CN101465981A - Method and apparatus for adjusting center frequency of filter - Google Patents

Abstract

The invention provides a method and a device for adjusting the center frequency of a filter. The method for adjusting a center frequency of a filter to retrieve information on a target channel includes: detecting adjacent channel interference aiming at the target channel to generate channel interference information; and adjusting the center frequency of the filter according to the channel interference information aiming at the target channel.

Description

Method and device for adjusting filter center frequency

technical field

The present invention relates to adjusting a center frequency of a filter, in particular to a method and device for adjusting a center frequency of a surface acoustic wave filter to extract information on a target channel, wherein the The target channel is, for example, a TV channel.

Background technique

The Digital Video Broadcasting-terrestrial (DVB-T) standard has been adopted by many countries. However, the bandwidths of broadcasting signals used in different regions of the world are different, and it is currently known that there are at least 5MHz, 6MHz, Four bandwidths of 7MHz and 8MHz are used for TV broadcasting. Therefore, if a product (such as a TV) with a single bandwidth is used in an area that uses a different bandwidth, it will result in poorer TV image quality or Even an unwatchable TV signal. There are two known methods used to resolve this issue. The first method is that the tuner uses several surface acoustic wave filters with different bandwidths to receive TV broadcast signals with different bandwidths; however, when several surface acoustic wave filters are used, and because the surface acoustic wave SAW filters are expensive, so using several SAW filters leads to increased product line management and material costs. The second method is for the tuner to use a single SAW filter with a maximum bandwidth among the multiple signal bandwidths available to transmit television signals to ensure that the desired signal is not filtered out; however, when When the bandwidth of the TV signal is smaller than the bandwidth of the SAW filter, the SAW filter cannot filter Adjacent Channel Interference (ACI), which will seriously affect and degrade the TV image quality.

Contents of the invention

Therefore one of the objects of the present invention is to provide a method and device for adjusting a center frequency of a surface acoustic wave filter to extract information on a target channel (target channel), to solve the above-mentioned problems, wherein the The target channel is, for example, a TV channel.

According to an embodiment of the present invention, a method for adjusting a center frequency of a filter to extract information on a target channel includes: detecting adjacent channel interference for the target channel to generate channel interference information ; and for the target channel, adjusting the center frequency of the filter according to the channel interference information.

According to another embodiment of the present invention, an apparatus for adjusting a center frequency of a filter to extract information on a target channel includes: an adjacent channel interference detector for targeting the target channel, adjacent channel interference is detected to generate channel interference information; and a tuner is used for adjusting the center frequency of the filter according to the channel interference information for the target channel.

According to the method and device provided by the present invention, the tuner has only one surface acoustic wave filter and can be used to adjust the center frequency of the filter to filter adjacent channel interference. Therefore, the product line does not need to be different for different regions. Changes, and the cost of management and materials will also be reduced.

Description of drawings

FIG. 1 is a schematic diagram of an apparatus for adjusting a center frequency of a SAW filter to extract information on a target channel according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of the bandwidth of the surface acoustic wave filter shown in FIG. 1 being larger than that of a TV channel.

FIG. 3 is a schematic diagram of shifting the center frequency of the surface acoustic wave filter shown in FIG. 2 .

Description of reference symbols

100 The device used to adjust the center frequency of the filter 110 tuner 112 SAW filter 120 Analog to Digital Converter 130 Demodulator 132 Adjacent Channel Interference Detector

Detailed ways

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a device 100 for adjusting a center frequency of a surface acoustic wave filter to extract information on a target channel in an embodiment of the present invention, wherein the The target channel is, for example, a TV channel. As shown in FIG. 1 , the device 100 includes a tuner 110 , an analog-to-digital converter 120 and a demodulator 130 . The tuner 110 is coupled to the analog-to-digital converter 120 and includes a SAW filter 112 having a maximum bandwidth among a plurality of signal bandwidths available for transmitting television signals. In addition, the demodulator 130 is coupled to the analog-to-digital converter 120 and the tuner 110 , and includes an adjacent channel interference detector 132 .

As shown in FIG. 1, the tuner 110 is used to receive a radio frequency signal (such as a TV broadcast signal) to generate an intermediate frequency signal, and the surface acoustic wave filter 112 included in the tuner 110 is used to filter the intermediate frequency signal to generate an intermediate frequency signal. The filtered signal, wherein the filtered signal is used as a television signal of the television channel; then, the analog-to-digital converter 120 receives the filtered signal to generate a digital television signal; the adjacent channel interference detector 132 detects the The adjacent channel interference of the digital TV signal, and classify the adjacent channel interference of the TV channel into high frequency band adjacent channel interference or low frequency band adjacent channel interference to generate a channel interference information; finally, the demodulator 130 notifies the tuner 110 according to The channel interference information generated by the adjacent channel interference detector 132 is used to adjust the center frequency of the SAW filter 112 to output a demodulated signal.

It should be noted that, in this embodiment, the adjacent channel interference detector 132 is included in the demodulator 130 and the channel interference information is transmitted from the demodulator 130 to the tuner 110, however, the adjacent channel interference detector 132 It does not have to be set in the demodulator 130, and the channel interference information can also be transmitted to the tuner 110 by other devices. As long as the tuner 110 can receive the channel interference information generated by the adjacent channel interference detector 132, these design changes all belong to the scope of the present invention.

In this embodiment, known TV broadcasting signal bandwidths are 5 MHz, 6 MHz, 7 MHz and 8 MHz, so the SAW filter with 8 MHz bandwidth is used as the SAW filter 112 hereinafter.

In the device 100 , assuming that the bandwidth of the TV channel is 6 MHz, the filtered signal will contain adjacent channel interference as shown in FIG. 2 . FIG. 2 is a schematic diagram of the bandwidth of the SAW filter 112 being larger than that of the TV channel. As shown in Figure 2, because the bandwidth of the surface acoustic wave filter 112 is greater than the bandwidth of the TV channel, the filtered signal not only includes the signal required by the TV channel, but also includes the signal of another TV channel, Where the signal of the other television channel is considered to be interference to the desired signal of the television channel, generally speaking, the interference is adjacent channel interference and will degrade the image quality of the television program on the desired signal.

In order to eliminate the adjacent channel interference, the center frequency of the surface acoustic wave filter 112 is adjusted to filter the adjacent channel interference. Before adjusting the center frequency of the surface acoustic wave filter 112, it is necessary to compare the high frequency band components and the low frequency To classify the adjacent channel interference of the TV channel into high-band adjacent channel interference or low-band adjacent channel interference, the degree of high-band or low-band adjacent channel interference can be simply calculated by measuring It is obtained by measuring the intensity in the high frequency band or the low frequency band bandwidth. When the degree of the high-band component of the adjacent channel interference is greater than that of the low-band component of the adjacent channel interference, the adjacent channel interference is classified as high-band adjacent channel interference; conversely, when the degree of the high-band component of the adjacent channel interference Adjacent channel interference is classified as low-band adjacent channel interference to a degree not greater than the low-band component of the adjacent channel interference.

Generally speaking, when the TV is turned on, it will automatically scan channels to detect whether there are TV programs on each channel. Adjacent channel interference detection can be performed during the channel automatic scan to generate the channel interference information, and the channel interference information includes channel Information such as whether there is adjacent channel interference and the classification result of adjacent channel interference.

After classifying the adjacent channel interference, the demodulator 130 notifies the tuner 110 via a serial control bus to adjust the center frequency of the SAW filter 112, the demodulator 130 transmits the channel interference information to the tuner 110, and The tuner 110 adjusts the SAW filter 112 according to the channel interference information. Assuming that the bandwidth of the television channel is represented as B, when the classification result indicates that the adjacent channel interference of the television channel is high-band adjacent channel interference, the tuner 110 moves the center frequency of the filter to a lower frequency and moves The amount is (8-B)/2, in other words, the amount of movement is equal to an overlapping bandwidth of the high frequency band adjacent channel interference and the bandwidth of the surface acoustic wave filter 112; when the classification result indicates that the TV channel When the adjacent channel interference is low-band adjacent channel interference, the tuner 110 shifts the center frequency of the filter to a higher frequency by an amount of (8-B)/2, in other words, the shift amount is equal to the low-band An overlapping bandwidth of the adjacent channel interference and the bandwidth of the SAW filter 112 . FIG. 3 is a schematic diagram of shifting the center frequency of the surface acoustic wave filter shown in FIG. 2 . As shown in Figure 3, the tuner shifts the center frequency of the SAW filter to a low frequency by 1 MHz, so that the SAW filter can filter adjacent channel interference as desired. Therefore, by using the center frequency shifting technique described above To filter adjacent channel interference can greatly improve the TV picture quality.

It should be noted that measuring the intensity of the high frequency band or low frequency band of the SAW filter 112 is only one of the methods for classifying adjacent channel interference. The methods for detecting ACI and classifying ACI into high-band ACI or low-band ACI can also be used in the embodiments of the present invention, and should belong to the scope of the present invention.

It should be noted that, in the embodiment of the present invention, the demodulator 130 notifies the tuner 110 through the serial control bus, however, the demodulator 130 can also notify the tuner 110 through firmware or other devices. In addition, the channel interference information may not only include the classification results of adjacent channel interference, but may also include information such as the adjusted center frequency or the shift amount of the center frequency of the SAW filter. These design changes should all belong to the present invention category.

In addition, if the device 100 is designed in a digital TV terrestrial broadcasting vehicle receiver (DVB-Tmobile receiver), the adjacent channel interference may change with the movement of the vehicle receiver, therefore, the adjacent channel interference detector can be designed To periodically automatically detect and classify the adjacent channel interference, if the generated channel interference information changes, the tuner 110 adjusts the center frequency of the SAW filter 112 according to the latest channel interference information.

Briefly summarizing the above content, the present invention proposes a method for adjusting the center frequency of a surface acoustic wave filter. First, an adjacent channel interference detector detects and classifies adjacent channel interference to generate channel interference information; then, the tuner generates channel interference information according to the channel interference information. to adjust the center frequency of the SAW filter; finally, in order to support automotive receiver applications, the adjacent channel interference detector can be implemented periodically to achieve the best signal quality.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims (18)

1. A method for adjusting a center frequency of a filter to extract information on a target channel, the method comprising: For the target channel, detecting adjacent channel interference to generate channel interference information; and For the target channel, the center frequency of the filter is adjusted according to the channel interference information. 2. The method of claim 1, wherein the filter is a surface acoustic wave filter. 3. The method of claim 1, wherein the target channel is a television channel. 4. The method of claim 3, further comprising: The filter is set such that the filter has a maximum bandwidth among a plurality of signal bandwidths available for transmitting television signals. 5. The method of claim 3, wherein the step of detecting adjacent channel interference to generate the channel interference information further comprises: classifying the adjacent channel interference of the target channel into high-band adjacent channel interference or low-band adjacent channel interference to generate a classification result; Wherein the center frequency of the filter is adjusted according to the classification result. 6. The method according to claim 5, wherein the step of classifying the adjacent channel interference of the target channel as high frequency band adjacent channel interference or low frequency band adjacent channel interference further comprises: Comparing the levels of high-band components and low-band components of adjacent channel interference to generate a comparison result; classifying the adjacent channel interference for the target channel as high-band adjacent channel interference when the magnitude of the high-band component of the adjacent channel interference is greater than the magnitude of the low-band component of the adjacent channel interference; and When the degree of the high-band component of the adjacent channel interference is not greater than the degree of the low-band component of the adjacent channel interference, the adjacent channel interference of the target channel is classified as low-band adjacent channel interference. 7. The method as claimed in claim 5, wherein the step of adjusting the center frequency of the filter according to the classification result further comprises: moving the center frequency of the filter to a lower frequency when the classification result indicates that the adjacent channel interference of the target channel is high-band adjacent channel interference; and When the classification result indicates that the adjacent channel interference of the target channel is low-band adjacent channel interference, moving the center frequency of the filter to a higher frequency. 8. The method of claim 7, wherein the center frequency of the filter is shifted by an amount equal to an overlapping bandwidth of the high-band adjacent channel interference or the low-band adjacent channel interference and a bandwidth of the filter. 9. The method of claim 1, wherein detecting adjacent channel interference for the target channel is performed periodically. 10. An apparatus for adjusting a center frequency of a filter to extract information on a target channel, the apparatus comprising: an adjacent channel interference detector, used for detecting adjacent channel interference to generate channel interference information for the target channel; and A tuner is used for adjusting the center frequency of the filter according to the channel interference information for the target channel. 11. The apparatus of claim 10, wherein the filter is a surface acoustic wave filter. 12. The apparatus of claim 10, wherein the target channel is a TV channel. 13. The apparatus of claim 12, wherein the filter has a maximum bandwidth among a plurality of signal bandwidths available for transmitting television signals. 14. The apparatus of claim 12, wherein the adjacent channel interference detector classifies the adjacent channel interference of the target channel into high-band adjacent channel interference or low-band adjacent channel interference to generate a classification result; wherein the filtering The center frequency of the detector is adjusted according to the classification result. 15. The apparatus as claimed in claim 14, wherein the adjacent channel interference detector compares the degree of the high frequency band component and the low frequency band component of the adjacent channel interference to generate a comparison result; when the degree of the high frequency band component of the adjacent channel interference The adjacent channel interference detector classifies the adjacent channel interference of the target channel as high-band adjacent channel interference when the magnitude of the low-band component of the adjacent channel interference is greater than that of the adjacent channel interference; The ACI detector classifies the ACI of the target channel as low-band ACI when the extent of the low-band component of the channel interference is determined. 16. The apparatus as claimed in claim 14, wherein when the classification result indicates that the adjacent channel interference of the target channel is high-band adjacent channel interference, the tuner moves the center frequency of the filter to a lower frequency; and when the classification result indicates that the adjacent channel interference of the target channel is low-band adjacent channel interference, the tuner moves the center frequency of the filter to a higher frequency. 17. The apparatus of claim 16, wherein the center frequency of the filter is shifted by an amount equal to an overlapping bandwidth of high-band adjacent channel interference or low-band adjacent channel interference and a bandwidth of the filter. 18. The apparatus of claim 10, wherein the adjacent channel interference detector periodically detects adjacent channel interference for the target channel.

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