), the spot of light on the screen is at the position 2 o'clock above the zero point of the coordinate origin, and the displacement distance is proportional to the voltage V2; and so on, at each of the moments t=3, t=4, ? , t = 8 at each moment, the position of the light point on the screen is 3, 4, ? , 8. The first cycle will be repeated in the second and third cycles of the AC voltage. If the frequency of the sinusoidal AC voltage applied to the vertical deflector plate is very low, only lHz to 2Hz, then a point of light moving up and down will be seen on the screen. The instantaneous value of the deflection of the point of light from the coordinate origin will be proportional to the instantaneous value of the voltage applied to the vertical deflector plate. If the frequency of the AC voltage applied to the vertical deflector plate is above 10Hz~20Hz, due to the afterglow of the screen and the persistence of human vision, instead of an up and down moving dot, you will see a vertical bright line on the screen. When the vertical amplification gain of the oscilloscope is constant, the length of the bright line depends on the peak-to-peak value of the sinusoidal AC voltage. If a sinusoidal AC voltage is applied to a horizontal deflector plate, a similar situation occurs except that the dot moves on the horizontal axis. If a voltage that varies linearly with time (e.g., a sawtooth wave voltage) is applied to a pair of deflector plates, how does the point of light move across the screen? When there is a sawtooth voltage on the horizontal deflection plate, at the moment of time t = 0, the voltage is VO (very negative), the point of light on the screen in the starting position to the left of the origin of the coordinates (zero), the displacement distance is proportional to the voltage Vo; at the moment of time t = 1, the voltage is V1 (negative), the point of light on the fluorescent screen in a point to the left of the origin of the coordinates, the distance of the displacement is proportional to the voltage v1; and so on, at t = 2, t = 3, ... . t = 8, the corresponding position of the light point on the screen is 2, 3, ... ,8. At the instant t=8, the sawtooth wave voltage jumps from a large positive value V8 to a large negative value Vo, and the point of light on the screen moves very rapidly from the 8 o'clock position to the left to the starting position zero. If the sawtooth wave voltage is periodic, the first cycle will be followed by the second cycle, the third cycle,... At this point, if the frequency of the sawtooth wave voltage applied to the horizontal deflector plate is very low, only 1 Hz to 2 Hz, on the screen, the point of light will move from the left starting position zero to the right eight o'clock position at a uniform speed, and then the point of light will move very quickly from the right eight o'clock position to the left starting position zero. This process is called scanning. Scanning is performed again and again when a periodic sawtooth wave voltage is applied to the horizontal axis. The instantaneous value of the dot starting position zero will be proportional to the instantaneous value of the voltage applied to the deflector plate. If the frequency of the sawtooth wave voltage applied to the deflector plate is above 10Hz~20Hz, a horizontal bright line will be seen due to the afterglow of the fluorescent screen and the transient of the human eye's vision. When the horizontal amplification gain of the oscilloscope is constant, the length of the horizontal bright line depends on the sawtooth voltage value. The sawtooth voltage value is proportional to the time change, and the displacement of the light point on the fluorescent screen is proportional to the voltage value, so the horizontal bright line on the fluorescent screen can represent the time axis. Any equal line segments on this bright line represent equal time periods. If the measured signal voltage is applied to the vertical deflector plate and the sawtooth wave scanning voltage is applied to the horizontal deflector plate, and the frequency of the measured signal voltage is equal to the frequency of the sawtooth wave scanning voltage, the periodic waveform curve of the measured signal voltage over time will be displayed on the screen. When the second and third cycles of the measured periodic signal... all repeat the first cycle, the trajectory depicted by the light point on the screen also overlaps with the trajectory depicted for the first time. Thus, the measured signal voltage displayed on the screen is a stable waveform curve over time. In order to stabilize the picture on the screen, the frequency of the measured signal voltage should maintain an integer ratio relationship, i.e. a synchronization relationship, with the frequency of the sawtooth waveform voltage. In order to realize this, it is required that the frequency of the sawtooth wave voltage can be continuously adjusted to adapt to the observation of periodic signals with different frequencies. Secondly, due to the relative instability of the measured signal frequency and the frequency of the sawtooth wave oscillating signal, even if the frequency of the sawtooth wave voltage is temporarily adjusted to an integer multiple of the frequency of the measured signal, the graph cannot always remain stable. Therefore, all oscilloscopes are equipped with a synchronization device. That is, a synchronization signal is added to some part of the sawtooth wave circuit to facilitate synchronization of the scan. For simple oscilloscopes (such as the domestic SB-10 oscilloscope, etc.) which can only produce a continuous scan (i.e., a continuous sawtooth wave), it is necessary to input a synchronization signal to its scanning circuit that is related to the frequency of the signal being observed. When the frequency of the added synchronization signal is close to the self-excited oscillation frequency of the sawtooth wave frequency (or close to an integer multiple thereof), the sawtooth wave can be altered. For oscilloscopes (such as the domestic ST-16 oscilloscope, SBT-5 synchronous oscilloscope, SR-8 dual trace oscilloscope, etc.). with a waiting scanning function (i.e., normally does not produce a sawtooth wave, only in the arrival of the measured signal to produce a sawtooth wave scanning once), it is necessary to input a trigger signal related to the measured signal into its scanning circuit, so that the scanning process is closely matched with the measured signal. In this way, any process to be studied can be synchronized with the sawtooth scanning frequency as long as the appropriate synchronization signal or trigger signal is selected as needed. Two-line oscillator method, in the process of electronic internship technology, often need to observe two (or more than two) signals at the same time with the process of time. And test and compare these different signals. In order to achieve this purpose, based on the principle of ordinary oscilloscopes, people use the following two methods to display multiple waveforms at the same time: one is a two-wire (or multi-wire) oscilloscope; the other is a two-trace (or multi-trace) oscilloscope method. Oscilloscopes manufactured with these two methods are called dual-line (or multi-line) oscilloscopes and dual-line (or multi-line) oscilloscopes, respectively. A dual-line (or multi-line) oscilloscope is realized with a dual-shot (or multi-shot) oscilloscope. The following is a brief description of the two-gun oscilloscope as an example. A two-gun oscilloscope has two independent electron guns to produce two electron beams. There are two independent deflection systems, each system controls a beam of electrons up and down, left and right. The fluorescent screen is *** used so that two different electrical signal waveforms can be displayed on the screen at the same time, and the dual-line oscilloscope can also be realized with a single-shot dual-line oscilloscope tube. This oscilloscope tube has only one electron gun and works by relying on a special electrode to split the electrons into two beams. Then, two independent deflection systems in the tube control the two electron beams to move up and down, left and right, respectively. A fluorescent screen is *** used to display two different electrical signal waveforms at the same time. Due to the high manufacturing requirements and high cost of dual trace oscilloscope tubes, their application is not very common. Dual-trace oscilloscope, dual-trace oscilloscope (or multi-trace oscilloscope) is a single-line oscilloscope based on the addition of a special electronic switch, with which to display two (or more) waveforms, respectively. As a result of dual-trace (or multi-trace) oscilloscope than dual-line (or multi-line) oscilloscope is easy to realize, and does not require the use of complex and expensive "dual-cavity" or "multi-cavity" oscilloscopes, so dual-trace (or multi-trace) oscilloscopes are widely used. In order to make the two signal waveforms displayed on the screen to maintain stability, the requirements of the measured signal frequency, scanning signal frequency and the switching frequency of the electronic switch must meet a certain relationship. First of all, the relationship between the two measured signal frequencies and the scanning signal frequency should be an integer ratio, that is, the requirement of "synchronization". This is the same principle as a single-line oscilloscope, except that there are two measurement signals and a scanning voltage. In practice, the two signals to be observed and compared are often intrinsically related, so the above synchronization requirements are generally easy to meet. In order to make the waveforms of the two measured signals displayed on the screen stable, in addition to meeting the above requirements, it is also necessary to reasonably select the switching frequency of the electronic switch, so that the number of waveforms displayed on the oscilloscope is appropriate and easy to observe. First of all, the working mode of the electronic switch is related to the switching frequency of the electronic switch. The electronic switch has two working modes: alternate switching and intermittent switching. The waveforms displayed in the alternate switching mode are very similar to those displayed by a two-wire oscilloscope without discontinuities. However, since the waveforms of the measured signals UA and UB alternate sequentially on the screen, if the alternating gap time exceeds the visual duration of the human eye and the afterglow time of the screen, the waveforms on the screen seen by people will flicker. In order to avoid this situation, the electronic switch is required to have a sufficiently high switching frequency. In other words, when the measured signal frequency is low, it is not appropriate to use the alternate switching mode, but should be used in the intermittent switching mode. When the electronic switch operates in the intermittent switching mode, the electronic switch samples each display signal to be measured several times with a sufficiently high switching frequency during each process of the X-axis scan. In this way, flickering of the waveform can be avoided even if the frequency of the measurement signal is low. The dual-trace oscilloscope is mainly composed of two Y-axis pre-amplification circuits, gating circuit, electronic switch, mixing circuit, time delay circuit, Y-axis post-amplification circuit, triggering circuit, scanning circuit, X-axis amplification circuit, Z-axis amplification circuit, calibration signal circuit, oscilloscope, and high- and low-voltage power supply circuits. When the display mode switch is placed in the alternate position, the electronic switch is a bistable circuit. It is controlled by the gate signal from the scanning circuit so that the two front channels of the Y-axis work alternately with the change of the gate signal from the scanning circuit. The number of alternating transitions per second is related to the repetition frequency of the scanning signal generated by the scanning circuit. The alternating operation state is suitable for observing measured signals with a low frequency. In order to observe the waveform of the measured signal over time, a linear scanning voltage (sawtooth wave voltage) must be added to the horizontal deflection plate of the oscilloscope. This scanning voltage is generated by the scanning circuit. When a trigger signal is applied to the trigger circuit, the scanning circuit is triggered and the scanning circuit generates a corresponding scanning signal; when no trigger signal is applied, the scanning circuit does not generate a scanning signal. There are two types of triggers, internal and external, which are selected by the trigger selector switch. When the switch is placed in the internal position, the trigger signal comes from the measurement signal sent through the Y-axis channel. When the switch is placed in the external position, the trigger signal is fed externally. This signal should be related to the frequency of the measured signal in an integer ratio. In the use of oscilloscopes, internal triggering is mostly used. The low voltage in the high-voltage and low-voltage power supply circuits supplies the low-voltage power required by the oscilloscopes at all levels, and the high voltage is supplied to the display system of the oscilloscopes. For more information, please contact Beijing Orient China Integrated Technology Co!