High speed automatic frequency tuning method

Abstract: A high speed automatic frequency tuning method for tuning a broadcasting frequency of a channel selected by a viewer is disclosed. For this, the high speed automatic frequency tuning method moves a tuning control frequency in one direction of the high or low band directions of the reference search frequency, according to the magnitudes between the reference search frequency and the active broadcasting frequency, thereby searching the broadcasting frequency.

Description: Field of the Invention The present invention relates to a method for controlling a tuner in a video receiving apparatus, and more particularly to the method for carrying out frequency tuning at a high speed. Background of the Invention Generally, a video receiving apparatus is an apparatus for receiving and displaying a video program transmitted from a broadcasting station through the air, and as a typical example, there is a television, a video tape recorder (hereinafter, referred to as a "VTR"), etc. Accordingly, a small-sized processor that has recently been developed and is commonly used in televisions or VTRs adds additional functions for increasing the convenience of the viewer using the processor and each circuit tends to be controlled by the processor. Accordingly, the video receiving apparatus has been converted so that the tuning of the broadcasting frequency for the broadcasting channel selected by a viewer is automatically carried out by the processor. However, up to now, the automatic frequency tuning method used in the video receiving apparatus has a problem of requiring an extensive amount of time to execute the frequency tuning process, which will be described with reference to the attached drawings FIGS.1 to 3. FIG.1 is a flow chart of a conventional automatic frequency tuning method, FIG.2 is a state diagram of the frequency tuning according to the flow chart shown in FIG.1, and FIG.3 is a block diagram of a VTR, which is a diagram of the circuit for carrying out the flow chart shown in FIG.1. For convenience, the circuit shown in FIG.3 will be described. A microcomputer 300 controls and processes the system. And a key input means 310 which may be a keyboard, a remote controlled receiver, etc. receives an order for the function selected by a viewer, information about channels, and any other needed control information, and then transfers it to the microcomputer 300 in the form of keyed input data. After selecting an arbitrary frequency band radio frequency signal among a radio frequency (hereinafter, referred to as "RF") signal entering into the RF converter 350 under the control of the microcomputer 300, a tuner 320 frequency-converts the selected radio frequency signal and supplies the frequency-converted intermediate frequency signal to the demodulator 330. The demodulator 330 demodulates the intermediate frequency signal supplied from the tuner 320, and supplies the demodulated video and audio signals to the signal processor 340, and generates an automatic frequency tuning signal having different logic states according to the magnitudes of the frequency of the intermediate frequency signal and the reference demodulation frequency, and then supplies the automatic frequency tuning signal to the microcomputer 300. The signal processor 340 records video and audio signals entering from the demodulator 330 on a recording medium or reproduces the video and audio signals recorded on the recording medium to be supplied to a radio frequency converter 350. The RF converter 350 modulates the video and audio signals entering from the signal processor 340 into radio frequency signals of the frequency band corresponding to television channels 3 or 4, to be output through connector OPT, and also outputs the radio frequency signal, received through the antenna ANT, through the connector OPT by a television / VTR mode selection switch, or supplies it to the tuner 320. A flow chart shown in FIG.1 is carried out by the microcomputer 300 of the circuit shown in FIG.3, which is described with reference to the circuit shown in FIG.3 and the state diagram of the tuning frequency shown in FIG.2 as follows. When keyed data for channel information selected by a viewer is received from the key input means 310, the microcomputer 300 initiates a frequency search mode, flag X assigned in one of its registers as "0" to set a high frequency search mode such as 20 shown in FIG.2, and initiates a frequency increase number N stored in one of its registers as "0" (in step 100). After processing step 100, the microcomputer 300 reads out a reference search frequency fo for channel information corresponding to the input key data among reference search frequencies for respective channel information stored in its ROM, and then sets the read reference search frequency fo as a reference tuning control frequency fto, and then supplies the set reference tuning control frequency with a strobe signal of a low logic state to the tuner 320 according to a clock pulse train (in step 101). After carrying out step 101, the microcomputer 300 checks whether the frequency increase number N stored in one of its registers is equal to a limited increase number 32 (in step 102). when the frequency increase number N is not equal to the limited increase number 32 in step 102, the microcomputer 300 adds "1" to the frequency increase number N (in step 103). After processing step 103, the microcomputer 300 stores a logic state of the automatic frequency tuning signal supplied from the demodulator 330 in its RAM (in step 104). After carrying out step 104, the microcomputer 300 multiplies the frequency increase number N by a unit frequency of 0.0625 MHz, and then adds the product to the reference tuning control frequency fto to set tuning control frequency ft, and then supplies the set tuning control frequency to the tuner 320 (in step 105). After carrying out step 105, microcomputer 300 checks whether the logic state of the automatic frequency tuning signal entering from the demodulator 330 is equal to that of the automatic frequency tuning signal stored in its RAM, and if they are different from each other, completion of the tuning process is determined and the automatic frequency tuning operation is completed, and on the other hand, if they are equal, the microcomputer goes back to step 102 (in step 106). And when the frequency increase number N is the limited increase number 32 in step 102, the microcomputer 300 checks whether the frequency search mode flag X assigned in one of its registers is set to "1", thereby determining whether the low frequency search mode has been set (in step 107). When the frequency search mode flag X is reset to "0" in step 107, i.e., when it is a high frequency search mode such as 20 of FIG.2, the microcomputer 300 sets the frequency search mode flag X to "1", so as to set a low frequency search mode such as 21 of FIG.2, and sets the set reference tuning control frequency fto, which has been set in step 101, to be smaller than the reference search frequency by 2 MHz, and initiates the frequency increase number N as "0", and then goes back to step 105 (in step 108). Inversely, when the frequency search mode flag X is set to "1" in step 107, i.e. when a low frequency search mode is set, the microcomputer 300 sets the reference search frequency fo as a tuning control frequency ft to be supplied to the tuner 320, and then completes the automatic frequency tuning operation (in step 109). Thus, as indicated by the flow chart shown in FIG.1, the search mode of a frequency band lower than the reference search frequency fo corresponding to a channel by approximately 2 MHz is set in steps 100 and 101, and a broadcasting frequency for the channel is searched in the frequency band within 2 MHz from the reference search frequency according to the set search mode in step 102 to 106, and when the broadcasting frequency can not be found in the frequency band within ± 2 MHz with reference to the reference search frequency, the reference search frequency is fixed and set as a tuning control frequency so as to complete the tuning operation in step 109. As described above with reference to FIGS.1 to 3, the conventional automatic frequency tuning method sets low and high band search modes, and carries out a search process of 32 steps by an increase from the reference search frequency fo to each limited frequency fo± 2MHz by a constant frequency according to each set mode, without regarding the relation between the currently tuned radio frequency signal frequency and the active broadcasting frequency. Thus, in the worst case, the search process of 64 steps is carried out to tune the broadcasting frequency, requiring an extensive amount of time to execute the frequency tuning process. US-A-4 763 195 discloses a tuning system for tuning non-standard frequency RF television signals provided by cable distribution networks and television accessories conducting first and second consecutive searches by changing the local oscillator frequency. The first search is limited to search frequencies corresponding to predictable non-standard frequencies associated with the major cable distribution networks. The second search includes more search frequencies and extends over a wider frequency range than the first. During an auto-programming mode, in which active channels are identified, for memorization in a channel list portion of a memory, only the first search is conducted to minimize the required time. Summary of the Invention Accordingly, it is an object of the present invention to provide a high speed automatic frequency tuning method which can carry out the frequency tuning process at a high speed in a video receiving apparatus. To achieve the object, according to the present invention, a method for controlling a tuner in a video receiving apparatus provided with a tuner for tuning a radio frequency signal from a plurality of radio frequency signals received through an antenna is as defined in claim 1. Brief Description of the Drawings The above object and other advantages of the present invention will become more apparent by by describing the preferred embodiment of the present invention with reference to the attached drawings, in which: FIG.1 is a flow chart showing a conventional automatic frequency tuning method; FIG.2 is a state diagram of frequency tuning according to the flow chart shown in FIG.1; FIG.3 is a diagram of a circuit for carrying out the flow chart shown in FIG.1; FIG.4 is a flow chart of an embodiment of the high speed automatic frequency tuning method according to the present invention; and FIG.5 is a state diagram of frequency tuning according to the flow chart shown in FIG.4. Detailed Description of the Invention With reference to FIG.4 which is a flow chart of the high speed automatic frequency tuning method of the present invention, a reference search frequency setting process is carried out in steps 400 and 401, and a tuning frequency search process is carried out in steps 402 to 408, and a compulsive tuning process corresponds to step 409. FIGS.5A and 5B are state diagrams of frequency tuning according to the flow chart shown in FIG.4, FIG.5A is a state diagram of frequency tuning when the reference search frequency fo is lower than an active broadcasting frequency, and FIG.5B is a state diagram of frequency tuning when the reference search frequency fo is higher than the active broadcasting frequency. Successively, the flow chart shown in FIG.4 will be described in conjunction with the circuit diagram shown in FIG.3 and the frequency tuning state diagram shown in FIG.5. The flowchart shown in FIG.4 is processed by microcomputer 300 of the diagram shown in FIG.3, and also microcomputer 300 of the diagram shown in FIG.3 processes the flow chart shown in FIG.4, when keyed data for channel information is received from key input means 310. And the flowcharted program shown in FIG.4 is stored in the ROM of microcomputer 300, and also the reference search frequencies fo for respective channels are stored in the ROM of microcomputer 300. The microcomputer 300 initiates a frequency increase number N assigned to one of its registers as "0", when keyed data for channel information selected by a viewer is input from the key input means 310 (in step 400). After processing step 400, microcomputer 300 reads out the reference search frequency fo corresponding to the channel information selected by the keyed input data among the reference search frequencies fo, for respective channel information stored in its ROM, and sets the read reference search frequency as a tuning control frequency ft, and then supplies the set tuning control frequency ft to the tuner 320 (in step 401). After carrying out step 401, the microcomputer 300 checks whether the frequency increase number N stored in one of its registers is equal to the limited increase number 32 (in step 402). When the frequency increase number N is not equal to the limited increase number 32 in step 402, the microcomputer 300 increases the frequency increase number N by "1" (in step 403). After processing step 403, microcomputer 300 compares the current logic state of the automatic frequency tuning signal entering from the demodulator 330 with that of the previous automatic frequency tuning signal assigned to its register, and when the compared logic states are different from each other, the completion of the tuning process is determined and completes the operation (in step 404). When the current logic state of the automatic frequency tuning signal is equal to that of the previous automatic frequency tuning signal in step 404, it is checked whether the logic state of the automatic frequency tuning signal entering from the demodulator 330 is in a high logic state, to determine whether the frequency of the radio frequency signal tuned by the tuning control frequency is higher than the active broadcasting frequency (in step 405). When the logic state of the automatic frequency tuning signal entering from the demodulator 330 is recognized as being in a high logic state via step 405, i.e. when the frequency of the radio frequency signal tuned by the tuning control frequency is higher than the active broadcasting frequency, microcomputer 300 sets the search direction mode flag X initially assigned to one of its registers as "-1" to a low band search mode (in step 406). When the logic state of the automatic frequency tuning signal entering from the demodulator 330 is recognized as being in a low logic state via step 405, i.e. when the the frequency of the radio frequency signal tuned by the tuning control frequency is lower than the active broadcasting frequency, microcomputer 300 sets the search direction mode flag X assigned to one of its registers as "1" to a high band search mode (in step 407). After carrying out step 406 or step 407, microcomputer 300 multiplies the frequency increase number N by a constant increase frequency of 0.0625 MHz, and then subtracts the product from the reference search frequency or adds the product to the reference search frequency according to the logic state of the search direction mode flag X set in step 406 or step 407 so as to set the tuning control frequency, and then supplies the set tuning control frequency to the tuner 320, and then goes back to the step 402 (in step 408). On the other hand, when the frequency increase number N is equal to the limited increase number 32 in step 402, microcomputer 300 sets the reference search frequency fo corresponding to the selected channel as a tuning control frequency ft, and then supplies the set tuning control frequency to the tuner 320, thereby completing the tuning operation (in step 409). In conclusion, the flow chart shown in FIG.4 checks whether the frequency of the radio frequency signal tuned by the reference search frequency corresponding to the channel information selected at the beginning is greater than the active broadcasting frequency, and then searches the broadcasting frequency by moving the tuning control frequency by a constant amount in one direction to the limited frequency fo± 2MHz of the low band as shown in FIG.5B or of the high band as shown in FIG.5A with respect to the reference search frequency. As described above, the present invention compares the magnitudes between the selected radio frequency signal frequency and the active broadcasting frequency, and tunes the active broadcasting frequency by moving the tuning control frequency in one direction of the low or high band directions with respect to the reference search frequency corresponding to the channel selected by the viewer according to the compared result, so that there is an advantage in reducing time needed to execute the automatic frequency tuning process.

Claims: A method for controlling a tuner in a video receiving apparatus for tuning a radio frequency signal from a plurality of radio frequency signals received through an antenna, comprising: a reference search frequency setting step for setting a reference search frequency (fo) corresponding to a broadcasting channel selected by a viewer as a tuning control frequency (ft) to enable the tuner to tune to a radio search frequency; a tuning frequency search step for making a determination of whether a frequency of the radio frequency signal tuned in by said tuner is greater than or less than a broadcasting frequency of the selected broadcasting channel, and moving the tuning control frequency (ft) within a predetermined number of frequency steps in one of an increasing direction and a decreasing direction from said reference search frequency (fo), until the frequency of the radio frequency signal tuned by the tuner is equal to the broadcasting channel, in dependence of said determination, to thereby enable the tuner to tune to the radio frequency signal corresponding to the tuning control frequency; and a compulsive tuning step for controlling said tuner to tune to the radio frequency signal of said reference search frequency corresponding to the selected broadcasting channel when the frequency of the radio frequency signal tuned by the tuner is not equal to the broadcasting frequency when the tuning control frequency reaches a limited frequency defined by the predetermined number of frequency steps in said tuning frequency search step.

Inventors: BAE TAE-SEOK, BAE, TAE-SEOK
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO. LTD.
Application year: 1991
Main classification: H04N5
IPC codes: H04B1, H03J7, H04N5, H03J1