High speed automatic frequency tuning method

A high speed automatic frequency tuning method for effectively tuning a broadcasting frequency of a channel selected by a viewer by moving a tuning control frequency in one direction in either a high or low band direction of a reference search frequency, in accordance with the magnitudes between the reference search frequency and an active broadcasting frequency.

FIELD OF THE INVENTION 
The present invention relates to a method for controlling a tuner in a 
video receiving apparatus, and more particularly to a method for frequency 
tuning of a broadcasting frequency of a broadcasting channel 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 
air, such as a television, or 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 comprises amplitude of additional 
functions in order to increase the efficiencies of the processor in 
controlling the televisions and the VTRs as well as to accommodate the 
viewer's desire to have greater commands of the processor. 
Accordingly, the video receiving apparatus has been converted so that the 
tuning of a broadcasting frequency for a 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 in 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. A key input means 310 
which may be a keyboard, or a remote controlled receiver, etc. receives a 
key input data representative of an order for the function selected by a 
viewer, information about channels, and any other needed control 
information, and then transfers the key input data to the microcomputer 
300. After selecting an arbitrary radio frequency signal among a plurality 
of radio frequency (hereinafter, referred to as "RF") signals receiving 
through a 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 a 
demodulator 330. Then the demodulator 330 demodulates the intermediate 
frequency signal supplied from the tuner 320, supplies the demodulated 
video and audio signals to a 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 a 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 the RF 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 a 
connector OPT, and also outputs the radio frequency signal, received 
through an antenna ANT, through the connector OPT according to 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 to be 
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 the key input data for a channel information selected by a viewer is 
received from the key input means 310, the microcomputer 300 initiates a 
frequency search mode to enable a flag X assigned in one of its registers 
as "0" to set to 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 the processing step 100, the microcomputer 300 reads out a reference 
search frequency f.sub.o for channel information corresponding to the key 
input data among reference search frequencies for respective channel 
information stored in its ROM, and then sets the read reference search 
frequency f.sub.o as a reference tuning control frequency f.sub.to, 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 f.sub.to to set a tuning 
control frequency f.sub.t, 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, a completion 
of the tuning process is determined and the automatic frequency tuning 
operation is completed. 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 f.sub.to, 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 f.sub.o as a tuning control frequency 
f.sub.t 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 f.sub.o 
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 steps 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 of increments or decrements from 
the reference search frequency f.sub.o to each limited frequency f.sub.o 
.+-.2 MHz 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. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a high 
speed automatic frequency tuning method for frequency tuning of a 
broadcasting frequency of a broadcasting channel 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 an arbitrary a plurality of radio frequency band signal among 
radio frequency band signals received through an antenna, comprises: 
a reference search frequency setting step for setting a reference search 
frequency corresponding to a broadcast channel selected by a viewer, 
thereby enabling a tuner to tune the radio frequency signal of the 
reference search frequency; 
a tuning frequency search step for checking whether the frequency of the 
radio frequency signal tuned in the reference search frequency setting 
step is greater than the broadcast radio frequency of a selected 
broadcasting channel, and moving the reference search frequency toward a 
limited frequency of either a low or a high band by a constant frequency 
until the frequency of the radio frequency signal tuned in the tuner is 
equal to the broadcasting radio frequency according to the result of the 
checking process and then enabling the tuner to tune to the radio 
frequency signal corresponding to a new reference search frequency; and 
a compulsive tuning step for controlling the tuner so as to tune the radio 
frequency signal of a reference search frequency corresponding to the 
broadcasting radio frequency selected in the reference search frequency 
setting step when the frequency of the radio frequency signal tuned by the 
tuner is not equal to the active broadcasting frequency, until the 
reference search frequency moves to the limited frequency in the tuning 
frequency search step.

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 the frequency tuning according to the 
flow chart shown in FIG. 4. FIG. 5A is a state diagram of the frequency 
tuning when the reference search frequency f.sub.o is lower than an active 
broadcasting frequency, and FIG. 5B is a state diagram of the frequency 
tuning when the reference search frequency f.sub.o 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 the microcomputer 300 as 
shown in FIG. 3, when the key input data for a channel information is 
received from a key input means 310. A flowchart program shown in FIG. 4 
is stored in a ROM of the microcomputer 300. Similarly reference search 
frequencies fo for respective broadcasting channels are stored in the ROM 
of the microcomputer 300. 
The microcomputer 300 initiates a frequency increase number N assigned to 
one of its registers as "0", when the key input data for a channel 
information selected by a viewer is input from the key input means 310 (in 
step 400). 
After the processing step 400, the microcomputer 300 reads out the 
reference search frequency f.sub.o corresponding to the channel 
information selected by the key input data among a plurality of reference 
search frequencies f.sub.o, for respective channel information stored in 
its ROM, and sets the read reference search frequency as a tuning control 
frequency f.sub.t, and then supplies the set tuning control frequency 
f.sub.t to the tuner 320 (in step 401). 
After performing step 401, 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 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 the processing step 403, the 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. If the compared logic states are different from each other, the 
tuning operation is completed (in step 404). 
When the logic state of the current 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 
in order to determine whether the frequency of the radio frequency signal 
tuned by the tuning control frequency is higher than an active 
broadcasting frequency (in step 405). 
When the logic state of the automatic frequency tuning signal entering from 
the demodulator 330 is recognized as 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, the 
microcomputer 300 sets a 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 a low logic state via step 405, i.e. 
when the frequency of the radio frequency signal tuned by the tuning 
control frequency is lower than the active broadcasting frequency, the 
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 performing step 406 or step 407, the 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, the microcomputer 300 sets the 
reference search frequency f.sub.o corresponding to the selected 
broadcasting channel as a tuning control frequency f.sub.t, 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 a radio frequency signal tuned by a tuning control frequency 
corresponding to a channel information selected at the beginning is 
greater than an active broadcasting frequency, and then searches the 
active broadcasting frequency by moving the tuning control frequency by a 
constant amount in one direction to the limited frequency f.sub.o .+-.2 
MHz 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 frequency of a radio frequency signal 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 with 
respect to the reference search frequency corresponding to the channel 
selected by the viewer according to the compared result, so that an amount 
of time needed to execute the automatic frequency tuning process can be 
reduced.