MXPA01010652A - If signal processing apparatus - Google Patents

Abstract

An IF signal processing arrangement for processing both analog and digital signals is disclosed in the present application. The signal processing arrangement includes a signal source for providing one of digital and analog IF signals, a first SAW filter having an output for filtering the IF signal, digital signal processing circuitry coupled to the output for processing a filtered digital IF signal, and analog signal processing circuitry coupled to the output for processing which includes filtering a filtered analog signal.

Description

PROCESSING DEPARTMENT OF SE AL IF FIELD OF THE INVENTION This application relates to an intermediate frequency (IF) signal processing.

BACKGROUND OF THE INVENTION Figure 1 is an example of a known tuner and an IF signal processing apparatus, generally indicated by the reference numeral 10. This tuner and the IF signal processing apparatus 10 is for use with analog signals of a specific standard of broadcasting, such as NTSC, PAL and SECAM. This application describes the NTSC application as an exemplary modality. The tuner / IF system 10 comprises a tuner 12 (with an RF input 14 and an IF output 16), the IF filter 18, and an IF signal processor 20. The tuner's IF output 16 is at the standard frequency (eg, a desired channel spectrum centered at 44 MHz, image carrier at 45.75 MHz and a sound carrier at 41.25 MHz). The IF filter 18, which usually consists of a SAW filter (acoustic wave surface) for IF systems inter. -porters or two SAWFs for the parallel IF and image systems, pass the desired channel and reject all others. In the parallel system, a SAW filter passes only the desired sound signal and the other passes only the desired image signal. In any case, the characteristics of the filter include a "Nyquist Tilt" across a double-sided band region of the image IF spectrum. The filtered signal is applied to a conventional IF processing circuit 20, which performs such general functions as demodulation, AGC generation and its like and provides a processed video signal output from the baseband to the video processing circuit. The video processing circuit performs conventional functions such as color demodulation and other functions such as brightness, dye control and color perception and their peers. With the introduction of digital television (DTV) and specifically terrestrial digital television such as HDTV (high definition television), the television receivers and the corresponding tuner / IF systems are required, which provide the required tuning and filtering to process both the NTSC and DTV signals. Figure 2 illustrates a modification of the unique NTSC system of Figure 1, to provide a tuner / IF system 22 capable of being used for both NTSC and DTV reception. In Figure 2, a tuner 24 is modified to provide reception of both the NTSC and DTV signals. The conversion signals are suitably selected so that both types of signals produce a common IF signal frequency (e.g., approximately 44 MHz). Two filters 26 and 28 SAW are coupled in parallel with the output of the NTSC / DTV tuner. The SAW BPF # 1 26 has the specific requirements for the reception and processing of the DTV signal, while the SAW BPF # 2 has specific requirements for the reception and processing of the NTSC signal. For example, both the SAW BPF # 1 and the SAW BPF # 2 28 have a center frequency of approximately 44 MHz. However, the SAW BPF # 1 has a flat pass band response, while the SAW BPF # 2 has the characteristics described above for the IF filter 18 in FIG. 1. The filtered DTV signal is applied to the digital IF processing circuitry 30. The digital IF processing circuitry 30 provides the processed and filtered DTV signal for the Digital Link circuitry (ie, the decoder) (not shown). The NTSX filtered signal is applied to the NTSC IF processing circuitry 32. The NTSC IF processing circuitry 32 provides the processed and filtered NTSC signal for the video processing circuitry (not shown). Due to the flat band requirements of the passband for the DTV signals, the tuner 24 DTV / NTSC in Figure 2 has a wider bandwidth than the tuner 12 NTSC in Figure 1. As a consequence, channel rejection adjacent NTSC of system 22 in Figure 2 is not as good as system 10 in Figure 1.

BRIEF DESCRIPTION OF THE INVENTION In the present application, an IF signal processing array is exposed to process both digital and analog signals. The signal processing array includes a signal source for providing one of the analog and digital IF signals, a first SAW filter having an output for filtering the IF signal, digital signal processing circuitry coupled with the output for processing of the signal. a filtered digital IF signal and analog signal processing circuitry coupled with the output for processing, which includes filtering a filtered analog signal.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in the accompanying drawings in which: Figure 1 (prior art) is a block diagram of a conventional NTSC tuner / IF configuration for processing NTSC television signals; Figure 2 is a block diagram of a parallel configuration of DTV / NYSC tuner / IF, for tuning both the DTV and NTSC signals; Figure 3 is a simplified block diagram of a dual DTV / NTSC tuner / IF apparatus embodying the features of the present invention; Figure 4 is a detailed block diagram illustrating a practical implementation and additional features of the embodiment of Figure 3; Figure 5 is a frequency response diagram of the tuner, comprising the response of a single conventional NTSC tuner to that of the modes of Figures 3 and 4; Figure 6 is a frequency response diagram of the tuner, which compares the selectivity of a single conventional NTSC receiver with that of the embodiments of Figures 3 and 4 of the present invention; and Figure 7 is a frequency response diagram of the tuner, which illustrates certain aspects of the processing of the intermediate sound frequency (SIF) for the embodiment of Figure 4.

DETAILED DESCRIPTION OF THE INVENTION The present invention recognizes that passing the NTSC signal through a SAW BPF # 1 (i.e., connecting the input of the SAW BPF # 2 with the output of the SAW BPF # 1, rather than with the output of the tuner) provides an adjacent channel and a spurious signal rejection much better than the system 10 of Figure 1. This change is illustrated in Figure 3. The benefits are important since the adjacent channel rejection NTSC (adjacent first, adjacent second , etc.) is a parameter that becomes more important during the HDTV transition period, in which the "taboos" of the VHF and UHF (ie, restrictions) on the adjacent channel frequency locations can be discarded or can be significantly reduce, to give more available spectral space for terrestrial HDTV broadcast channels, while also accommodating current NTSC terrestrial channel locations. A simplified diagram of the signal processing NTSC / DTV tuner / IF of the present invention is illustrated in Figure 3 and is indicated generally by the reference number 40. Figure 4 shows a more detailed diagram, which illustrates other features of the signal processing of the tuner / IF of the present invention. Figures 3 and 4 show that the input for the NTSC SAW filter is taken from the DTV SAW filter output. In this way, the received NTSC signal is "double filtered". With some advantage, the configurations of Figures 3 and 4 provide a significant improvement in the rejection of the adjacent NTSC channel and the rejection of other unwanted out-of-band signals, compared to the examples in Figures 1 and 2. In Figure 3 , the NTSC / DTV tuner / IF signal processor 40 is provided with conversion frequencies that result in NTSC and DTV reception modes. The NTSC / DTV tuner / IF signal processor 40 includes a single conversion tuner 42 capable of receiving both NTSC and DTV signals. The tuner 42 provides the received NTSC and DTV signals to a first SAW filter 44. The output of the first filter SAW 44 is provided for the first and for the second filter 46 SAW and the digital IF processing circuitry 48. The digital IF processing circuitry 48 receives the filtered signal from the first SAW filter 44 and provides a near baseband output signal towards a digital "link" or decoding circuitry (see Figure 4). When the NTSC signal is received, the received signal is provided to a first filter 44 SAW. The first SAW filter 44 filters the received NTSC signal and provides the filtered signal to the second SAW filter 46. In this way, the IF signal passes through both filters to be applied to the NTSC IF processing circuitry 50, which reduces the undesirable effects of the adjacent channel interference described above. Figure 4 is a practical implementation of Figure 3 and includes more details. With current state-of-the-art technology, the filter characteristics required for the IF DTV signal can not be achieved with a single SAW filter, as illustrated by SAW BPF # 1 44 of Figure 3. That is, the selectivity requirements are not they can be fulfilled without excessive loss of insertion. Excessive insertion loss will result in a final noise figure in a lower system or a severe linearity requirement for a preamplifier. In practice, the required filter and performance characteristics are achieved by cascading two identical SAW filters, SAW # 1 digital and SAW # 2 digital, with amplifiers between levels Post-amp 54 and Pre-amp 56, as shown in Figure 4. In this way, when a DTV signal is selected by the NTSC / DTV tuner 42, it is processed through the cascade circuits comprised of the digital SAW # 1, Post-amp 54, Pre-amp 56 and the SAW # 2 digital 58, with the input of a second circuit 60 converter. The post-amp 54 provides an optimum load impedance for the digital SAW # 1 and compensates for its loss. Similarly, the pre-amp 56 provides an optimum source impedance for the digital SAW # 2 and compensates for its loss. The output of the second circuit 60 of the converter is converted from an analog signal into a digital signal by the converter 76 A / D, the digital processing 78 demodulates the digital signal and separates the image and sound signals, and the signals are converted back in a similar format by a pair of converters 80 digital to analog. When an NTSC signal is selected by the NTSC / DTV tuner 42, there are separate paths for the image and sound signals. The image signal is processed through the digital SAW # 1 44 and by the post-amp 54 before being processed through the pre-amp 64 and the conventional NTSC image SAW # 3 for the 68 NTSC processing. Since the sound carrier frequency is at the bandwidth of the SAW # 1 Digital 44 and the frequency response inclined through the sound channel will have an undesirable effect (see Figure 7), the sound signal does not pass through. of the SAW # 1 Digital and the post-amp 54. Instead, the sound signal is processed through Pre-amp 70 and the SAW # 4 of NTSC 72 sound to the 68 NTSC IF processor. The pre-amp 54 provides an optimal source impedance for the NTSC image SAW # 3 66 and compensates for its loss. Similarly, the pre-amp 70 provides the optimum source impedance for the SAW # 4 NTSC sound and compensates for its loss. The processing of the image signal through the SAW # 1 digital 44 and post-amp 54 provides the advantage of a better selectivity (eg, an adjacent channel rejection and spurious signal immunity). IF NTSC processing demodulates sound and picture signals and provides audio and composite video baseband outputs. Both the second digital IF converter 60 and the IF NTSC processor generate AGC RF control signals that are applied to an RF AGS switch 54. The output of the RF AGC switch 74 controls the gain of the NTSC / DTV tuner 42. Similarly, the 68 IF NTSC processor and the sound and image signals of the 80 D / A converter, whose output drives the internal or external display unit 84. When the system is installed in a new location, an automatic adjustment processing determines what type of signal (NTSC or DTV) is present in each channel and stores the results in memory (not shown). So, each time a new channel is selected, the system microprocessor (not shown) uses the data stored in the memory to appropriately adjust the AG AGC switch 74 and the audio-video selection switch 82. Figure 5 compares the frequency response of the single tuner 12 NTSC (Figure 1) and the tuner 42 NTSC / DTV (Figure 4) of the present invention. The wider bandwidth (i.e., poor selectivity) of the NTSC / DTV tuner is a negative consequence of being able to maintain the flat band requirements of the passband for DTV signals. Figure 6 compares the frequency response of the single NTSC tuner 12 (Figure 1) with the frequency response through the tuner 42 NTSC / DTV, SAW # 1 digital 44, and post amp 54 (Figure 4). Since the frequency response of the subsequent circuits is the same for both systems, this illustrates the great advantage of passing the NTSC image IF signal through the digital SAW # 1 44 and the post-amp 54 instead of directly to the input of pre-amp 64 on the NTSC IF 50. By doing this, the relatively poor selectivity of the NTSC / DTV tuner 42 is compensated for. The selectivity of the present invention, as shown in Figure 6, is indicative of excellent rejection of adjacent channel and spurious signal immunity. It should be noted that the embodiment of Figure 4 has two SAW filters in the DTV signal path and the NTSC image signal is only passed through the first of two SAW filters. This is a preferred configuration since it achieves the selectivity requirements with negligible degradation for the sound figure of the system. This is to pass the NTSC image signal through the SAW filters in the path of the DTV signal is not necessary from a neutral point of selectivity, and further degradation in the system sound figure can be important. Figure 7 is a graph illustrating the effects of passing the NTSC sound IF signal through the first opposite filter SAW 44 going through the first SAW filter 44. The results obtained by passing the NTSC sound signal through the first 44 SAW filter differ drastically from the results obtained by passing through the first 44 SAW filter. As can be seen from this Figure, when the sound IF signal is provided from a single conversion tuner 42 directly to the NTSC sound SAW filter 72, the frequency response across the sound channel is constant. This is not the case for passing the NTSC sound IF signal through the first filter 44. In this way, it is beneficial that the NTSC sound IF signal passes the first SAW filter 44. Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been described by way of example and that changes can be made to the details of the arrangement without departing from the spirit of the invention. invention. For example, analog television signals may include PAL and SECAM television signals and digital television (DTV) signals may include digital VSB and QAM television signals. In addition, the processing of the DTV signal after the digital SAW # 2 can use another measurement (for example, A / D conversion and digital demodulation immediately after the SAW # 2 digital).

Claims (20)

1. A signal processing array, which comprises: a signal source for providing one of the digital and analog IF signals; a first SAW filter having an output to filter the IF signal; a digital signal processing means coupled to the output to process a filtered digital IF signal; and an analogous signal processing means coupled with the processing output, which includes filtering a filtered analog signal.

2. The arrangement according to claim 1, wherein the digital signal processing means includes a second SAW filter.

3. The arrangement according to claim 1, wherein the analog signal processing means includes a third SAW filter.

4. The arrangement according to claim 2, wherein the analog signal processing means includes a third SAW filter.

5. The arrangement according to claim 4, wherein the digital signal processing means is decoupled from a subsequent signal processing circuit while the analogous IF signal is applied thereto.

6. The arrangement according to claim 4, wherein the analog signal processing means is decoupled from the subsequent signal processing circuit while the digital IF signal is applied thereto.

7. The arrangement according to claim 1, wherein the analog IF signal is an IF NTSC signal.

8. An IF signal processing apparatus, which comprises: a single conversion tuner for receiving IF signals having sound and image signals and including one of the digital and analogous content; a first SAW filter connected to a single conversion tuner for filtering received IF signals, the first SAW filter has an output; digital IF circuitry connected to the output of the first SAW filter to receive and digitally process the filtered IF signals; analog IF circuitry also connected to the output of the first SAW filter to receive and develop the analogous processing of the filtered IF signals, the analog IF circuitry performs the second filtering operation on the filtered IF signal.

9. The apparatus according to claim 8, wherein the digital processing circuitry includes a second SAW filter for double filtering the filtered IF signal.

10. The apparatus according to claim 8, wherein the analogous processing circuitry includes a third filter SAW includes a third SAW filter for double filtering the filtered IF signal.

11. The apparatus according to claim 9, wherein the analog processing circuitry includes a third SAW filter for carrying out a second filtering of the received IF signal.

12. The apparatus according to claim 11, wherein the digital IF circuitry is capable of determining whether the filtered IF signal includes analog or digital content, a digital IF circuitry that blocks the filtered IF signal from passing through it when determining the signal Filtered IF includes analogous content.

13. The apparatus according to claim 11, wherein the analog IF circuitry is capable of determining whether the filtered IF signal includes digital or analogous content, the analogous IF circuitry blocks the filtered IF signal from passing through it when determining the IF signal. filtered includes digital content.

14. The apparatus according to claim 8, wherein the digital IF circuitry includes a cascade connection of the first digital SAW, a preamplifier, a buffer amplifier, a second SAW filter and a second converter.

15. The apparatus according to claim 14, wherein the amplifier has an input connected to the output of the preamplifier, an analog SAW and an analogous IF processor to produce a composite video signal and an audio signal to be provided to the deployment.

16. The apparatus according to claim 15, wherein the analog IF circuitry also includes a second damping amplifier connected to receive an analog sound signal from the single conversion tuner and an analog sound SAW to filter the analog sound signal and provide the analog sound signal filtered to the analog IF processor.

17. A method for filtering IF signals including one of the analog and digital content, the method comprises the steps of: receiving the IF signal by a single conversion tuner; filter the IF signal in a first SAW filter; providing a filtered IF signal to both the digital IF circuit and an analogous IF circuit; filtering the filtered IF signal a second time in the digital IF circuit; and filtering the IF signal filtered a second time in the analog IF circuit.

18. The method according to claim 17, further comprising the steps of providing the sound component of the IF signal received by a single conversion tuner to a sound SAW filter.

19. The method according to claim 18, wherein the first SAW filter filters the image component of the IF signal.

20. The method according to claim 19, further comprising the step of amplifying the filtered signal before providing the filtered signal for the digital IF circuit and for the analog IF circuit.