MXPA99011454A - Using equalized data for filter selection in hdtv receiver - Google Patents

Abstract

A digital television receiver includes a filter for minimizing NTSC interference with a received signal (IN) having a constant symbol rate. An equalizer (54) has two one-symbol delays for each tap. A filtered and a non-filtered version of the received signal are applied to a multiplexer (56) at the input of the equalizer, which is operated at twice the symbol rate. The outputs of the multipliers in the equalizer are combined and applied to a demultiplexer (80). The filtered and non-filtered equalized signals are compared and a selection as to which of the filtered or non-filtered received signals is to be processed is made based upon the comparison.

Description

USE OF EQUALIZED DATA FOR THE SELECTION OF FILTERS ON A HIGH TELEVISION RECEIVER DEFINITION FIELD OF THE INVENTION This invention relates generally to equalization circuits and specifically to equalizing or equalizing circuits that are used in High Definition Television (HDTV) receivers.

BACKGROUND OF THE INVENTION In the recently adopted standards of advanced digital television systems, there will be a relatively long period when both NTSC signals and HDTV signals can be broadcast in the same service areas. HDTV receivers will incorporate a filter, such as a comb filter, which cooperates with precoding the transmitted signals, to minimize the effects of contiguous channel interference on HDTV receivers according to the Advanced Television System Committee (NTSC) . These circuits are already well known in the art and have the disadvantage of reducing the signal to noise ratio of the received signal by approximately 3 dB. Consequently, unless there is a need for REF. : 32044 use a filter (ie, that there is a significant NTSC signal interference), the filter is not desirable. A certain form of decision making circuit is incorporated into the receiver, to essentially compare errors with or without filtering and to disable the filter if no substantial benefit is obtained. The receiver also includes a signal equalizer to neutralize certain types of interference, especially phantom signals. The equalizer includes a series of corresponding delays and multipliers, through which the symbols of the received signal pass. The coefficients of the multipliers are changed according to the determined equalization of the received signal. These circuits and their operation are already well known in the art. The circuits of the preceding art make a determination to know whether or not it includes an NTSC filter, based on the non-equalized signals. This has a disadvantage, since interference between symbols can be present in the received signals (due primarily to phantom interference) and resulting in erroneous decisions. The present invention makes a decision based on the equalized data and therefore, allowing a better decision to be made, with respect to whether the filter should be included in the processing of the received signal.

Objectives of the Invention A principal object of the invention is to provide a television receiver having an improved rejection of NTSC interference. Another object of the invention is to provide an improved configuration for determining when the filter will be used for NTSC interference. A further object of the invention is to provide a novel equalizer for use in a television receiver having an NTSC interference rejection filter.

Brief Description of the Drawings These and other objects and advantages of the invention will be apparent upon reading the following description, in conjunction with the Drawings, in which: Figure 1 is a simplified block diagram of a television receiver of the preceding art, having a NTSC interference filter, in the form of a comb filter; Figure 2 is the comb and equalizer portion of the prior art diagram of Figure 1; Figure 3 is the same portion of Figure 1, illustrating one aspect of the invention; Figure 4 is a block diagram of the comb equalizer portion, showing another aspect of the invention; and Figure 5 is a more detailed illustration of Figure 4.

Description of the Preferred Modality Referring now to Figure 1, a prior art television receiver includes a tuner, a Sierra Fl and a demodulator 10 that are supplied with terrestrial signals comprising a plurality of multilevel symbols received at a constant symbol rate. through an antenna 12. The output of block 10 is supplied to an analog to digital converter 14, which in turn supplies it to a DC suppression circuit 16. The output of the DC suppression circuit supplies to a clock and synchronization restorer circuit 18, a mode detector circuit VSB 22, a linear filter such as a filter comb 24 and a decision making circuit 28. The conjunction of the above-mentioned circuits is labeled IN. A voltage-controlled crystal oscillator 20 supplies the oscillation signals to the circuit 18, which develops a signal, fsym corresponding to the ratio of the received symbols and other necessary timing signals in the receiver. It should also be noted that in addition to fs? M (which may also be referred to as fcik), the circuit may immediately develop a 2fc? K signal (double symbol ratio), as used in some of the following circuits, which is incorporate in the invention. The decision making circuit 28, as discussed above, is also supplied with the comb filtered signal and determines whether the received signal will benefit or not, using the NTSC reject filter. The decision making circuit 28, as discussed above, is also supplied together with the comb filtered signal and determines whether the received signal will benefit from the use of the NTSC reject filter or not. The decision making circuit 28 can take the form of a comparator, to compare the filtered and unfiltered signals. The output is also supplied to an equalizer 26 of conventional construction and operation. The output of the equalizer is labeled OUT and is supplied to a block 30 which includes, among other circuits, a phase follower, an RS decoder, a lattice decoder, symbol decoders, and a video processing circuit. which all are already well known in art. As mentioned, the information supplied to the decision making circuit 28 is obtained before that of the equalizer 26 and consequently subject to disparity of signals, such as interference between symbols, which the equalizer can minimize. Consequently, NTSC interference filtering decisions are frequently made with less than optimal signals. Figure 2 illustrates the comb filter and the equalizer in more detail. The received signal is applied to IN and passes through a delay circuit of two symbols 32, to an output of a subtracter 40 and directly to another input of subtracter 40. The output of the subtracter comprises a comb filtered signal and is coupled to the decision making circuit 28, which may comprise a comparator, and a C terminal (combed) of a switch 44. The received signal is also supplied, without combing, to the decision making circuit 28 and to an N (non-combed) terminal of switch 44. The decision making circuit 28 is also well known in the art. and determines, for example, the input signal having the least number of errors and accordingly operating the switch 44. The switch couples the selected signal of the combed or non-combed received signals to the equalizer 26 for further processing. In Figure 3, an aspect of the invention is shown. Here, the information supplied to determine if it is filtered or not filtered is taken after the equalization. The filtered input signal is supplied to a first conventional equalizer 50, output from which it is supplied to the C terminal of the switch 44 and the decision making circuit 28. Similarly, the unfiltered input signal is supplied to a second conventional equalizer. 52, output from which it is supplied to terminal N of switch 44 and the decision making circuit 28. Here, the decision is made whether or not to filter the data that have been equalized and with which, optimizing the opportunity to do a correct decision. Figure 4 illustrates another aspect of the invention that uses a modified equalizer 54 that is operated at a rate of 2fclk, which is double the ratio d symbol d5 input signal. The outputs of the equalizer or modified equalizer 54 are supplied to the decision making circuit and terminals C and N of switch 44. Thus, the filtered equalized signal appears in terminal C and the unfiltered equalized signal appears in terminal N. Here too , the decision making circuit 28 makes its decisions based on the equalized data. Figure 5 shows in more detail the modified equalizer circuit of the. Figure 4. Specifically, the filtered input signal is applied to an input of a multiplexer 56 and the unfiltered input signal is applied to another input of the multiplexer 56. The output of the multiplexer 56 is supplied to a series of delay pairs of a single symbol, comprising scales of type D 58, 60; 62, 64; and 66, 68. It should be appreciated that there may be thirty-two, sixty-four, or a greater number of pairs of scales, depending on the accuracy of the desired equalizer. As in a conventional equalizer, each pair of delays of a single symbol is coupled to a multiplier for example, multipliers 70, 72, 74 and 76, whose outputs are supplied to an adder 78. The multipliers are supplied with coefficients c0, cl f c2, -cn from known circuits (not shown) to equalize the signal. The multiplexer 56, the scales 58-68 and the multipliers 70-76 are operated at a ratio of 2fc? K, that is, twice the symbol ratio. Consequently, filtered and unfiltered signals will be processed alternately by means of the equalizer, each at a faith ratio. *. A demultiplexer 80 is connected to the output of the adder 78 and operates at double the symbol ratio to separate the multiplexed output of the adder 78, in a filtered signal to be applied to the C terminal and the decision making circuit 28, and in an unfiltered equalized signal to be applied to the N terminal and the decision making circuit 28. What has been described is a novel circuit configuration to improve the decision to include or not an NTSC interference rejection filter in a receiver TV. Unlike the circuits of the previous art, the circuits of the invention provide equalized data, which facilitates more optimal conditions for decision making. It is recognized that numerous changes to the described embodiment of the invention will be apparent, without departing from its true essence and field. The invention should be limited only as defined in the claims. It is noted that, with regard to this date, the best method known by the requested, to carry out the present invention, is that which is clear from the present, discovering the invention. Having described the invention as above, the content of the following is claimed as property.

Claims (10)

1. A method for operating a digital television receiver, having a filter for reducing the effects of NTSC interference on a received signal, having a constant symbol ratio, characterized in that it comprises: develop signals received 10 filtered and not filtered; equalize or equalize filtered and unfiltered received signals; compare received and filtered equalized and unfiltered signals; and 15 selecting one of the received signals to be processed, based on the comparison step.

The method according to claim 1, characterized in that, 20 further, it comprises: provide a pair of equalizers or equalizers; and apply the filtered and unfiltered received signals to the pair of equalizers.

3. The method according to claim 1, characterized in that, in addition, it comprises: provide an equalizer that has a delay of the symbols for each shot; operate the equalizer to double its 10 reason of symbols; apply filtered and unfiltered received signals to the equalizer; Y compare the outputs of the equalizer, to generate the equalized signals 15 filtered and not filtered.

4. The method according to claim 3, characterized in that the application step comprises multiplexing to the filtered received signals and not 20 filtered to apply to the - equalizer and further, comprising: to ultiplex the equalizer outputs before the comparison step.

A method for operating a digital television receiver, having a filter for reducing NTSC interference with a received signal, having a constant symbol ratio, characterized in that it comprises: develop filtered and unfiltered received signals; provide an equalizer that has a delay of the symbols for each shot; 10 operate the equalizer at twice its symbol ratio; multiplex and apply the filtered and unfiltered received signals to the equalizer; 15 demultiplex the equalizer output to develop filtered and unfiltered equalized signals; compare filtered and unfiltered equalized signals; and selecting a desired signal from the filtered and unfiltered received signals, to be processed based on the comparison step.

A high definition digital television receiver for receiving a signal having a signal at a constant symbol rate, characterized in that it comprises: filtering means for reducing the effects of NTSC interference on the received signal; means for supplying the received signal to the filtering means, for 10 develop filtered and unfiltered signals; means to equalize filtered and unfiltered signals; means to compare signals 15 filtered and not filtered; Y means to select one of the filtered and unfiltered equalized signals, to be processed based on the comparison.

The television receiver according to claim 6, characterized in that the equalization means comprise a pair of equalizers.

The television receiver according to claim 6, characterized in that the equalization means comprise: an equalizer having a plurality of sockets, a plurality of corresponding multipliers and two delays of a single symbol for each of the plurality of sockets; means to operate the equalizer, to 10 double the ratio of symbols; multiplexing means for applying the filtered and unfiltered signals to the equalizer; Y means to demultiplex the output 15 of the equalizer to 'develop filtered and unfiltered equalized signals.

The television receiver according to claim 8, characterized in that the equalizer includes a pair of delays of 20 scale for each of the plurality of shots and including, in addition: means to operate multipliers at double their symbol ratio; and means for supplying the outputs of the multipliers to the multiplexing means.

10. The high-definition digital television receiver for receiving a signal having a signal at a constant symbol rate, characterized in that it comprises: filter means to reduce the effects of NTSC interference on the signal 10 received; means for supplying the received signal to the filtering means, to develop filtered and unfiltered signals; 15 equalization means comprising an equalizer having a plurality of sockets, a plurality of corresponding multipliers and two delays of a single symbol for each of the plurality of 20 shots; means to operate the equalizer at double its symbol ratio; multiplexing means to apply the filtered and unfiltered signals to the 25 equalizer; means for demultiplexing the output of the equalizer, to develop filtered and unfiltered equalized signals; means for comparing filtered and unfiltered equalized signals; and means for selecting a signal from the filtered and unfiltered equalized signals, to be processed based on the comparison.