JPS5848586A - Digital receiver - Google Patents

Abstract

PURPOSE:To improve the quality of reception in receiving character broadcast, by detecting the state of group delay characteristics and switching the characteristics of a surface acoustic wave filter in response to the detection for the correction. CONSTITUTION:An error detection pulse (a) is outputted from a Fleming code comparator 41. This detected pulse (a) is given to a relay drive circuit 44 via a logical circuit 42. The relay drive circuit 44 drives a relay 46 to make the relay 46 on. A cross direction type transducer is interrupted. Inversely, when a detected pulse (b) is outputted, the pulse (b) is given to a relay drive circuit 43 via the logical circuit 42. A relay drive circuit 43 makes on the contact of a relay 45 to interrupt another cross direction type transducer.

Description

DETAILED DESCRIPTION OF THE INVENTION This transmission is particularly useful in digital signal receivers, such as television character-intensive reception where the clock run-in signal and the Fleming code signal are sent sequentially before the data. Signal reception.

Teletext broadcasting is known as a digital transmission system for television receivers.

As is well known, this teletext system uses an appropriate IH (
In this method, a digital signal representing data such as a character 0 figure is inserted and transmitted within the horizontal scanning period (H-horizontal scanning period).

FIG. 1 is an illustrative diagram showing an example of a television text multiplex signal. FIG. 1 shows the 1H of the 20th H in the vertical blanking period in which character signals (data) are inserted in a TV text system. In other words, these 20
In the 8th period ■, the clock run-in signal (CRI ), an 8-pit framing code signal (FRC) following this CRI signal, and a data signal (DA) continuing from the next pit of this FRC signal to IH4DII are inserted.

As mentioned above, the ORI signal is "1".

It is configured as a 16 or 18 pit signal consisting of repeating "0", and serves as a standard mix when creating sampling pulses for sampling the data signal (OA) in the television receiver. . In addition, the F
RC1@ is an 8-pit code signal selected to provide 1-pit error protection capability, and serves as a time reference when converting the sampled data signal in parallel by 8 pits. It is. And this F
There are many possible code configurations for RCI numbers, so you can choose the appropriate one. For example, NHK's 055 system uses 11" tooioi, and the British Teletext system uses 111001.
00, but in France's seven-tenant system, it is 11.
100111 are adopted respectively.

FIG. 2 is a schematic block diagram of the main parts of a conventional character multiplex signal receiver. In the figure, a text multiplex transmitter 10 transmits a radio wave f! that contains the TV text multiplex signal shown in FIG. 1 as well as a television video signal. believe This radio wave is received by receiver-20 via an antenna. That is, receiver 2
A tuner or video detection circuit 21 included in the video signal is supplied to a video signal and a video circuit 28, and a TV character multiplex signal is supplied to a gate circuit 22. This gate @Wi22 is a gate for character signal extraction which extracts 1H to several H portions into which a character multiplex signal is inserted from the detection output of the video detection circuit. The character signal extracted by this gate circuit 22 is given to a slicer circuit 23, where it is sliced at 172 levels of its amplitude and converted into a rectangular wave. Slicer eye 1
The character signal converted into a rectangular wave at I23 is applied to the sampling reproducing circuit 24, as well as to the framing code detecting circuit 5 and the serial/parallel converting circuit 26. Sampling clock...Raw @1i24G! A sampling clock is created by obtaining 0RII@ from the character multiplexed signal shown in FIG.

This sampling clock is given to the fleming code detection circuit 25. The framing code detection circuit 25 detects the FRC signal from among the output signals of the slicer circuit 23, creates timing pulses for every 8 pits of the data signal based on the sampling clock, and supplies them to the digital processing circuit 27.

The serial/parallel conversion circuit 26 samples and extracts data signals from the output signals of the slicer circuit 23 using sampling pulses, and converts the sequentially extracted data signals into parallel signals of 8 pits at a time using timing pulses. Then, the converted signal is supplied to the digital processing circuit 2.The digital processing Ipgl path 27 is connected to each 8
Digital processing is performed so that the PIT and G signals are output to an appropriate position on the TV IIM. The output signal of this digital processing circuit 27 is given to a single circuit 28.

The video circuit 28 blurs the character signal given from the digital processing circuit 27 with the television video signal output from the video detection circuit 21 and supplies it to the receiver 1129. The conventional receiver is configured as described above, but what should be noted here is that the signal from the modulator (not shown) included in the text multiplexing device 10 to the tuner or video detector 1 in the receiver 20 is
This is the overall group delay characteristic up to the output point of 11121.

That is, in general, in a television receiver, the group delay IE@ characteristic of the tuner or video detection circuit 21 causes the transmission ll1l!
It is selected so that it is canceled out by the group delay characteristic of the 10th side. However, this is the ^ line part (
3 to 4 MH211), and the low frequency part of the video signal band (0 to 2 MH2 band) is not necessarily prefixed in this way. Therefore, the group delay characteristic at point A in Figure 2 That is, transmitting device 1
As shown in Figure 3, the low-frequency part of the overall group delay characteristic including the 011 and receiving-20 sides (hereinafter referred to as the low-frequency group delay characteristic) is flat in some cases, and in other cases sloped. ,c
There is also a modulator on the transmitter 10 side and a receiver 2
It is determined by the group delay characteristics of each tuner or video detector 811121 in 0.

By the way, the bit rate of the above-mentioned character multiplex signal is, for example, NHK's 055 system, which is 5°73 Mb/s.
has been selected. For this reason, the above-mentioned clock run-in (CR1) like the l1 &: NJ for each pit, r
In the case of an OJ repetition signal, its repetition frequency i
This corresponds to a pit rate of 172, or approximately 2.86 MH2. This means that the CRI signal is
This means that it is hardly affected by the low frequency part (0 to 2 MH2 band) of the group delay characteristic shown in 1I.

On the other hand, the pit range of the Fleming code (FRC) signal in the character multiplex signal is also M%5.73 Mb/3. However, this FRC signal is not a periodic repeating signal for each pit as described above. This means that FRC signals are relatively low (i.e. below 2MH2).
It means that frequency components are included, therefore F
The RC signal is subjected to the low frequency group delay characteristic shown in FIG.

Note that as a method for constant evaluation of waveform distortion, there is a method of determining the eye-hide ratio using an eye pattern, and an increase in transmission distortion corresponds to a decrease in the eye-hide ratio.゛Therefore, the main purpose of the present invention is to improve the reduction in the fibyte rate caused by group delay distortion in the low frequency range in the transmission path, and to improve the reduction in the fibyte rate caused by the group delay distortion in the transmission path, so that the data signal and the Fleming code signal sent prior to the data signal can be It is an object of the present invention to provide a digital signal receiver that can prevent detection from becoming undetectable due to distortion.

To summarize this invention, an elastic surface filter whose group delay characteristic is switchable is provided in the video intermediate frequency amplification circuit of a digital signal receiver, and the group delay of the transmission system from the transmitting side to the receiver is achieved. It is configured to detect a distorted ridge and switch the group delay characteristic of the surface acoustic wave filter based on the detected signal to prevent the data signal and the Fleming code signal sent prior to the data signal from not being detected. be.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

FIGS. 4 and 5 are diagrams showing group delay characteristics for explaining the concept of an embodiment of the present invention.

As shown in Section 3@l above, the low-frequency group delay characteristic may be flat in some cases, or sloped in others, but in one embodiment of the present invention, the low-frequency group delay characteristic is sloped. If there is
Correct this so that it becomes flat.

That is, when the low frequency group delay characteristic increases as shown in FIG. 4(a), the 51ii! As shown in I (a), the low frequency group delay characteristic is flattened by a filter having a decreasing characteristic. Furthermore, if the low-frequency group delay characteristic is flat as shown in FIG. 4<a>, the filter characteristic is also flat as shown in FIG. 5(1)).

Furthermore, if the low-band group delay characteristic is decreasing as shown in FIG. 4(C), the filter's group delay characteristic is
! Increase as shown in l I >. In this way, send! The object of the present invention can be achieved by switching the low-band group delay characteristics of the filter according to the mutual group delay characteristics from the device 10 to the receiver 20. For this,
In one embodiment of the present invention, a surface acoustic wave filter is used as a filter, and the low-frequency group delay characteristics of the surface acoustic wave filter are adjusted according to the overall If II spread characteristic in FIG.
This is done by switching as shown.

#16aI& is a diagram showing the electrode configuration of a surface acoustic wave filter, and FIG. 7 is a diagram showing its characteristics.

In recent years, surface acoustic wave filters have become widely used as bandpass filters for video amplification channels in television receivers. One of the features of this electronic jump wave filter is the amplitude of the filter by changing the electrode structure for surface wave excitation and detection.

The point is that the phase characteristics (group delay characteristics) can be designed independently from each other. The so-called interdigital transducer (hereinafter referred to as interdigital transducer) is used as a surface-excited transducer.
As shown in FIG. 6, a so-called regular type IDT 32 whose electrode width and pitch are constant is arranged on one side, and a desired amplitude in combination with the regular type IDT 32 is placed on the other side. Electrical crossover width to obtain 9 phase characteristics.

It is common to have a configuration in which so-called weighted IDTs with varying pitches are arranged. In such a configuration, the frequency characteristics of the elastic i-plane filter are given as the product of the frequency characteristics of each EDT. Regular I! J! The characteristics of the 10-32 are determined by the electrode pitch and the number of electrodes, the amplitude characteristics are symmetrical with respect to the center frequency, the phase characteristics are linear, and the group delay characteristics are constant. On the other hand, weighted I
Various methods and methods have been proposed for electrical design of DT, but
The most common method is to obtain the relative axis response by inversely Fourier-transforming the frequency characteristics that the 10T31 should have, which are determined from the general characteristic specifications of the surface acoustic wave filter and the normal type characteristics, and to obtain this so-called impulse response waveform. This method determines the electrode shape that achieves this. This takes advantage of the fact that the impulse response of the surface acoustic wave filter is similar to the geometrical shape of the IDT.

By the way, as shown in FIG. 7, the shape of the IDT designed by the above method has an asymmetrical amplitude characteristic a, and a phase characteristic that is not linear (the group delay characteristic is not constant). Both the electrode crossing width and pitch of the weighted IQT 31 are not constant. Figure 8 shows an example in which the weighted electrodes of the surface acoustic wave Lylter are symmetrical.
Figure 119 shows an example of the same non-contrastive case.

10 and W411 are illustrative diagrams for explaining the propagation state of the surface acoustic wave filter, and FIG.
Table I shows the differences in characteristics depending on the i-person orientation in 5Il.
ii'wt beams move toward the IDT 31 on the same propagation path in one direction. Normally, there is another positive 1 on the propagation path of one of the i-Us λ as shown at 115Il! '1l
A fill gate is constructed by arranging the DT32. Now, as shown in FIG. 11, there is an equidistant i on both sides of one IDT 31 with an abscess, which is normal! Place IDT32.33. Then, weighted IDT31 and normal type IDT3
Combination A with 3 and IDT31 with regular type I
Considering the filter characteristics for each combination 8 with DT32, as shown in the 12th factors (a) and (, b), the amplitude characteristics a are the same, but the a*g characteristics are reversed. Recognize. In other words, it can be seen that the propagation function representing the characteristics to the combination and that of combination 8 are in a mutually conjugate relationship. I want to do it, Figure 12 (
If you choose a harmony with the characteristics shown in each of a, ) and (b), Filterara 1! It is possible to make the group delay characteristic constant within the region.

FIG. 13 is a diagram showing the characteristics of an elastic 11 plane wave filter included in an embodiment of the present invention, and FIG. 14 is a diagram showing the renal properties shown in FIG. 13 in baseband. ,
, , , Section 1.1 above
As shown in the figure, a configuration is adopted in which normal type IDTs 32 and 33 are arranged on the same surface wave propagation path on both sides of the weighted IDT 31, and for example, the -wave reception characteristic of combination A is set to 13.
Figure (a>) and set the frequency characteristics of combination B to the 13th
Make it as shown in the figure ((j). Then, add both 1 and the characteristics ^
By doing so, the characteristics shown in FIG. 13(b) can be realized. When converted into baseband characteristics, these correspond to the characteristics shown in Sections 14s(a) to 14C), and are found to be suitable as characteristics for correcting IIMII distortion occurring in the transmission path.

FIG. 15 is a block diagram showing one embodiment of the present invention. - In some cases, this No. 15N3 is the same as FIG. 2, with the following exceptions: That is, the Fleming code signal from the slicer circuit 23 is sent to the Fleming code comparator 4.
1 is given. This Fleming code comparator 4
1 is given a sampling clock from a sampling clock recovery circuit 24. The Fleming code comparator 41 compares the input Fleming code with a preset Fleming code and determines whether a pit error has occurred in the Fleming code. When a pit error occurs, the Fleming code comparator 41 generates an error detection pulse a depending on whether the group delay characteristic is b or C shown in FIG.
, b are added to the logic circuit 42. The logic S circuit 42 detects the detection pulse.

b&-Iris τ relay drive @1i43.44 This is to drive the relay 45, and the relay drive circuit 4
4 is a relay that drives 46.

The surface acoustic wave filter 30 is connected between the tuner 211 and the video-intermediate frequency detection circuit 212, and is connected to the electrode combination A.
The characteristics of combination B are selected as shown in FIG. 13(a), and the characteristics of combination B are selected as shown in FIG. 13 (0>.Relay 4
5 and 46& are off in the state shown in FIG. 15, and at this time both IDTs 2.3 are conductive.

Therefore, in this state, the characteristics of the surface acoustic wave filter are A+8, that is, as shown in FIG. 13(b, . . .).

Next, the operation will be explained. If the group delay characteristic of the transmission line up to the video intermediate frequency detection circuit 212 is in the state shown in FIG. 3(a) after the power is turned on, the error detection pulse a is output from the Fleming code comparator 41. This detection pulse a is given to a relay drive circuit 44 via a logic circuit 42. Relay drive circuit 4
4 drives the relay 46 and turns on the contact of the relay 46. Therefore, the IDT 3 is blocked, and the characteristics of the surface acoustic wave filter correspond to combination A. In other words, the characteristics of the surface acoustic wave filter are as shown in No. 1311(a), so they are corrected to have flat characteristics.

Conversely, when detection pulse b is output, this detection pulse b
That's the argument! It is applied to a relay drive circuit 43 via a circuit 42. Relay drive circuit 43 turns on the contacts of relay 45. Then, the IDT 2 is cut off, and the characteristics of the surface acoustic wave filter 30 become those corresponding to combination B, that is, the characteristics shown in 13th!11(0), and are corrected to flat characteristics. In this way, various things that actually occur b
If the relays 45 and 46 are respectively switched according to the input mode of the logic a 1142 and the state of the output mode at that time, the characteristics can be corrected most effectively.

As described above, according to the present invention, when receiving text broadcasting, the state of the group delay characteristic of the transmission path that may occur due to various uses such as deviation in the group delay characteristic of the transmitting device is detected,
In response to this, the characteristics of the surface acoustic wave filter 1- are switched to perform correction, so that the reception quality when receiving teletext can be improved. Furthermore, by correcting transmission distortion in this manner, it is possible to expect not only an improvement in the reception quality of teletext broadcasts, but also a similar effect when receiving general telepicture broadcasts.

[Brief explanation of the drawing]

FIG. 1 is an illustrative diagram showing an example of a television text multiplex signal. FIG. 2 is a schematic block diagram of the main parts of a conventional character multiplex signal receiver. FIG. 3 is a diagram showing a low part of the group delay characteristic. FIGS. 4 and 5 are diagrams showing group delay characteristics for explaining the concept of an embodiment of the present invention. FIG. 6 is a diagram showing the electrode configuration of a surface acoustic wave filter. FIG. 7 is a diagram similarly showing the characteristics of the surface acoustic wave filter. 8th
The figure shows an example of a case where the weighted electric machines of the surface acoustic wave filter are symmetrical. FIG. 9 is a diagram showing an example of a non-contrastive case. FIGS. 10 and 11 are illustrative diagrams for explaining the propagation pattern of a surface acoustic wave filter. FIG. 12 is a diagram for explaining the difference in characteristics depending on the propagation direction in FIG. 11. FIG. 13 is a diagram showing the characteristics of a surface acoustic wave filter included in an embodiment of the present invention. FIG. 14 is a diagram showing the characteristics shown in FIG. 13 in terms of baseband. 158 is a block diagram showing an embodiment of the present invention. In the figure, 211 is a tuner, 212 & is a video Nakazono frequency detection port, 22 is a gate circuit, 23 is a slicer circuit,
24 is a sampling clock recovery path, 30 is a surface acoustic wave filter, 41 is a Fleming code comparator, 4
2 is the logic S@ path, 43°44 is the relay drive circuit, 45
．． 46 indicates a relay, Patent applicant: Sanyo Electric Co., Ltd. Procedural amendment - October 31, 1980 Dear Commissioner of the Japan Patent Office 1, Indication of case: 1981 Patent Application No. 147563M 2, Title of invention Digital receiver 3, Relationship with the person making the amendment Patent applicant address 2-18 Keihan Hondori, Moriguchi City, Osaka Name
(188) Sanyo Electric Co., Ltd. Representative Iue
Kaoru 4, Agent address Yachiyo Daiichi Building 2-3-9 Tenjinbashi, Kita-ku, Osaka Voluntary amendment Kame Column 7 of the detailed explanation of the invention in the specification subject to the amendment, Contents of the amendment (17 Specification, page 817, 1116) Line 1 If it is tilted, correct baeJ [if it is slow or fast, correct aJK〇(2) “If it is tilted” in line 4 of page 110 of the specification
Correct it to “In case of slow or fast phase”〇(3)
Specification j [0 “Increasing” in line 8
〇(5) In the 9th line of the irises on page 10 of the specification appendix, change ``r down, descend'' to ``slow phase''.
Correct it to “negative, i.e. progressive” 〇(6) Statement! On page 10, line J114, ``If it is falling'' should be corrected to ``if it is in advanced phase.'' (7) ``Increase ◎'' on page 15 of page JlEIO of the specification should be changed to ``Positive, ie, slow phase pressure.'' JK correct @ri8)
rIDTJ on page 11, line 20 of the specification is rIDT3
0 (9) Correct "Fourier inverse transform" on page 11, line 20 of the specification to "Fourier inverse transform" K. Above 487-

Claims (3)

[Claims] (1) A clock run-in signal that determines the data sampling timing and a clock run-in signal that determines the data sampling timing.
D parallel conversion tie 9. Decide on the In the digital signal receiver used in the 71 ASTEM, there is further provided a digital signal amount--a digital wave filter which is provided in the video intermediate frequency amplification circuit included in the device and whose group delay characteristic is switchable. and a detection means for detecting the group delay distortion state of the transmission system from the transmitter to the digital signal receiver; ゛Based on the detection signal of the detection means,
``A digital signal receiver comprising: switching means for switching the group delay characteristic number of the surface acoustic wave filter. (2) "The surface acoustic wave filter includes a recessed transducer electrode provided almost at the center of its surface; and a first and a recessed transducer electrode provided on both sides of the transducer electrode. 2 regular type transducer electrodes, and the --i stage is configured to switch between the first and second regular type transducer electrodes. signal receiver. (3) The surface acoustic wave filter has a group delay characteristic of 2 MHz lower than the video carrier frequency by switching between the weighted regular transducer electrode and the weighted regular transducer electrode. A special '1Fi1' that descends or rises linearly to a point and remains constant thereafter.
A digital signal receiver according to claim 2.