JPH0551232B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a teletext receiver with a built-in TV (television receiver).

``Prior Art'' In general, in this type of teletext receiver, the teletext signal is greatly affected by the frequency characteristics of the TV tuner. For example, if the frequency characteristics of a TV tuner deteriorate, a phase shift or amplitude fluctuation of the character signal will occur, causing the character signal to be distorted from the normal value shown by the solid line P in Figure 3a to the dotted line Q, and to the character signal shown in Figure 3b. In the sampling at the rising edge of the extraction clock shown in FIG. 2, the noise margin N becomes small and correct teletext data cannot be extracted. If the frequency characteristics of the TV tuner deteriorate in this way (particularly in the high frequencies), it will be difficult to receive teletext by simply making minor adjustments within the range that does not affect the receiving screen of all TV broadcast channels. was making fine adjustments to the TV tuner for each selected channel.

``Problems to be Solved by the Invention'' As described above, in the past, the TV tuner had to be finely adjusted for each selected channel, which caused the problem that the adjustment was complicated.

An object of the present invention is to obtain a teletext receiver with a built-in TV that automatically makes fine adjustments to the TV tuner.

"Means for Solving Problems" The present invention provides a receiver that extracts teletext data from a television video signal tuned and received by a TV tuner 1, and receives the teletext data. An error rate detection circuit 6 which doubles as an error correction circuit detects the error rate, which is data D on the number of errors occurring in one packet of 296 bits, and data D on the number of errors detected by the error rate detection circuit 6.
and the allowable error occurrence data _D0 set in advance for 8 bits out of 296 bits of one packet.
The teletext receiver with a built-in TV is characterized in that it includes a local oscillation control circuit 9 that also functions as an image processing MPU and controls the local oscillation frequency of the TV tuner 1 in a direction that reduces the error rate.

"Function" When the frequency characteristics of the TV tuner 1 deteriorate and the error rate of extracted teletext data increases, the local oscillator control circuit 9 controls the local transmission of the TV tuner 1 based on the detection output of the error rate detection circuit 6. The oscillation frequency is controlled to be higher or lower, and feedback control is performed in the direction in which the detection output of the error rate detection circuit 6 becomes smaller (that is, in the direction in which the error rate becomes smaller).

Embodiment FIG. 1 shows an embodiment of the present invention, and in this figure, 1 is a TV tuner. This TV
The tuner 1 includes an input circuit 42 that amplifies a high frequency signal input from an antenna 41, and a local oscillation circuit 4.
3 and a mixing/detecting circuit 44. The output side of the mixing/detecting circuit 44 is coupled to a synchronizing signal generating circuit 3 and a data clock generating circuit 4 via a waveform equalizing circuit 2.

An error correction circuit (BEST) 6 is connected to the output side of the data clock generation circuit 4 via an interface 5, and this error correction circuit 6 is connected to a packet buffer 7 for temporarily storing program data and a bus buffer. 8 are combined.

9 is an MPU for image processing;
9, a program ROM 11 for teletext broadcasting, a memory 12 for storing program data for teletext broadcasting, a CGROM 16, a printer interface 17, a melody processing MPU 18,
A CRTC 19 and a system control MPU 20 are coupled to each other.

The error correction circuit 6 includes an error rate detection circuit that detects the error rate of the teletext data extracted by the data clock generation circuit 4 (for example, data D on the number of errors occurring in one packet (296 bits)). Also used for the image processing via the signal line 13
It is configured to output error occurrence number data D to the MPU 9.

The image processing MPU 9 transmits the data to the TV based on the error occurrence number data D via the signal line 13.
A local oscillation control circuit is provided which controls the local oscillation frequency (hereinafter simply referred to as local oscillation frequency) of the local oscillation circuit 43 of the tuner 1 and performs feedback control in a direction in which the error occurrence number data D becomes smaller.

The image processing MPU 9 is connected to an interrupt circuit 21, the printer interface 17 is connected to an external printer 22, and the melody processing MPU 18 is connected to buffer data.
The RAM 23 and the FM sound source circuit 24 are combined, and the
A V-RAM 26 is coupled to the CRTC 19, and the output side of the FM sound source circuit 24 and the CRTC 19 are coupled to a TV connection terminal 28 via a TV interface 25.

The system control MPU 20 is coupled to a light receiving section 31 of a memo controller 30, and is also connected to a system reset output terminal 32 and a power on/off terminal 33.

Next, the operation of the above embodiment will be explained with reference to FIG. 2.

(a) The television video signal received by the TV tuner 1 is guided to the data clock generation circuit 4 via the waveform equalization circuit 2. The data clock generation circuit 4 extracts the character signal, converts it into a digital signal, and sends it to the error correction circuit 6 via the interface 5 as teletext data. The teletext data whose errors have been corrected by the error correction circuit 6 is sequentially stored in the program data storage memory 12 by the image processing MPU 9.

(b) Next, when the desired teletext program is selected using the remote control 30, the program selection number data is sent to the image processing MPU 9 via the light receiving unit 31 and the system control MPU 20, and the program selection number data is sent to the image processing MPU 9.
The program data of the selected program is read out from the memory 12 by the MPU9, and CRTC19 and
The image signal is output from the TV connection terminal 28 to the TV via the TV interface 25.

(c) The local oscillation frequency of the local oscillation circuit 43 of the TV tuner circuit 1 when receiving the above teletext broadcast is set as an initial value.

(d) Next, the image processing MPU 9 connects the signal line 13
The error occurrence number data D sent via the error occurrence number data D is checked to determine whether this D is greater than the allowable error occurrence number data _D0 . Here, D ₀ is a number that is greater than or equal to the number of bits that can be error corrected in the error correction circuit 6 (for example, 8 bits when errors can be corrected up to 8 bits in one packet (296 bits)) and is the allowable number of error occurrences. Set to data.

(E) Now, when the frequency characteristics of the TV tuner circuit 1 deteriorates and D>D ₀ , the question "Are there many errors?" becomes "YES", and the local oscillation circuit 43 is activated by the control signal from the image processing MPU 9. Increase the local frequency by one step (one step is a small frequency set in advance for fine adjustment).

(F) The image processing MPU 9 compares the data D based on this increased local oscillation frequency with the data D based on the immediately previous local oscillation frequency, and if the former is smaller, it asks "Has the error rate decreased?""YES"
Therefore, it is determined whether the local oscillation frequency is further increased by one step and the error rate is reduced.

(g) If the error rate is reduced by the above (f),
Repeat the operation in (f) above until the error rate becomes large, and when the error rate becomes large, reduce the local oscillation frequency by 1.
The value is decreased in steps and fixed at an optimal value that also satisfies D<D ₀ .

(H) In the comparison in (F) above, if the data D due to the increased local oscillation frequency is larger than the data D due to the previous local oscillation frequency, "Has the error rate decreased?" will be "NO", so It is determined whether the error rate has decreased by decreasing the oscillation frequency by one step.

(li) If the error rate is reduced by the above (h),
Repeat the operation in (H) above until the error rate increases, and when the error rate increases, reduce the local oscillation frequency by 1.
The value is increased in steps and fixed at an optimal value that also satisfies D<D ₀ .

"Effects of the Invention" (a) When the frequency characteristics of the TV tuner deteriorate and the error rate of extracted teletext data increases, the local oscillator control circuit activates the local oscillator circuit based on the detection output of the error rate detection circuit. The local oscillation frequency is sequentially controlled higher or lower, and feedback control is performed in the direction in which the detection output of the error rate detection circuit becomes smaller (that is, in the direction in which the error rate becomes smaller), thereby eliminating the need for the complicated The local oscillation frequency of the TV tuner can be automatically controlled to the optimum value without any adjustment.

(b) The detection output of the error rate detection circuit can be used as is, so the circuit configuration is simple.

(c) Whether the error rate is small or not is determined by setting the allowable error count data _D0 to 8 bits out of 296 bits, so even if there are always errors in one packet, there will be 100% error. Can be detected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the teletext receiver with a built-in TV according to the present invention, Fig. 2 is a flowchart explaining the operation of the present invention, and Fig. 3 is a diagram showing what happens when the frequency characteristics of the TV tuner deteriorates. This figure shows the extraction of teletext data, in which a is a waveform diagram of the character signal and b is a timing chart of the extraction clock. 1...TV tuner, 4...Data clock generation circuit, 6...Error correction circuit (also serves as error rate detection circuit), 9...MPU for image processing (equipped with local control circuit), 43...Local Oscillation circuit.

Claims (1)

[Claims] 1 In a receiver configured to receive text broadcasts by extracting text broadcast data from a television video signal selected and received by TV tuner 1, the data D is the number of errors in one packet of 296 bits of said text broadcast data. An error rate detection circuit 6 which also serves as an error correction circuit for detecting an error rate, data D on the number of errors detected by this error rate detection circuit 6, and a preset allowable error occurrence in 8 bits out of 296 bits in one packet. The built-in TV is characterized by comprising a local oscillation control circuit 9 which also serves as an image processing MPU and which compares and determines the local oscillation frequency of the TV tuner ₁ in a direction that reduces the error rate by comparing and determining the error rate with the numerical data D0. Teletext receiver.