JP4564724B2 - Digital broadcast receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital broadcast receiver capable of receiving digital television broadcasts and the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, development of an orthogonal frequency division multiplexing (hereinafter, abbreviated as “OFDM” from Orthogonal Frequency Division Multiplex) scheme is underway as a transmission method for terrestrial digital television broadcasting. The OFDM scheme is a form of multi-carrier transmission scheme, and performs signal transmission by applying amplitude phase modulation (QAM) to 5300 subcarriers arranged at 1 kHz intervals, for example. In terrestrial digital television broadcasting, a high frequency band of about 90 MHz to 800 MHz is used.
[0003]
A digital TV receiver that receives a digital television broadcast such as a terrestrial digital television broadcast selects a high-frequency broadcast by a tuner circuit, and converts and amplifies the signal in an intermediate frequency band. Is a system that performs analog / digital conversion (hereinafter may be abbreviated as “A / D” or “A / D conversion” from Analog / Digital) and performs demodulation by digital signal processing. In this process, an intermediate frequency band signal input to an A / D converter that performs analog / digital conversion needs to be maintained at a constant level, and AGC (Auto Gain Controller) control is performed.
[0004]
In a digital TV receiver that is used in a fixed manner, since the change in the intensity of the received electric field is small, the responsiveness of AGC control is set constant and late. If the response of AGC control is fast, there is a change in amplification gain when pulsed noise or the like is mixed, and even after the instantaneous noise mixing is finished, the level of the received signal is changed due to fluctuation of the amplification gain. This is because it tends to fluctuate. However, in a digital broadcast receiver mounted on a mobile body such as an automobile, the received electric field is likely to change steeply. Therefore, when the response of AGC control is set to be slow, it can follow a sharp change in the received electric field. If it does not move, there is a problem that reception may not be possible despite a stable reception electric field.
[0005]
Not only digital broadcasting but also traveling in a tunnel by car, the radio wave of the broadcasting station does not reach the antenna, and the reception electric field is very weak, so the amplification gain is large. After exiting the tunnel, the radio wave of the tuned broadcasting station reaches the antenna with a sufficiently large electric field strength. If the time constant of the AGC control is large and the control is delayed, it takes time until the AGC control loop converges and returns to a stable state, and the input quality is excessive and the sound quality to be demodulated and reproduced deteriorates. To do. In a certain prior art, when the AGC control is performed so that the output of the high-frequency amplifier circuit is taken out and amplified separately from the reception process and the output becomes constant, the time constant is changed by detecting a sudden change in the input level. (For example, refer to Patent Document 1). In other prior art, in a television broadcast receiver, in order to prevent the video from being disturbed during an excessive phenomenon such as channel selection switching, the lock state of a PLL (Phase Lockerd Loop) in the tuner circuit is determined, When the lock is released, the AGC control time constant is shortened so as to be able to follow a sudden level change at the time of channel selection, and the time constant is lengthened after returning to the locked state (for example, Patent Document 2). reference).
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 5-199137
[Patent Document 2]
JP 2001-148819 A
[0007]
[Problems to be solved by the invention]
FIG. 7 shows the influence of the responsiveness of AGC control with a schematic waveform. FIG. 7A shows the waveform of the input signal. For example, with an in-vehicle OFDM digital TV receiver, broadcast reception starts at time t0 in a strong electric field, pulse noise is mixed at time t1, and weakly passes through the tunnel from time t2 to t3. It is assumed that the electric field is generated and the tunnel exits the tunnel and returns to the strong electric field after time t3. As described above, the frequency of digital television broadcasting is several hundreds of MHz, and a tunnel having a weak electric field inside is considered to have a length of several hundreds of meters or more. Therefore, the waveforms in the figure are just for convenience.
[0008]
FIG. 7B shows a change in amplification gain when the time constant of AGC control is large. From time t0 to t2, the amplification gain is relatively small and does not change even when pulsed noise is mixed at time t1. After time t2, the amplification gain increases. When the tunnel exits at time t3, the amplification gain decreases until time t4 and returns to the same state as from time t0 to t2. FIG.7 (c) shows the change of the output with respect to the amplification gain under AGC control like FIG.7 (b). The pulse noise at time t1 is clipped at the peak. Even if the electric field suddenly changes from a strong electric field to a weak electric field at time t2, the increase in amplification gain is relatively low, and the output decreases. Even after exiting the tunnel from time t3 and returning to a strong electric field, the amplification gain remains high, so the output becomes excessive and the excessive portion is clipped. When the output is clipped, the high frequency component is lost and the television image cannot be fully reproduced.
[0009]
FIG. 7D shows a change in amplification gain when the time constant of AGC control is small. When the time constant is small, the amplification gain is lowered in response to the mixing of pulse noise such as time t1. For this reason, as shown in FIG. 7E, the amplitude of the output becomes small, and there is a possibility that the input level necessary for analog / digital conversion may not be reached. It is not easily affected by the passage of the tunnel from time t2 to t3. As described above, when the digital television broadcast is to be received while traveling with an in-vehicle receiver, it is necessary to always control the responsiveness of the AGC to an appropriate state.
[0010]
In the above-described prior art, the time constant is electrically changed by an analog circuit in order to control the responsiveness of the AGC according to the variation of the received electric field. When these ideas are applied to a digital broadcast receiver, digital signal processing for broadcast demodulation and analog signal processing for AGC control must coexist.
[0011]
An object of the present invention is to provide a digital broadcast receiver capable of adaptively controlling the responsiveness of AGC control in accordance with fluctuations in a received electric field such as when moving by digital signal processing.
[0012]
[Means for Solving the Problems]
  The present invention relates to a digital broadcast receiver that receives a broadcast modulated with a digital signal of a predetermined format in a high frequency band, converts the received signal to an intermediate frequency band, performs analog / digital conversion, and demodulates the digital signal processing. In
  A digital detection means for detecting an analog / digital converted signal and deriving an output value corresponding to an input signal level to the analog / digital conversion;
  Digital comparison means for comparing the output value from the digital detection means with a preset reference value;
  Fluctuations in the received electric fieldBased on the amount of change in the output value of the digital detection meansdetectionAnd select a predetermined characteristic according to the detected fluctuation of the received electric field.Variation detection means;
  The comparison value of the digital comparison means is input and the fluctuation detection meansSelected byCharacteristics, low-pass filteringAnd outputLPF means;
  LPF meansSo that the time constant of the object to be controlled is shortened when the variation detection means detects that the amount of change in the received electric field is large.Amplification gain of received signalcontrolDoOutput a control signal forIncluding AGC control meansSee
  The fluctuation detection means calculates the absolute value of the difference from the output from the digital detection means and the output obtained by delaying the output from the digital detection means for a fixed time, thereby changing the output value of the digital detection means per fixed time. Detects fluctuations in the received electric field based on the obtained change amount per fixed timeThis is a digital broadcast receiver characterized by the above.
[0013]
According to the present invention, a digital broadcast receiver receives a broadcast modulated with a digital signal of a predetermined format in a high frequency band, converts the received signal into an intermediate frequency band, performs analog / digital conversion, and converts the digital signal. In order to demodulate by processing, digital detection means, digital comparison means, fluctuation detection means, LPF means, and AGC control means are included. When the digital detection means detects the analog / digital converted signal and derives an output value corresponding to the input signal level to the analog / digital conversion, the output value is compared with a preset reference value by the digital comparison means. The The LPF means performs a low-pass filtering process on the comparison result of the digital comparison means with a characteristic corresponding to the fluctuation of the received electric field detected by the fluctuation detection means. The AGC control means digitally / analog converts the low-pass filtering result of the LPF means to generate an AGC control voltage for adjusting the amplification gain of the received signal, and so on until the received signal is converted to analog / digital. The gain is controlled at the stage of amplification, and the level of the received signal input to the analog / digital conversion can be kept within a predetermined range. The comparison result of the digital comparison means that performs digital / analog conversion is low-pass filtered by the LPF means, and characteristics such as a low-pass filtering coefficient are selected according to the variation of the received electric field. Using digital signal processing, adaptive control can be performed in accordance with fluctuations in the received electric field.
[0015]
  Further, the fluctuation detection means calculates the absolute value of the difference from the output from the digital detection means and the output delayed from the digital detection means by a predetermined time, thereby obtaining a constant per unit time of the output value of the digital detection means. The variation in the received electric field is detected based on the obtained variation per fixed time.Since the output value of the digital detection means changes corresponding to the fluctuation of the received electric field, the fluctuation of the received electric field is detected based on the amount of change, and the coefficient of the LPF means is selected so as to correspond to a state with a short time constant. By doing so, the responsiveness of AGC control can be adaptively controlled.
[0022]
  Further, in the present invention, the AGC control means only includes an intermediate frequency amplifier that amplifies the signal converted into the intermediate frequency band.InControl of the amplification gainOutput control signal forIt is characterized by that.
[0023]
  According to the present invention, control of amplification gain by AGC controlControl signal output forIs,Only the intermediate frequency amplifier that amplifies the signal converted to the intermediate frequency bandInTherefore, the high-frequency amplifier can maximize the amplification gain, and can realize AGC control effective in a weak electric field with a simple configuration.
[0024]
  Further, in the present invention, the AGC control means can only be a high frequency amplifier that amplifies a signal received in the high frequency band.InControl of the amplification gainOutput control signal forIt is characterized by that.
[0025]
  According to the present invention, control of amplification gain by AGC controlControl signal output forIs,Only high-frequency amplifiers that amplify signals received in the high-frequency bandInAs a result, the amplification gain of the high-frequency amplifier can be reduced in a strong electric field, and the cross modulation characteristics can be improved.
[0026]
  Further, in the present invention, the AGC control means may have the amplification gain for both a high frequency amplifier that amplifies the signal received in the high frequency band and an intermediate frequency amplifier that amplifies the signal converted to the intermediate frequency band. controlOutput control signal forIt is characterized by that.
[0027]
  According to the present invention, control of amplification gain by AGC controlControl signal output forIs,Since both the high-frequency amplifier that amplifies the signal converted to the high-frequency band and the intermediate-frequency amplifier that amplifies the signal converted to the intermediate-frequency band, input to analog / digital conversion by changing the wide amplification gain range The level can be optimized.
[0030]
  The present invention further includes frequency detection means for detecting the reception frequency,
  The characteristic of the low-pass filtering process performed by the LPF means is the reception frequency detected by the frequency detecting means.And fluctuations in the received electric field detected by the fluctuation detection meansIn response to the, Selected by fluctuation detection meansIt is characterized by being.
[0031]
According to the present invention, the higher the reception frequency, the more likely the steep electric field fluctuation occurs. Therefore, the selection of the low-pass filtering coefficient performed by the LPF unit is changed according to the reception frequency detected by the frequency detection unit. By changing the characteristics such as the above, it is possible to adaptively control the responsiveness of AGC control according to the reception frequency.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic electrical configuration of a digital TV receiver 1 according to a first embodiment of the present invention. The digital TV receiver inputs an OFDM television broadcast radio wave to the antenna 2 to generate an electric signal, and performs high frequency amplification of about 90 MHz to 800 MHz received by the tuner 3 and frequency conversion to an intermediate frequency band. The intermediate frequency is, for example, the 57 MHz band, and the frequency band is about 5.6 MHz. IFamp4 amplifies the received signal converted to the intermediate frequency, and the A / D circuit 5 A / D converts the output of IFamp4. The A / D converted received signal is Fourier-transformed by the FFT means 6, demodulated into a signal compressed by the MPEG (Motion Picture coding Experts Group) system by the demodulating means 7, and subjected to error processing by the error detection / correction means 8. Then, the MPEG decoder 9 reproduces images and sounds.
[0033]
Tuning at the tuner 3 is performed under the control of the CPU 10. The tuner 3 includes a high frequency amplifier, and its amplification gain is controlled in accordance with an AGC control signal supplied from the IF / RF-AGC control means 11. The IF / RF-AGC control means 11 gives an AGC control signal to IFamp4 to control the amplification gain. The AGC control by the IF / RF-AGC control means 11 can adaptively control the responsiveness according to the variation of the received electric field. The fluctuation of the received electric field is obtained by detecting the output from the A / D circuit 5 by the AGC detection means 12 and detecting the change amount such as the slope of the time change of the output value by the change amount detection means 13. Further, the variation of the received electric field can be obtained by detecting the change of the frequency characteristic by the frequency characteristic changing means 14 from the output obtained by converting the received signal into the frequency domain signal by the FFT means 6. Further, the fluctuation of the received electric field can be obtained based on the error detection amount from the error detection / correction means 8.
[0034]
The processing of the received signal after being converted into a digital signal by the A / D circuit 5 is performed by digital arithmetic processing using a DSP (Digital Signal Processor) or the like. That is, the FFT means 6, the demodulation means 7, the error detection / correction means 8, the IF / RF-AGC control means 11, the AGC detection means 12, the change amount detection means 13, and the frequency characteristic change detection means 14 include one or more DSPs. It can be realized by program processing of the CPU.
[0035]
That is, the digital TV receiver 1 which is a digital broadcast receiver receives a broadcast modulated with a digital signal in a predetermined format in a high frequency band, converts the received signal into an intermediate frequency band, and performs analog / digital conversion. In order to demodulate by digital signal processing, AGC detection means 12 which is digital detection means is included. The IF / RF-AGC control means 11 receives an output corresponding to the fluctuation of the received electric field from the change amount detection means 13, the frequency characteristic detection means 14 or the error detection / correction means 8, and when the fluctuation is large, as will be described later. Is adaptively controlled to enable quick response and to suppress response fluctuations when fluctuations are small.
[0036]
FIG. 2 shows the influence of the responsiveness of AGC control with a schematic waveform. FIG. 2A shows the waveform of an input signal similar to that in FIG. FIG. 2B shows a change in amplification gain by AGC control in the digital TV receiver 1. From time t0 to t2, the amplification gain is relatively small, and, as in FIG. 7B, there is no change even if pulsed noise is mixed at time t1. After time t2, as in FIG. 7 (d), it is not easily affected by the passage of the tunnel from time t2 to t3. FIG. 2C shows a change in output.
Even when a digital television broadcast is received while traveling with an in-vehicle receiver, “AGC responsiveness can always be controlled to an appropriate state.
[0037]
FIG. 3 partially shows a schematic electrical configuration of a digital TV receiver 21 according to the second embodiment of the present invention. In this embodiment, parts corresponding to those of the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. In addition, there is a portion that is basically the same as the embodiment of FIG. In the digital TV receiver 21, AGC control is performed only on IFamp4.
[0038]
The change amount detection unit 13 includes a delay unit 22, a comparison unit 23, an ABS calculation unit 24, and a memory 25. The comparison unit 23 compares the signal representing the detection output from the AGC detection unit 12 with the signal delayed by a predetermined time by the delay unit 22. The difference calculated by the comparison means 23 is input to the ABS calculation means 24 to calculate an absolute value, and data stored in advance in the memory 25 is selected based on the absolute value of the difference. The selected data is used to change the responsiveness of the IF-AGC control means 30.
[0039]
That is, the digital TV receiver 21 receives a broadcast modulated with a digital signal in a predetermined format in a high frequency band, converts the received signal to an intermediate frequency band, performs analog / digital conversion, and demodulates the digital signal processing. Therefore, the AGC detection means 12 as a digital detection means for detecting the analog / digital converted signal and deriving an output value corresponding to the input signal level to the analog / digital conversion, and the AGC detection means 12 A comparison unit 31 that is a digital comparison unit that compares the output value with a preset reference value; a change amount detection unit 13 that is a variation detection unit that detects a variation in the received electric field from a state change corresponding to the variation; The comparison value of the comparison means 31 is input, and low-pass filtering is performed with a coefficient selected according to the fluctuation detected by the change amount detection means 13. LPF calculating means 32, which is LPF means, and AGC control means for generating an AGC control voltage for adjusting the amplification gain of the received signal by digital / analog conversion of the low-pass filtering processing result in the LPF calculating means 32 And a D / A circuit 33.
[0040]
The digital TV receiver 21 which is a digital broadcast receiver detects the output value corresponding to the input signal level to the analog / digital conversion when the AGC detection means 12 detects the analog / digital converted signal and derives the output value. Is compared with a preset reference value Ref by the comparison means 31. The LPF calculation means 32 performs a low-pass filtering process on the comparison result of the comparison means 31 with a coefficient selected according to the variation of the received electric field detected by the change amount detection means 25. The D / A circuit 33 performs digital / analog conversion on the low-pass filtering processing result in the LPF calculation means 32 and generates it as an AGC control voltage for adjusting the amplification gain of the reception signal. The gain is controlled at the stage of amplification before conversion, and the level of the received signal input to the analog / digital conversion can be kept within a predetermined range. The comparison result of the comparison means 31 for digital / analog conversion is low-pass filtered by the LPF calculating means 32, and the coefficient of the low-pass filtering, that is, the characteristics of the LPF is selected according to the variation of the received electric field. Responsiveness can be adaptively controlled according to fluctuations in the received electric field using digital signal processing. Here, as the adaptive control, since the output value of the AGC detection means 12 changes corresponding to the fluctuation of the received electric field, the fluctuation of the received electric field is detected based on the amount of change, and the coefficient of the LPF calculation means 32 is set. By selecting the time constant so as to correspond to a short state, the responsiveness of AGC control can be adaptively controlled.
[0041]
As described above, IF-AGC control means 30 performs AGC control only on IFamp4, and includes comparison means 32, LPF (Low Pass Filter) calculation means 32, and D / A circuit 30. The comparison unit 31 compares the value output from the ADC detection unit 12 with a preset reference value Ref, and outputs a value representing the difference. This output is low-pass filtered by the LPF calculating means 32, and the data from the variation detecting means 13 is used as a coefficient used for the low-pass filtering processing by the LPF calculating means 32.
[0042]
In this embodiment, the ID-AGC control means 30 that is an AGC control means controls the amplification gain only for IFamp4 that is an intermediate frequency amplifier that amplifies the signal converted to the intermediate frequency band. Since the gain control by the AGC control is performed only by the intermediate frequency amplifier that amplifies the signal converted to the intermediate frequency band, the amplification gain of the tuner 3 is set to the maximum, and the intermediate frequency amplifier having a large amplification gain has a wide range. Control can be realized with a simple configuration. Since the amplification gain of the tuner 3 is always maximized, effective reception processing can be performed particularly in the case of a weak electric field.
[0043]
Only the high-frequency amplifier of the tuner 3 that amplifies the signal received in the high-frequency band can also control the amplification gain. Amplification gain control by AGC control is performed only by a high-frequency amplifier that amplifies a signal converted into a high-frequency band. Therefore, in the case of a strong electric field, the amplification gain of the high-frequency amplifier is reduced, and the received signal is deteriorated by cross modulation. Can be avoided.
[0044]
Further, the amplification gain can be controlled for both the high-frequency amplifier that amplifies the signal received in the high-frequency band and the IFamp4 that amplifies the signal converted to the intermediate frequency band. Amplification gain control by AGC control is performed for both the high frequency amplifier that amplifies the signal in the high frequency band and the IFamp4 that amplifies the signal converted to the intermediate frequency band, so the analog / digital conversion is performed by changing the wide amplification gain range. The input level can be optimized. The advantages and disadvantages of performing AGC control on both the high-frequency amplifier and the intermediate frequency amplifier or performing AGC control on only one of them are the same in the other embodiments, and either method is selected. be able to.
[0045]
  FIG. 4 illustrates the present invention.PremiseThe schematic electrical configuration of a digital TV receiver 41 according to the third embodiment is partially shown. In this embodiment, parts corresponding to those of the embodiment of FIG. 1 or FIG. 3 are denoted by the same reference numerals, and redundant description is omitted. In addition, there is a portion that is basically the same as the embodiment of FIG. In the digital TV receiver 41, the fluctuation of the received electric field is detected by the upper and lower clip detection means 50, the coefficient of the LPF calculation means 32 is selected according to the detection result, and the responsiveness of the AGC control is adaptively controlled.
[0046]
The upper and lower clip detection means 50 includes comparison means 51 and 52, an OR operation means 53, and a memory 54. The comparison means 51 determines whether or not the detection output value of the AGC detection means 12 is all bits “0”. The comparison unit 52 determines whether or not the detection output value of the AGC detection unit 12 is “1”. The OR operation means 53 reads different data from the memory 54 when one of them is satisfied and when none of them is satisfied, and gives it to the LPF operation means 32 as a count. That is, the upper and lower clip detection means 50 as the fluctuation detection means detects the fluctuation of the received electric field based on the fact that the output value of the AGC detection means 12 has the same logical value for all bits.
The output value of the AGC detection means 12 is a digital value having a predetermined number of bits, and the magnitude thereof changes corresponding to the fluctuation of the received electric field. The AGC control is performed so that the input is within an appropriate range so that the A / D circuit 5 can effectively perform analog / digital conversion of a predetermined number of bits. When the input to the analog / digital conversion falls outside the range of the level represented by the digital value of the number of bits due to fluctuations in the received electric field, all the bits of the output value become 1 or 0. It can be seen that the fluctuation of the received electric field is large. When the variation of the received electric field is large, the response of AGC control can be adaptively controlled by selecting the low-pass filtering coefficient of the LPF calculating means 32 so as to correspond to a state with a short time constant.
[0047]
  FIG. 5 illustrates the present invention.PremiseA schematic electrical configuration of a digital TV receiver 61 according to a fourth embodiment is partially shown. In this embodiment, parts corresponding to those of the embodiment of FIG. 1, FIG. 3, or FIG. In addition, there is a portion that is basically the same as the embodiment of FIG. In the digital TV receiver 61, the fluctuation of the received electric field is detected by the frequency characteristic change detecting means 14, and the response of the IF / RF-AGC control means 11 is adaptively controlled according to the detection result. The IF / RF-AGC control unit 11 includes a comparison unit 62, an LPF calculation unit 63, a D / A circuit 64, an LPF calculation unit 65, and a D / A circuit 66. The frequency characteristic change detection unit 14 includes a delay unit 67, a comparison unit 68, and a memory 69. The frequency characteristic change detecting means 14 which is a fluctuation detecting means detects the fluctuation of the received electric field based on the change of the frequency characteristic of the analog / digital converted signal. In digital broadcast reception, signal processing is performed to divide into frequency components by FFT processing by the FFT means 6, so that changes in frequency characteristics can be easily detected. When the change in frequency characteristics is large, adaptive control can be performed by selecting the low-pass filtering coefficient of the LPF calculation means 63 and 65 so as to accelerate the response of AGC control.
[0048]
  FIG. 6 illustrates the present invention.PremiseA schematic electrical configuration of a digital TV receiver 71 according to a fifth embodiment is partially shown. In this embodiment, parts corresponding to those of the embodiment of FIG. 1, FIG. 3, FIG. 4 or FIG. In addition, there is a portion that is basically the same as the embodiment of FIG. In the digital TV receiver 71, the fluctuation of the received electric field is detected based on the error amount detected by the error detection / correction means 8, and the responsiveness of the IF / RF-AGC control means 11 is adaptively controlled according to the detection result. To do. That is, the fluctuation of the received electric field is detected based on the error detection amount at the time of demodulation by digital signal processing of the analog / digital converted signal. If there is a large amount of error detection, there is a high possibility of a reception environment with a weak electric field range or a large electric field fluctuation, so the low pass filtering coefficient of the LPF calculation means 63, 65 is selected so as to accelerate the response of AGC control Adaptive control can be performed. The error amount detected by the error detection / correction means 8 is counted by an error amount counting means 72 serving as a fluctuation detection means, and coefficient data stored in advance in the memory 73 is selected according to the counted value, and the LPF calculation means. 63, 65.
[0049]
In each embodiment, a speed detection means for detecting the movement speed is further included, and the selection of the low-pass filtering coefficient performed by the LPF calculation means 32, 63, 65 is changed according to the movement speed detected by the speed detection means. You may make it do. When the moving speed is fast, the reception environment is likely to change, and steep electric field fluctuations are likely to occur. Therefore, the low-pass filtering coefficients of the LPF calculation means 32, 63, 65 are selected so as to correspond to a short time constant. Thus, it is possible to perform adaptive control with respect to the traveling speed when mounted on a vehicle.
[0050]
1 is further included as frequency detection means for detecting the reception frequency, and the selection of the low-pass filtering coefficient performed by the LPF calculation means 32, 63, 65 is changed according to the detected reception frequency. It may be. As the reception frequency is higher, steep electric field fluctuations are more likely to occur. Therefore, the selection of the low-pass filtering coefficient performed by the LPF calculation means 32, 63, 65 is changed according to the detected reception frequency, and the reception frequency is changed. Thus, the responsiveness of AGC control can be adaptively controlled.
[0051]
【The invention's effect】
As described above, according to the present invention, when the AGC control means digital / analog converts the low-pass filtering processing result in the LPF means and generates it as an AGC control voltage for adjusting the amplification gain of the received signal, Since the characteristics of the low-pass filtering process are changed according to the variation of the received electric field, the responsiveness of AGC control can be adaptively controlled according to the variation of the received electric field using digital signal processing.
[0052]
  Also, ReceivedBased on the change amount of the output value of the digital detection means corresponding to the fluctuation of the received electric field, the response of AGC control is selected by selecting the coefficient of the LPF means so as to correspond to a state with a short time constant when the change amount is large. Can be adaptively controlled with respect to fluctuations in the received electric field.
[0056]
In addition, according to the present invention, amplification gain control by AGC control is performed only with an intermediate frequency amplifier, and AGC control effective in a weak electric field can be realized with a simple configuration.
[0057]
Further, according to the present invention, amplification gain control by AGC control is performed only by a high-frequency amplifier, and AGC control effective in a strong electric field can be realized with a simple configuration.
[0058]
In addition, according to the present invention, the gain control by the AGC control is performed by both the high frequency amplifier and the intermediate frequency amplifier, and a wide range of the amplification gain is changed to optimize the input level to the analog / digital conversion. it can.
[0060]
Also, according to the present invention, the higher the reception frequency, the more likely the steep electric field fluctuations to occur. Therefore, by changing the characteristics such as changing the selection of the low-pass filtering coefficient performed by the LPF means, Thus, the responsiveness of AGC control can be adaptively controlled.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic electrical configuration of a digital TV receiver 1 according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram schematically showing the influence of responsiveness of AGC control in the embodiment of FIG.
FIG. 3 is a block diagram partially showing a schematic electrical configuration of a digital TV receiver 21 according to a second embodiment of the present invention.
FIG. 4 of the present inventionPremiseIt is a block diagram which shows partially the schematic electric constitution of the digital TV receiver 41 which is 3rd Embodiment.
FIG. 5 shows the present invention.PremiseIt is a block diagram which shows partially the schematic electric constitution of the digital TV receiver 61 which is 4th Embodiment.
FIG. 6 of the present inventionPremiseIt is a block diagram which shows partially the schematic electric constitution of the digital TV receiver 71 which is 5th Embodiment.
FIG. 7 is a waveform diagram schematically showing the influence of responsiveness of conventional AGC control.
[Explanation of symbols]
1, 21, 41, 61, 71 Digital TV receiver
3 Tuner
4 IFamp
5 A / D circuit
6 FFT operation means
7 Demodulation means
8 Error detection / correction means
10 CPU
11 IF / RF-AGC control means
12 AGC detection means
13 Change amount detection means
14 Frequency characteristic change detection means
22, 67 Delay means
23, 31, 51, 52, 62 comparison means
25, 54, 69, 73 memory
30 IF-AGC control means
32, 63, 65 LPF calculation means
33, 64, 66 D / A circuit
50 Upper and lower clip detection means
72 Error amount counting means

Claims (5)

In a digital broadcast receiver that receives a broadcast modulated with a digital signal of a predetermined format in a high frequency band, converts the received signal to an intermediate frequency band, performs analog / digital conversion, and demodulates by digital signal processing.
A digital detection means for detecting an analog / digital converted signal and deriving an output value corresponding to an input signal level to the analog / digital conversion;
Digital comparison means for comparing the output value from the digital detection means with a preset reference value;
Fluctuation detecting means for detecting the fluctuation of the received electric field based on the amount of change in the output value of the digital detection means, and selecting a predetermined characteristic according to the detected fluctuation of the received electric field ;
Comparison value for the digital comparator means is input, by selected characteristics by variation detecting means, and LPF means for outputting the facilities to low-pass filtering process,
In order to control the amplification gain of the received signal so that the time constant to be controlled is shortened when the output from the LPF means is digital / analog converted and the fluctuation detecting means detects that the amount of change in the received electric field is large. look including an AGC control means for outputting a control signal,
The fluctuation detection means calculates the absolute value of the difference from the output from the digital detection means and the output obtained by delaying the output from the digital detection means for a fixed time, thereby changing the output value of the digital detection means per fixed time. A digital broadcast receiver characterized by obtaining a quantity and detecting a change in a received electric field based on the obtained change per fixed time . 2. The digital broadcasting according to claim 1, wherein the AGC control means outputs a control signal for controlling the amplification gain only to an intermediate frequency amplifier that amplifies the signal converted into the intermediate frequency band. Receiving machine. 2. The digital broadcast receiver according to claim 1, wherein the AGC control means outputs a control signal for controlling the amplification gain only to a high-frequency amplifier that amplifies the signal received in the high-frequency band. . The AGC control means controls the amplification gain for both a high frequency amplifier that amplifies the signal received in the high frequency band and an intermediate frequency amplifier that amplifies the signal converted to the intermediate frequency band. The digital broadcast receiver according to claim 1, wherein the digital broadcast receiver outputs a signal . A frequency detection means for detecting the reception frequency;
The characteristic of the low-pass filtering performed by the LPF means is selected by the fluctuation detection means according to the reception frequency detected by the frequency detection means and the fluctuation of the received electric field detected by the fluctuation detection means. digital broadcast receiver as claimed in any one of claims 1-4.

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