JP2005192060A - Automatic gain control apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic gain controller for performing a reception without being affected by a large disturbing wave other than a desired wave even when including the disturbing wave with respect to the configuration of an automatic gain control amplifier and the control method thereof in a digital television broadcast receiver. <P>SOLUTION: The automatic gain controller is provided with: an RF automatic gain controller for amplifying an RF signal; a frequency converter for converting an amplified RF signal into an IF signal; and an IF automatic gain controller for amplifying a frequency-converted IF signal. The RF automatic gain controller is provided with a reference signal input for controlling a gain by feeding back and input signal of the frequency converter and for setting a maximum value for an output level of the RF automatic gain controller further in comparison with the fed-back signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  INDUSTRIAL APPLICABILITY The present invention is used in the field of digital television broadcast receivers. In the configuration and control method of an automatic gain control amplifier, even if a large interference wave other than a desired wave is included, reception that is not affected by the interference wave It is related with the automatic gain control apparatus for performing.

  An example of a conventional automatic gain control device will be described as prior art 1. This configuration is shown in FIG.

  The automatic gain control device of Prior Art 1 includes a wideband bandpass filter 501, an RF-AGC amplifier 502, a local oscillator 503, a frequency converter 504, an IF tuning filter 505, an IF-AGC amplifier 506, an A / D converter 507, The level detector 510 includes an RF-AGC control unit 509 and an IF-AGC control unit 508.

  The RF input signal 520 made incident by the wideband bandpass filter is removed only to the digital broadcast band signal. Thereafter, the signal selected by the local oscillator 503 is used and converted to the IF signal 521 by the frequency converter 504. At this time, the IF signal 521 includes adjacent interference waves in addition to the desired wave. Next, the interference wave is removed through the IF channel selection filter to obtain only the desired wave, and the signal enters the A / D converter 507.

  The signal converted into the digital signal 522 by the A / D converter is digitally processed to obtain an average amplitude of the signal. Based on this signal level, the RF-AGC control signal 524 and IF-AGC control signal 523 are fed back by a predetermined gain distribution, and the gains of the RF-AGC amplifier 502 and the IF-AGC amplifier 506 are controlled. The input signal to the / D converter 507 is made constant (see, for example, Patent Document 1).

  An example of an automatic gain control device according to another conventional technique will be described as Conventional Technique 2. This configuration is shown in FIG.

  This automatic gain control device includes a wideband bandpass filter 601, an RF-AGC amplifier 602, a local oscillator 603, a frequency converter 604, an image signal removal filter 605, an IF channel selection filter 606, an IF-AGC amplifier 607, and an A / D. It comprises a converter 608, level detectors 609, 613, 614, an RF-AGC control unit 615, and an IF-AGC control unit 610.

  The RF input signal 620 made incident by the wideband bandpass filter is removed only to the digital broadcast band signal. Thereafter, the signal selected by the local oscillator 603 is converted into an IF signal 621 by the frequency converter 604. At this time, the IF signal 621 includes an adjacent interference wave in addition to the desired wave. From this signal, the signal levels of the desired wave and the interference wave are obtained by the IF filter 611 that passes only the desired wave and the IF filter 612 that passes only the desired wave. The RF-AGC control signal 625 is fed back by the gain determined by the ratio of the desired wave to the disturbing wave and the magnitude of the desired wave, and the RF-AGC amplifier 602 is controlled.

The A / D converter 608 receives a signal obtained by removing the interference wave through the IF tuning filter 606 and making only the desired wave. The signal converted into the digital signal 623 by the A / D converter is digitally processed to obtain the average amplitude of the signal. Based on this signal level, the IF-AGC control signal 624 is fed back to control the gain of the IF-AGC amplifier 607 (see, for example, Patent Document 2).
JP 2002-84205 A JP 2001-7669 A

  In the case of the automatic gain controller shown as the prior art 1, it is necessary to determine in advance the gain and distribution of the RF-AGC amplifier and IF-AGC amplifier based on the output of the level detector. Assuming that it is included in the signal, it is necessary to take a margin in the input level to the frequency converter. This is because, when an interference wave more than expected by the actual RF input signal is input, the waveform is distorted by the frequency converter and good demodulation cannot be performed.

  Further, when there is no interference wave assumed by the actual RF input signal, the reception sensitivity is sacrificed because of the assumed margin even though the input level to the frequency converter can be increased.

  Further, it is complicated to simultaneously control the gains of the RF-AGC amplifier and the IF-AGC amplifier, and when one of them is operated, one side is stopped. It was very difficult to set the input level to the / D converter appropriately.

  In the case of the automatic gain controller shown as the prior art 2, the RF-AGC control signal needs to obtain the magnitude of the desired wave of the IF signal and the magnitude of the interference wave, and an IF filter having a sharp frequency characteristic is required. And very expensive. In addition, when the IF filter is composed of an inexpensive filter, there is a problem that it is difficult to separate a desired wave and an interference wave and accuracy is deteriorated. In addition, two or more level detectors for the desired wave and the interference wave are required. Furthermore, since the RF-AGC control signal level is determined based on the ratio of the desired wave and the interference wave, a complicated RF-AGC control unit is required, and there is a problem that a very high cost and a large space are required.

  The present invention has been made in view of the above-described conventional technical problems. In the receiver for digital television broadcasting, the configuration of the automatic gain control amplifier and the control method thereof include a large interference wave other than the desired wave. Even in such a case, an automatic gain control device for performing reception that is not affected by the interference wave is provided.

  To achieve the above object, an automatic gain control device according to the present invention includes an RF automatic gain controller that amplifies an RF signal, a frequency converter that converts the amplified RF signal into an IF signal, and a frequency converted signal. An IF automatic gain controller for amplifying an IF signal, wherein the RF automatic gain controller is gain-controlled by feeding back an input signal of the frequency converter and further comparing the RF automatic gain controller by comparing with a feedback signal; A reference signal input for setting a maximum value of the output level of the gain controller is provided.

  According to the automatic gain control apparatus of the present invention, there is provided an automatic gain control method and apparatus capable of good reception without causing adverse effects such as distortion cross modulation even when a large interference wave enters an RF input signal. It becomes possible.

  Further, it is not necessary to take a margin for an interference wave assumed for the input level of the frequency converter, and it is possible to input the signal to the frequency converter at a signal level in accordance with the modulation method, thereby improving the reception sensitivity. Further, it is possible to control the gain with high accuracy by following the fluctuation of the input signal seen in the moving body or the like.

(Embodiment 1)
Hereinafter, an exemplary embodiment of an automatic gain control device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a block diagram of the entire automatic gain control apparatus according to the present embodiment. In FIG. 1, an incident RF input signal 120 is input to a wideband bandpass filter 101 that extracts only a digital broadcast band signal, and its output is input to an RF automatic gain controller having a feedback loop.

  This RF automatic gain controller includes an RF-AGC amplifier 102 that amplifies an RF band signal with a variable gain, an RF level detector 110 that detects an output level of the RF-AGC amplifier 102 and outputs it as a DC voltage signal, and an RF level detector The level comparator 111 that compares the voltage level of the output of the comparator 110 and the RF reference signal and outputs the gain increase / decrease control signal of the RF-AGC amplifier 102, and the gain of the feedback loop can be increased or decreased based on the RF loop gain control signal 126. The gain of the circuit system is automatically controlled by forming a feedback loop.

  The RF signal 121 amplified by the RF automatic gain controller is input to the frequency converter 104 that converts the RF signal into an intermediate frequency band signal, and is output as an IF signal. This frequency conversion is performed by mixing the output of the local oscillator 103 that oscillates at a frequency corresponding to the selected channel. This IF signal is input to the IF automatic gain controller through the IF channel selection filter 105 that passes only the selected desired wave.

  This IF automatic gain controller includes an IF-AGC amplifier 106 that amplifies an intermediate frequency band signal with a variable gain, an A / D converter 107 that converts an analog signal into a digital signal at a predetermined clock, and an input signal by quadrature detection. A quadrature demodulator 113 that demodulates I and Q signals, a filter that limits the band after satisfying the Nyquist criterion, a roll-off filter 114 that removes noise on the propagation path, and a reflected wave generated by the influence of the transmission path A waveform equalizer 115 for removing a ghost waveform, a demodulation level detector 108 for detecting the level of a signal after quadrature detection by digital calculation and outputting a signal corresponding to the level, and the output of the demodulation level detector 108 The IF-AGC control unit 109 for controlling the gain of the IF-AGC amplifier 106 forms a feedback loop. And automatically controlling the gain of the circuit system in Rukoto.

  Regarding the automatic gain control apparatus according to the present invention configured as described above, first, the operation of controlling the output level of the RF automatic gain controller will be described.

  The RF signal removed by the wideband bandpass filter 101 only to the digital broadcast band signal is input to the RF-AGC amplifier 102. Thereafter, the RF level detector 110 detects the magnitude of the RF signal 121 amplified through the RF-AGC amplifier 102. Since this signal includes an interference wave such as an adjacent wave in addition to the desired wave, the output of the RF level detector 110 has the magnitude of a signal that combines the desired wave and the interference wave.

  When the signal 121 entering the frequency converter 104 exceeds the saturation level, cross modulation or the like occurs in the frequency converter 104 and reception characteristics deteriorate. Further, when the signal 121 entering the frequency converter 104 is small, the influence of the noise of the frequency converter 104 is increased, the C / N is deteriorated, and the reception characteristic is deteriorated. Therefore, the RF signal 121 to the frequency converter 104 is feedback-controlled by setting the RF reference signal 125 so that the RF-AGC amplifier 102 can keep the frequency converter 104 constant at a signal level that does not saturate the frequency converter 104.

  The RF reference signal 125 gives a reference value for determining a feedback amount so as to keep the output level of the RF-AGC amplifier 102 constant, and is compared with the output level of the RF level detector 110 by the level comparator 111. Thus, the gain of the RF-AGC amplifier 102 is controlled through the RF loop gain amplifier 112. That is, when the RF reference signal 125 is larger than the output level of the RF level detector 110, feedback control is performed so as to increase the current gain of the RF-AGC amplifier 102, and when it is smaller, the current gain is decreased. Feedback controlled. Therefore, when the RF reference signal 125 and the output level of the RF level detector 110 become equal, the gain of the RF-AGC amplifier 102 is maintained.

  Therefore, the normal RF reference signal 125 is a magnitude of the signal level output from the RF level detector 110 when a signal equivalent to the signal of the maximum input level that does not saturate the frequency converter is passed through the RF level detector 110. It is good to set it. In this way, gain control can be performed so that the output level of the RF-AGC amplifier 102 is always the same as the maximum input level at which the frequency converter is not saturated.

  In addition, since the degree of performance degradation such as cross modulation due to saturation of the frequency converter differs depending on the modulation method, it may be changed to a reference level for each modulation method obtained experimentally.

  The RF-AGC amplifier 102, the RF level detector 110, the level comparator 111, and the RF loop gain amplifier 112 are composed of analog components, and their characteristics may vary greatly depending on the gain of the amplifier / detector. At this time, the magnitude of the RF signal 121 entering the frequency converter 104 is measured with a spectrum analyzer or the like, and the RF reference signal is adjusted in accordance with the maximum input of the frequency converter 104 which is not saturated, thereby causing variations in analog components. It is possible to eliminate the deterioration of the characteristics due to.

  The relationship between the RF input signal level and the RF-AGC gain will be described with reference to FIGS.

  FIG. 2 is a graph showing the relationship between the RF input signal level and the RF-AGC gain when there is no interference wave in the RF input signal. At point P1 when the frequency converter 104 is not saturated and the maximum RF signal is input, the gain of the RF-AGC amplifier 102 is set to 0 dB. As the RF input signal level decreases, the RF-AGC gain increases proportionally. When the RF-AGC amplifier reaches the maximum gain point Q1, it maintains a constant value even if the RF input signal level decreases.

  FIG. 3 is a graph showing the relationship between the RF input signal level and the RF-AGC gain when the RF input signal includes an interference wave. When the RF input signal includes a desired wave and an interference wave, the frequency converter 104 is not saturated and the input point with the maximum RF signal level is P2. When the RF input signal level (the sum of the desired wave and the disturbing wave) decreases, the RF-AGC gain increases proportionally. When the RF-AGC amplifier 102 reaches the maximum gain point Q2, it maintains a constant value even if the RF input signal level decreases. Considering the relationship between the input signal level of the desired wave and the RF-AGC gain when the RF input signal includes an interference wave, a straight line R2-S2 obtained by subtracting the level of the interference wave from the straight line P2-Q2 Become. This is to realize the gain of the RF-AGC amplifier 102 that automatically takes the margin for the size of the amplifier and gains the gain of the amplifier without taking a margin at all and automatically optimizes the interference wave. Is.

  FIG. 4 illustrates the relationship between the input signal and the output signal of the RF-AGC amplifier 102. When the input signal shown in FIG. 4A is only the desired wave, it can be seen that the output signal has a maximum input level that does not saturate the frequency converter 104. Next, when the desired wave and the interference wave enter the input signal shown in FIG. 4B at the same level, the output signal is 3 dB lower than the maximum input level of the frequency converter 104 that is not saturated. Finally, when a desired wave and a large disturbance wave are included in the input signal shown in FIG. 4C, it can be seen that the desired signal is a very small signal compared to the case described above.

  Next, the operation of the IF automatic gain controller in the automatic gain control apparatus according to the present invention will be described.

  The amplified RF signal 121 that has passed through the RF-AGC amplifier 102 is converted into an IF signal without saturation by the frequency converter 104 using the signal selected by the local oscillator 103. Thereafter, the interference wave is removed by passing through the IF channel selection filter to obtain only the desired wave and enters the IF-AGC amplifier 106.

  The output of IF-AGC amplifier 106 enters A / D converter 107 and is digitally processed with quadrature demodulator 113, roll-off filter 114, and waveform equalizer 115. The quadrature modulator 113 converts the signal into an I signal and a Q signal, the roll-off filter 114 reduces noise on the propagation path, and the waveform equalizer 115 removes ghosts such as multipath. The demodulation level detector 108 digitally calculates the signal magnitude of the I signal from which unnecessary signals such as noise and ghost on the propagation path have been removed, and feeds it back to the IF-AGC control unit 109. This makes it possible to perform accurate demodulation while keeping the magnitudes of the I and Q signals going to the demodulation unit constant. The signal for level detection may be not only the I signal but also the Q signal or both signals.

  FIG. 4 further shows the relationship between the output signal of the RF-AGC amplifier 102 and the output signal of the IF-AGC amplifier 106. The signal of only the desired wave shown in FIG. 4A does not change even if it passes through the IF channel selection filter 105, and is amplified to the optimum I / Q signal level by the IF-AGC amplifier 106. Next, when the desired wave and the disturbing wave are included in the input signal shown in FIG. 4B at the same level, the interference wave is removed by the IF channel selection filter 105, and the IF-AGC is compared to the case of only the desired wave. Amplifier 106 is amplified to an optimum IQ signal level with a gain of 3 dB. Finally, when a desired wave and a large disturbing wave are included in the input signal shown in FIG. 4C, the desired wave after the IF channel selection filter 105 is a very small signal compared to the above case. A large gain is given by the AGC amplifier 106 to obtain the optimum I / Q signal level.

  Next, response speeds of the RF automatic gain controller and the IF automatic gain controller will be described.

  The RF automatic gain controller roughly adjusts the signal level in an analog manner, and takes charge of a response at a feedback speed of about 0.1 Hz to 20 Hz. The IF automatic gain controller finely adjusts the signal level digitally and responds at a feedback speed of about 20 Hz to 1000 Hz. When amplifiers having two independent feedback loops are arranged in series, the response speed is different as described above, so that mutual interference such as oscillation phenomenon is prevented, and the operation of the present invention is more reliable. It can be.

  In addition, the said numerical value was described as an example, and is not limited to it. The feedback response speed of the RF automatic gain controller may be set slower than the feedback response speed of the IF automatic gain controller.

  In the RF automatic gain controller, this response speed can be made variable by changing the gain of the RF loop gain amplifier 112. When the gain of the RF loop gain amplifier 112 is increased, the gain increase / decrease control is greatly performed even if the difference between the output level of the RF-AGC amplifier 102 and the RF reference signal is small. As a result, a predetermined amplification factor is obtained. The time to become is shortened. That is, the feedback response speed is increased. Conversely, if the gain of the RF loop gain amplifier 112 is reduced, the response speed of feedback can be reduced.

  The response speed of the RF automatic gain controller is normally set very slow when the level of the received signal does not fluctuate, such as a home television. When a mobile object such as a car TV is used, if the response speed of the RF automatic gain controller is increased and the feedback speed is set to several tens of Hz (for example, about 10 Hz to 100 Hz), the signal fluctuation also occurs in the mobile object. Can follow.

  According to the automatic gain control device of the present invention configured as described above, first, even when a large interference wave enters the RF input signal, the input signal level including the interference wave in the desired wave is detected, By performing feedback easily and accurately in accordance with the input limit of the frequency converter, it is possible to receive well without causing adverse effects such as distortion cross modulation on the waveform.

  Secondly, it is not necessary to take a margin for the interference wave assumed for the input level of the frequency converter, and the reception sensitivity can be improved. In addition, by changing the reference signal level of the level comparator, the input level of the frequency converter can be easily changed, and a signal at the optimum level according to the modulation method can be input to the frequency converter. It is.

  Third, since the RF automatic gain controller and IF automatic gain controller operate independently and the feedback loop gain can be set individually, it is possible to accurately follow the fluctuations in the input signal found in a moving body or the like. Control becomes possible.

  The automatic gain control apparatus according to the present invention enables optimum amplification even in an environment where a large interference wave exists or an input signal fluctuates greatly. AV equipment such as a television receiver in a home or mobile body It is useful for devices that receive broadcast waves and operate.

The block diagram which shows the structure of embodiment of the automatic gain control apparatus of this invention A graph showing the relationship between the RF input signal level and the RF-AGC gain when there is no interference wave in the RF input signal A graph showing the relationship between the RF input signal level and the RF-AGC amplification factor when there is an interference wave in the RF input signal The figure which shows the relation of the output level with respect to the input where the desired wave and the interference wave are mixed The block diagram which shows the structure of an example of 1st prior art The block diagram which shows the structure of an example of 2nd prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Wideband band pass filter 102 RF-AGC amplifier 103 Local oscillator 104 Frequency converter 105 IF tuning filter 106 IF-AGC amplifier 107 A / D converter 108 Demodulation level detector 109 IF-AGC control part 110 RF level detector 111 Level comparator 112 RF loop gain amplifier 113 Quadrature demodulator 114 Roll-off filter 115 Waveform equalizer 120 RF input signal 121 RF signal entering frequency converter 122 I signal with waveform equivalent output 123 IF-AGC control signal 124 RF-AGC control Signal 125 RF reference signal 126 RF loop gain control signal

Claims (5)

An RF automatic gain controller for amplifying an RF signal, a frequency converter for converting the amplified RF signal into an IF signal, and an IF automatic gain controller for amplifying the frequency-converted IF signal, the RF automatic gain control And a reference signal input for setting a maximum value of the output level of the RF automatic gain controller by controlling the gain by feeding back the input signal of the frequency converter and comparing it with the signal level fed back. An automatic gain control device. 2. The automatic gain control device according to claim 1, wherein the level of the reference signal is switched in accordance with the modulation method of the input signal. 3. The response speed of feedback of the RF automatic gain controller is made variable by changing an amplification factor of a loop gain amplifier provided between feedback loops of the RF automatic gain controller. The automatic gain control device described. 4. The automatic gain control device according to claim 3, wherein the feedback response speed of the RF automatic gain controller is set slower than the feedback response speed of the IF automatic gain controller. The gain control is performed by feeding back the signal level of the I signal or the Q signal after quadrature detection in which the IF automatic gain controller removes an unnecessary signal on the propagation path output from the waveform equalizer. The automatic gain control apparatus according to any one of 1 to 4.

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