Television receiver for teletext

Details Television receiver for teletext Television receiver for teletext

1996-09-26

2003-03-11

Harvey, David E. (Department: 2614)

Television

Nonpictorial data packet in television format

Including teletext decoder or display

C348S564000, C348S600000, C348S586000

Reexamination Certificate

active

06532041

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a television receiver for teletext for receiving a composite video signal having text information multiplexed on a television signal, and more particularly to a television receiver for teletext for displaying television video signal and teletext signal simultaneously on a picture screen by superimposing or dividing the screen.
Further particularly it relates to a television receiver for teletext for displaying a television video signal and teletext signal simultaneously on a screen of aspect ratio of 16:9 known as wide television.
FIG. 1
shows a schematic constitution of a television receiver for teletext of a prior art. In the diagram, reference numeral
11
is an input signal of demodulated composite video signal,
12
is a television video signal processing circuit for receiving a composite video signal and converting into a television signal a (signal of three primaries R, G, B),
13
is a teletext signal receiving circuit for extracting a teletext signal superposed in a vertical blanking period of input composite video signal to convert into teletext video signal b (signal of three primaries R, G, B), and generating a composite control signal (YS signal ) c synchronized with the teletext video signal b,
14
is a synthesizing circuit for superimposing a teletext video signal b from the teletext signal receiving circuit
13
for the television video signal a from the television video signal processing circuit
12
on the basis of the composite control signal (YS signal) c from the teletext signal receiving circuit
13
, and
15
is a display device such as CRT and LCD for displaying the composite video signal d.
The operation is described below. FIG.
2
(
a
) shows a television video signal a in part of one horizontal line, and FIG.
2
(
b
) shows a teletext video signal b in part of one horizontal line. FIG.
2
(
c
) shows a composite control signal (YS signal) c generated completely at same timing (in same time width) synchronously with the teletext video signal b.
The teletext video signal b, for example, at the timing of horizontal line
16
of letter “l” in FIG.
3
(
a
), produces two waveforms as shown in FIG.
3
(
b
). and the composite control signal (YS signal) c is generated at the same timing as the teletext video signal b as shown in FIG.
3
(
c
).
FIG.
2
(
d
) shows the composite video signal d having the television video signal a and teletext video signal b synthesized according to the composite control signal (YS signal) c. In the composite video signal d, the television video signal a is extracted at the timing of teletext video signal b.
FIG. 4
shows the detail of the teletext signal receiving circuit
13
in the television receiver for teletext. In this diagram, reference numeral
31
is a teletext signal decoder for extracting and decoding the teletext signal superposed in the vertical blanking period from the input composite video signal,
61
is a memory for storing decoded teletext data,
62
is a memory control circuit for controlling writing and reading of the memory
61
,
35
is a line memory for storing the teletext data for the portion of one horizontal line temporarily,
42
is a look-up table for converting the teletext data read out from the line memory
35
into color data of R, G, B, and
37
is a D/A converting circuit for converting the developed color data into analog video signal. Reference numeral
43
is an opaque color control signal generating circuit for receiving bit map data from the line memory
35
, generating YM signal (opaque color control signal), and issuing into a video chroma signal processing circuit
23
, and
44
is a changeover signal generating circuit of teletext signal/video chroma signal for receiving bit map data, generating YS signal (changeover signal of teletext signal/video chroma signal), and issuing into a switch
26
. By changing over the switch by the YS signal, both video chroma signal and teletext signal are displayed simultaneously on the picture screen. In the case of superimposed broadcast of YM signal, the background of the script is opaque, and in the case of teletext, not superimposed broadcast, the text is displayed and accompanied by foreground color and background color.
Furthermore,
FIG. 5
shows a constitution of a television receiver for teletext for explaining the prior art especially from the aspect of synchronizing signal. In this diagram, reference numeral
501
is an antenna, and
502
is a receiving circuit for receiving television broadcast wave and extracting a composite video signal of base band. The composite video signal from the receiving circuit
502
is supplied simultaneously also to a video chroma signal processing circuit
503
, a teletext signal receiving circuit
504
, and a synchronism separating circuit
505
. The video chroma signal processing circuit
503
is a circuit for demodulating the composite video signal, and extracting color signals of three primaries R, G, B, and the teletext signal receiving circuit
504
is a circuit for extracting the teletext signal superposed on the composite video signal, and converting into color signals of three primaries R, G, B. Reference numeral
506
is a double speed converting circuit for compressing the image of R, G, B signals from the video chroma signal processing circuit
503
by ½ in the horizontal direction, and
507
is a double speed converting circuit for compressing the image of R, G. B signals from the teletext signal receiving circuit
504
by ½ in the horizontal direction. These double speed converting circuits
506
,
507
are individually composed of three A/D converters for converting R. G, B signals into digital data, three line memories for storing the converted data and reading out at double speed of writing speed, and three D/A converters for converting the read data into analog R, G, B signals. Reference numeral
510
is a changeover circuit having a switch
508
and a switch
509
. The switch
508
is for changing over the signal from the double speed converting circuit
506
and the signal from the double speed converting circuit
507
at high speed in order to display the television video signal and teletext signal simultaneously, and the switch
509
is for selectively changing over the signal from the video chroma signal processing circuit
503
, the signal from the teletext signal receiving circuit
504
and the signal from the switch
508
. Reference numeral
511
is a picture tube drive circuit, and
512
is a picture tube.
The switches
508
,
509
in the changeover circuit
510
are designed to be changed over by a control signal from a controller
513
. The horizontal synchronizing signal and vertical synchronizing signal separated in the synchronism separating circuit
505
are respectively supplied into a horizontal deflection circuit
514
and a vertical deflection circuit
515
.
The signal generated by the double speed converting circuits
506
,
507
are compressed by ½ in the horizontal direction. On a wide screen of the picture tube
512
, when displaying both television video signal and teletext signal simultaneously, generally, the aspect ratio is 4:3 in both signals (see FIG.
6
). Accordingly, in both signals, the screen must be compressed also in the vertical direction, and a vertical amplitude changeover circuit
516
and a vertical screen position control circuit
517
are provided, and their outputs are supplied into the vertical deflection circuit
515
. The vertical amplitude changeover circuit
516
and vertical screen position control circuit
517
are designed to be controlled by the controller
513
. The vertical amplitude changeover circuit
516
reduces the amplitude of the sawtooth wave supplied to the vertical deflection circuit
515
. The vertical screen position control circuit
517
adds a direct-current voltage to the sawtooth wave reduced in amplitude, and the timing of the sawtooth wave is adjusted in the vertical direction.
As a result, as shown in
FIG. 6
, on the wide screen of

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