Abstract:
A channel scanning method for reducing scanning time of a channel in automatic channel memory of TV, VCR, or other video appliance is disclosed. To reduce the scanning time, a microcomputer detects synchronization signals for 300 ms after transmitting frequency data for broadcasting channel to tuner and the micom detects synchronization signals for 30 ms per step in dropping frequency data. The synchronization signal detecting time is 360 ms and is shorter than the prior time of 780 ms.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a method of automatic programming by which the channels where broadcasting signals exist are automatically searched and memorized in VTR or TV etc, and especially to a channel scanning method which reduces the scanning time of the whole channel to have the automatic program be completed in a shorter time. 
     2. Description of the Prior Art 
     Recently, as the use of cable TV has spread, the number of receivable broadcasting channels has increased rapidly. Because increase of scanning time of the whole channel is caused by the increase in the number of the broadcasting channels, the execution time of the automatic program which memorizes and programs the broadcasting channels needs more time. 
     FIG. 2 is a change view of tuning frequency to illustrate the traditional method of channel scanning. 
     With FIG. 2, the traditional method of channel scanning is looked into. 
     The frequency data fo of a specific channel is transmitted to the tuner by the micom. 
     Then, for 300 ms after transmission of the frequency data fo, the synchronizing signal is detected. 
     At this time, if the synchronizing signal is not detected, the detection of the synchronizing signal is continued with the frequency data being increased 8 steps each of 0.25 MHz. 
     That is, if the synchronizing signal is not detected in 300 ms after transmission of frequency data fo, the frequency data is increased 0.25 MHz and the synchronizing signal is detected for 30 ms. 
     If the synchronizing signal is not detected at this time, too, the frequency data is again increased 0.25 MHz and synchronizing signal is detected for 30 ms. 
     Such a detection of the synchronizing signal is continued until the frequency data is fo+2 MHz, the frequency data is decreased to fo 2 MHz. 
     And then, the synchronizing signal is detected for 30 ms per each step with the frequency data being increased 8 steps each fo 0.25 MHz once. 
     If the synchronizing signal is detected while the synchronizing signal is detected in this way, the channel of that frequency is judged as the channel in which the broadcasting exists and memorized by micom. In succession, the synchronizing signal of the next channel is detected. 
     As mentioned above, when the synchronizing signal is detected by the traditional channel scanning method, the synchronizing signal detection time consumed per a channel is 780 ms as shown in FIG. 2. 
     Hence, much time is needed to scan the whole channel. 
     Especially, there is a demerit that the scanning time of the whole channel becomes longer and longer as the number of broadcasting channels increase. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to reduce the detection time of the synchronizing signal which needs much more time in the traditional method of channel scanning. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is the system constitution view of the present invention. 
     FIG. 2 is the traditional change view of the tuning frequency in a specific channel. 
     FIG. 3 is the change view of the tuning frequency of the present invention in a specific channel. 
     FIG. 4 is the disposition state view of the NTSC broadcasting signal. 
     FIG. 5 is the view of the state and selectivity properties of the intermediate frequency signal when the n-channel is tuned. 
     FIG. 6 is the flow chart of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the channel scanning method according to the present invention is described with figures. 
     FIG. 1 is the system constitution view according to the present invention. 
     The system which realizes the present invention is made up of the micom 1, the tuner 2, the demodulation circuit 3 and the homodyne detection circuit 4. 
     The clock and the data with the tuning data of a specific channel is delivered to the tuner 2 in the phase locked loop system by the micom. 
     When this tuning data is applied to the tuner 2, a specific channel is tuned. 
     Then, the intermediate frequency signal(IF signal) is outputted from the tuner 2. 
     This IF signal is applied to the demodulation circuit 3 and is demodulated. 
     Accordingly, the video signal is outputted from the demodulation circuit 3 and this video signal is delivered to the homodyne detection circuit 4. Thus, the synchronizing signal which exists in the video signal is detected by the homodyne detection circuit 4. If the synchronizing signal is detected at this time, the synchronizing signal decision output according to the detection of the synchronizing signal in the homodyne detection circuit 4 is applied to the micom 1. 
     According to it, the specific channel in which the synchronizing signal is detected is memorized by the micom 1 and the process mentioned above is repeated using the next channel. 
     In the case that the synchronizing signal is not detected in the homodyne detection circuit 4, the process mentioned above is repeated with the frequency of a specific channel being increased. 
     Now, how much the channel scanning time is reduced by the channel scanning method according to the present invention is to be described. 
     FIG. 3 is the change view of the tuning frequency to illustrate the channel scanning method according to the present invention. 
     The selected frequency data fo of a specific channel is transmitted to the tuner 2 by the micom 1. 
     If the synchronizing signal is not detected in 300 ms from that time, the frequency data is dropped to fo -0.25 MHz and the synchronizing signal is detected for 30 ms. 
     If the synchronizing signal is not detected at this time, the frequency data is dropped to fo -0.5 MHz again and the synchronizing signal is detected for 30 ms. 
     If the synchronizing signal is not detected at this time, too, the synchronizing signal of the next channel is detected. 
     Accordingly, the time needed to detect the synchronizing signal of one channel is 360 ms. 
     As mentioned above, the traditional channel scanning method detects the synchronizing signal by changing the tuning frequency to fo±2 MHz and the channel scanning method of the present invention detects the synchronizing signal by changing the tuning frequency to fo-0.5 MHz. So, the channel scanning time by the channel scanning method of the present invention becomes shorter than that of the traditional method. 
     Next, the reason why the frequency is altered only to fo-0.5 MHz in the channel scanning time shortening method according to the present invention is discussed. 
     FIG. 4 shows the disposition state of the frequency of the NTSC broadcasting signal and FIG. 5 shows the states and selectivity properties of the intermediate frequency signal when the n-channel is tuned. 
     When the IF signal is looked around on the basis of the frequency Pn(FIG. 5), the detection of the synchronizing signal is possible in the static tuning state from the frequency PnI-4 MHz to PnI+1. So, if the tuning frequency is detuned to do-0.5 MHz, the detection of the synchronizing signal from the frequency of the intermediate frequency signal PnI-4 MHz to PnI+5.1 MHZ becomes possible. This means that, from the thinking of the frequency of the broadcasting signal(RF), the detection of the synchronizing signal from the frequency Pn+4 MHz to Pn-1.5 MHz is possible. That is, the detection of the synchronizing signal from the frequency fo+4 MHz to fo-1.5 MHz is possible without execution of the automatic fine tuning(AFT). So, the detection time of the synchronizing signal consumed per a channel in an automatic program is shorted by over 1/2 the time from 780 ms in the traditional case to 360 ms. 
     The scanning method of channel according to the present invention of which the detection time of the synchronizing signal of the channel is shortened as mentioned above is described in detail with the flow chart shown in FIG. 6. 
     When the automatic program is started, the frequency data of the first channel fo is transmitted to the tuner 2 by the micom 1 and the synchronizing signal is detected for 300 Ms. If the synchronizing signal is detected in 300 ms, the channel in which the synchronizing signal is detected is memorized. 
     Contimuously, the process mentioned above is repeated with the channel being increased and the channel in which the synchronizing signal is detected is memorized. The detection of the synchronizing signal like this is executed to the last channel. 
     If the synchronizing signal is not detected in 300 ms, the frequency data f1 that the tuning frequency is changed to fo-0.25 MHz is transmitted and the synchronizing signal is detected for 30 ms. If the synchronizing signal is detected at this time, the channel of that time is memorized and the operation of scanning the next channel is executed. In the case that the synchronizing signal is not detected, the frequency data that the frequency is changed to f1-0.25 MHz is transmitted again and the synchronizing signal is detected for 30 ms. If the synchronizing signal is detected at this time, too, the channel is memorized and the synchronizing signal is not detected, the channel of this time is judged as the channel where the synchronizing signal does not exist or the broadcasting signal does not exist. 
     If the synchronizing signal is not detected in the first 300 ms like this, the synchronizing signal is detected twice for 30 ms with the frequency being dropped 0.25 MHz. In doing so, if the synchronizing signal is not detected, it is judged as the channel where the broadcasting signal does not exist, and if the synchronizing signal is detected in the said 360 ms, the channel of that time is memorized and the synchronizing signal of the next channel is detected. 
     Therefore, while the detection time of the synchronizing signal of a channel in the automatic program by the traditional channel scanning method is 780 ms, that of the channel scanning method according to the present invention is 360 ms, and the scanning time of the channel can be reduced to at least one half of the scanning time.