Abstract:
The present invention provides a single-cable transmission device for signals and a power supply of a surveillance system, which only requires a single cable to transmit various signals and a power supply; which transmits signals in a carrier manner, allowing longer-distance transmission; which transmits signals in a frequency division manner, allowing bi-directional transmission. A power-supply-voltage/output-load status display is further provided, thereby facilitating a user to directly find the cause of a failure so as to eliminate the failure promptly.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a transmission device for signals via cables, and more particularly to a single-cable transmission device for signals and a power supply of a surveillance system. 
     In current surveillance systems, taking a unidirectional surveillance system for an example, base band signals such as video signals, audio signals, control signals, etc. and a power supply between cameras at remote side and monitors at local side are typically transmitted by use of many cables (for example, coaxial cables), respectively. However, such a transmission manner has a number of defects: (1) requiring plural cables, making it difficult to install the system and thus increasing system cost; (2) requiring additional repeaters for longer-distance transmission due to gradual decrease in signal intensity under base band transmission with longer-distance transmission; (3) compounding the problems resulting from the above defects (1) and (2) when the system is to be expanded to a bi-directional one; and (4) generally not easy to directly find whether the power supply or the load (for example, the camera) is out of order when the remote side: which receives the power supply from the local side fails, even though professionals have to take advantage of proper instruments or equipment for assistance to find the cause of the failure so as to eliminate it, not to mention common consumers by DIY (Do-It-Yourself). 
     SUMMARY OF THE INVENTION 
     In view thereof, the present invention provides an improved single-cable transmission device for signals and a power supply of a surveillance system, which can solve the problems encountered by the above prior art surveillance system techniques. 
     One object of the present invention is to provide a transmission device, which only requires a single cable to transmit various signals and a power supply, thereby making the system installation convenient, decreasing system cost, and facilitating common consumers to use by DIY. 
     Another object of the present invention is to provide a transmission device, which transmits signals in a carrier manner, allowing longer-distance transmission. 
     Still another object of the present invention is to provide a transmission device, which transmits signals in a frequency division manner, allowing bi-directional transmission, and thus facilitating operation drills and improving friendliness with operators. 
     Yet another object of the present invention is to provide a transmission device, which is equipped with a power-supply-voltage/output-load status display, thereby facilitating a user to directly find the cause of a failure so as to eliminate the failure promptly, and thus saving repair time and enabling common consumers to use by DIY. 
     According to one embodiment of the present invention, the innovative single-cable transmission device for signals and a power supply of a surveillance system comprises a remote device, said remote device having a first modulator for transforming a first set of base band signals inputted externally into a first modulated carrier signal, and having a first filter module for receiving said first modulated carrier signal and a power supply inputted from said single cable, and for separating said first modulated carrier signal from said power supply through different frequency bands, and then outputting said separated first modulated carrier signal and power supply, respectively, wherein said outputted first modulated carrier signal is applied to said single cable. 
     According to another embodiment of the present invention, the innovative single-cable transmission device for signals and a power supply of a surveillance system comprises a local device, said local device having a second filter module for receiving said first modulated carrier signal inputted from said single cable and receiving a power supply inputted externally, and for separating said first modulated carrier signal from said power supply through different frequency bands, and then outputting said separated first modulated carrier signal and power supply, respectively, wherein said outputted power supply is applied to said single cable, and having a first demodulator of transforming said first modulated carrier signal outputted from said second filter module into said first set of base band signals. 
     According to a further embodiment of the present invention, the first filter module of the remote device of the innovative single-cable transmission device for signals and a power supply of a surveillance system further receives a second modulated carrier signal inputted from said single cable, and separates said second modulated carrier signal from said first modulated carrier signal and said power supply through different frequency bands, and then outputs said separated second modulated carrier signal; and said remote device further comprises a second demodulator for transforming said second modulated carrier signal outputted from said first filter module into a second set of base band signals. 
     According to another embodiment of the present invention, the local device of the innovative single-cable transmission device for signals and a power supply of a surveillance system comprises a second modulator for transforming a second set of base band signals inputted externally into a second modulated carrier signal; a second filter module for receiving said first modulated carrier signal inputted from said single cable, said second modulated carrier signal from said second modulator, and a power supply inputted externally, and for separating said first modulated carrier signal, said second modulated carrier signal, and said power supply through different frequency bands, and then outputted said separated first modulated carrier signal, second modulated carrier and power supply, respectively, wherein said outputted second modulated carrier signal and power supply are applied to said single cable; and a first demodulator for receiving said first modulated carrier signal outputted from said second filter module and transforming said first modulated carrier signals into said first set of base band signals. 
     According to another embodiment of the present invention, the remote device of the innovative single-cable transmission device for signals and a power supply of a surveillance system comprises a power-supply-voltage/output-load status display connected between the power supply outputted from said first filter module and external devices for detecting the operation status of the power supply voltage and the external device loads. 
     According to another embodiment of the present invention, the innovative single-cable transmission device for signals and a power supply of a surveillance system receives a power supply at said remote device rather than at said local device as mentioned above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to more clearly understand the above and other features and advantages of the present invention, a further description with reference to the accompanying drawings is given below, wherein: 
     FIG. 1 is a circuit block diagram of the first preferred embodiment of the single-cable transmission device for signals and a power supply of a surveillance system according to the present invention; 
     FIG. 2 is a circuit block diagram of a preferred embodiment of the filter module in FIG. 1; 
     FIG. 3 is a schematic frequency spectrum diagram for the filter module in FIG. 2; 
     FIG. 4 is a circuit block diagram of the second preferred embodiment of the single-cable transmission device for signals and a power supply of a surveillance system according to the present invention; 
     FIG. 5 is a circuit block diagram of a preferred embodiment of the filter module in FIG. 4; 
     FIG. 6 is a schematic frequency spectrum diagram for the filter module in FIG. 5; 
     FIG. 7 is a circuit block diagram of the third preferred embodiment of the single-cable transmission device for signals and a power supply of a surveillance system according to the present invention; 
     FIG. 8 is a circuit block diagram of a preferred embodiment of the power-supply-voltage/output-load status display in FIG. 7; 
     FIG. 9 is a schematic circuit diagram of a preferred embodiment of the circuit block diagram in FIG. 8; and 
     FIG. 10 is a truth table of the status display in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, there shows a circuit block diagram of the first preferred embodiment of the single-cable transmission device for signals and a power supply of a surveillance system according to the present invention, which comprises a remote device  10  and a local device  11 . The remote device  10  includes a modulator  12  and a filter module  13 . The modulator  12  receives a set of base band signals inputted from external devices, such as a video signal and an audio signal from a camera (not shown) and a control signal from other control devices such as a switch (not shown), and transforms said base band signals into a modulated carrier signal. The modulation can be performed in a coherent AM manner, for example. Alternatively, it is done in a non-coherent manner, and the modulator  12  is further provided with an adder to integrate modulated carrier signals. 
     The filter module  13  receives the modulated carrier signal outputted from the modulator  12 , and a power supply from a single cable  14 , and separates the modulated carrier signal from the power supply through different frequency bands, and then outputs the separated modulated carrier signal and power supply, respectively, wherein the outputted modulated carrier signal is applied to the single cable  14 , and the outputted power supply is applied to the modulator  12  and external devices such as the camera, respectively, through a line  15 . 
     The local device  11  includes a filter module  16  and a demodulator  17 . The filter module  16  receives the modulated carrier signal inputted from the single cable  14 , and a power supply inputted externally through line  18 , and separates the modulated carrier signal from the power supply through different frequency bands, and then outputs the separated modulated carrier signal and power supply, respectively, wherein the outputted power supply is applied to the single cable  14 . 
     The demodulator  17  receives the modulated carrier signal outputted from the filter module  16  and transforms the modulated carrier signal into the set of base band signals such as the video signal, the audio signal and the control signal. If the modulator  12  is performed in a coherent AM manner, the demodulation can be done in an AM detection manner. If the modulator  12  is performed in a non-coherent manner, the demodulation can be done with phase-locked loop (PLL). And the external power supply can be applied to the demodulator  17 . 
     The external power supply can be a DC or AC power supply. The voltage range of the power supply varies with the length of the single cable  14 . In case of an RG-59/U coaxial cable of 100 to 200 meters, tests reveal that a range of 6 to 24V DC power supplies can be applied. Instead, an AC power supply with similar voltages and a frequency less than 800 Hz can be used. Upon using an AC power supply, the power supply outputted from the filter module  13  through line  15  is rectified and then applied to the modulator  12  and external devices, respectively. 
     Next, referring to FIG. 2, a circuit block diagram of a preferred embodiment of the filter modules  13  and  16  in FIG. 1 is shown. The filter module  13  includes a band-pass filter  21  and a low-pass filter  22 . The filter module  16  includes a band-pass filter  23  and a low-pass filter  24 . The band-pass filter  21  and the low-pass filter  22  have different frequency band features, and the band-pass filter  23  and the low pass filter  24  also have different frequency band features. The band-pass filter  21  and the band-pass filter  23  have the same frequency band feature, and the low-pass filter  22  and the low-pass filter  24  also have the same frequency band feature. For example, the band-pass filter  21  and the band-pass filter  23  can have a frequency band  31  as shown in the frequency spectrum diagram of FIG. 3, wherein the frequency bands  33 ,  34 , and  35  can be for the video signal, the audio signal and the control signal, respectively, in the modulated carrier signal, while the low-pass filter  22  and the low-pass filter  24  can have a frequency band  32  for the DC or AC power supply. In this arrangement, with the band-pass filter  21  and the low-pass filter  22 , the filter module  13  can separate the modulated carrier signal from the modulator  12  from the power supply from the single cable  14  through different frequency bands, and then output the separated modulated carrier signal and power supply, respectively. With the band-pass filter  23  and the low-pass filter  24 , the filter module  16  can separate the modulated carrier signal from the single cable  14  from the external power supply through different frequency bands, and then output the separated modulated carrier signal and power supply, respectively. 
     FIG. 4 shows a circuit block diagram of the second preferred embodiment of the single-cable transmission device for signals and a power supply of a surveillance system according to the present invention. The second preferred embodiment is based on the single-cable transmission device for signals and a power supply as shown in FIG. 1 which can transmit bi-directional signals together with a power supply. The second preferred embodiment comprises a remote device  40  and a local device  41 . The modulator  42  and the filter modulator  43  in the remote device  40 , the single cable  44 , and the filter module  47  and the demodulator  48  in the local device  41  function as the modulator  12 , the filter module  13 , the single cable  14 , the filter module  16 , and the demodulator  17  of FIG. 1, for transforming a set of base band signals inputted externally into a modulated carrier signal, separating the modulated carrier signal from a power supply through different frequency bands, transmitting the separated modulated carrier signal, and then transforming transmitted modulated carrier signal into the set of base band signals. The difference therebetween resides in that the local device  41  further includes a modulator  49  for transforming another set of base band signals into a modulated carrier signal to be separated through different frequency bands by the filter module  47 , to be transmitted via the single cable  44 , to be separated through different frequency bands by the filter module  43 , and to be transformed into the another set of base band signals by a demodulator  45  additionally included in the remote device  40 . And, the externally inputted power supply received by the local device  41  is to be separated through different frequency bands by the filter module  47 , to be transmitted via the single cable  44 , to be separated through different frequency bands by the filter module  43 , and to be applied to the modulator  42 , the demodulator  45  and external devices. 
     A circuit block diagram of a preferred embodiment of the filter modules  43  and  47  is shown in FIG.  5 . The filter module  43  includes a band-pass filter  51  and a low-pass filter  52 , as the band-pass filter  21  and the low-pass filter  22  in FIG.  2 . The filter module  47  includes a band-pass filter  54  and a low-pass filter  55 , as the band-pass filter  23  and the low-pass filter  24  in FIG.  2 . The filter module  43  further includes a band-pass filter  53 , and the filter module  47  further includes a band-pass filter  56 . The band-pass filter  51 , and the band-pass filter  53  and the low-pass filter  52  have different frequency band features, and the band-pass filter  54 , the band-pass filter  56  and the low-pass filter  55  also have different frequency band features. The band-pass filter  51  and the band-pass filter  54  have the same frequency band feature, the band-pass filter  53  and the band-pass filter  56  have the same frequency band feature, and the low-pass filter  52  and the low-pass filter  55  have the same frequency band feature. For example, the band-pass filter  51  and the band-pass filter  54  can have a frequency band  61  as shown in the frequency spectrum diagram of FIG. 6, wherein the frequency bands  64 ,  65  and  66  can be for the video signal, the audio signal and the control signal, respectively, in the modulated carrier signal; the band-pass filter  53  and the band-pass filter  56  can have a frequency band  62  as shown in the frequency spectrum diagram of FIG. 6, wherein the frequency bands  67 ,  68  and  69  can be for the video signal, the audio signal and the control signal, respectively, in the modulated carrier signal; and the low-pass filter  52  and the low-pass filter  55  can have a frequency band  63  for the DC or AC power supply. Thus, the filter modules  43  and  47  can separate the two modulated carrier signals and the power supply from each other through different frequency bands, and then output the separated modulated carrier signals and power supply, respectively. 
     FIG. 7 is a circuit block diagram of the third preferred embodiment of the present invention, wherein the remote device  71  includes a modulator  72  and a filter module  73 , functioning as the remote device  10  of FIG. 1. A modulated carrier signal and a power supply are respectively transmitted via a single cable  74 , and the power supply outputted from the filter module  73  is transmitted on a line  75 . The remote device  71  further includes a power-supply-voltage/output-load status display  76  connected between the power supply outputted from the filter module  73  through the line  75  and the external devices for detecting the operation status of the power supply voltage and the external device loads. 
     FIG. 8 illustrates a circuit block diagram of a preferred embodiment of the power-supply-voltage/output-load status display  76  in FIG. 7, which includes a power-supply-voltage status detector  81 , a load status detector  82 , and a display module  83 . The power-supply-voltage status detector  81  is to detect a status of the voltage of the power supply outputted from the filter module  73  through the line  75 , and output on a line A a signal indicative of the status of the power supply voltage. The load status detector  82  is to detect a status of the load of the external devices connected to the power supply outputted from the filter module  73  through the line  75 , and output on a line B a signal indicative of the status of the load. The display module  83  is to make a proper manipulation to the signal indicative of the status of the power supply voltage from the line A and to the signal indicative of the status of the load from the line B so as to display the status of the power supply voltage and the load. 
     FIG. 9 is a schematic circuit diagram of a preferred embodiment of the circuit block diagram in FIG.  8 . As shown in FIG. 9, the power-supply-voltage status detector  81  includes an operational amplified  91  with its positive (+) input pin connected to the positive electrode of a reference voltage  92 , and its negative (−) input pin connected to the power supply outputted from the filter module  73  through the line  75 . The negative electrode of the reference voltage  92  is grounded. The reference voltage  92  is designed to have a voltage value close to a power supply voltage that enables external devices to work normally. Hence, the operational amplifier  91  can detect the status of the voltage of the power supply outputted from the filter module  73  through the line  75 , and output on the line A a signal indicative of the status of the power supply voltage. The load status detector  82  includes an operational amplifier  93  with its negative (−) input pin connected to the negative electrode of a reference voltage  94 . The positive electrode of the reference voltage  94  is coupled to the power supply from the line  75  and one end of a resistor  95 . The other end of the resistor  95  is coupled to the positive (+) input pin of the operational amplifier  93 , and outputs the power supply from the line  75  to external devices. An operation current in external device loads will pass through the resistor  95 . The reference voltage  94  is designed to have a voltage value close to a voltage on the resistor  95  caused by the operation current. As a result, the operational amplifier  93  can detect the status of the load of the external devices connected to the power supply outputted from the filter module  73  through the line  75 , and output on the line B a signal indicative of the status of the load. The display module  83  includes an inverter  96 , a NAND gate  97 , or OR gate  98 , and LED display  99  and current-limiting resistors  97 G and  98 R. The LED display  99  consists of a green LED  99 G and a red LED  99 R. The inverter  96 , the NAND gate  97  and the OR gate  98  are together to function as a signal decoder for decoding the signal from the line A indicative of the status of the power supply voltage, and the signal from the line B indicative of the status of the load. The decoded signals indicative of the status of the power supply voltage and the status of the load are outputted on the lines G and R and pass through the current-limiting resistors  97 G and  97 R, respectively, to cause the green LEd  99 G and red LED  99 R together to display the status. 
     Next, the operation principle of the status display  76  in FIG. 9 is further described with reference to the truth table of FIG. 10 as follows: 
     1. When the power supply is sufficient and there is no load, the operational amplifier  91  outputs a low (L) voltage on the line A, and the operational amplifier  93  also outputs a low (L) voltage on the line B, causing a high (H) voltage on the line G and a low (L) voltage on the line R such that only the green LED  99 G is turned on and thus the LED display  99  is in green; 
     2. When the power supply is sufficient and there is a load, the operational amplifier  91  outputs a low (L) voltage on the line A, and the operational amplifier  93  outputs a high (H) voltage on the line B, causing a low (L) voltage on the line G and a high (H) voltage on the line R such that only the red LED  99 R is turned on and thus the LED display  99  is in red; 
     3. When the power supply is insufficient and there is no load, the operational amplifier  91  outputs a high (H) voltage on the line A, and the operational amplifier  93  outputs a low (L) voltage on the line B, causing a high (H) voltage on the line G and a high (H) voltage on the line R such that the green LED  99 G and the red LED  99 R are both turned on and thus the LED display  99  is in yellow; and 
     4. When the power supply is insufficient and there is a load or the load makes the power supply insufficient, the operational amplifier  91  outputs a high (H) voltage on the line A, and the operational amplifier  93  also outputs a high (H) voltage on the line B, causing a high (H) voltage on the line G and a high (H) voltage on the line R such that the green LED  99 G and the red LED  99 R are both turned on the thus the LED display  99  is in yellow. 
     In addition, based on the same principle, the embodiments of the single-cable transmission device for signals and a power supply of a surveillance system according to the present invention can apply a power supply at the remote device to the local device. 
     Please be advised that the transmission devices of the current cable TV system as well as the outdoor down-converter transmission device of the satellite TV receiver also adopt a carrier signal transmission and provide a power supply in the transmission line. However, the cable TV system pertains to a signal transmission in broadcasting form, which has numerous end user devices, and which provides the power supply only for the signal amplifiers on the transmission line rather than for the end user devices. And, the outdoor down-converter transmission device of the satellite TV receiver mainly forms a frequency conversion, and the power supply therein is for use of the outdoor down-converter. Both of the above two transmission devices are different from the present invention. 
     Although the present invention has been described in detail with reference to the above illustrated embodiments, other modifications, substitutions and changes thereof can be made by one of ordinary skill on the above basis. For example, with a proper signal decoder and LCD display, and display module  83  can display the status of the power supply voltage and the load in a manner of Chinese, English characters or numbers, symbols. Therefore, it is intended to encompass such modifications, substitutions and changes with the scope of the attached claims.