JP4404742B2 - Automatic gain control system for cross modulation and intermodulation distortion - Google Patents

Description

  The present invention relates to a digital information transmission system, and more particularly to a digital receiver having an automatic gain control (AGC) system that improves distortion resistance performance of a reception tuner and a digital demodulator.

  In the prior art of the receiver AGC in the digital information transmission system, the AGC circuit has two stages, that is, a radio frequency automatic gain control (RF-AGC) in the receiver radio frequency (RF frequency) stage, and an intermediate frequency of the receiver. (IF frequency) In a receiver comprising an intermediate frequency automatic gain control (IF-AGC), an IF amplifier is connected in series with the RF amplifier, and the IF-AGC and RF-AGC controlling these two amplifiers. Good reception performance is realized by two AGC circuits.

  In the control of the two AGC circuits in the receiver having such a configuration, “IF-AGC is maintained at a constant gain until the RF-AGC gives the maximum gain to the input RF signal. When the maximum RF-AGC is reached, the IF-AGC circuit is activated to further amplify the IF signal. In contrast to the conventional general configuration, when the input signal is amplified at the gain limit of the RF amplifier, the RF amplifiers are mutually connected. In consideration of the influence of modulation distortion and intermodulation distortion, when distortion is detected by monitoring the distortion at the outer peripheral point of the signal point arrangement (constellation), the RF− is increased in the direction of decreasing the gain of the RF amplifier. It is a conventional technique to search for AGC and obtain a good reception state when distortion near the maximum gain of the RF amplifier exists. It has been proposed (e.g., see Patent Document 1).

  FIG. 8 shows an example of a prior art receiver having a distortion avoidance function by RF amplification. The conventional tuning operation will be described with reference to FIG. In the figure, 200 is an RF input unit for inputting a received signal to the receiver, 211 is an RF amplifying unit for amplifying the received signal with a gain corresponding to the RF-AGC signal, and 212 is a frequency for converting the RF amplified received signal to an IF signal. A local oscillator that generates a local oscillation frequency for conversion, 213 is a mixer that mixes an RF-amplified reception signal and a local oscillation signal and converts them to an IF frequency, and 214 is a filter for filtering the frequency-converted reception signal A band-pass filter (BPF), 215 an IF amplifying unit for amplifying the band-filtered IF signal with a gain corresponding to the IF-AGC signal, and 216 a band-pass filter (BPF) for band-filtering the IF-amplified received signal ) 217 is an analog / digital converter (A / D converter) for quantizing the band-filtered received signal after IF amplification, and 218 is a quantized signal. A demodulator that demodulates the received signal into digital received data, 221 detects a level of the quantized received signal, calculates a required signal level, and 222 demodulates from the demodulator 218 A distortion detection unit that receives parameters and detects distortion information indicating whether the received signal is distorted, or 223 generates RF-AGC and IF-AGC AGC control information based on the required signal level adjustment information and distortion information. An AGC signal control unit 224 represents an AGC signal generation unit that generates an RF-AGC signal and an IF-AGC signal from AGC control information, respectively. Reference numeral 210 denotes a reception signal processing unit from the RF amplification unit 211 to the demodulation unit 218, and 220 denotes an AGC system unit from the level detection unit 221 / distortion detection unit 222 to the AGC signal generation unit 224.

  Referring to the tuning operation of the receiver shown in FIG. 8, the AGC signal control unit 223 passes initial value information to the AGC signal generation unit 224 as RF-AGC control information, and the AGC signal generation unit 224 follows the RF-AGC control information. An RF-AGC signal is generated. The RF signal input from the RF input unit 200 to the receiver is amplified by the RF amplification unit 211 with a gain corresponding to the RF-AGC signal, mixed with the signal generated from the local oscillator 212 by the mixer 213, and received at the IF frequency. Frequency converted to signal.

  Next, the received signal frequency-converted to the IF frequency is filtered by the band pass filter (BPF) 214 and amplified by the IF amplifying unit 215 with a gain according to the IF-AGC signal generated from the IF-AGC initial value information. The signal is again filtered by the band pass filter (BPF) 216, quantized by the analog / digital converter (A / D converter) 217, and passed to the demodulator 218 and the level detector 221.

  At this time, if the quantized signal level input to the level detector 221 is not within a predetermined range, the level detector 221 passes the required total gain adjustment information to the AGC signal controller 223. The AGC signal control unit 223 resets the AGC control information of the RF-AGC and IF-AGC based on the adjustment information, and passes the AGC control information to the AGC signal generation unit 224.

  The AGC signal generation unit 224 generates an RF-AGC signal and an IF-AGC signal according to the AGC control information. The reception signal processing unit 210 and the AGC system unit 220 have a loop structure, and are controlled so that the quantized signal level of the reception signal input to the demodulation unit 218 is optimized by this loop processing.

  Further, when the distortion detection unit 222 that has received the demodulation information detects distortion, the AGC signal control unit 223 performs RF-AGC setting in a direction to decrease the gain of the RF amplification unit 211, and IF− AGC is set, and control is performed so that the signal level to the demodulator 218 is optimized by AGC loop processing. In accordance with the series of loops, the search is continued until the distortion detection in the distortion detection unit 222 receiving the data from the demodulation unit 218 is eliminated.

  FIG. 9 is a diagram showing the relationship between the gain of the RF amplifier based on RF-AGC, the gain of the IF amplifier based on IF-AGC, and the total gain, and the concept of the turnover point of AGC. Here, when the maximum RF-AGC set in advance is reached, the point at which the IF-AGC circuit enters the operating state (in other words, the switching point from the RF-AGC operating state to the IF-AGC operating state) is the AGC turnover. Let's call it a point. This definition also applies to the present invention.

  In FIG. 9, the IF-AGC gain is constant until the total amplifier gain (horizontal axis in FIG. 9) reaches the AGC turnover point, and the total gain is set by increasing or decreasing the RF-AGC. When the RF-AGC setting exceeds the AGC turnover point, the gain of the RF-AGC is constant, and the setting is adjusted so that the total gain is obtained by increasing or decreasing the IF-AGC. The IF amplification unit, the RF amplification unit, and the total gain scale are arbitrary.

In the prior art, the AGC turnover point immediately after tuning always takes a preset maximum value, and until the distortion is detected by the constellation data (signal point arrangement data) from the demodulation unit, This turnover point is fixed, and after judging the distortion based on the constellation data, the RF-AGC signal is searched in the direction of decreasing the gain of the RF amplification section, and distortion evaluation is repeated to eliminate the distortion.
JP-A-10-65750

  According to the AGC based on the distortion evaluation according to the conventional technique described above, when tuning to a frequency having a distortion near the maximum gain of the RF amplification unit due to the intermodulation and intermodulation constantly, it takes time for the distortion search until a good reception parameter is obtained. There is a problem that it takes. Furthermore, distortion in the RF amplifier may occur due to the relationship between the signal level between the band where the tuning frequency exists and the adjacent band adjacent to the band (for example, tuning is performed when the signal level of the adjacent band is large). This signal level sometimes appears as distortion), especially when this occurs when the transmission line is relatively stable in a wired network such as a cable network rather than wirelessly. There arises a problem that many things exist.

  An object of the present invention is to provide an AGC system capable of adjusting an appropriate RF-AGC without performing an RF-AGC search from an RF-AGC set value at a preset AGC turnover point. is there.

In order to solve the above problems, the present invention mainly adopts the following configuration.
Radio frequency (RF) amplifier, intermediate frequency (IF) amplifier, RF automatic gain control (RF-AGC) and IF automatic gain control (IF-AGC) for controlling the gain of each of the RF amplifier and IF amplifier A two-stage AGC circuit, a demodulator that demodulates an output signal that has passed through the IF amplifier, a distortion detector that detects intermodulation distortion and intermodulation distortion in the demodulated data from the demodulator, and reduces the distortion In order to reduce the gain of the RF amplifier, an AGC signal controller for reducing the gain of the RF amplifier,
A strain information storage unit that stores, for each tuning frequency, whether or not distortion correction has been performed based on the output from the strain detector, and whether or not to perform strain correction by the RF-AGC; An RF-AGC information storage unit for storing a set value of AGC;
When tuning this time, the presence or absence of distortion correction at the frequency corresponding to the previous tuning is detected from the strain information storage unit,
When there is distortion correction, the RF-AGC stored in the RF-AGC information storage unit as the RF-AGC set value of the switching point (AGC turnover point) from the RF-AGC operating state to the IF-AGC operating state Using AGC setting value,
When there is no distortion correction, an initial set value is used as the RF-AGC set value of the AGC turnover point.

  According to the present invention, in a band having a steady distortion (or a frequency within the band), in particular, in a transmission line in which the influence of distortion and the signal level do not vary greatly, the RF-AGC setting initial value at the AGC turnover point. RF-AGC search is not required, and the next tuning time after distortion correction is reduced.

  In addition, it is possible to accurately cope with distortion caused by an RF amplifier that is steadily present at a specific tuning frequency, and RF-AGC is excessively adjusted for distortion caused by an RF amplifier that is not stationary. Can be prevented. Further, according to the present invention, it is possible to follow the strain rather than change with time.

  A receiver having an AGC system according to an embodiment of the present invention will be described in detail below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a receiver having an AGC system according to the first embodiment of the present invention.

  In FIG. 1, 200 is an RF input unit, 211 is an RF amplification unit, 212 is a local oscillator, 213 is a mixer, 214 band pass filter (BPF), 215 is an IF amplification unit, 216 is a band pass filter (BPF), and 217 is Analog / digital converter (A / D converter), 218 demodulation unit, 221 level detection unit, 222 distortion detection unit, 223 AGC signal control unit, 224 AGC signal generation unit, 232 distortion information storage unit Reference numeral 233 denotes an RF-AGC information storage unit, and 231 denotes an AGC signal control unit.

  In FIG. 1, reference numeral 232 denotes a distortion information storage unit for recording whether or not the RF-AGC is adjusted by the distortion of the RF amplification unit in the previous tuning for each tuning frequency (presence / absence of adjustment). RF-AGC information storage unit for storing RF-AGC setting information in tuning, 231 includes required signal level adjustment information, strain information indicating presence / absence of current strain, strain information indicating presence / absence of previous strain, Also, RF-AGC and IF-AGC AGC control information is generated based on RF-AGC setting information indicating RF-AGC setting information at the time of the previous tuning, and distortion correction by the RF amplification unit 211 is performed at the tuning frequency. In some cases, the presence / absence of strain is stored in the strain information storage unit 232 and the RF-AGC setting information is stored. Which is the AGC signal control unit 231 to be stored in the RF-AGC information storage unit 233. Reference numeral 230 denotes an AGC system unit from the level detection unit 221 and the distortion detection unit 222 to the AGC signal generation unit 224, as shown in FIG.

  The tuning operation of the receiver will be described below with reference to FIG. The AGC signal control unit 231 passes initial value information as RF-AGC control information to the AGC signal generation unit 224, and the AGC signal generation unit 224 generates an RF-AGC signal according to the RF-AGC control information. The RF signal input from the RF input unit 200 to the receiver is amplified by the RF amplification unit 211 with a gain corresponding to the RF-AGC signal, mixed with the signal generated from the local oscillator 212 by the mixer 213, and received at the IF frequency. Frequency converted to signal.

  The received signal frequency-converted to the IF frequency is filtered by the band pass filter (BPF) 214 and amplified by the IF amplifying unit 215 with a gain corresponding to the IF-AGC signal generated from the IF-AGC initial value information, and again. It is filtered by a band pass filter (BPF) 216, quantized by an analog / digital converter (A / D converter) 217, and passed to a demodulator 218 and a level detector 221.

  At this time, if the quantized signal level input to the level detection unit 221 is not within a predetermined range, the level detector 221 passes the required total gain adjustment information to the AGC signal control unit 231. The AGC signal control unit 231 resets the AGC control information of the RF-AGC and IF-AGC based on the adjustment information, and passes the AGC control information to the AGC signal generation unit 224. The AGC signal generation unit 224 generates an RF-AGC signal and an IF-AGC signal according to the AGC control information. The reception signal processing unit 210 and the AGC system unit 230 have a loop structure, and are controlled so that the quantized signal level of the reception signal input to the demodulation unit 218 is optimized by this loop processing.

  Next, when the distortion detection unit 222 that has received the demodulation information detects distortion, the AGC signal control unit 231 performs RF-AGC setting in a direction to decrease the gain of the RF amplification unit 221, and IF in a direction to compensate for the gain decrease. -AGC is set, and control is performed so that the signal level to the demodulator 218 is optimized by AGC loop processing. In accordance with the series of loops, the search is continued until the distortion detection in the distortion detection unit 222 receiving the data from the demodulation unit 218 is eliminated.

  To illustrate using the gain characteristics of the amplifier shown in FIG. 9, the signal level is first detected at an appropriate total gain point at the characteristic slope portion of the RF amplifier, and when the signal level is not within the predetermined range, The total amplifier gain setting required is calculated from the amplifier gain and signal level, and the RF amplifier and IF amplifier gains are repeatedly set in accordance with the amplifier gain characteristics shown in FIG. Within the range of. Next, distortion detection is performed at the total gain point for obtaining this predetermined signal level. If distortion is detected, the gain of the RF amplifier is lowered to a level at which distortion is not detected, and in order to ensure a constant value of the total gain, The gain of the IF amplifier is increased by the amount corresponding to the decrease in the gain of the RF amplifier. At this time, the AGC turnover point decreases corresponding to the reduction in the gain of the RF amplifier. In this way, the RF-AGC information and strain information when strain is no longer detected are stored in the RF-AGC information storage unit 233 and strain information storage unit 232, respectively.

  When entering a series of these tunings, if the strain information storage unit 232 stores that the tuning of the RF-AGC according to the strain is not performed at the same frequency tuning as the previous time, the operating state of the RF-AGC Since a predetermined initial value is used as the RF-AGC setting value at the transition point from IF to the IF-AGC operation state, that is, the AGC turnover point, the RF-AGC search in the IF-AGC operation state is performed by the RF- The search is performed from the AGC setting initial value, and the same search as the conventional method is performed. Therefore, the tuning time is not different from the conventional time.

  Next, when entering a series of these tunings, when it is stored in the strain information storage unit 232 that “adjustment” of RF-AGC due to strain is performed at the same frequency tuning as the previous time, AGC turnover is performed. By setting the RF-AGC setting value of the point as the previous RF-AGC setting value stored in the RF-AGC information storage unit 233, the frequency having a steady distortion, in particular, the influence of distortion and the signal level RF-AGC at the AGC turnover point at a transmission system (wired) frequency that does not vary significantly (if a distortion occurs in a wired transmission system with stable transmission characteristics, this distortion becomes a steady distortion). The RF-AGC search from the set initial value becomes unnecessary, and the tuning time is reduced as compared with the conventional method.

  FIG. 3 shows distortion information and RF-AGC information storage data for each tuning frequency and an operation example at the next tuning in the first embodiment. According to FIG. 3, when the tuning frequency is 545 MHz, there is distortion correction and the RF-AGC set value is lowered from the RF-AGC value at the turnover point of AGC to +12 dB (the distortion is not detected as a result of the reduction). ) RF-AGC at the AGC turnover point at the next tuning is +12 dB. When the tuning frequency is 551 MHz, distortion correction is not required (no correction), and the RF-AGC set value is +12 dB, indicating that a predetermined signal level has been obtained. At the next tuning, the RF at the AGC turnover point -AGC is an initial set value (+15 dB). Even when the tuning frequency is 557 MHz, the operation is performed as illustrated. Here, it can be said that the RF-AGC at the turn-over point of the AGC is preferably not lowered over all tuning frequencies in consideration of the case where the reception sensitivity is lowered.

  As the determination method of the distortion detector 222 described above, not only the distortion evaluation by the direct amplifier based on the signal point arrangement (constellation) as in the prior art but also the total information such as the synchronization signal information, BER (bit error rate), etc. The reception parameter of the demodulator 218 used for distortion evaluation can be used. In particular, judging the outer circumference of the constellation is that the signal level is high, that is, the distortion expected to be caused by the RF amplification unit can be observed directly, while the probability of taking the maximum outer circumference point by increasing the number of constellation points In addition, it is difficult to make a correct judgment unless a large number of samples are taken until distortion is detected, such as the variation in data taking the maximum outer peripheral point and the determination of analog signal level in consideration of noise. That is, it takes time until strain detection. On the other hand, the synchronization signal information and BER evaluation can periodically acquire data, and since it is a digital evaluation, it can be judged with a smaller number of samples than constellation evaluation, but it catches reception defects due to all distortions. As a result, the probability of capturing the expected distortion due to the RF amplification unit is reduced. In other words, it is important to accurately and quickly detect the distortion in order to further speed up the tuning to a frequency with distortion.

  Also, by reducing the gain of the RF amplifier, if the distortion characteristics are not improved, the search in the decreasing direction is terminated, and the RF-ACG information at the AGC turnover point is returned to the increasing direction, thereby causing an erroneous operation of the RF-AGC search. Can be prevented.

  Next, a receiver having an AGC system according to a second embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a block diagram showing a configuration of a receiver having an AGC system according to the second embodiment of the present invention.

  In FIG. 2, reference numeral 241 denotes an RF-AGC information storage unit that stores setting information of the RF-AGC when the previous distortion is detected for each frequency (stores an RF-AGC setting value for each frequency when the previous distortion is detected). 242 is RF-AGC information based on required signal level adjustment information, distortion information indicating the presence or absence of current distortion, and RF-AGC setting information indicating RF-AGC setting information at the previous tuning. AGC signal for generating AGC control information of AGC and IF-AGC, and additionally storing the RF-AGC setting information in the RF-AGC information storage unit 233 when distortion correction is performed on the tuning frequency by the RF amplification unit 211 It is a control unit. 2 indicates the entire configuration of the AGC system unit from the level detection unit 221 and the strain detection unit 222 to the AGC signal generation unit 224 in FIG. 2, and the other components in FIG. 2 are the same as those in FIG. The description of FIG. 1 is used.

  In the second embodiment, the RF-AGC control information (RF-AGC setting) set in the RF-AGC information storage unit 241 only when the strain is detected by the strain detector 222 and the RF-AGC control based on the strain is performed. Value) is stored together with the tuning frequency, and the initial value of the AGC turnover point is entered into the RF-AGC information storage unit 241 during other control.

  As described above, in the second embodiment, without storing the presence or absence of the previous distortion, the RF-AGC setting of the AGC turnover point is set from the RF-AGC setting information even during tuning, as shown in FIG. A configuration of an AGC system that brings about the same effect as that of the first embodiment without having such a strain information storage unit 232 becomes possible. In the first embodiment, the presence / absence of strain is stored, but this can be described later, to detect the time history of the presence / absence of strain when the strain does not occur steadily and grasp the history of distortion. Therefore, it is necessary to provide a strain information storage unit. If distortion occurs every time a large number of tunings are performed, the RF-AGC set value controlled by RF-AGC is set as the set value for the next tuning (details will be described in the description of FIG. 7).

  FIG. 4 shows RF-AGC information storage data for each tuning frequency and an operation example at the next tuning in the second embodiment. The second column in FIG. 4 corresponds to the third column in FIG. In FIG. 4, if distortion is not detected at a certain tuning frequency (for example, 551 MHz), the RF-AGC setting information storage data (third column) stores the RF-AGC setting value at the AGC turnover point. This data is used for the next tuning. The RF-AGC value adjusted so that the distortion is eliminated only when the distortion is detected is stored in the RF-AGC setting information storage data.

  Next, an operation example in the receiver having the AGC system according to the first and second embodiments of the present invention will be described with reference to FIG. FIG. 5 is a flowchart showing an operation example of RF-AGC setting by distortion search in the receiver having the AGC system according to the embodiment of the present invention. RF-AGC and IF-AGC are set so that the total gain setting is not changed so that the quantized signal level input to the level detector 221 during normal demodulation after tuning falls within a predetermined range. If there is a direction in which the distortion is improved by a minute change, the AGC turnover point is shifted in that direction to follow the distortion. In other words, the overall gain is not changed and large distortion does not occur. For example, the RF-AGC is increased and the IF-AGC is decreased (distortion recovery tracking type).

  According to FIG. 5, in step 1, RF-AGC is increased by 0.1 dB and IF-AGC is decreased by 0.1 dB, and it is determined whether or not the distortion has deteriorated (step 2). The RF-AGC setting at the over point is updated (step 3). In step 4, the RF-AGC and IF-AGC are returned to the original state, and the improvement in distortion is checked. If NO, in step 8, RF-AGC is increased by 0.1 dB again, and IF-AGC is decreased by 0.1 dB. If the distortion is not improved in step 2, RF-AGC is reduced by 0.1 dB, IF-AGC is increased by 0.1 dB, and further, in step 4, the distortion improvement is checked with the same up-down tendency. Here, the flow of FIG. 5 is to increase the reception sensitivity by increasing the RF-AGC as much as possible so that the distortion is not improved or generated without changing the total gain.

  Next, still another operation example in the receiver having the AGC system according to the first and second embodiments of the present invention will be described with reference to FIG. FIG. 6 is a flowchart showing another operation example of RF-AGC setting by distortion search when the power is turned off in the receiver having the AGC system according to the embodiment of the present invention. When the power is turned off, the frequency search is tuned to confirm the presence or absence of distortion, and the user can be made aware of the distortion without detecting it. As a matter of course, a power source for strain search is secured even if the power is turned off.

  According to FIG. 6, a tuning frequency for checking the distortion is set, and the distortion is searched at this frequency. If there is distortion, for example, in the first embodiment, the distortion information and the RF-AGC setting information are updated, the next frequency to be checked for distortion is set, and the distortion search is similarly performed. At this time, the search for distortion is useful because it is possible to know the elimination of the corresponding distortion even by performing only the frequency previously corrected by the distortion by the RF amplification unit 211.

  Next, another operation example in the receiver having the AGC system according to the first embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing requirements for realizing another operation in the receiver having the AGC system according to the first embodiment. When the so-called strain recovery follow-up type configuration described in FIG. 5 or FIG. 6 is executed using the first embodiment shown in FIG. 1, the strain information includes not only the previous strain presence but also the strain. The stationary strain can be extracted by adding information indicating the continuity of detection, and the RF-AGC information at the previous tuning stored in the RF-AGC information storage unit 232 can be used only when there is a stationary strain. It is something that can be done.

  According to FIG. 7, the strain information storage unit 232 (see FIG. 1) stores two times of the presence / absence of the previous strain correction and the current strain correction, and the RF-AGC information storage unit 233 stores the current RF-AGC. The set value is stored. Here, in the next tuning, the RF-AGC setting value of the RF-AGC information storage unit 233 is set only when there is distortion correction both in the previous time and this time, as in the example of the first line in FIG. As shown in the example of the second to fifth lines in FIG. 7, if there is no correction in either the previous time or the current time, it is determined that there is no steady distortion, and the RF-AGC (AGC turnover point) The initial value is a set value. Also here, the initial set value is set as much as possible in order to increase the reception sensitivity (for example, RF-AGC is set to +15 dB instead of +12 dB in the example of the second row). As described above, in an environment in which distortion due to the RF amplifier changes, it is intended to prevent depending on only the RF-AGC information at the previous tuning stored in the RF-AGC information storage unit 232.

  As described above, the main features of the present invention have the following configurations and functions. That is, for each tuning frequency, a distortion information storage unit that stores presence / absence of gain adjustment by RF-AGC due to distortion near the maximum gain of the RF amplification unit by cross modulation and intermodulation, and RF-AGC of the previous tuning An RF-AGC information storage unit for storing an adjustment value, and when the gain of the RF amplifier due to the previous tuning frequency is adjusted, the RF-AGC setting value in the previous tuning is used to adjust the RF of the current tuning. -Set the RF-AGC setting value at the turnover point of AGC. As a result, when there is a constant intermodulation and intermodulation distortion of the RF amplifier, there is no need to perform an RF-AGC search from an RF-AGC set value at a preset AGC turnover point. Tuning time can be shortened.

It is a block diagram which shows the structure of the receiver which has an AGC system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the receiver which has an AGC system concerning the 2nd Embodiment of this invention. It is a figure which shows the operation | movement example at the time of the distortion information for every tuning frequency in the AGC system which concerns on 1st Embodiment, RF-AGC information storage data, and the next tuning. The figure which shows the operation example at the time of next tuning in RF-AGC setting value for every tuning frequency in the AGC system which concerns on 2nd Embodiment, RF-AGC setting information storage data (RF-AGC setting value of the turnover point of AGC) It is. It is a flow which shows the operation example of RF-AGC setting by the distortion search in the receiver which has the AGC system which concerns on embodiment of this invention. It is a flow which shows the other operation example of RF-AGC setting by the distortion search at the time of the power-off in the receiver which has the AGC system which concerns on embodiment of this invention. It is a figure which shows the requirements for implement | achieving another operation | movement with the receiver which has the AGC system which concerns on 1st Embodiment. It is a block diagram which shows the structure of the receiver which has an AGC system regarding a prior art. It is a figure which shows the concept of the turnover point of AGC while showing the relationship of the gain of RF amplifier by RF-AGC, the gain of IF amplifier by IF-AGC, and a total gain.

Explanation of symbols

200 RF Input Unit 210 Received Signal Processing Unit 211 RF Amplifying Unit 212 Local Oscillator 213 Mixer 214 Band Pass Filter (BPF)
215 IF amplifier 216 Band pass filter (BPF)
217 Analog / digital converter (A / D converter)
218 Demodulator 220, 230, 240 AGC system 221 Level detector 222 Distortion detector 223, 231, 242 AGC signal controller 224 AGC signal generator 232 Distortion information storage 233, 241 RF-AGC information storage

Claims (6)

Radio frequency (RF) amplifier, intermediate frequency (IF) amplifier, RF automatic gain control (RF-AGC) and IF automatic gain control (IF-AGC) for controlling the gain of each of the RF amplifier and IF amplifier A two-stage AGC circuit, a demodulator that demodulates an output signal that has passed through the IF amplifier, a distortion detector that detects intermodulation distortion and intermodulation distortion in the demodulated data from the demodulator, and reduces the distortion In order to reduce the gain of the RF amplifier, an AGC signal controller for reducing the gain of the RF amplifier,
A strain information storage unit that stores, for each tuning frequency, whether or not distortion correction has been performed based on the output from the strain detector, and whether or not to perform strain correction by the RF-AGC; An RF-AGC information storage unit for storing a set value of AGC;
When tuning this time, the presence or absence of distortion correction at the frequency corresponding to the previous tuning is detected from the strain information storage unit,
When there is distortion correction, the RF-AGC stored in the RF-AGC information storage unit as the RF-AGC set value of the switching point (AGC turnover point) from the RF-AGC operating state to the IF-AGC operating state Using AGC setting value,
An AGC system, wherein an initial set value is used as an RF-AGC set value at the AGC turnover point when there is no distortion correction. Radio frequency (RF) amplifier, intermediate frequency (IF) amplifier, RF automatic gain control (RF-AGC) and IF automatic gain control (IF-AGC) for controlling the gain of each of the RF amplifier and IF amplifier A two-stage AGC circuit, a demodulator that demodulates an output signal that has passed through the IF amplifier, a distortion detector that detects intermodulation distortion and intermodulation distortion in the demodulated data from the demodulator, and reduces the distortion In order to reduce the gain of the RF amplifier, an AGC signal controller for reducing the gain of the RF amplifier,
When tuning for each tuning frequency, the set value of RF-AGC when the distortion correction by the RF-AGC is performed based on the output from the strain detector is stored together with the corresponding tuning frequency, and the distortion correction is further performed. An RF-AGC information storage unit that stores an initial setting value of the RF-AGC when not performed together with a corresponding tuning frequency;
In this tuning, the RF-AGC set value memorized in the previous tuning is used as the RF-AGC set value at the switching point (AGC turnover point) from the RF-AGC operating state to the IF-AGC operating state. AGC system. The AGC system according to claim 1 or 2,
A level detector for detecting the level of the output signal of the IF amplifier, and configured to control the AGC circuit based on the level detector;
The RF amplifier when the gain of the RF amplifier and the gain of the IF amplifier are increased or decreased by the AGC circuit under the condition that the total gain of the RF amplifier and the IF amplifier is not changed during normal operation after tuning Detect and evaluate strain caused by
An AGC system, wherein the RF-AGC set value stored in the RF-AGC information storage unit when the distortion is reduced corresponds to the time-varying distortion. The AGC system according to claim 1 or 2,
When tuning this time, the RF-AGC set value of the AGC turnover point when the distortion correction is performed at the corresponding frequency in the previous tuning and when the distortion correction is not performed is executed when the power is turned off. AGC system characterized by The AGC system according to claim 1,
The strain information storage unit stores the presence or absence of strain correction at the time of a plurality of tunings including immediately before and the previous one,
An AGC system characterized in that when there is at least two successive distortion corrections, the distortion correction is applicable.   A digital receiver comprising the AGC system according to any one of claims 1 to 5.

Images