TELEVISION RECEIVER

Abstract: Television receiver with a receiving section, a circuit for processing a received television signal which preferably contains digital data, whereby the circuit has a selection stage (4, 5), and a measuring circuit (9), which has an output (8), for measuring the signal quality or a measured variable representative for that (quality) like, e.g., signal-to-noise ratio, field intensity, bit error rate, etc, of the received television signal. The selection stage (4, 5) possesses a controllable transmission band (range) and has a control input (6, 7). The control input of the selection stage is connected with the output (8) of the measuring circuit (9). The measuring circuit controls the transmission band of the selection stage depending on the measured signal quality in such a way that upon worsening/improving of the signal quality of the received television signal, transmission band of the selection stage is reduced/increased.

Description: Television receiver The invention concerns a television receiver with a receiving section, a circuit for processing a received television signal which preferably contains digital data, whereby the circuit is provided with a selection stage, and a measuring circuit for measuring the signal quality or a measured variable representative for that (quality) like, for example, signal-to-noise ratio, field intensity, bit error rate, etc., of the received television signal. Such a television receiver is generally known and serves for the reproduction of television signals. If the television receiver receives television signals of poor signal quality or a poor signal-to-noise ratio, i.e. with a low signal-to-noise ratio between the wanted television signal and the interference signals, then as a rule, visible disturbance results on the screen. This interference is accidental and in particular manifests itself in the form of small, extremely white points on dark or black areas of the television screen or black points in white or light areas of the screen. Such disturbances are also referred to as "sparklies" or noise spots. For the determination of the signal quality, or a measured variable representative of that of the received television signal, measuring circuits for measuring the signal quality, or a representative measured variable - for example, signal-to-noise ratio, field intensity, bit error rate, etc. - are known, which control the amplification of the received television signal in such a way that, for example, with low signal-to-noise ratio, the amplification is increased, whereby with suitable measures the disturbing influences are partly suppressed. However, this leads to an insufficiently improved television picture because the interference is also amplified so that the separation of wanted and interference signal is only marginally improved. It is the object of the invention to avoid the afore¬ mentioned disadvantages and improve the picture quality in a television receiver using simple means. This task is solved according to the invention with a television of the type described above by the features of claim 1. Further advantages follow from the subclaims. The invention is based on the knowledge that limiting the transmission band (range) of a filter raises the selectivity upon receiving a disturbed television signal, increases the signal-to-noise (S/N) ratio of the signal and therewith, improves the signal quality despite loss in the bandwidth of the television signal. An improvement in the S/N ratio of the demodulated television signal is achieved by means of the invention-type solution, corresponding to an obvious improvement in picture quality. This happens, owing to the transmission band limitation of the selection stages upon receiving a weak wanted television signal, actually at the expense of the television signal bandwidth - consequently the chrominance and luminance information; in total however, the invention- type solution leads to a considerable improvement in picture quality. Through this, the total reception and the reproduction of the television signal also exhibits an increased tolerance with respect to time variant impairments. As an essential criterion for the signal quality, the measuring circuit measures the field intensity or the S/N ratio or, upon receiving television signals containing digital data like, for example, teletext data, VPS data, digital audio data (MAC video signal), etc., which are provided with a error detecting code like, for example, a Hamming code, the bit error rate of the television signal. The bit error rate (BE ) , in particular, is a measured variable representative for the signal quality. The BER can be measured, for example, in a known circuit like the DMA 2280 DMAC decoder IC in a television receiver upon receiving a MAC television signal. The selection stages for the luminance and/or chrominance signals are advantageously constructed as • lowpass filters with transmission bands that can be restricted, and can be switched depending on the measured BER or field intensity. The filters can also be built into the above-mentioned DMA decoder IC and can be switched by means of software commands triggered by the BER or field intensity measurement. Through the invention, in particular, with a low S/N ratio in a received television signal, the number of "sparklies" is reduced by using the invention, and therefore, the picture quality is subjectively clearly improved. In the following, the invention is better clarified by means of an embodiment example illustrated by a drawing. Represented in the drawings are: Fig. 1 an block circuit diagram of a circuit for processing a television signal, Fig. 2 an alternative to the circuit according to Fig. 1, Fig. 3 the frequency response of a digital lowpass filter for the chrominance signal with various settings, Fig. 4 the frequency response of a digital lowpass filter for the luminance signal with various settings. Fig. 1 shows an analog-to-digital converter 1 to which a MAC video signal is fed. The MAC video signal contains digital data, like audio, teletext or VPS (video programming system) data, which is provided with an error detecting code, preferably a Hamming code. The analog-to-digital converter apportions the picture components of the MAC video signal into a luminance and chrominance component and supplies both signal components to the digital filters 4 and 5 as eight bit words via respective outputs 2 and 3. The digital filters are constructed as digital lowpass filters (or interpolation filters) and have a control inputs 6 and 7 each. The control input 6 of the luminance filter and the control input 7 of the chrominance filter are connected, via a joint databus - here an intermetallic (IM) bus 12 - , to an output 8 of a bit error rate measuring switch 9. The measuring circuit 9 is connected, via an input 10, with a third output 11 of the analog-to-digital converter 1 via which the digital data signals or the so-called data burst of the MAC video signal is fed to the measuring circuit. The luminance and chrominance signals are sent via the outputs 21 and 22 of the digital lowpass filter for further signal processing. The measuring circuit 9 measures the BER the MAC video signal as the representative value for the signal quality and controls, via the IM bus 12, the transmission band of the digital filters 4 and 5 depending on the BER so that with increment/decrement (small) BER, consequently with worsening/improvement of the signal quality, the transmission band or the bandwidth of the filter is decreased (increased) . ~With a small BER, consequently with good signal quality, the transmission band of the filter is larger than with a large BER. The Figures 3 and 4 illustrate the changes to the transmission band of the digital filters depending on the BER of the received video signal. The following cross reference list is valid for this: chrominance filter (Fig. 3) IV VIII VIII VIII The greater the BER the smaller the transmission band of the digital lowpass filters. By limiting the transmission bands of the digital lowpass filters with a poor S/N ratio in a MAC video signal, some luminance and chrominance information is actually lost; however, the S/N ratio is increased which finally leads to an improvement in picture quality. A further development of the block diagram shown in Fig. 1 is illustrated in Fig. 2. Here, an integrator 13 (or a picture brightness (luminance) measuring unit) is additionally present which calculates the brightness of areas of the picture or a complete picture from the MAC video signal and, via an output 15, transmits a representative value for the brightness to an input of a filter control unit 14. The filter control unit (CCU) has a further input 17 which is connected with the output 8 of the BER measuring unit 9 and an output which is connected with the control inputs 6 and 7 of the digital lowpass filters 4 and 5 via the IM bus 127 The filter control unit 14 controls the filters 4 and 5 via the IM bus 12 in such a way that the transmission bands of the filters are only narrowed or restricted if the picture brightness integrator 13 measures dark or black areas of the picture and simultaneously the BER measuring unit outputs a high bit error rate. Owing to the fact that the "sparklies" have a greater chance of appearing as white points on a dark area of the picture than black points on a light area of the picture, such a limiting of the transmission band in the filters is also sensible, particularly for dark areas-of the picture and poor S/N ratios, because subjectively white points on a dark area are more disturbing than black points on a light area. Furthermore, arranged between the analog-to-digital converter 1 and the digital lowpass filters 4 and 5 are the delay stages 19 and 20 respectively which serve to improve the time adaption (coordination) and synchronization of the selection of the luminance and chrominance signal components with the measuring of the BER and the picture brightness. In addition, an indicator (display) unit is provided (not illustrated) which is connected with a further output 18 of the bit error rate measuring circuit 9, and shows the measured signal quality, for example, as the number of BER per minute measured. Such an indicator unit can be, for example, a display unit like an LED or LCD independent of a television screen or a character generator of a teletext decoder which displays the measured values of the BER on the screen. However, other forms are also possible.

Claims: P a t e n t C l a i m s 1. Television receiver with a receiving section, a circuit for processing a received television signal which preferably contains digital data, whereby the circuit has a selection stage (4, 5), and a measuring circuit (9) , which has an output (8) , for measuring the signal quality or a measured variable representative for that (quality) like, for example, signal-to-noise ratio, field intensity, bit error rate, etc., of the received television signal, c h a r a c t e r i z e d i n t h a t the selection stage (4, 5) possesses a controllable transmission band (range) and has a control input (6, 7), that the control input of the selection stage is connected with the output (8) of the measuring circuit (9) , that the measuring circuit controls the transmission band of the selection stage depending on the measured signal quality in such a way that upon worsening/improving of the signal quality of the received television signal, the transmission band of the selection stage is reduced/increased. 2. Television receiver according to claim 1, c h a r a c t e r i z e d i n t h a t with poor signal quality of the received television signal the transmission band of the selection stage is smaller than with better signal quality. 3. Television receiver according to claim 1 and/or 2, c h a r a c t e r i z e d i n t h a t the selection stage is constructed as a lowpass filter or interpolation filter. 4. Television receiver according to one of the preceding claims, c h a r a c t e r i z e d i n h a t a separate selection stage (5) is provided for the chrominance signal of the television signal. 5. Television receiver according to one of the claims 1 through 3, c h a r a c t e r i z e d i n t h t separate selection stages (4, 5) are respectively provided for the chrominance and luminance signals of the television signal. 6. Television receiver according to one of the preceding claims, c h a r a c t e r i z e d i n t h a t the circuit for the processing of the received television signal contains an analog-to- digital converter (1) which can be fed with a video signal from the receiving section of the television receiver, that the analog-to-digital converter has a first output (3) for the chrominance signal which is connected with the input of the selection stage (5) for the chrominance signal, whereby the selection stage is constructed as a digital lowpass filter, that the analog-to-digital converter has a second output (2) for the luminance signal which is connected with the input of the selection stage (4) for the luminance signal, whereby the selection stage is also constructed as a digital lowpass filter. 7. Television receiver according to claim 6, c h a r a c t e r i z e d i n t h a t the received television signal is a MAC television signal or a television signal which contains other digital data provided with an error protection code, and that the measuring circuit (9) is constructed as a bit error rate (BER) measuring circuit to which the digital data of the television signal are fed and which measures the bit error rate of the received television signal. 8. Television receiver according to claim 7, c h a r a c t e r i z e d i n t h a t the analog- to-digital converter (1) has a third output (11) which is connected with the input (10) of the bit error rate measuring circuit, and the digital data of the television signal are fed to the bit error rate measuring circuit via the third output of the analog- to-digital converter, and that the output (8) of the bit error rate measuring circuit (9) is connected with the control inputs (6, 7) of the selection stages (4, 5) via a line (12) . 9. Television receiver according to claim 8, c h a r a c t e r i z e d i n t h a t the line (12) is a bus. 10. Television receiver according to claim 9, c h a r a c t e r i z e d i n t h a t the bus (12) is an intermetallic (IM) bus. 11. Television receiver according to one of the claims 8 through 10, c h a r a c t e r i z e d i n t h a t with a climbing/sinking bit error rate the transmission band of the lowpass filters is reduced/increased. 12. Television receiver according to one of the claims 6 through 11, c h a r a c t e r i z e d i n t h a t a delay stage (19, 20) each is provided between the analog-to-digital converter (1) and the two selection stages (4, 5) , that a filter control unit (14) , which has a first input (17) connected with the output (8) of the bit error rate measuring circuit, is wired between the bit error rate measuring circuit and the digital lowpass filters, that the filter control unit has a second input (16) which is connected with Λo output (15) of a picture brightness integrator (13) which calculates the picture brightness of areas of the picture from the television signals, and that the filter control unit has an output which is connected with the control inputs (6, 7) of the digital lowpass filters. 13. Television receiver according to claim 12, c h a r a c t e r i z e d i n t h a t the filter control unit (14) reduces the transmission band of the lowpass filters if the bit error rate measuring circuit (9) measures a large bit error rate and the picture brightness integrator (13) measures dark or black areas of the picture at the same time.

Inventors: SHELLARD CHRISTOPHER JOHN, SHELLARD, CHRISTOPHER, JOHN
Applicants: FERGUSON LTD, FERGUSON LIMITED
Application year: 1991
Main classification: H04N11
IPC codes: H04N7, H04N9, H04N11