U.S. patent application number 08/579156 was filed with the patent office on 2003-04-10 for dual hdtv/ntsc receiving method using symbol timing recovery and sync signal detection and apparatus thereof.
Invention is credited to HAN, DONG-SEOG.
Application Number | 20030067555 08/579156 |
Document ID | / |
Family ID | 19404021 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030067555 |
Kind Code |
A1 |
HAN, DONG-SEOG |
April 10, 2003 |
DUAL HDTV/NTSC RECEIVING METHOD USING SYMBOL TIMING RECOVERY AND
SYNC SIGNAL DETECTION AND APPARATUS THEREOF
Abstract
A dual HDTV/NTSC receiver for recovering one of a HDTV signal
and a NTSC signal coexisting in a desired channel includes a tuning
unit for converting a desired one of HDTV signals and NTSC signals
into an intermediate frequency (IF) signal, a sync detector,
coupled to receive the IF signal for detecting a sync signal of the
NTSC signal, a timing recovery unit, coupled to receive the IF
signal for self-recovering symbol timing of the applied HDTV
signal, and providing a symbol timing lock signal corresponding to
the IF signal and an analog-to-digital converted HDTV signal, a
controller for judging whether a currently received television
signal is either a NTSC signal or a HDTV signal based on the sync
detection result of the sync detector and the symbol timing lock
signal from the timing recovery unit, and for outputting a control
signal according to the determination result, and a tuning
controller for initially controlling the tuning unit so that one
desired HDTV signal is received, and for subsequently controlling
the tuning unit on the basis of the signal selected by the control
signal among respective HDTV and NTSC signals output, respectively,
from the tuning unit and the timing recovery unit. The receiver
automatically determines whether a received signal is the NTSC
signal or the HDTV signal.
Inventors: |
HAN, DONG-SEOG;
(ANYANG-CITY, KR) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20037
|
Family ID: |
19404021 |
Appl. No.: |
08/579156 |
Filed: |
December 27, 1995 |
Current U.S.
Class: |
348/558 ;
348/554; 348/725; 348/E5.017; 348/E5.114 |
Current CPC
Class: |
H04N 5/08 20130101; H04N
5/46 20130101; H04N 21/42638 20130101 |
Class at
Publication: |
348/558 ;
348/554; 348/725 |
International
Class: |
H04N 005/46 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1994 |
KR |
94-37542 |
Claims
What is claimed is:
1. A receiver for selectively receiving one of a HDTV television
signal and a NTSC television signals coexisting in a plurality of
television channels, the apparatus comprising: tuning means for
converting a desired one of said HDTV and said NTSC signals into an
intermediate frequency signal; sync detection means, coupled to
receive said intermediate frequency signal output from said tuning
means, for detecting a sync signal of the NTSC signal; timing
recovery means, coupled to receive the intermediate frequency
signal output from said tuning means, for self-recovering symbol
timing of an applied HDTV signal, and outputting a symbol timing
lock signal and an analog-to-digital converted HDTV signal; control
means for judging whether a currently received television signal is
said NTSC signal or said HDTV signal based on the sync detection
result of said sync detection means and the symbol timing lock
signal from said timing recovery means, and for outputting a
control signal according to a respective determination result; and
tuning control means for initially controlling said tuning means so
that the desired HDTV signal is received, and for subsequently
controlling said tuning means on the basis of the respective signal
selected by said control signal among said HDTV and NTSC signals
output from said tuning means and said timing recovery means.
2. The receiver as claimed in claim 1, wherein said timing recovery
means comprises: a band converter for converting the intermediate
frequency signal output from said tuning means into a base band
signal; an A/D converter for sampling and analog-to-digital
converting the base band signal output from said band converter,
according to an applied clock signal; and symbol timing recovery
unit for recovering symbol timing based on the output signal of
said A/D converter, and supplying the symbol timing recovered clock
signal to said A/D converter, so as to sample the HDTV signal
corresponding to the base band signal.
3. The receiver as claimed in claim 2, wherein said band converter
comprises: a local oscillator for producing an oscillation
frequency signal; and a mixer for mixing the intermediate frequency
signal of said tuning means with the oscillation frequency signal
of said local oscillator so as to convert the HDTV signal into said
base band signal.
4. The receiver as claimed in claim 2, wherein said A/D converter
samples the base band signal at a frequency which is an integer
multiple of a respective symbol transmission rate in said HDTV
signal.
5. The receiver as claimed in claim 2, wherein said symbol timing
recovery means comprises: a timing error information generator for
generating error information between an optimized sampling point in
time and a sampling point in time of the HDTV signal supplied from
said A/D converter; a loop filter, receiving the error information
from said timing error information generator, for generating a
control voltage; a lock detector for monitoring said error
information output by said timing error information generator and
said control voltage output by said loop filter and for generating
a symbol timing lock signal corresponding to a monitoring result;
and a clock generator for generating a clock signal having an
oscillation frequency which is varied according to said control
voltage of said loop filter.
6. The receiver as claimed in claim 5, wherein operational
characteristics of said loop filter at an (n+1)-th point in time
are represented by the following equation: 2 s ( n + 1 ) = { s ( n
) - 1 P n ( 1 s t ) s ( n ) - 1 P n - 2 k = 1 n P k ( 2 n d ) where
.tau..sub.s(n+1) and .tau..sub.s(n) are output signals of said loop
filter at said (n+1)-th and n-th points in time, respectively,
P.sub.n and P.sub.k are error information, and respective first and
second cases represent the operation of said loop filter in first
phase locked loop (PLL) and second PLL modes of operation,
respectively.
7. The receiver as claimed in claim 5, wherein said lock detector
generates the symbol timing lock signal indicating that sampling is
carried out at the optimized point of time, when an average value
of said error information is about "O" or the control voltage of
the loop filter is substantially constant.
8. The receiver as claimed in claim 5, wherein said clock generator
generates a clock signal having a frequency which is an integer
multiple of the symbol transmission rate in said HDTV signal.
9. The receiver as claimed in claim 1, wherein said control means
determines that the currently received television signal is said
HDTV signal when the symbol timing lock signal is supplied from
said timing recovery means, and determines that the currently
received television signal is said NTSC signal when a horizontal
sync signal or a vertical sync signal is supplied from said sync
detector.
10. The receiver as claimed in claim 1, wherein said tuning control
means comprises: a first frequency phase sync loop circuit, coupled
to receive the output signal of said tuning means, for judging
whether the carrier of a desired said NTSC signal is exactly
recovered and generating a first correcting value of frequency
error according to a judgement result; a second frequency phase
sync loop circuit, coupled to receive the analog-to-digital
converted said HDTV signal of said timing recovery means, for
judging whether a carrier of a desired said HDTV signal is exactly
recovered and generating a second correcting value of frequency
error according to the judgement result; a switching unit for
selecting the correcting values of respective frequency errors
applied from said first and second frequency phase sync loop
circuits according to the control signal of said control means; and
a microprocessor for controlling said tuning means based on the
selected one of said first and said second correcting values
supplied from said switching unit.
11. The receiver as claimed in claim 1, wherein said receiver
further comprises display means for displaying that no receivable
signal is in the selected channel, in the case that the control
signal of said control means indicates that neither said HDTV
signal nor said NTSC signal are in said selected channel.
12. A method of receiving a signal of a desired channel in
HDTV/NTSC television receiver, the method comprising the steps of:
(a) initially tuning a receiving signal to correspond to a HDTV
signal of the desired channel and converting the tuned signal into
an intermediate frequency signal; (b) attempting a self-recovery
operation with respect to symbol timing using the intermediate
frequency signal generated during said step (a) and generating a
first signal indicating a respective self-recovery result; (c)
tuning a receiving signal corresponding to an NTSC signal of the
desired channel and converting the tuned signal into an
intermediate frequency signal, when said self-recovery operation is
not accomplished during said step (b); (d) detecting one of
horizontal and vertical sync signals of the NTSC signal using the
intermediate frequency signal generated during said step (c), and
generating a second signal indicative of a respective detection
result; and (e) continuously receiving one of the HDTV signal when
said first signal indicates that symbol timing is self-recovered,
and continuously receiving the NTSC signal when said second signal
indicates that one of said horizontal and said vertical sync
signals is detected.
13. The method as claimed in claim 12, wherein said step (b)
comprises the step of judging whether the self-recovery of symbol
timing is accomplished after a predetermined time period has
elapsed.
14. The method as claimed in claim 12, wherein said step (d)
comprises the step (d) of judging whether one of said horizontal or
said vertical sync signals is detected after a predetermined time
period.
15. The method as claimed in claim 12, wherein said method further
comprises the step (f) of iterating said steps (a) to (e) when said
first signal indicates no self-recovery and said second signal
indicates no detection of one of said horizontal and said vertical
sync signals.
16. The method as claimed in claim 15, wherein said method further
comprises the step (g) of displaying that no receivable signal is
in the selected channel, in the case that neither said
self-recovery operation of the symbol timing is achieved nor one of
said horizontal and said vertical sync signals is detected after
performing said step (f) a predetermined number of times.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a high definition
television (HDTV) receiver and, more particularly, to a HDTV
receiver that is also capable of receiving NTSC signals.
[0003] The instant application is based on Korean Patent
Application No. 94-37542, which is incorporated herein by reference
for all purposes.
[0004] 2. Brief Discussion of Related Art
[0005] Recently, the United States has elected the 8-VSB (Vestigial
Side Band) modulation method as the designated method for HDTV
transmission. It will be noted that HDTV broadcasting is initially
planned to be put into service together with a conventional NTSC
broadcasting. Thus, the HDTV receiver will be required to have a
function capable of receiving both HDTV signals and conventional
NTSC signals.
[0006] A dual-mode receiver for receiving HDTV signals and NTSC
signals has been developed which is capable of processing the
received signals by a HDTV or NTSC method according to a user's
selection. One such receiver, which is disclosed in U.S. Pat. No.
5,283,653 entitled "DUAL HDTV/NTSC RECEIVER USING SEQUENTIALLY
SYNTHESIZED HDTV AND NTSC CO-CHANNEL CARRIER FREQUENCIES" to Citta
(Feb. 1, 1994) includes a dual HDTV/NTSC television receiver able
to automatically select an appropriate signal when tuned to a
selected television channel. This receiver selectively receives
HDTV and NTSC television signals in one channel, among a plurality
of channels, in which HDTV signals are of an inherently lower power
than the co-channel NTSC signals. A tuner in the receiver initially
synthesizes a carrier frequency associated with the HDTV signal of
the selected channel, and a narrow band sync detector detects the
HDTV signal using the synthesized HDTV carrier frequency. A
microprocessor enables further processing of either the HDTV signal
or the NTSC according to the detection result of the HDTV
signal.
[0007] The present invention was motivated by a desire to provide
an improved HDTV/NTSC receiver while avoiding the problems inherent
in the conventional receiver discussed above.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a novel
HDTV/NTSC receiver using symbol timing recovery and a sync signal
detection.
[0009] Another object of the present invention is to provide a
method of receiving both HDTV signals and NTSC signals using symbol
timing recovery and sync signal detection.
[0010] These and other objects, features and advantages according
to the present invention are provided by a receiver for selectively
receiving HDTV television signals and NTSC television signals in a
plurality of television channels. Preferably, the receiver
includes:
[0011] a tuning unit for converting a desired one of HDTV signals
and NTSC signals into an intermediate frequency signal;
[0012] a sync detector, coupled to receive the intermediate
frequency signal output from the tuning unit, for detecting a sync
signal of the NTSC signal;
[0013] a timing recovery unit, coupled to receive the intermediate
frequency signal output from the tuning unit, for self-recovering
symbol timing of the applied HDTV signal, and outputting a symbol
timing lock signal and an analog-to-digital converted HDTV
signal;
[0014] a controller for judging whether the currently received
television signal is either a NTSC signal or a HDTV signal based on
the sync detection result of the sync detector and the symbol
timing lock signal from the timing recovery unit, and for
outputting a control signal according to the determination result;
and
[0015] a tuning controller for initially controlling the tuning
unit so that one desired HDTV signal is received, and for
subsequently controlling the tuning unit on the basis of the signal
selected by the control signal among respective signals output from
the tuning unit and the timing recovery unit.
[0016] These and other objects, features and advantages according
to the present invention are provided by a method of receiving a
signal of a desired channel in HDTV/NTSC television receiver.
Advantageously, the method includes steps for:
[0017] (a) initially tuning a receiving signal to accept an HDTV
signal of a desired channel and converting the tuned signal into an
intermediate frequency signal;
[0018] (b) performing a self-recovery operation of symbol timing
using the intermediate frequency signal generated during step (a)
and generating a signal indicating a respective self-recovery
result;
[0019] (c) tuning a receiving signal to accept a NTSC signal of the
desired channel and converting the tuned signal into an
intermediate frequency signal, if self-recovery operation of symbol
timing is not accomplished during step (b);
[0020] (d) carrying out detection of the horizontal/vertical sync
signal of the NTSC signal using the intermediate frequency signal
generated in step (c), and providing a signal indicative of a
detection result; and
[0021] (e) continuously receiving the HDTV signal when the
self-recovery result signal indicates that symbol timing is
self-recovered, and continuously receiving the NTSC signal when the
detection result signal indicates that the horizontal/vertical sync
signal is detected.
[0022] These and other objects, features and advantages of the
invention are disclosed in or will be apparent from the following
description of preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The preferred embodiments are described with reference to
the drawings in which:
[0024] FIG. 1 is a high level block diagram showing a dual
HDTV/NTSC receiver in accordance with a preferred embodiment of the
present invention;
[0025] FIG. 2 is a high level block diagram illustrating an
exemplary internal structure of a symbol timing recovery unit which
is usable in the HDTV/NTSC receiver of FIG. 1; and
[0026] FIG. 3 is a flow chart for illustrating an operation the
apparatus of FIG. 1, with particular emphasis on the operation of a
mode controller depicted in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] A preferred embodiment of the present invention will be
described below in more detail with reference to the accompanying
drawings of FIGS. 1 to 3.
[0028] It will be appreciated that HDTV signals are suppressed so
that video and audio information can be transmitted in frequency
bands of 6 MHz for every channel. The HDTV signals provided by the
transmitter are randomized for signal power, so as to be uniformly
distributed in the television channel broadcasting bands of 6 MHz.
This randomization makes a receiver perform a channel equalization
operation, the randomized signal advantageously allows the receiver
to recover symbol timing using a self-timing recovery
procedure.
[0029] In the case of the HDTV signal according to the U.S.
standard, i.e., the 8-VSB modulation method, a separate segment
sync signal for symbol timing recovery and a reference signal
having a constant frequency for carrier recovery are transmitted
together with data. Preferably, the segment sync signal of four (4)
bits is inserted between each 828 data symbols. Thus, the HDTV
receiver can be tuned to frequencies of the input HDTV signal using
the segment sync signal and reference signal. However, since a HDTV
signal is transmitted at a low power level when compared with the
NTSC signal, at the initial operation of the system, detection of
the segment sync signal and the reference signal may be difficult.
Therefore, almost complete recovery for the carrier from the low
power HDTV signal should be carried out first. The more complete
the recovery of carrier is, the more accurate the symbol timing
recovery can be.
[0030] It should be noted that, in order to shorten an initializing
time of the HDTV receiver, it is advantageous to, in the first
place, adopt self-timing recovery by a symbol timing recovery unit
rather than a sync signal. It will be appreciated that the NTSC
signal is formatted so that the HDTV receiver can not extract data
of the transmission rate of the HDTV signal from the NTSC signal
passed through the symbol timing recovery unit. Accordingly, it is
impossible that symbol timing recovery unit can be stably operated.
The present invention proposes a dual receiver capable for
receiving HDTV and NTSC signals, which automatically detects the
type of signal source and determines an optimal receiving mode
based on the difference of HDTV signals and NTSC signals.
[0031] It should be noted that a preferred embodiment of the
present invention employs symbol timing recovery unit having a
self-timing recovery operation. Of course, it is possible to
develop an alternative embodiment of the dual HDTV/NTSC receiver
employing monitoring of the operation of symbol timing recovery
unit using the segment sync signal.
[0032] Turning now to the figures, FIG. 1 shows the dual HDTV/NTSC
receiver in accordance with a preferred embodiment of the present
invention. A tuner 1 of FIG. 1 advantageously receives a
broadcasting signal of a desired channel among UHF/HF broadcasting
signals and converts it to an intermediate frequency (IF) signal. A
microprocessor 2 selects a channel that is to be output by tuner 1
while also controlling the ancillary operations of tuner 1. The IF
signal output by tuner 1 is applied to a surface acoustic wave
(SAW) filter 3, which exactly filters the IF signal to produce a
signal having 6 MHz band width. An intermediate frequency (IF)
amplifier 4 advantageously controls the gain of the filtered IF
signal input from SAW filter 3 according to the output signal from
a NTSC signal processing unit 6 or a HDTV signal processing unit 12
feedback via a second switch 18, and outputs a signal amplified to
an appropriate level. Output signals from IF amplifier 4 are
supplied to a horizontal/vertical sync detector 5, mixer 9 and NTSC
frequency phase locked loop (FPLL) circuit 15, respectively. It
will be appreciated that the above described tuner 1, SAW filter 3
and IF amplifier 4 can be used for processing both HDTV signals and
NTSC signals.
[0033] Horizontal/vertical sync detector 5 detects horizontal and
vertical sync signals from the output signal of IF amplifier 4, and
signals a mode controller 14 whether a sync signal is detected or
not. In case that the received signal is a NTSC signal,
horizontal/vertical sync detector 5 denotes the detection of the
sync signal to mode controller 14. NTSC signal processing unit 6
processes the output signal of horizontal/vertical sync detector 5
so that the output signal can be displayed on a monitor 7, and
outputs the processed signal via a first switch 17. FPLL circuit 15
for recovering a carrier of the NTSC signal receives the output
signal of IF amplifier 4, judges whether a carrier signal of the
desired channel is accurately recovered, and outputs a correcting
value of frequency error as the judgement result to a third switch
19.
[0034] Preferably, mixer 9 multiplies the output signal of IF
amplifier 4 by an oscillation signal having a constant frequency
from a local oscillator 8. It should also be noted that mixer 9 can
alter the output signal of intermediate frequency amplifier 4 to a
signal about the base band through frequency band conversion, so
that full digital signal processing for the HDTV signal can be
performed. Local oscillator 8 has a fixed oscillation frequency. A
low pass filer (LPF) 10 removes unnecessary frequency components
from the output signal of mixer 9.
[0035] An analog-to-digital converter 11 samples a HDTV signal of
the base band output from LPF 10 under the control of symbol timing
recovery unit 13. Since the symbol transmission rate Fs of the HDTV
signal is about 10.76 MHz, A/D converter 11 samples the input
signal about the base band responsive to frequency NFs, i.e.,
integer N times of symbol transmission rate Fs. The output signal
of A/D converter 11 advantageously is applied to symbol timing
recovery unit 13, HDTV signal processing unit 12 and HDTV FPLL
circuit 16, respectively. Symbol timing recovery unit 13 receives
the sampled HDTV signal and designates a sampling point to be used
by A/D converter 11 in order to sample the input signal in the same
interval and phase as that occurring at the transmitter. Detailed
construction and operation of symbol timing recovery unit 13 will
now be described with particular reference to FIG. 2.
[0036] Referring to symbol timing recovery unit 13 of FIG. 2,
timing error information generator 20 calculates an error between
an optimized sampling point of time and a sampling point of time of
the sampled HDTV signal supplied from A/D converter 11. The
calculation result, i.e., error information Pn is advantageously
individually applied to a loop filter 21 and a symbol timing lock
detector 22. Loop filter 21 is employed for filtering the input
error information P.sub.n, and preferably includes a phase locked
loop (PLL) circuit (not shown). Characteristics of loop filter 21
may be represented by the following equation: 1 s ( n + 1 ) = { s (
n ) - 1 P n ( 1 s t ) s ( n ) - 1 P n - 2 k = 1 n P k ( 2 n d )
[0037] where .tau..sub.s(n+1) and .tau..sub.s(n) are output signals
of the loop filter at (n+1)-th point of time and n-th points in
time, respectively, P.sub.n and P.sub.k are error information, and
the first and second cases represent the operation of loop filter
of the first PLL and second PLL in (n+1)-th point of time,
respectively. The output signal .tau..sub.n of loop filter 21 is
supplied to both symbol timing lock detector 22 and a voltage
controlled oscillator (VCO) 23, respectively. Symbol timing lock
detector 22 monitors either the output signal P.sub.n of timing
error information generator 20 or the output signal .tau..sub.n of
loop filter 21, and judges whether the symbol timing recovery is
successfully made according to the variation degree of each value.
More specifically, if an average value of the output signal P.sub.n
of timing error information generator 20 is about "O" or the output
signal .tau..sub.n of loop filter 21 is constant without variation,
symbol timing lock detector 22 determines that sampling is made at
the optimized point and outputs the symbol timing lock signal. VCO
23 outputs an analog sine wave signal having an oscillation
frequency which is varied according to the output signal
.tau..sub.n of loop filter 21. A clock generator 24, which is
connected to an output terminal of VCO 23, compares the sine wave
signal with a reference signal and outputs a clock signal of
frequency NFs, i.e., integer N times the symbol transmission rate
Fs, to A/D converter 11, as previously described.
[0038] Referring again to FIG. 1, HDTV signal processing unit 12
receives the HDTV signal sampled by A/D converter 11, and processes
it for display on monitor 7 by output of the processed signal via
first switch 17. HDTV FPLL circuit 16, which is a circuit for
recovering a carrier of the HDTV signal, receives the output signal
of A/D converter 11, judges whether a carrier signal of a desired
channel is accurately recovered, and outputs a correcting value
representing frequency error.
[0039] Mode controller 14, which is preferably coupled to output
terminals of horizontal/vertical sync detector 5 and symbol timing
recovery unit 13, determines whether the receiver is to be operated
in either a HDTV mode or a NTSC mode. The determination depends on
whether a sync signal and a symbol timing lock signal are input or
not, and control signals based on such determination are supplied
to first through third switches 17-19. Of these first through third
switches 17-19, first switch 17 is coupled to selectively supply
the output signal of either NTSC signal processing unit 6 or HDTV
signal processing unit 12 to monitor 7. Second switch 18 is coupled
to selectively output the output signal of either NTSC signal
processing unit 6 or HDTV signal processing unit 12 to intermediate
frequency amplifier 4. Third switch 19 is connected to selectively
output the output signal of either NTSC FPLL circuit 15 or HDTV
FPLL circuit 16 to microprocessor 2, which controls the oscillation
frequency of tuner 1 in response to the correcting value of a
frequency error value supplied from NTSC FPLL circuit 15 or HDTV
FPLL circuit 16.
[0040] The operation of the FIG. 1 apparatus will now be described
in more detail with reference to the flow chart of FIG. 3 showing
the signal processing process of mode controller 14.
[0041] When the FIG. 1 apparatus initially operates according to
the supply of system power, mode controller 14 controls first to
third switches 17-19 so that the HDTV mode is `on` and the NTSC
mode is `off` (step 101). During step 101, first and second
switches 17 and 18 select the output of HDTV signal processing unit
12, and third switch 19 chooses that of HDTV FPLL circuit 16. At
this time, microprocessor 2 controls tuner 1 so that it is tuned
for the recovery of the HDTV signal from the selected channel.
[0042] Symbol timing recovery unit 13 performs the self-recovery
operation of symbol timing. By this operation, when the data
transmitted at transmission rate Fs has a randomized
characteristic, symbol timing can be exactly extracted within
hundreds and thousands of symbols.
[0043] The symbol timing lock signal representative of the result
of self-recovery is applied to mode controller 14 (step 102). Mode
controller 14 judges whether the HDTV signal is input, based on the
input symbol timing lock signal, and thereby judges whether the
symbol timing lock signal is input from symbol timing recovery unit
13, after a predetermined time T1 during step 103, at step 104.
When it is judged that the symbol timing lock signal is present at
step 104, mode controller 14 judges that symbol timing recovery
unit 13 has stabilized and controls switches 17-19 in order to
receive the HDTV signal continuously (step 105). During step 104,
if the symbol timing lock signal is absent, mode controller 14
controls first to third switches 17-19 so that the NTSC mode is
`on` and the HDTV mode is `off` (step 106). During step 106, first
and second switches 17 and 18 select the output of NTSC signal
processing unit 6 and third switch 19 chooses that of NTSC FPLL
circuit 15. Mode controller 14 judges the presence or absence of
the NTSC signal based on whether a horizontal or vertical sync
signal from horizontal/vertical sync detector 5 is present or not.
When a predetermined time T2 expires during performance of step
107, it is judged whether the horizontal or vertical sync signal is
input following the preset time T2 (step 108). At step 108, if the
horizontal or vertical sync signal is present, mode controller 14
controls switches 17-19 in order to receive the NTSC signal
subsequently. If the horizontal or vertical sync signal is not
detected at step 108, a set of the above processes (steps 101-108)
are iterated, after determining as the NTSC signal is not present.
During step 110, when the number of iteration times becomes `N`,
mode controller 14 determines that no signal is received and takes
a set of predetermined actions, such as displaying information
indicating that no signal has been received on a screen (step
111).
[0044] As described above, the present invention automatically
determines whether a receiving television signal is either a NTSC
signal or a HDTV signal to thereby improving convenience to the
user, based on symbol timing self-recovered from the received HDTV
signal and a sync signal detected from the received NTSC signal.
Particularly, as the receiving signal is automatically determined,
receivable signals with respect to the whole channels can be stored
in advance in memory when setting up the television receiver. The
apparatus of the present invention provides an effect that no
checking process as to the receiving signal is input with regard to
each channel, is required, whenever the user turns on the
system.
[0045] While only certain embodiments of the invention have been
specifically described herein, it will apparent that numerous
modifications may be made thereto without departing from the spirit
and scope of the invention.
* * * * *