CN108243324B - Video monitoring system - Google Patents

Video monitoring system Download PDF

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Publication number
CN108243324B
CN108243324B CN201611205171.3A CN201611205171A CN108243324B CN 108243324 B CN108243324 B CN 108243324B CN 201611205171 A CN201611205171 A CN 201611205171A CN 108243324 B CN108243324 B CN 108243324B
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resistor
capacitor
pass filter
filter circuit
diode
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CN108243324A (en
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闫云鹏
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Hangzhou Hikvision Digital Technology Co Ltd
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Hangzhou Hikvision Digital Technology Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/18—Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast

Abstract

The embodiment of the invention provides a video monitoring system which comprises a front-end device and a back-end device. The front-end equipment comprises a first high-pass filter circuit and a first low-pass filter circuit, wherein the first high-pass filter circuit passes through a video signal with the frequency of HZ level and above and isolates a direct current signal; the video signal output port of the front-end equipment is connected with the coaxial cable through the first high-pass filter circuit, and the coaxial cable is connected with the power supply input port of the front-end equipment through the first low-pass filter circuit; the rear-end equipment comprises a second high-pass filter circuit and a second low-pass filter circuit, the second high-pass filter circuit is used for isolating direct-current signals through video signals, the second low-pass filter circuit is used for isolating the video signals through the direct-current signals, a power output port of the rear-end equipment is connected with the coaxial cable through the second low-pass filter circuit, and the coaxial cable is connected with a video signal input port of the rear-end equipment through the second high-pass filter circuit. The scheme can reduce the application cost of the coaxial power supply technology and enlarge the frequency range of the video signal suitable for the coaxial power supply technology.

Description

Video monitoring system
Technical Field
The invention relates to the technical field of video monitoring, in particular to a video monitoring system.
Background
With the rapid development of video monitoring technology, the application of the coaxial power supply technology in the video monitoring system is more and more extensive. In general, a video surveillance system includes: the front-end equipment is connected with the back-end equipment through a coaxial cable. The coaxial power supply technology is a technology for simultaneously transmitting a direct current power supply signal and a video signal between front-end equipment and back-end equipment through a coaxial cable. When the existing coaxial power supply technology is adopted, the specific process of transmitting the video signal through the coaxial cable is as follows: the front-end equipment modulates the video signal to a higher frequency by using a special modulation chip, then couples the modulated video signal to a coaxial cable, and transmits the modulated video signal to the rear-end equipment through the coaxial cable; the back-end equipment receives the modulated video signal through the coaxial cable, and then restores the video signal by using the special demodulation chip, so that the back-end equipment can obtain the initial video signal.
It should be noted that, the transmission of video signals through coaxial cables requires the use of dedicated modulation chips and demodulation chips, which are often expensive, and accordingly, the application cost of the existing coaxial power supply technology is also high. In addition, the existing coaxial power supply technology is only suitable for the transmission of video signals with the frequency of 0-6MHz between the front-end equipment and the back-end equipment due to the limitation of a special modulation chip and a special demodulation chip.
Therefore, it is an urgent problem for those skilled in the art to reduce the application cost of the coaxial power supply technology and to expand the frequency range of the video signal suitable for the coaxial power supply technology.
Disclosure of Invention
An object of the embodiments of the present invention is to provide a video monitoring system, so as to effectively implement coaxial power supply, reduce application cost of a coaxial power supply technology, and expand a frequency range of a video signal applicable to the coaxial power supply technology.
An embodiment of the present invention provides a video monitoring system, including: a front-end device and a back-end device; wherein the content of the first and second substances,
the front-end device includes: a first high-pass filter circuit and a first low-pass filter circuit;
the first high-pass filter circuit is used for passing video signals with frequencies of HZ level and above HZ level and isolating direct-current power signals, the first low-pass filter circuit is used for passing the direct-current power signals and isolating the video signals, a video signal output port of the front-end equipment is connected with a first end of a coaxial cable through the first high-pass filter circuit, and the first end of the coaxial cable is further connected with a direct-current power input port of the front-end equipment through the first low-pass filter circuit;
the backend apparatus includes: a second high-pass filter circuit and a second low-pass filter circuit;
the second high-pass filter circuit is used for passing through a video signal and isolating a direct-current power supply signal, the second low-pass filter circuit is used for passing through the direct-current power supply signal and isolating the video signal, a direct-current power supply output port of the rear-end equipment is connected with the second end of the coaxial cable through the second low-pass filter circuit, and the second end of the coaxial cable is further connected with a video signal input port of the rear-end equipment through the second high-pass filter circuit.
In the scheme, for the front-end equipment, the collected video signals flow out from the video signal output port of the front-end equipment and then enter the first high-pass filter circuit. At this time, the video signal can smoothly flow into the first end of the coaxial cable through the first high-pass filter circuit. The video signal is then transmitted to the second end of the coaxial cable, flows from the second end of the coaxial cable into the second high-pass filter circuit in the back-end device, and finally flows through the second high-pass filter circuit into the video signal input port of the back-end device, so that the back-end device successfully obtains the video signal from the front-end device. For the back-end device, the dc power signal will enter the second low-pass filter circuit after flowing out from the dc power output port thereof. At this time, the dc power signal can smoothly flow into the second end of the coaxial cable through the second low pass filter circuit. Then, the dc power signal is transmitted to the first end of the coaxial cable, flows into the first low-pass filter circuit in the front-end device from the first end of the coaxial cable, and finally flows into the dc power input port of the front-end device through the first low-pass filter circuit, so that the front-end device obtains the dc power signal from the back-end device, and the dc power signal can supply power for the operation of the front-end device. It is easy to see that through setting up first high-pass filter circuit and first low-pass filter circuit in the front-end equipment, and set up second high-pass filter circuit and second low-pass filter circuit in the back-end equipment, this scheme has realized the superposition transmission on the coaxial cable of DC power supply signal and video signal better, namely coaxial power supply. In the scheme, a special modulation chip and a special demodulation chip are not required to be utilized, so that the application cost of the coaxial power supply technology is greatly reduced, and the frequency range of the video signal applicable to the coaxial power supply technology can be free from the limitations of the modulation chip and the demodulation chip. In addition, the first high-pass filter circuit can pass the video signals with frequencies of HZ level and above HZ level, so that the frequency range of the video signals suitable for the coaxial power supply technology is effectively expanded.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a video monitoring system according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a first high-pass filter circuit in a video monitoring system according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a first low-pass filter circuit in the video monitoring system according to the embodiment of the present invention;
fig. 4 is a schematic structural diagram of a first low-pass filter circuit in the video monitoring system according to the embodiment of the present invention;
fig. 5 is a schematic structural diagram of a constant current output control circuit in the video monitoring system according to the embodiment of the present invention;
fig. 6 is a schematic structural diagram of a second low-pass filter circuit in the video monitoring system according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to solve the problems in the prior art, the embodiment of the invention provides a video monitoring system.
Referring to fig. 1, a schematic structural diagram of a video monitoring system according to an embodiment of the present invention is shown. As shown in fig. 1, the video surveillance system includes: a front-end device and a back-end device. Specifically, the backend device may be a hard disk video recorder, and the front-end device may be an analog high-definition video camera, and of course, the types of the backend device and the front-end device are not limited thereto, and may be determined specifically according to an actual situation, which is not limited in this embodiment.
Wherein, the front-end equipment can include: a first high-pass filter circuit 200 and a first low-pass filter circuit 300.
The first high-pass filter circuit 200 is configured to pass video signals with frequencies of HZ level and above HZ level and isolate a dc power signal, the first low-pass filter circuit 300 is configured to pass the dc power signal and isolate the video signal, a video signal output port of a front-end device is connected to a first end (a right end shown in fig. 1) of the coaxial cable 600 through the first high-pass filter circuit 200, and the first end of the coaxial cable 600 is further connected to a dc power input port of the front-end device through the first low-pass filter circuit 300.
It should be noted that, in order to ensure that the first high-pass filter circuit 200 can pass the video signal with the frequency of HZ level and above HZ level and isolate the dc power signal, and ensure that the first low-pass filter circuit 300 can pass the dc power signal and isolate the video signal, there are many possible structural forms for both the first high-pass filter circuit 200 and the first low-pass filter circuit 300, and for the sake of layout clarity, the following description is given by way of example.
The backend device may include: a second high-pass filter circuit 400 and a second low-pass filter circuit 500.
The second high-pass filter circuit 400 is configured to pass a video signal and isolate a dc power signal, the second low-pass filter circuit 500 is configured to pass the dc power signal and isolate the video signal, a dc power output port of the rear-end device is connected to the second end of the coaxial cable 600 through the second low-pass filter circuit 500, and the second end of the coaxial cable 600 is further connected to a video signal input port of the rear-end device through the second high-pass filter circuit 400.
It should be noted that the second low-pass filter circuit 500 has various structural forms, and the following examples are given for clarity of layout. In addition, any high-pass filter circuit capable of passing the video signal and isolating the dc power signal in the prior art may be used as the second high-pass filter circuit 400, and the specific structure of the second high-pass filter circuit 400 is not limited in this embodiment.
In this scheme, for the front-end device, the collected video signal flows out from its own video signal output port and then enters the first high-pass filter circuit 200. At this time, the video signal can smoothly flow into the first end of the coaxial cable 600 through the first high pass filter circuit 200. Then, the video signal is transmitted to the second end of the coaxial cable 600, flows from the second end of the coaxial cable 600 into the second high-pass filter circuit 400 in the back-end device, and finally flows into the video signal input port of the back-end device through the second high-pass filter circuit 400, so that the back-end device successfully obtains the video signal from the front-end device. For the back-end device, the dc power signal will enter the second low-pass filter circuit 500 after flowing out from the dc power output port thereof. At this time, the dc power signal can smoothly flow into the second end of the coaxial cable 600 through the second low pass filter circuit 400. Then, the dc power signal is transmitted to the first end of the coaxial cable 600, flows into the first low-pass filter circuit 300 in the front-end device from the first end of the coaxial cable 600, and finally flows into the dc power input port of the front-end device through the first low-pass filter circuit 300, so that the front-end device obtains the dc power signal from the back-end device, and the dc power signal can supply power for the operation of the front-end device.
It is easy to see that, by providing the first high-pass filter circuit 200 and the first low-pass filter circuit 300 in the front-end device and the second high-pass filter circuit 400 and the second low-pass filter circuit 500 in the back-end device, the scheme better realizes the superposition transmission of the dc power signal and the video signal on the coaxial cable 600, i.e. the coaxial power supply. In the scheme, a special modulation chip and a special demodulation chip are not required to be utilized, so that the application cost of the coaxial power supply technology is greatly reduced, and the frequency range of the video signal applicable to the coaxial power supply technology can be free from the limitations of the modulation chip and the demodulation chip. In addition, the first high-pass filter circuit 200 can pass the video signals with frequencies of HZ level and higher, so that the frequency range of the video signals suitable for the coaxial power supply technology is effectively expanded.
It should be noted that, in order to be able to pass the video signal with the frequency of HZ level and above HZ level and isolate the dc power signal, there are many possible configurations of the first high-pass filter circuit 200, which will be described below by way of example.
Referring to fig. 2, a schematic structural diagram of a first high-pass filter circuit 200 in a video surveillance system according to an embodiment of the present invention is shown. As shown in fig. 2, the first high-pass filter circuit 200 may include: a first resistor 11, an operational amplifier 12, a second resistor 13, a third resistor 14, a fourth resistor 15, a first capacitor 16, a fifth resistor 17, a second capacitor 18 and a sixth resistor 19.
The first end (the lower end shown in fig. 2) of the first resistor 11 is grounded, the second end (the upper end shown in fig. 2) of the first resistor 11 is connected to the positive input end of the operational amplifier 12, and the positive input end of the operational amplifier 12 is further connected to the video signal output port (at a shown in fig. 2, the video signal collected by the front-end device specifically flows out therefrom) of the front-end device. As can be seen from fig. 2, the video signal output port of the front-end device is also grounded.
The output terminals of the operational amplifier 12 are connected to a first terminal (upper terminal shown in fig. 2) of the second resistor 13 and a first terminal (left terminal shown in fig. 2) of the first capacitor 16, respectively, a second terminal (lower terminal shown in fig. 2) of the second resistor 13 is connected to a first terminal (upper terminal shown in fig. 2) of the third resistor 14 and a first terminal (left terminal shown in fig. 2) of the fifth resistor 17, respectively, a first terminal (left terminal shown in fig. 2) of the second capacitor 18 is connected to a second terminal (right terminal shown in fig. 2) of the fifth resistor 17, a first terminal (left terminal shown in fig. 2) of the sixth resistor 19 is connected to a second terminal (right terminal shown in fig. 2) of the first capacitor 16 and a second terminal (right terminal shown in fig. 2) of the second capacitor 18, respectively, and a second terminal (right terminal shown in fig. 2) of the sixth resistor 19 is connected to a first terminal of the coaxial cable 600 in fig. 1.
The negative input terminal of the operational amplifier 12 is connected to the second terminal (lower terminal shown in fig. 2) of the third resistor 14 and the first terminal (upper terminal shown in fig. 2) of the fourth resistor 15, respectively, and the second terminal (lower terminal shown in fig. 2) of the fourth resistor 15 is grounded.
Wherein, the resistance values of the first resistor 11 and the sixth resistor 19 are matched with the coaxial cable 600. Specifically, the resistance values of the first resistor 11 and the sixth resistor 19 may be 75 Ω, and certainly, the resistance values of the first resistor 11 and the sixth resistor 19 are not limited to 75 Ω, and may be determined according to actual situations, which is not limited in this embodiment.
The resistance values of the second resistor 13 and the fourth resistor 15 can be both 1 Ω -10k Ω. It should be noted that the resistance of the second resistor 13 and the resistance of the fourth resistor 15 may be the same or different, which is also feasible. Specifically, the resistance of the second resistor 13 may be 1 Ω, 1k Ω, 2.3k Ω or 10k Ω, and the resistance of the fourth resistor 15 may be 1 Ω, 1k Ω, 1.2k Ω or 10k Ω, although the resistances of the second resistor 13 and the fourth resistor 15 are not limited to the above listed cases, and are not described herein again.
The third resistor 14 and the fifth resistor 17 have a resistance of 470 Ω -4.7k Ω, respectively. It should be noted that the third resistor 14 and the fifth resistor 17 may have the same resistance value or different resistance values, which is also possible. Specifically, the resistance of the third resistor 14 may be 470 Ω, 580 Ω, 2.3k Ω, or 4.7k Ω, and the resistance of the fifth resistor 17 may be 470 Ω, 820 Ω, 2.3k Ω, or 4.7k Ω, although the resistances of the third resistor 14 and the fifth resistor 17 are not limited to the above listed cases, and are not described herein again.
The ratio of the capacitances of the first capacitor 16 and the second capacitor 18 is greater than 2. Specifically, the capacitance of the first capacitor 16 may be 47uF, and the capacitance of the second capacitor 18 may be 22uF, although the capacitances of the first capacitor 16 and the second capacitor 18 are not limited thereto, and may be determined specifically according to the actual situation, and are not described herein again. In addition, when the first capacitor 16 and the second capacitor 18 are selected, the ratio of the second capacitor 18 of the first capacitor 16 can be ensured to be close to 2 as much as possible, so that the capacitances of the first capacitor 16 and the second capacitor 18 can be both small, the volumes of the first capacitor 16 and the second capacitor 18 are both small, and accordingly, the space occupied by the first high-pass filter circuit 200 is also small.
In this embodiment, by reasonably designing the circuit structure of the first high-pass filter circuit 200, the operational amplifier 12 can selectively amplify the ac signal flowing through itself. Specifically, the operational amplifier 12 amplifies only the video signal having a frequency of the order of HZ, for example, 1HZ to 100HZ flowing therethrough, and thus the video signal having a frequency of 1HZ to 100HZ is also amplified into a high-frequency ac signal. Thus, after the video signal flows into the first high-pass filter circuit 200, the video signal with most frequencies can pass through smoothly and is transmitted to the back-end device through the coaxial cable 600, so that the frequency range of the video signal suitable for the coaxial power supply technology can be effectively expanded.
It should be noted that there are many possible configurations of the first low-pass filter circuit 300 in order to enable the dc signal and isolate the video signal, and a specific configuration of the first low-pass filter circuit 300 is described below with reference to fig. 3.
As shown in fig. 3, the first low pass filter circuit 300 may include: seventh resistor 21, eighth resistor 22, third capacitor 23, first transistor 24, ninth resistor 25, second transistor 26, and tenth resistor 27.
Wherein a first end of the coaxial cable 600 in fig. 1 is connected to a first end (left end shown in fig. 3) of the seventh resistor 21, a collector of the first transistor 24, and a collector of the second transistor 26, a dc power input port of the front-end device is connected to a first end (right end shown in fig. 3) of the eighth resistor 22, a first end (right end shown in fig. 3) of the third capacitor 23, and a first end (right end shown in fig. 3) of the tenth resistor 27, respectively, a second end (left end shown in fig. 3) of the third capacitor 23 is connected to a second end (right end shown in fig. 3) of the seventh resistor 21, a second end (left end shown in fig. 3) of the eighth resistor 22, and a base of the first transistor 24, an emitter of the first transistor 24 is connected to a first end (upper end shown in fig. 3) of the ninth resistor 25, and a second end (lower end shown in fig. 3) of the ninth resistor 25 is connected to a base of the second transistor 26, the emitter of the second transistor 26 is connected to a second terminal (right terminal shown in fig. 3) of the tenth resistor 27.
Wherein, the resistance values of the seventh resistor 21 and the eighth resistor 22 are both 1 Ω -50k Ω. It should be noted that, it is possible that the resistance values of the seventh resistor 21 and the eighth resistor 22 may be the same or different. Specifically, the resistance of the seventh resistor 21 may be 1 Ω, 1k Ω, 5.1k Ω or 50k Ω, and the resistance of the eighth resistor 22 may be 1 Ω, 1k Ω, 10k Ω or 50k Ω, although the resistances of the seventh resistor 21 and the eighth resistor 22 are not limited to the above listed cases, and are not described herein again.
The ninth resistor 25 has a resistance of 1 Ω -1K Ω. Specifically, the resistance of the ninth resistor 25 may be 1 Ω, 2.2 Ω, 0.5K Ω or 1K Ω, and certainly, the resistance of the ninth resistor 25 is not limited thereto, and may be determined according to actual situations, which is not limited in this embodiment.
The tenth resistor 27 has a resistance value of 1 Ω -10 Ω. Specifically, the resistance of the tenth resistor 27 may be 1 Ω, 2.2 Ω, 5 Ω or 10 Ω, and certainly, the resistance of the tenth resistor 27 is not limited to the above listed cases, and is not described herein again.
The capacitance of the third capacitor 23 is 47uF to 1000 uF. Specifically, the capacitance of the third capacitor 23 may be 47uF, 470uF, 500uF, or 1000uF, and certainly, the capacitance of the third capacitor 23 is not limited thereto, and may be determined according to an actual situation, which is not limited in this embodiment.
The maximum withstand voltage of the collectors of the first triode 24 and the second triode 26 is larger than 60V, the maximum allowable current of the collectors is larger than 1A, and the maximum dissipation power is larger than 50 mW.
It should be noted that, as shown in fig. 3, each of the first transistor 24 and the second transistor 26 may have three pins, but it is also possible that, as shown in fig. 4, each of the first transistor 24 and the second transistor 26 may have four pins.
In addition, as can be seen in fig. 3, first transistor 24 and second transistor 26 form a darlington transistor that can operate in an amplified state. Because of the base capacitance of the first transistor 24, the Vbe voltage of the lindaton transistor does not abruptly change, and ultimately, the current flowing through the second transistor 26 does not abruptly change. Therefore, when the first low-pass filter circuit 300 adopts the above structure and the parameters related to the components in the first low-pass filter circuit 300 satisfy the above conditions, the first low-pass filter circuit 300 can be equivalent to an inductor with very large inductance, and the inductance of the inductor can reach 1H or more. At this time, the first low-pass filter circuit 300 has a strong blocking effect on the video signal, and the video signal cannot flow into the first low-pass filter circuit 300 at all, so that the interference of the dc power signal on the video signal can be better avoided, and meanwhile, the dc power signal flowing out from the coaxial cable 600 can smoothly pass through the first low-pass filter circuit 300 and flow into the dc power input port of the front-end device to supply power to the front-end device.
With continued reference to fig. 3, the first low pass filter circuit 300 may further include: an eleventh resistor 28. Wherein a first terminal (an upper terminal shown in fig. 3) of the eleventh resistor 28 is connected to a second terminal (a left terminal shown in fig. 3) of the third capacitor 23, and a second terminal (a lower terminal shown in fig. 3) of the eleventh resistor 28 is connected to the base of the first transistor 24.
Wherein, the resistance value of the eleventh resistor 28 is 1 Ω -100 Ω. Specifically, the resistance of the eleventh resistor 28 may be 1 Ω, 2.2 Ω, 50 Ω or 100 Ω, and certainly, the resistance of the eleventh resistor 28 is not limited thereto, and may be determined according to actual situations, which is not limited in this embodiment.
As can be seen from a plurality of experiments, when the eleventh resistor 28 is disposed in the first low-pass filter circuit 300, the display effect of the video image corresponding to the video signal transmitted to the backend device through the coaxial cable 600 will be better, so that the monitoring effect of the entire video monitoring system can be effectively improved.
It is easily understood that junction capacitance is often present in the lindaton transistor formed by the first transistor 24 and the second transistor 26, and therefore, the impedance of the first low-pass filter circuit 300 to low-frequency components in the video signal is low, and the low-frequency components in the video signal are likely to flow into the first low-pass filter circuit 300.
In order to avoid the above situation, as shown in fig. 3, the first low-pass filter circuit 300 may further include: a first inductor 29. Wherein a first end (left end shown in fig. 3) of the first inductor 29 is connected to a first end (right end shown in fig. 3) of the eighth resistor 22, a first end (right end shown in fig. 3) of the third capacitor 23, and a first end (right end shown in fig. 3) of the tenth resistor 27, respectively, and a second end (right end shown in fig. 3) of the first inductor 29 is connected to the dc power input port of the front-end device.
The inductance of the first inductor 29 is 470uH-3.3 mH. Specifically, the inductance of the first inductor 29 may be 470uH, 1mH, 2mH, or 3.3mH, but of course, the inductance of the first inductor 29 is not limited thereto, and may be determined according to the actual situation, and this embodiment does not limit this.
In the present embodiment, the first inductor 29 is provided in the first low-pass filter circuit 300, so that the first low-pass filter circuit 300 can present a high impedance even for a low-frequency component in the video signal, and accordingly, a low-frequency cost in the video signal cannot flow into the first low-pass filter circuit 300. It can be seen that the present embodiment can better ensure the isolation of the dc power signal and the video signal.
Optionally, the first low-pass filter circuit 300 may further include: a twelfth resistor 30 and a first diode 31. Wherein a first end (left end shown in fig. 3) of the first inductor 29 is connected to a first end (left end shown in fig. 3) of the twelfth resistor 30 and a negative end (left end shown in fig. 3) of the first diode 31, respectively, and a second end (right end shown in fig. 3) of the first inductor 29 is connected to a second end (right end shown in fig. 3) of the twelfth resistor 30 and a positive end (right end shown in fig. 3) of the first diode 31, respectively.
The resistance of the twelfth resistor 30 may be 330 Ω -3.3k Ω. Specifically, the resistance of the twelfth resistor 30 may be 330 Ω, 470 Ω, 1K Ω or 3.3K Ω, and certainly, the resistance of the twelfth resistor 30 is not limited to the above listed cases, and is not described herein.
In this embodiment, due to the arrangement of the first diode 31, when the voltage across the first inductor 29 fluctuates, the energy generated by the voltage fluctuation on the first inductor 29 can be discharged through the first diode 31, thereby ensuring the normal operation of the first low-pass filter circuit 300.
Optionally, the first low-pass filter circuit 300 may further include: and a second diode 32, a positive terminal (left terminal shown in fig. 3) of the second diode 32 being connected to a second terminal (right terminal shown in fig. 3) of the twelfth resistor 30, a second terminal (right terminal shown in fig. 3) of the first inductor 29, and a positive terminal (left terminal shown in fig. 3) of the first diode 31, respectively, and a second terminal (right terminal shown in fig. 3) of the second diode 32 being connected to the dc power input port of the front-end device, wherein the second diode 32 may be a zener diode.
It can be understood that, for the dc power signal, it only flows in from the positive terminal of the second diode 32 and flows out from the negative terminal of the second diode 32, it is impossible to flow in from the negative terminal of the second diode 32 and flow out from the positive terminal of the second diode 32, therefore, when the whole front-end device is in a power-down state, the present embodiment can preferably avoid the reverse flow of the dc power signal in the first low-pass filter circuit 300.
Optionally, the first low-pass filter circuit 300 may further include: a third diode 33, wherein a positive terminal (a left terminal shown in fig. 3) of the third diode 33 is connected to the first terminal of the coaxial cable 600 in fig. 1, and a negative terminal (a right terminal shown in fig. 3) of the third diode 33 is connected to the first terminal (a left terminal shown in fig. 3) of the seventh resistor 21, the collector of the first transistor 24, and the collector of the second transistor 26, respectively, wherein the third diode 33 may be a zener diode.
It can be understood that, for the dc power signal, it can only flow in from the positive terminal of the third diode 33 and flow out from the negative terminal of the third diode 33, it is impossible to flow in from the negative terminal of the third diode 33 and flow out from the positive terminal of the third diode 33, therefore, when the whole front-end device is in a power-down state, the present embodiment can preferably avoid the reverse flow of the dc power signal in the first low-pass filter circuit 300.
Optionally, the first low-pass filter circuit 300 may further include: first magnetic beads 34. A first end (a left end shown in fig. 3) of the first magnetic bead 34 is connected to a first end of the coaxial cable 600 in fig. 1, and a second end (a right end shown in fig. 3) of the first magnetic bead 34 is respectively connected to a first end (a left end shown in fig. 3) of the seventh resistor 21, a collector of the first transistor 24, and a collector of the second transistor 26.
In the present embodiment, the first magnetic bead 34 is disposed in the first low-pass filter circuit 300, so that the first low-pass filter circuit 300 can present a high impedance even for the low-frequency component in the video signal, and accordingly, the low-frequency component in the video signal cannot flow into the first low-pass filter circuit 300. It can be seen that the present embodiment can better ensure the isolation of the dc power signal and the video signal.
Optionally, the first low-pass filter circuit 300 may further include: a fourth capacitor 35. Wherein a first terminal (an upper terminal shown in fig. 3) of the fourth capacitor 35 is connected to a first terminal (a right terminal shown in fig. 3) of the eighth resistor 22, a first terminal (a right terminal shown in fig. 3) of the third capacitor 23, and a first terminal (a right terminal shown in fig. 3) of the tenth resistor 27, respectively, and a second terminal (a lower terminal shown in fig. 3) of the fourth capacitor 35 is grounded.
The capacitance of the fourth capacitor 35 is 100uF-1000 uF. Specifically, the capacitance of the fourth capacitor 35 may be 100uF, 300uF, 500uF, or 1000uF, and certainly, the capacitance of the fourth capacitor 35 is not limited thereto, and may be determined according to an actual situation, which is not limited in this embodiment.
It is easy to understand that, in an ideal state, the signal frequency of the dc power signal is 0HZ, but in an actual operation process, the dc power signal often contains a certain amount of ac components, and at this time, the signal frequency of the dc power signal is not 0HZ, and at this time, the operating frequency of the front-end device fluctuates to some extent due to the presence of the ac components. In this embodiment, when the operating frequency of the front-end device fluctuates significantly, the fourth capacitor 35 may store a part of the electrical energy in time, so that the fluctuation amplitude of the operating frequency of the front-end device is significantly reduced.
It can be seen that, in this embodiment, the front-end device can operate at a relatively stable operating frequency.
Optionally, the front-end device may further include: and a voltage conversion chip. The first end of the voltage conversion chip is connected to the first end of the eighth resistor 22, the first end of the third capacitor 23, and the first end of the tenth resistor 27, respectively, the second end of the voltage conversion chip is connected to the dc power input port of the front-end device, and the voltage conversion chip is configured to convert the input voltage into a voltage with a set value and output the voltage.
The model of the voltage conversion chip may be TPS54260, and the operating frequency thereof may be 1-2.5MHZ, and certainly, the model and the operating frequency of the voltage conversion chip are not limited to the above case, and may be determined according to actual situations, which is not limited in this embodiment.
It should be noted that the operating voltage of the front-end device may be 12V, and if the energy loss of the dc power signal in the transmission process is not considered, the back-end device only needs to provide the dc power signal with the voltage of 12V for the front-end device through the coaxial cable 600, however, the dc power signal often has a large amount of energy loss in the transmission process, and therefore, the back-end device needs to provide the dc power supply with the voltage of more than 12V for the front-end device through the coaxial cable 600. Specifically, the voltage of the dc power signal provided by the back-end device to the front-end device via the coaxial cable 600 may be 48V.
In this embodiment, after the dc power signal flows out of the first low-pass filter circuit 300, the voltage of the dc power signal is between 12V and 48V, at this time, the voltage conversion chip converts the voltage of the dc power signal into a voltage with a set value, for example, 12V, and then the dc power signal with the voltage of 12V flows into the dc power input port of the front-end device to supply power to the front-end device, thereby ensuring the normal operation of the front-end device.
As shown in fig. 5, in this embodiment, the front-end device may further include: a constant current output control circuit and a switching circuit 100. The constant current output control circuit may include: a fourth diode 41, a thirteenth resistor 42, a fifth diode 43, a fourteenth resistor 44, a sixth diode 45, a fifteenth resistor 46, a fifth capacitor 47, a second inductor 48, a sixth capacitor 49, a sixteenth resistor 50, a seventh capacitor 51, and a buck regulator chip 52. Wherein the content of the first and second substances,
a first pin (pin 1 in fig. 5) of the buck regulator chip 52 is connected to a first end (right end shown in fig. 5) of the second inductor 48 and a positive end (right end shown in fig. 5) of the fourth diode 41, respectively, a second pin (pin 2 in fig. 5) and a third pin (pin 3 in fig. 5) of the buck regulator chip 52 are both grounded, a fourth pin (pin 4 in fig. 5) of the buck regulator chip 52 is connected to a first end (right end shown in fig. 5) of the sixteenth resistor 50 and a first end (upper end shown in fig. 5) of the seventh capacitor 51, respectively, the switching circuit 100 is connected to a second end (left end shown in fig. 5) of the sixteenth resistor 50 to control the on/off of the buck regulator chip 52, a second end (lower end shown in fig. 5) of the seventh capacitor 51 is grounded, and a fifth pin (pin 5) of the buck regulator chip 52 is connected to a first end (upper end shown in fig. 5) of the sixth capacitor 49 and a fifth end (upper end shown in fig. 5) of the sixth capacitor 49, respectively The second terminal of the voltage converting chip is connected, the second terminal (the lower terminal shown in fig. 5) of the sixth capacitor 49 is grounded, and the sixth pin (pin 6 in fig. 5) of the buck regulator chip 52 is connected to the first terminal (the lower terminal shown in fig. 5) of the thirteenth resistor 42, the first terminal (the left terminal shown in fig. 5) of the fifth capacitor 47, the negative terminal (the left terminal shown in fig. 5) of the sixth diode 45, the negative terminal (the left terminal shown in fig. 5) of the fifth diode 43, and the dc power input port of the front-end device, respectively.
A positive terminal (right terminal shown in fig. 5) of the fifth diode 43 is connected to a first terminal (left terminal shown in fig. 5) of the fourteenth resistor 44, a positive terminal (right terminal shown in fig. 5) of the sixth diode 45 is connected to a first terminal (left terminal shown in fig. 5) of the fifteenth resistor 46, a second terminal (right terminal shown in fig. 5) of the second inductor 48 is connected to a second terminal (right terminal shown in fig. 5) of the fourteenth resistor 44, a second terminal (right terminal shown in fig. 5) of the fifteenth resistor 46 and a second terminal (right terminal shown in fig. 5) of the fifth capacitor 47, a second terminal (upper terminal shown in fig. 5) of the thirteenth resistor 42 is connected to a negative terminal (left terminal shown in fig. 5) of the fourth diode 41, a second terminal of the voltage conversion chip, and a first terminal (upper terminal shown in fig. 5) of the sixth capacitor 49, respectively.
Wherein, the fourth diode 41, the fifth diode 43 and the sixth diode 45 may be zener diodes.
The capacitance of the fifth capacitor 47 and the sixth capacitor 49 is 1uF to 100 uF. It should be noted that the resistance values of the fifth capacitor 47 and the sixth capacitor 49 may be the same or different, which is also feasible. Specifically, the capacitance of the fifth capacitor 47 may be 1uF, 10uF, 50uF, or 100uF, and the capacitance of the sixth capacitor 49 may be 1uF, 10uF, 50uF, or 100uF, although the capacitances of the fifth capacitor 47 and the sixth capacitor 49 are not limited to the above listed cases, and are not described again.
The fourteenth resistor 44 and the fifteenth resistor 46 have a resistance of 1 Ω -2 Ω. It should be noted that, it is possible that the resistance values of the fourteenth resistor 44 and the fifteenth resistor 46 may be the same or different. Specifically, the resistance of the fourteenth resistor 44 may be 1 Ω, 1.2 Ω, 1.5 Ω, or 2 Ω, and the resistance of the fifteenth resistor 46 may be 1 Ω, 1.2 Ω, 1.5 Ω, or 2 Ω, although the resistances of the fourteenth resistor 44 and the fifteenth resistor 46 are not limited to the above-mentioned cases, and are not described herein again.
The inductance of the second inductor 48 is 2.2uH-47 uH. Specifically, the inductance of the second inductor 48 may be 2.2uH, 10uH, 30uH, or 2.2uH, and certainly, the inductance of the second inductor 48 is not limited to the above-mentioned cases, and is not described herein again.
The capacitance of the seventh capacitor 51 is 100nH-10 uH. Specifically, the capacitance of the seventh capacitor 51 may be 100nH, 1uH, 51uH, or 10uH, and certainly, the capacitance of the seventh capacitor 51 is not limited thereto, and may be determined according to actual situations, which is not limited in this embodiment.
It should be noted that the thirteenth resistor 42 is formed by connecting at least two resistors with a resistance value of 0.1 Ω -10 Ω in parallel. Specifically, as shown in fig. 5, the thirteenth resistor 42 may be formed by connecting 3 resistors with a resistance value of 0.1 Ω -10 Ω in parallel, and of course, the number of the resistors forming the thirteenth resistor 42 in a parallel connection manner is not limited to 3, and may be determined according to actual situations, which is not limited in this embodiment.
It should be noted that the type of the buck regulator chip 52 may be AN _ SY8707, and certainly, the type of the buck regulator chip 52 is not limited thereto, and may be determined according to actual situations, which is not limited in this embodiment.
It will be appreciated that the switching circuit 100 may be selected from any of a variety of existing circuit configurations for controlling the start and stop of an electrical component.
It should be noted that the constant current output control circuit may further include an eighth capacitor 53, a first end (an upper end shown in fig. 5) of the eighth capacitor 53 is connected to the fifth pin of the constant current output control circuit, and a second end (a lower end shown in fig. 5) of the eighth capacitor 53 is grounded.
In this embodiment, through the reasonable design of the structure of the constant current output control circuit and the reasonable selection of the relevant parameters of each component in the constant current output control circuit, the dc power signal flowing from the constant current output control circuit into the dc power input port of the front-end device will be relatively stable, so the operating frequency of the front-end device will not fluctuate significantly, and thus the influence of fluctuation of the operating frequency of the front-end device on the transmission of the video signal can be better avoided, and meanwhile, the electric energy required to be stored by the fourth capacitor 35 will be less, so the fourth capacitor 35 can select a capacitor with a smaller capacitance, such as a ceramic capacitor, and the volume of the fourth capacitor 35 will be greatly reduced.
It should be noted that there are many possible configurations of the second low-pass filter circuit 500 to pass the dc power signal and isolate the video signal, which will be described as an example.
Referring to fig. 6, a schematic structural diagram of a second low-pass filter circuit 500 in the video surveillance system according to the embodiment of the present invention is shown. As shown in fig. 6, the second low pass filter circuit 500 may include: a seventeenth resistor 61, an eighteenth resistor 62, a ninth capacitor 63, a third transistor 64, a nineteenth resistor 65, a fourth transistor 66 and a twentieth resistor 67.
Wherein the dc power output port of the back-end device is respectively connected to a first end (left end shown in fig. 6) of the seventeenth resistor 61, a collector of the third transistor 64, and a collector of the fourth transistor 66, a second end of the coaxial cable 600 in fig. 1 is respectively connected to a first end (right end shown in fig. 6) of the eighteenth resistor 62, a first end (right end shown in fig. 6) of the ninth capacitor 63, and a first end (right end shown in fig. 6) of the twentieth resistor 67, a second end (left end shown in fig. 6) of the ninth capacitor 63 is respectively connected to a second end (right end shown in fig. 6) of the seventeenth resistor 61, a second end (left end shown in fig. 6) of the eighteenth resistor 62, and a base of the third transistor 54, an emitter of the third transistor 64 is connected to a first end (upper end shown in fig. 6) of the nineteenth resistor 65, a second terminal (lower terminal shown in fig. 6) of the nineteenth resistor 65 is connected to a base of a fourth transistor 66, and an emitter of the fourth transistor 66 is connected to a second terminal (left terminal shown in fig. 6) of a twentieth resistor 67.
Wherein, the resistance values of the seventeenth resistor 61 and the eighteenth resistor 62 are both 1 Ω -50k Ω. It should be noted that, it is possible that the resistance values of the seventeenth resistor 61 and the eighteenth resistor 62 may be the same or different. Specifically, the resistance of the seventeenth resistor 61 may be 1 Ω, 1k Ω, 5.1k Ω or 50k Ω, and the resistance of the eighteenth resistor 62 may be 1 Ω, 1k Ω, 10k Ω or 50k Ω, although the resistances of the seventeenth resistor 61 and the eighteenth resistor 62 are not limited to the above listed cases, and are not described herein again.
The nineteenth resistor 65 has a resistance of 1 Ω -1K. Specifically, the resistance of the nineteenth resistor 65 may be 1 Ω, 2.2 Ω, 0.5K Ω or 1K Ω, and certainly, the resistance of the nineteenth resistor 65 is not limited thereto, and may be determined according to actual situations, which is not limited in this embodiment.
The twentieth resistor 67 has a resistance of 1 Ω -10 Ω. Specifically, the resistance of the twentieth resistor 67 may be 1 Ω, 2.2 Ω, 5 Ω or 10 Ω, and certainly, the resistance of the twentieth resistor 67 is not limited to the above listed cases, and is not described herein again.
The capacitance of the ninth capacitor 63 is 47uF to 1000 uF. Specifically, the capacitance of the ninth capacitor 63 may be 47uF, 470uF, 500uF, or 1000uF, and certainly, the capacitance of the ninth capacitor 63 is not limited thereto, and may be determined according to an actual situation, which is not limited in this embodiment.
The maximum voltage withstanding value of the collector of the third triode 64 and the maximum allowable current of the collector of the fourth triode 66 are larger than 60V, larger than 1A and larger than 50 mW.
It should be noted that the number of pins of third transistor 64 and fourth transistor 66 may be three or four, which is also possible.
It will be readily seen that third transistor 64 and fourth transistor 66 form a darlington transistor that is operable in an amplified state. Because of the base capacitance of the third transistor 64, the Vbe voltage of the lindaton transistor does not abruptly change, and ultimately, the current flowing through the fourth transistor 66 does not abruptly change. Therefore, when the second low-pass filter circuit 500 adopts the above structure and the parameters related to the components in the second low-pass filter circuit 500 satisfy the above conditions, the second low-pass filter circuit 500 can be equivalent to an inductor with very large inductance, and the inductance of the inductor can reach 1H or more. At this moment, the second low-pass filter circuit 500 has a strong blocking effect on the video signal, and after the video signal flows into the back-end device through the coaxial cable 600, the video signal cannot flow into the second low-pass filter circuit 500, so that the interference of the dc power signal to the video signal can be better avoided, and meanwhile, the dc power signal can smoothly pass through the second low-pass filter circuit 500, and then flows into the dc power input port of the front-end device through the coaxial cable 600 to supply power to the front-end device.
Optionally, as shown in fig. 6, the second low-pass filter circuit 500 may further include: a twenty-first resistor 68. A first terminal (an upper terminal shown in fig. 6) of the twenty-first resistor 68 is connected to a second terminal (a left terminal shown in fig. 6) of the ninth capacitor 63, and a second terminal (a lower terminal shown in fig. 6) of the twenty-first resistor 68 is connected to a base of the third transistor 64.
Wherein the twenty-first resistor 68 has a resistance of 1 Ω -100 Ω. Specifically, the resistance of the twenty-first resistor 68 may be 1 Ω, 2.2 Ω, 50 Ω or 100 Ω, and certainly, the resistance of the twenty-first resistor 68 is not limited thereto, and may be determined according to an actual situation, which is not limited in this embodiment.
Through a plurality of experiments, when the twenty-first resistor 58 is disposed in the second low-pass filter circuit 500, the display effect of the video image corresponding to the video signal obtained by the back-end device will be better, and thus the monitoring effect of the entire video monitoring system will be effectively improved.
It is easily understood that junction capacitance is often present in the lindaton transistor formed by the third transistor 64 and the fourth transistor 66, and therefore, the impedance of the second low-pass filter circuit 500 to low-frequency components in the video signal is low, and the low-frequency components in the video signal are likely to flow into the second low-pass filter circuit 500.
In order to avoid the above situation, as shown in fig. 6, the second low-pass filter circuit 500 may further include: a third inductor 69; wherein a first end (left end shown in fig. 6) of the third inductor 69 is connected to a first end (right end shown in fig. 6) of the eighteenth resistor 62, a first end (right end shown in fig. 6) of the ninth capacitor 63, and a first end (right end shown in fig. 5) of the twentieth resistor 67, respectively, and a second end (left end shown in fig. 5) of the third inductor 69 is connected to a second end of the coaxial cable 600 in fig. 1.
Wherein the inductance of the third inductor 69 is 470uH-3.3 mH. Specifically, the inductance of the third inductor 69 may be 470uH, 1mH, 2mH, or 3.3mH, and certainly, the inductance of the third inductor 69 is not limited thereto, and may be determined according to the actual situation, which is not limited in this embodiment.
In the present embodiment, the third inductor 69 is provided in the second low-pass filter circuit 500, so that the second low-pass filter circuit 500 can present a high impedance even for the low-frequency component in the video signal, and accordingly, the low-frequency cost in the video signal cannot flow into the second low-pass filter circuit 500. It can be seen that the present embodiment can better ensure the isolation of the dc power signal and the video signal.
Optionally, the second low-pass filter circuit 500 may further include: a twenty-second resistor 70 and a seventh diode 71. Wherein the content of the first and second substances,
a first end (left end shown in fig. 6) of the third inductor 69 is connected to a first end (left end shown in fig. 6) of the twenty-second resistor 70 and a negative end (left end shown in fig. 6) of the seventh diode 71, respectively, and a second end (right end shown in fig. 6) of the third inductor 69 is connected to a second end (right end shown in fig. 6) of the twenty-second resistor 70 and a positive end (right end shown in fig. 6) of the seventh diode 71, respectively.
Wherein the resistance of the twenty-second resistor 70 is 330 Ω -3.3k Ω. Specifically, the resistance of the twenty-second resistor 70 may be 330 Ω, 470 Ω, 1K Ω or 3.3K Ω, and certainly, the resistance of the twenty-second resistor 70 is not limited to the above listed cases, and is not described herein again.
In this embodiment, due to the arrangement of the seventh diode 71, when the voltage across the third inductor 69 fluctuates, the energy generated by the voltage fluctuation on the third inductor 69 can be discharged through the seventh diode 71, so as to ensure the normal operation of the second low-pass filter circuit 500.
Optionally, the second low-pass filter circuit 500 may further include: an eighth diode 72, a positive terminal (left terminal shown in fig. 6) of the eighth diode 72 being connected to the second terminal (right terminal shown in fig. 6) of the twenty-second resistor 70, the second terminal (right terminal shown in fig. 6) of the third inductor 69, and a positive terminal (right terminal shown in fig. 6) of the seventh diode 71, respectively, and a negative terminal (right terminal shown in fig. 6) of the eighth diode 72 being connected to the second terminal of the coaxial cable 600 in fig. 1, wherein the eighth diode 72 is a zener diode.
It can be understood that, for the dc power signal, it only flows in from the positive terminal of the eighth diode 72 and flows out from the negative terminal of the eighth diode 72, it is impossible to flow in from the negative terminal of the eighth diode 72 and flows out from the positive terminal of the eighth diode 72, so that the reverse flow of the dc power signal in the second low-pass filter circuit 500 can be better avoided when the whole backend device is in a power-down state.
Optionally, the second low-pass filter circuit 500 may further include: a ninth diode 73, wherein a positive terminal (left terminal shown in fig. 6) of the ninth diode 73 is connected to the dc power output port of the backend device, and a negative terminal (right terminal shown in fig. 6) of the ninth diode 73 is connected to a first terminal (left terminal shown in fig. 6) of the seventeenth resistor 61, a collector of the third transistor 64, and a collector of the fourth transistor 66, respectively, wherein the ninth diode 73 is a zener diode.
It can be understood that, for the dc power signal, it only flows in from the positive terminal of the ninth diode 73 and flows out from the negative terminal of the ninth diode 73, it is impossible to flow in from the negative terminal of the ninth diode 73 and flow out from the positive terminal of the ninth diode 73, therefore, when the whole backend device is in a power-down state, the embodiment can preferably avoid the reverse flow of the dc power signal in the second low-pass filter circuit 500.
Optionally, the second low-pass filter circuit 500 may further include: second magnetic beads 74; a first end (a left end shown in fig. 6) of the second magnetic bead 74 is connected to the dc power output port of the back-end device, and a second end (a right end shown in fig. 6) of the second magnetic bead 74 is respectively connected to a first end (a left end shown in fig. 6) of the seventeenth resistor 61, a collector of the third transistor 64, and a collector of the fourth transistor 66.
In the present embodiment, the second magnetic bead 74 is disposed in the second low-pass filter circuit 500, so that the second low-pass filter circuit 500 can present a higher impedance even for the low-frequency component in the video signal, and accordingly, the low-frequency component in the video signal cannot flow into the second low-pass filter circuit 500. It can be seen that the present embodiment can better ensure the isolation of the dc power signal and the video signal.
Optionally, the second low-pass filter circuit 500 may further include: a tenth capacitor 75; wherein a first end (upper end shown in fig. 6) of the tenth capacitor 75 is connected to a first end (right end shown in fig. 6) of the eighteenth resistor 62, a first end (right end shown in fig. 6) of the ninth capacitor 63, and a first end (right end shown in fig. 6) of the twentieth resistor 67, respectively, and a second end (lower end shown in fig. 6) of the tenth capacitor 75 is grounded.
Wherein the capacitance of the tenth capacitor 75 is 100uF to 1000 uF. Specifically, the capacitance of the tenth capacitor 75 may be 100uF, 500uF, 800uF or 1000uF, and certainly, the capacitance of the tenth capacitor 75 is not limited thereto, and may be determined according to the actual situation, which is not limited in this embodiment.
It is easy to understand that, in an ideal state, the signal frequency of the dc power signal is 0HZ, but in an actual operation process, the dc power signal often contains a certain amount of ac components, and at this time, the signal frequency of the dc power signal is not 0HZ, and at this time, the operating frequency of the front-end device fluctuates to some extent due to the presence of the ac components. In this embodiment, the tenth capacitor 75 can store a part of the electric energy in time, so that the fluctuation amplitude of the operating frequency of the front-end equipment can be obviously reduced.
It can be seen that, in this embodiment, the front-end device can operate at a relatively stable operating frequency.
It can be seen that the present embodiment better implements coaxial power supply, reduces the application cost of the coaxial power supply technology, and simultaneously enlarges the frequency range of the video signal applicable to the coaxial power supply technology.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (18)

1. A video surveillance system, comprising: a front-end device and a back-end device; wherein the content of the first and second substances,
the front-end device includes: a first high-pass filter circuit (200) and a first low-pass filter circuit (300);
the first high-pass filter circuit (200) is used for passing video signals with frequencies of an HZ level and above the HZ level and isolating direct-current power signals, the first low-pass filter circuit (300) is used for passing the direct-current power signals and isolating the video signals, a video signal output port of front-end equipment is connected with a first end of a coaxial cable (600) through the first high-pass filter circuit (200), and a first end of the coaxial cable (600) is also connected with a direct-current power input port of the front-end equipment through the first low-pass filter circuit (300);
the backend apparatus includes: a second high-pass filter circuit (400) and a second low-pass filter circuit (500);
the second high-pass filter circuit (400) is used for passing through a video signal and isolating a direct-current power supply signal, the second low-pass filter circuit (500) is used for passing through the direct-current power supply signal and isolating the video signal, a direct-current power supply output port of the rear-end equipment is connected with the second end of the coaxial cable (600) through the second low-pass filter circuit (500), and the second end of the coaxial cable (600) is further connected with a video signal input port of the rear-end equipment through the second high-pass filter circuit (400).
2. The system according to claim 1, wherein the first high-pass filter circuit (200) comprises: a first resistor (11), an operational amplifier (12), a second resistor (13), a third resistor (14), a fourth resistor (15), a first capacitor (16), a fifth resistor (17), a second capacitor (18) and a sixth resistor (19); wherein the content of the first and second substances,
the first end of the first resistor (11) is grounded, the second end of the first resistor (11) is connected with the positive input end of the operational amplifier (12), and the positive input end of the operational amplifier (12) is also connected with the video signal output port of the front-end equipment;
the output end of the operational amplifier (12) is respectively connected with the first end of the second resistor (13) and the first end of the first capacitor (16), the second end of the second resistor (13) is respectively connected with the first end of the third resistor (14) and the first end of the fifth resistor (17), the first end of the second capacitor (18) is connected with the second end of the fifth resistor (17), the first end of the sixth resistor (19) is respectively connected with the second end of the first capacitor (16) and the second end of the second capacitor (18), and the second end of the sixth resistor (19) is connected with the first end of the coaxial cable (600);
the negative electrode input end of the operational amplifier (12) is respectively connected with the second end of the third resistor (14) and the first end of the fourth resistor (15), and the second end of the fourth resistor (15) is grounded;
the resistance values of the first resistor (11) and the sixth resistor (19) are matched with the coaxial cable (600), the resistance values of the second resistor (13) and the fourth resistor (15) are both 1 omega-10 k omega, the resistance values of the third resistor (14) and the fifth resistor (17) are both 470 omega-4.7 k omega, and the ratio of the capacitance of the first capacitor (16) to the capacitance of the second capacitor (18) is larger than 2.
3. The system according to claim 1, wherein the first low-pass filter circuit (300) comprises: a seventh resistor (21), an eighth resistor (22), a third capacitor (23), a first triode (24), a ninth resistor (25), a second triode (26) and a tenth resistor (27); wherein the content of the first and second substances,
a first end of the coaxial cable (600) is respectively connected with a first end of the seventh resistor (21), a collector of the first triode (24) and a collector of the second triode (26), the direct current power supply input port of the front-end equipment is respectively connected with the first end of the eighth resistor (22), the first end of the third capacitor (23) and the first end of the tenth resistor (27), a second end of the third capacitor (23) is respectively connected with a second end of the seventh resistor (21), a second end of the eighth resistor (22) and a base of the first triode (24), the emitter of the first triode (24) is connected with the first end of the ninth resistor (25), the second end of the ninth resistor (25) is connected with the base of the second triode (26), the emitter of the second triode (26) is connected with the second end of the tenth resistor (27);
the resistance values of the seventh resistor (21) and the eighth resistor (22) are both 1 omega-50K omega, the resistance value of the ninth resistor (25) is 1 omega-1K omega, the resistance value of the tenth resistor (27) is 1 omega-10 omega, the capacitance of the third capacitor (23) is 47uF-1000uF, the maximum withstand voltage value of the collector electrodes of the first triode (24) and the second triode (26) is greater than 60V, the maximum allowable current of the collector electrode is greater than 1A, and the maximum dissipated power is greater than 50 mW.
4. The system of claim 3, wherein the first low pass filter circuit (300) further comprises: an eleventh resistor (28); wherein the content of the first and second substances,
the first end of the eleventh resistor (28) is connected with the second end of the third capacitor (23), the second end of the eleventh resistor (28) is connected with the base electrode of the first triode (24), and the resistance value of the eleventh resistor (28) is 1-100 omega.
5. The system of claim 3, wherein the first low pass filter circuit (300) further comprises: a first inductor (29); wherein the content of the first and second substances,
a first end of the first inductor (29) is connected with a first end of the eighth resistor (22), a first end of the third capacitor (23) and a first end of the tenth resistor (27), respectively, a second end of the first inductor (29) is connected with a direct current power supply input port of the front-end equipment, and an inductance of the first inductor (29) is 470uH-3.3 mH.
6. The system of claim 5, wherein the first low pass filter circuit (300) further comprises: a twelfth resistor (30) and a first diode (31); wherein the content of the first and second substances,
the first end of the first inductor (29) is respectively connected with the first end of the twelfth resistor (30) and the negative end of the first diode (31), the second end of the first inductor (29) is respectively connected with the second end of the twelfth resistor (30) and the positive end of the first diode (31), and the resistance value of the twelfth resistor (30) is 330-3.3 k omega.
7. The system of claim 6,
the first low-pass filtering circuit (300) further comprises: a second diode (32), a positive terminal of the second diode (32) is respectively connected with a second terminal of the twelfth resistor (30), a second terminal of the first inductor (29) and a positive terminal of the first diode (31), a second terminal of the second diode (32) is connected with a direct current power supply input port of the front-end device, wherein the second diode (32) is a voltage regulator diode; and/or the presence of a gas in the gas,
the first low-pass filtering circuit (300) further comprises: and the positive end of the third diode (33) is connected with the first end of the coaxial cable (600), the negative end of the third diode (33) is respectively connected with the first end of the seventh resistor (21), the collector electrode of the first triode (24) and the collector electrode of the second triode, and the third diode (33) is a voltage stabilizing diode.
8. The system of claim 3, wherein the first low pass filter circuit (300) further comprises: a first magnetic bead (34); wherein the content of the first and second substances,
the first end of the first magnetic bead (34) is connected with the first end of the coaxial cable (600), and the second end of the first magnetic bead (34) is respectively connected with the first end of the seventh resistor (21), the collector of the first triode (24) and the collector of the second triode (26).
9. The system of claim 3, wherein the first low pass filter circuit (300) further comprises: a fourth capacitor (35); wherein the content of the first and second substances,
the first end of the fourth capacitor (35) is respectively connected with the first end of the eighth resistor (22), the first end of the third capacitor (23) and the first end of the tenth resistor (27), the second end of the fourth capacitor (35) is grounded, and the capacitance of the fourth capacitor (35) is 100-1000 uF.
10. The system of claim 3, wherein the head-end equipment further comprises: a voltage conversion chip; wherein the content of the first and second substances,
the first end of the voltage conversion chip is respectively connected with the first end of the eighth resistor (22), the first end of the third capacitor (23) and the first end of the tenth resistor (27), the second end of the voltage conversion chip is connected with the direct-current power supply input port of the front-end equipment, and the voltage conversion chip is used for converting the input voltage into the voltage with the set value and then outputting the voltage.
11. The system of claim 10, wherein the head-end equipment further comprises: a constant current output control circuit and a switch circuit; the constant current output control circuit includes: a fourth diode (41), a thirteenth resistor (42), a fifth diode (43), a fourteenth resistor (44), a sixth diode (45), a fifteenth resistor (46), a fifth capacitor (47), a second inductor (48), a sixth capacitor (49), a sixteenth resistor (50), a seventh capacitor (51) and a buck regulator chip (52); wherein the content of the first and second substances,
a first pin of the buck and voltage regulation chip (52) is connected with a first end of the second inductor (48) and a positive end of the fourth diode (41) respectively, a second pin and a third pin of the buck and voltage regulation chip (52) are both grounded, a fourth pin of the buck and voltage regulation chip (52) is connected with a first end of the sixteenth resistor (50) and a first end of the seventh capacitor (51) respectively, the switching circuit is connected with a second end of the sixteenth resistor (50) to control the start and stop of the buck and voltage regulation chip (52), a second end of the seventh capacitor (51) is grounded, a fifth pin of the buck and voltage regulation chip (52) is connected with a first end of the sixth capacitor (49) and a second end of the voltage conversion chip respectively, a second end of the sixth capacitor (49) is grounded, and a sixth pin of the buck and voltage regulation chip (52) is connected with a first end of the thirteenth resistor (42) respectively The first end of the fifth capacitor (47), the negative end of the sixth diode (45), the negative end of the fifth diode (43) and the direct-current power supply input port of the front-end equipment are connected;
a positive terminal of the fifth diode (43) is connected to a first terminal of the fourteenth resistor (44), a positive terminal of the sixth diode (45) is connected to a first terminal of the fifteenth resistor (46), a second terminal of the second inductor (48) is respectively connected to a second terminal of the fourteenth resistor (44), a second terminal of the fifteenth resistor (46) and a second terminal of the fifth capacitor (47), and a second terminal of the thirteenth resistor (42) is respectively connected to a negative terminal of the fourth diode (41), a second terminal of the voltage conversion chip and a first terminal of the sixth capacitor (49);
the fourth diode (41), the fifth diode (43) and the sixth diode (45) are voltage stabilizing diodes, the capacitance of the fifth capacitor (47) and the capacitance of the sixth capacitor (49) are 1uF-100uF, the resistance of the fourteenth resistor (44) and the resistance of the fifteenth resistor (46) are 1 omega-2 omega, the inductance of the second inductor (48) is 2.2uH-47uH, the capacitance of the seventh capacitor (51) is 100nH-10uH, and the thirteenth resistor (42) is formed by connecting at least two resistors with the resistance of 0.1 omega-10 omega in parallel.
12. The system according to claim 1, wherein the second low-pass filter circuit (500) comprises: a seventeenth resistor (61), an eighteenth resistor (62), a ninth capacitor (63), a third triode (64), a nineteenth resistor (65), a fourth triode (66) and a twentieth resistor (67); wherein the content of the first and second substances,
the direct current power output port of the back-end device is respectively connected with the first end of a seventeenth resistor (61), the collector of a third triode (64) and the collector of a fourth triode (66), the second end of a coaxial cable (600) is respectively connected with the first end of an eighteenth resistor (62), the first end of a ninth capacitor (63) and the first end of a twentieth resistor (67), the second end of the ninth capacitor (63) is respectively connected with the second end of the seventeenth resistor (61), the second end of the eighteenth resistor (62) and the base of the third triode (64), the emitter of the third triode (64) is connected with the first end of a nineteenth resistor (65), the second end of the nineteenth resistor (65) is connected with the base of the fourth triode (66), the emitter of the fourth triode (66) is connected with the second end of the twentieth resistor (67);
the resistance values of the seventeenth resistor (61) and the eighteenth resistor (62) are both 1 omega-50K omega, the resistance value of the nineteenth resistor (65) is 1 omega-1K omega, the resistance value of the twentieth resistor (67) is 1 omega-10 omega, the capacitance of the ninth capacitor (63) is 47uF-1000uF, the maximum withstand voltage value of the collector electrodes of the third triode (64) and the fourth triode (66) is greater than 60V, the maximum allowable current of the collector electrodes is greater than 1A, and the maximum dissipated power is greater than 50 mW.
13. The system of claim 12, wherein the second low pass filter circuit (500) further comprises: a twenty-first resistor (68); wherein the content of the first and second substances,
the first end of the twenty-first resistor (68) is connected with the second end of the ninth capacitor (63), the second end of the twenty-first resistor (68) is connected with the base electrode of the third triode (64), and the resistance value of the twenty-first resistor (68) is 1-100 omega.
14. The system of claim 12, wherein the second low pass filter circuit (500) further comprises: a third inductor (69); wherein the content of the first and second substances,
the first end of the third inductor (69) is respectively connected with the first end of the eighteenth resistor (62), the first end of the ninth capacitor (63) and the first end of the twentieth resistor (67), the second end of the third inductor (69) is connected with the second end of the coaxial cable (600), and the inductance of the third inductor (69) is 470uH-3.3 mH.
15. The system of claim 14, wherein the second low pass filter circuit (500) further comprises: a twenty-second resistor (70) and a seventh diode (71); wherein the content of the first and second substances,
the first end of the third inductor (69) is respectively connected with the first end of the twenty-second resistor (70) and the negative electrode end of the seventh diode (71), the second end of the third inductor (69) is respectively connected with the second end of the twenty-second resistor (70) and the positive electrode end of the seventh diode (71), and the resistance value of the twenty-second resistor (70) is 330-3.3 k omega.
16. The system of claim 15,
the second low-pass filter circuit (500) further comprises: an eighth diode (72), a positive terminal of the eighth diode (72) being connected to the second terminal of the twenty-second resistor (70), the second terminal of the third inductor (69), and a positive terminal of the seventh diode (71), respectively, a negative terminal of the eighth diode (72) being connected to the second terminal of the coaxial cable, wherein the eighth diode (71) is a zener diode; and/or the presence of a gas in the gas,
the second low-pass filter circuit (500) further comprises: a ninth diode (73), a positive terminal of the ninth diode (73) is connected to the dc power output port of the back-end device, a negative terminal of the ninth diode (73) is connected to the first terminal of the seventeenth resistor (61), the collector of the third transistor (64), and the collector of the fourth transistor (66), respectively, wherein the ninth diode (73) is a zener diode.
17. The system of claim 12, wherein the second low pass filter circuit (500) further comprises: a second magnetic bead (74); wherein the content of the first and second substances,
the first end of the second magnetic bead (74) is connected with the direct-current power supply output port of the back-end device, and the second end of the second magnetic bead (74) is respectively connected with the first end of the seventeenth resistor (61), the collector (64) of the third triode and the collector of the fourth triode (66).
18. The system of claim 12, wherein the second low pass filter circuit (500) further comprises: a tenth capacitor (75); wherein the content of the first and second substances,
the first end of the tenth capacitor (75) is respectively connected with the first end of the eighteenth resistor (62), the first end of the ninth capacitor (63) and the first end of the twentieth resistor (67), the second end of the tenth capacitor (75) is grounded, and the capacitance of the tenth capacitor (75) is 100-1000 uF.
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