MXPA06006310A

MXPA06006310A - Apparatus and method for providing automatic gain control

Info

Publication number: MXPA06006310A
Application number: MXPA/A/2006/006310A
Authority: MX
Inventors: Thomas Mayer Matthew; Ward Muterspaugh Max
Original assignee: Thomas Mayer Matthew; Ward Muterspaugh Max; Thomson Licensing Sa
Priority date: 2003-12-22
Filing date: 2006-06-02
Publication date: 2006-10-17

Abstract

Signal processing apparatus (100) such as a television signal receiver provides automatic gain control (AGC) in a manner that avoids excessive tuner gain reduction and compensates for interference from both analog and digital s signals. According to an exemplary embodiment, the signal processing apparatus (100) includes a tuner (10) operative to tune an RF signal to generate an 1F signal. A first filter (20) is operative to filter the IF signal to generate a filtered IF signal. An AGC detector (30) is operative to enable generation of an AGC signal for the tuner (10) responsive to the filtered IF signal. The AGC detector (30) includes a second filter (35) operative to attenuate a predetermined carrier frequency.

Description

APPARATUS AND METHOD FOR PROVIDING AUTOMATIC GAIN CONTROL FIELD OF THE INVENTION The present invention in general relates to automatic gain control (AGC) for apparatus such as television signal receivers, and more in particular, with an apparatus and method for providing the AGC which prevents excessive reduction. in the gain of the tuner and compensates for the interference of the analog and digital signals.

BACKGROUND OF THE INVENTION Apparatus as television signal receivers use the AGC to control the gain of a tuner in order to maintain the amplitude of the tuner output signal at a relatively constant level. A problem associated with current AGC techniques can occur when a relatively weak signal is received in the presence of much stronger adjacent signals, which overload the tuner and interfere with the reception of the desired signal. The above problem applies in particular with television signal receivers with the capability of receiving analog and digital signals. Prior to the introduction of digital television, adjacent channel frequencies were never assigned in the same geographical areas. This practice, in most cases, prevented interference from adjacent channels. However, with the introduction of digital television, adjacent channels are required to be used so that both analog and digital signals can be transmitted during a transition period until virtually all television signal receivers are replaced with new ones. units with the capacity of digital reception. As a result, a desired, relatively weak analog or digital television signal may experience interference from adjacent, stronger, unwanted digital or analog signals. Known AGC techniques detect the presence of unwanted, stronger adjacent signals and compensate for them by reducing the gain of the tuner. However, in certain cases, the gain of the tuner can be reduced to a very low level, so that the desired signal is below a critical level for proper demodulation. For example, in cases where adjacent unwanted signals are 20 to 40 dB stronger than the desired signal, known AGC techniques often reduce the gain of the tuner to a level that prevents proper demodulation. Known AGC techniques are also deficient in that they fail to provide the appropriate provision for the interference of digital and analog signals. Accordingly, there is a need for an apparatus and method for providing the AGC which solves the above problems, and thus avoids excessive gain reduction of the tuner and compensates for the interference of the analog and digital signals. The present invention solves these and / or other cases.

BRIEF DESCRIPTION OF THE INVENTION In accordance with one aspect of the present invention, a signal processing apparatus is described. In accordance with an exemplary embodiment, the signal processing apparatus comprises a tuning means for tuning an RF signal to generate an IF signal. A first filtering means filters the IF signal to generate a filtered IF signal. An AGC detection means allows the generation of an AGC signal for the tuning means, which responds to the filtered IF signal. The AGC detection means includes a second filtering means for attenuating the predetermined carrier frequency. In accordance with another aspect of the present invention, a method for providing the AGC is described. According to an exemplary embodiment, the method comprises the steps of using a tuner to tune an RF signal to generate an IF signal, filter the IF signal to generate a filtered IF signal, generate an AGC signal that responds to the filtered IF signal, wherein the step of generating includes attenuating the predetermined carrier frequency, and providing the AGC signal to the tuner. In accordance with another aspect of the present invention, a television signal receiver is described. In accordance with an exemplary embodiment, the television signal receiver comprises a tuner that operates to tune an RF signal to generate an IF signal. A first filter that operates to filter the IF signal to generate an IF signal. An AGC detector operates to allow generation of an AGC signal for the tuner, which responds to the filtered IF signal. The AGC detector includes a second filter that operates to attenuate a predetermined carrier frequency.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned and other features and advantages of this invention, and how to achieve them will be evident and the invention will be better understood by referring to the following description of the embodiments of the invention taken together with the accompanying drawings, in which: Figure 1 is a block diagram of a signal processing apparatus in accordance with an exemplary embodiment of the present invention. Figure 2 is a circuit schematic digital of the AGC detector of Figure 1, in accordance with an exemplary embodiment of the present invention. Figure 3 is a frequency response graph illustrating the relationships between the output voltage and the input frequency in accordance with an exemplary embodiment of the present invention, and Figure 4 is a flow chart illustrating the steps of compliance with an exemplary embodiment of the present invention. The examples set forth herein illustrate the preferred embodiments of the invention, and such examples should not be construed as limiting the scope of the invention in any way.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, and more particularly to Figure 1, there is shown a signal processing apparatus 100 in accordance with the exemplary embodiment of the present invention. The signal processing apparatus 100 may represent the processing circuitry of the main end of a receiving device, such as a television signal receiver and / or other device. As shown in Figure 1, the signal processing apparatus 100 comprises a tuning means such as a tuner 10, a first filtering means, such as a surface acoustic wave (SAW) filter 20, an AGC detection means as an AGC detector 30, an AGC processing means such as an AGC processing block 40, an amplification means such as an amplifier 50, another filter means such as a SAW filter 60, a demodulation means and processing as a block 70 of demodulation and processing, an audio processing and output means such as a processing block 80 and speakers and a display means as a video display 90. Some of the aforementioned elements of Figure 1 can be incorporated with the use of integrated circuits (IC), and certain elements, for example, can be included in one or more ICs. For clarity of description, certain elements associated with the signal processing apparatus 100, such as certain control signals (e.g., channel selection signals), energy signals and / or other elements may not be shown in Figure 1. The tuner 10 operates to perform a signal tuning function. In accordance with an exemplary embodiment, the tuner 10 receives an RF input signal from a signal source, such as a terrestrial, cable, satellite, Internet and / or other signal source and performs the tuning function. signal when filtering and converting the frequency (ie a multi-stage or single-stage downward conversion) into a descending order, the RF input signal to generate an IF signal between 41 and 47 MHz. This IF signal is represented in the point A of Figure 1. The RF input signal and the IF signal may include audio, video and / or data content, and may be of a similar modulation scheme (eg, NTSC, PAL, SECAM, etc.) and / or a digital modulation scheme (for example, ATSC, QAM, etc.). Also, in accordance with an exemplary embodiment, the tuner 10 receives an RF AGC signal from the AGC processing circuitry 40, which enables the AGC function. The SAW filter 20 operates to filter the IF signal provided from the tuner 10 in order to generate different filtered IF signals. These filtered IF signals are represented in point B of Figure 1. In accordance with an exemplary embodiment, the SAW filter 20 includes one or more individual SAW filters, which remove a substantial portion of the adjacent unwanted channel energy from the IF signal provided from the tuner 10 to generate different filtered IF signals. The differential or balanced operation with respect to a ground circuit minimizes interference from the parasitic coupling, including the capacitive coupling of the SAW filter input 20, which can degrade the band rejection of the SAW filter 20. In accordance with this exemplary embodiment, the frequency response of the SAW filter 20 slightly exceeds the frequency range of 41 to 47 MHz. In this way, the adjacent digital channel interference can be controlled well since the digital television signals are characterized by having a very even distribution of energy over its bandwidth. As indicated in Figure 1, one of the different, filtered IF signals emitted from the SAW filter 20 is provided to the AGC detector 40 to enable the AGC function of the tuner 10. The AGC detector 30 operates to sample a predetermined signal and enabling the generation of an AGC RF signal for the tuner 10. In accordance with the exemplary embodiment of Figure 1, the AGC detector 30 samples one of the filtered, different IF signals from the SAW filter 20 and generates an output signal that allows the generation of the AGC RF signal. Since only a portion of the adjacent, unwanted channel energy is present in the different filtered filtered IF signal provided from the SAE filter 20, the AGC RF signal can be generated with an optimal balance of the digital adjacent channel interference and the desired signal. As will be described later, the AGC detector 30 also includes a filtering means for attenuating a predetermined carrier frequency, namely an analogous sound carrier, in order to minimize any adjacent adjacent channel interference. The AGC detector 30 can be used in multiple tuning environments. As such, the AGC detector 30 can receive control signals (not shown) that vary its operating characteristics as a function of the selected tuner. Other details regarding the AGC detector 30 will be provided later. The AGC processing block 40 operates to carry out the processing functions associated with the generation of an AGC RF signal for the tuner 10. In accordance with an exemplary embodiment, the AGC processing block 40 performs functions including , but are not limited to, monitor thresholds on which the gain reduction begins, and adjust the AGC speed. The AGC processing block 40 can be implemented, for example, with the use of an IC as an NXT2004 manufactured by ATI. However, with respect to the inventive concepts of the present invention, the AGC processing block 40 is not required. Accordingly, the output signal of the AGC detector 30 can be applied directly to the tuner 10 as the AGC RF signal. The amplifier 50 operates to amplify the filtered IF signal provided from the SAW filter 20 so as to generate an amplified IF signal. The SAW filter 60 operates to filter the amplified IF signal provided from the amplifier 50 to thereby generate another set of filtered IF signals, different for demodulation and other processing. The demodulation and processing block 70 operates to demodulate and process (eg, decode, etc.) the filtered, different IF signals provided from the SAW filter 60 in order to generate the demodulated audio and / or video signals for output. In accordance with an exemplary embodiment, the demodulation and processing block 70 operates to perform different types of signal demodulation including analog demodulation (e.g., NTSC, PAL, SECAM, etc.) and digital demodulation (e.g., ATSC, QAM, etc.) as well as various types of signal decoding including analog decoding (eg, NTSC, PAL, SECAM, etc.) and digital decoding (eg, MPEG, etc.). The processing block 80 and audio speakers operate to process the demodulated audio signals provided by the demodulation and processing block 70 and provide an audio output. The video display 90 operates to provide a video display corresponding to the demodulated video signals provided from the demodulation and processing block 70. With reference to Figure 2, a schematic circuit diagram of the AGC detector 30 of Figure 1 is shown, in accordance with an exemplary embodiment of the present invention. As shown in Figure 2, the AGC detector 30 comprises resistors R1 to R13, capacitors C1 to C10, inductors L1 to L3, transistors Q1 and Q2, diodes D1 and D2, a ceramic resonator X1. The exemplary values for resistors R1 to R13, capacitors C1 to C10, and inductors L1 to L3 are shown in Figure 2. Other values can be used. Each of the transistors Q1 and Q2 of Figure 2 are incorporated as a double gate metal oxide semiconductor field effect transistor (MOSFET), such as a model BF1005 transistor manufactured by Infineon. Each of the diodes D1 and D2 of Figure 2 are incorporated as a Schottky diode, such as the diode 1PS76SB17 manufactured by Philips. The ceramic resonator X1 of Figure 2 can be incorporated, for example, as a ceramic filter model MKTGA47M2CAHP00B05 manufactured by Murata. As shown in Figure 2, the resistor R9, the capacitor CP, the inductor L3 and the ceramic resonator X1, represent a "capture" filter 35. In accordance with an exemplary embodiment, the capture filter 35 operates to attenuate a predetermined carrier frequency, namely an analog sound carrier of 47.25 MHz. In analog television, such as NTSC, the energy of the signal is concentrated near the carriers, specifically in the image and sound carriers. In the presence of analog channel interference, the adjacent 47.24 MHz sound carrier is very close to the band edge of the desired signal. The presence of this sound carrier can produce too much energy and thus cause the gain of the tuner 10 to be adversely reduced more than desired. With the capture filter 35 of Figure 2, this problem is solved, since the ceramic resonator X1 is tuned to deflect the frequencies of 47.25 MHz. The inductor L3 and the capacitor C9 are provided to optimize the impedances and the resistor R9 is provided to control the attenuation amount of the 47.25 MHz sound carrier. By controlling the frequency response of the SAW filter 20 and providing the capture filter 35 as described above, the resulting RF AGC signal applied to the tuner 10 is not only optimized to avoid the overload of a much higher variation of the interfering signal levels, but also it is optimized for the analog and digital interfering signals. The benefits of the present invention are apparent from the frequency response graph of Figure 3, described below. With reference to Figure 3, a frequency response plot 300 is shown illustrating the relationships between the output voltage and the input frequency according to an exemplary embodiment of the present invention. In particular, Figure 3 shows a schematic of the output voltage versus the input frequency for a signal applied to the SAW filter 20 at point A of Figure 1 and an output voltage measured at point C of Figure 1. two frequency responses are shown in the graph 300 of Figure 3. The X curve is taken without the addition of the capture filter 35 of Figure 2. The Y curve is taken with the addition of the capture filter 35 and shows the adjustment in the frequency response made to optimize the operation for the analogous interfering signals. In graphic 300 of Figure 3, the frequency response between 47 and 48 MHz is the bandwidth of the adjacent channel which is processed to effect the gain control of the tuner 10 in the presence of the interference of the adjacent analog channel. With reference to Figure 4, a flow diagram 400 illustrating the steps in accordance with an exemplary embodiment of the present invention is shown. For purposes of explanation and example, the steps of Figure 4 will be described with reference to the elements of the signal processing apparatus 100 of Figure 1. The steps of "Figure 4 are merely exemplary and are not intended to limit the present invention in no sense In step 410, the signal processing apparatus 100 tunes an RF signal to generate a corresponding IF signal In accordance with an exemplary embodiment, the tuner 10 receives an RF input signal from a signal source as a terrestrial, cable, satellite, Internet and / or other signal source, and performs the signal tuning function by filtering and down-converting the frequency (ie, multistep or multi-stage downconversion). single stage), the RF input signal to thereby generate an IF signal between 41 and 47 MHz in step 410. This IF signal is represented at point A of Figure 1. Com or indicated above, the RF input signal and the IF signal may include audio, video and / or data content, and may be of a similar modulation scheme (eg, NTSC, PAL, SECAM, etc.) and / or of a digital modulation scheme (for example, ATSC, QAM, etc.). In step 420, the signal processing apparatus 100 filters the IF signal to generate filtered IF signals. According to an exemplary embodiment, filter SAW filters the IF signal generated by tuner 10 in step 410, in order to generate filtered IF signals different in step 420. These filtered IF signals are represented in point B of Figure 1. As mentioned above, the frequency response of the SAW filter 20 exceeds a bit the frequency range of 41 to 47 MHz and thus contains some interference of the adjacent digital channel. In step 430, the signal processing apparatus 100 generates an AGC signal in response to one of the filtered IF signals by attenuating a predetermined carrier frequency. In accordance with an exemplary embodiment, the AGC detector 30 displays one of the different filtered IF signals generated by the SAW filter 20 in step 420 and generates an output signal that allows generation of the AGC RF signal in step 430 As mentioned before, the AGC detector 30 includes a capture filter 35 which attenuates the analog sound carrier of 47.25 MHz and thus controls the adjacent analog channel interference. The AGC signal generated in step 430 may be output directly from the AGC detector 30 or may be the output of the AGC processing block 40, as described above. In step 440, the signal processing apparatus 100 provides the AGC signal to its tuner 10. In accordance with an exemplary embodiment, the AGC signal generated in step 430 is provided to the tuner 10 from the AGC detector 30 or from the block 40 of AGC processing, depending on the particular mode. The AGC signal, in turn, controls the gain of the tuner 10 and thus facilitates the RF AGC function of the signal processing apparatus 100. As described herein, the present invention provides an apparatus and method for providing the AGC which prevents excessive reduction of tuner gain and compensates for the interference of analog and digital signals. The present invention can be applied in several apparatuses, either with or without a deployment device. Accordingly, the phrases "signal processing apparatus" and "television signal receiver", as used herein, refer to systems or apparatus that include, but are not limited to,, television sets, computers or monitors that include a display device, and apparatus systems such as transcoders, video cartridge recorders (VCR), digital versatile disc players (DVD), video game boxes, personal video recorders (PVR), radios, computers or other devices that may not include a deployment device. While this invention has been described with a preferred design, the present invention can also be modified within the spirit and scope of this description. Therefore, this application is intended to encompass any variation, use or adaptation of the invention with the use of its general principles. Furthermore, this application is intended to encompass such sections of the present invention, which fall within the practice customary or known in the art to which the invention pertains and which fall within the limits of the appended claims.

Claims

6 CLAIMS

1. A signal processing apparatus (100), characterized in that it comprises: a tuning means (10) for tuning an RF signal to generate an IF signal; a first filtering means (20) for filtering the IF signal to generate a filtered IF signal; an AGC detection means (30) for enabling the generation of an AGC signal for the tuning means (10) in response to the filtered IF signal; and wherein the AGC detection means (30) includes a second filtering means (35) for attenuating a predetermined carrier frequency.

2. The signal processing apparatus (100) according to claim 1, characterized in that the IF signal is between 41 and 47 MHz.

3. The signal processing apparatus (100) according to claim 1, characterized in that the first filtering means (20) includes a SAW filter. The signal processing apparatus (100) according to claim 1, characterized in that the predetermined carrier frequency corresponds to an analog sound carrier frequency. 5. The signal processing apparatus (100) according to claim 1, characterized in that the predetermined carrier frequency corresponds to approximately 47.25 MHz. 6. The signal processing apparatus (100) according to claim 1, characterized in that the second filtering means (35) includes a tuned ceramic resonator to derive the predetermined carrier frequency. 7. A method (400) for providing AGC, characterized in that it comprises the steps of: using a tuner to tune an RF signal to generate an IF signal (410); filtering the IF signal to generate a filtered IF signal (420); generating an AGC signal that responds to the filtered IF signal, wherein the step of generating includes attenuating a predetermined carrier frequency (430); and provide the AGC signal to the tuner (440). The method (400) according to claim 7, characterized in that the IF signal is between 41 and 47 MHz. The method (400) according to claim 7, characterized in that the filtering step includes using a filter SAW The method (400) according to claim 7, characterized in that the predetermined carrier frequency corresponds to a similar sound carrier frequency. The method (400) according to claim 7, characterized in that the predetermined carrier frequency corresponds to approximately 47.25 MHz. 12. The method (400) according to claim 7, characterized in that the step of generating (430) also it includes using a ceramic resonator to derive the predetermined carrier frequency. 13. A television signal receiver (100), characterized in that it comprises: a tuner (10) that operates to tune an RF signal to generate an IF signal; a first filter (20) that operates to filter the IF signal to generate a filtered IF signal; an AGC detector (30) that operates to allow the generation of an AGC signal for the tuner (10) that responds to the filtered IF signal; and wherein the AGC detector (30) includes a second filter (35) that operates to attenuate a predetermined carrier frequency. 1

4. The television signal receiver (100) according to claim 13, characterized in that the IF signal is between 41 and 47 MHz. The television signal receiver (100) according to claim 13, characterized in that The first filter (20) includes a SAW filter. 16. The television signal receiver (100) according to claim 13, characterized in that the predetermined carrier frequency corresponds to a similar sound carrier frequency. 17. The television signal receiver (100) according to claim 13, characterized in that the predetermined carrier frequency corresponds to approximately 47.25 MHz. 18. The television signal receiver (100) according to claim 13, characterized in that the second filter (35) includes a tuned ceramic resonator to derive the predetermined carrier frequency.