JP2007088880A - Tuner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tuner capable of preventing deterioration of receiving performance by preventing malfunctions of an AGC circuit by a jamming signal. <P>SOLUTION: The tuner has a receiving part 1 which receives a radio signal, an RF_AGC circuit 3 which performs level adjustment of the received radio signal, a mixer circuit 5 which performs frequency conversion to the radio signal whose level is adjusted into an IF signal by multiplying the radio signal whose level is adjusted by a local oscillation signal, an OFDM demodulation IC 14 which demodulates the IF signal, a filter 21 for detection which attenuates components outside a predetermined band among frequency components of the IF signal and a detection circuit 9 which detects a level of the IF signal passing through the filter 21 for detection and the RF_AGC circuit 3 performs the level adjustment based on detection results of the detection circuit 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tuner, and more particularly to a tuner including an AGC (Auto Gain Control) circuit.

As an example of a tuner that receives radio waves of terrestrial digital broadcasting (hereinafter also referred to as terrestrial digital tuner), Patent Document 1 discloses the following tuner. That is, an antenna that receives radio waves of the terrestrial ATSC (Advanced Television Systems Committee) system, a tuning unit that has an AGC circuit that receives an RF (Radio Frequency) signal from the antenna, an IF-AGC circuit, and an 8-VSB (Vestigial A / D (Analog Digital) detection circuit that performs sideband demodulation, a synchronization detection circuit that determines segment synchronization and field synchronization, and a waveform equalization circuit that detects distortion due to multipath in the input signal and removes the distortion And a C / N (Carrier to Noise Ratio) measurement circuit that measures and calculates carrier and noise values, a trellis decoding circuit that decodes convolutionally coded modulation data, and a Reed-Solomon decoding circuit .
JP 2002-218341 A

  Incidentally, the AGC circuit for RF signals in the tuner described in Patent Document 1 has a function of lowering the level of the received signal in the case of a strong electric field. Such a tuner generally includes a detection circuit that detects the reception level of radio waves, and the AGC circuit changes the gain based on the reception level detected by the detection circuit. Here, when the interference signal that is a signal other than the main signal is included in the input signal of the detection circuit, if the level of the interference signal fluctuates, the level of the detection circuit does not change even though the level of the main signal does not fluctuate. Since the detection result varies, the AGC circuit does not adjust the level according to the level of the main signal, and the reception performance is deteriorated. For example, if the gain of the AGC circuit is lowered too much, the level of the main signal is lowered and C / N deteriorates. If the gain of the AGC circuit is raised too much, distortion due to cross modulation (cross modulation) occurs in the AGC circuit and the mixer. And reception performance deteriorates.

  Therefore, an object of the present invention is to provide a tuner capable of preventing deterioration of reception performance by preventing malfunction of an AGC circuit due to an interference signal.

  In order to solve the above problems, a tuner according to an aspect of the present invention includes a receiving unit that receives a radio signal, an AGC circuit that adjusts the level of the received radio signal, a radio signal that has been level-adjusted, and a local oscillation signal A mixer circuit that frequency-converts a radio signal that has been level-adjusted by multiplying the signal to an IF signal, a demodulation circuit that demodulates the IF signal, and a detection filter that attenuates a component outside the predetermined band of the frequency components of the IF signal And a detection circuit that detects the level of the IF signal that has passed through the detection filter, and the AGC circuit adjusts the level based on the detection result of the detection circuit.

Preferably, the detection filter can change a frequency characteristic.
Preferably, the detection circuit outputs the detection result to the outside.

  Preferably, the tuner outputs a plurality of AGC circuits connected in series and a detection result received from the detection circuit to each AGC circuit, and outputs to another AGC circuit to at least one of the AGC circuits. And a delay circuit that outputs detection results at different timings.

  More preferably, the delay circuit sequentially outputs detection results from the last AGC circuit to the preceding AGC circuit.

  According to the present invention, it is possible to prevent deterioration of reception performance by preventing malfunction of the AGC circuit due to interference signals.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a functional block diagram of a tuner according to the first embodiment of the present invention.

  Referring to the figure, this tuner includes an input terminal (receiver) 1, a single tuning filter 2, an RF_AGC circuit 3, a double tuning filter 4, a mixer oscillator PLL_IC (Phase-Locked Loop Integrated Circuit) 10, and , A SAW (Surface Acoustic Wave) filter 11, an IF_AGC circuit 12, an IF amplifier 13, and an OFDM (Orthogonal Frequency Division Multiplexing) demodulation IC (demodulation circuit) 14. The mixer oscillator PLL_IC 10 includes a mixer circuit 5, a local oscillation circuit 6, a PLL circuit 7, an IF amplifier 8, a detection circuit 9, and a filter circuit 15.

The input terminal 1 inputs an RF signal (wireless signal) from an antenna (not shown).
The single tuning filter 2 operates with the frequency corresponding to the reception channel in the RF signal input from the input terminal 1 as the pass center frequency, that is, attenuates the component outside the predetermined band among the frequency components of the radio signal. The RF signal is, for example, a UHF (Ultra High Frequency) signal of 470 MHz to 770 MHz.

  The RF_AGC circuit 3 changes the gain based on the detection result of the detection circuit 9, that is, adjusts the level of the RF signal that has passed through the single tuning filter 2.

  The double-tuned filter 4 operates using the frequency corresponding to the reception channel in the RF signal whose level has been adjusted by the RF_AGC circuit 3, that is, out of a predetermined band among the frequency components of the RF signal whose level has been adjusted. Attenuate.

  The PLL circuit 7 controls the oscillation frequency of the local signal. The local oscillation circuit 6 oscillates under the control of the PLL circuit 7 and outputs a local signal.

  The mixer circuit 5 frequency-converts the RF signal into an IF (Intermediate Frequency) signal by multiplying the RF signal that has passed through the double-tuned filter 4 and the local signal. For example, the IF signal is 57 MHz in Japan.

  The filter circuit 15 performs band limitation for the purpose of suppressing the interference signal output to the IF amplifier 8 and the detection circuit 9, that is, attenuates a component outside the predetermined band among the frequency components of the IF signal received from the mixer circuit 5. Let

The IF amplifier 8 amplifies the IF signal that has passed through the filter circuit 15.
The detection circuit 9 detects the level of the IF signal received from the IF amplifier 8. The detection circuit 9 is provided to control the gain of the RF_AGC circuit 3 so that the output signal level of the IF amplifier 8 is kept below a predetermined level.

  The SAW filter 11 attenuates a component outside a predetermined band among the frequency components of the IF signal received from the IF amplifier 8.

  The IF_AGC circuit 12 adjusts the level of the IF signal that has passed through the SAW filter 11 under the control of the OFDM demodulation IC 14.

IF amplifier 13 amplifies the IF signal received from IF_AGC circuit 12.
The OFDM demodulation IC 14 OFDM-demodulates the IF signal received from the IF amplifier 13 and outputs it as a transport stream signal (hereinafter also referred to as a TS signal). The OFDM demodulation IC 14 controls the IF_AGC circuit 12 so that the IF signal received from the IF amplifier 13 becomes a predetermined level.

  In this tuner, when the level of the IF signal received by the OFDM demodulating IC 14 changes, the RF_AGC circuit 3 and the IF_AGC circuit 12 adjust the level when the level of the RF signal input from the input terminal 1 changes. It is controlled to be 5 Vpp.

  That is, in this tuner, when the level of the IF signal detected by the detection circuit 9 is equal to or higher than a predetermined level, the RF_AGC circuit 3 adjusts the level of the RF signal. On the other hand, when the level of the IF signal detected by the detection circuit 9 is less than a predetermined level, the IF_AGC circuit 12 adjusts the level of the IF signal.

  By the way, in the tuner described in Patent Document 1, when the level of the disturbing signal varies, the detection result of the detection circuit varies despite the fact that the level of the main signal does not vary. There was a problem that the level adjustment was not performed and the reception performance deteriorated. However, in the tuner according to the first embodiment of the present invention, the filter circuit 15 suppresses the interference signal output to the IF amplifier 8 and the detection circuit 9. Therefore, even if the level of the interference signal varies, the detection result of the detection circuit 9 does not vary, so that the RF_AGC circuit 3 can be appropriately controlled, and deterioration of reception performance can be prevented.

  Here, in the terrestrial digital broadcast, the transmission output of the terrestrial digital broadcast is lower than the transmission output of the terrestrial analog broadcast so that no trouble occurs in the reception of the terrestrial analog broadcast that has been broadcast conventionally. It can be suppressed. Thereby, in terrestrial digital broadcasting, a level difference of −30 dB or more is generated in the RF band in terms of D / U (Desired Undesired) ratio in comparison with terrestrial analog broadcasting. Therefore, as a performance of the terrestrial digital tuner, for example, a high adjacent channel interference removal performance with a D / U ratio of around −40 dB is required, and a high spurious interference removal performance with a D / U ratio of around −55 dB, for example, is required. . Here, the adjacent channel signal is a channel signal other than the channel currently received (hereinafter also referred to as a reception channel). The spurious signal is a signal such as an image signal and a harmonic of a local signal.

  When the input level of the interference wave to the terrestrial digital tuner becomes a strong electric field level of, for example, −20 dBm or more, cross modulation distortion in the RF_AGC circuit 3 and the mixer oscillator PLL_IC10 increases, and reception performance deteriorates. Therefore, in the tuner according to the first embodiment of the present invention, by providing the detection circuit 9, when the level of the interference wave is large, the gain of the RF_AGC circuit 3 is lowered to reduce the reception performance due to cross modulation distortion. Suppress. However, if the gain of the RF_AGC circuit 3 is lowered too much, C / N deteriorates in the RF_AGC circuit 3, a reception error occurs in the OFDM demodulation IC 14, and reception performance deteriorates. The reception performance deterioration due to cross modulation distortion in the RF_AGC circuit 3 and the mixer oscillator PLL_IC 10 and the reception performance deterioration due to C / N deterioration are in an inversely proportional relationship.

  FIG. 2A is a graph showing the frequency characteristics of the single tuning filter 2. That is, FIG. 2A shows the frequency characteristic of the signal in A of FIG.

FIG. 2B is a graph showing the frequency characteristics of the double-tuned filter 4.
FIG. 2C is a graph showing the combined frequency characteristics of the single tuning filter 2 and the double tuning filter 4. That is, FIG. 2C shows the frequency characteristics of the signal in B of FIG. 2A to 2C, F1 is the center frequency of the signal of the reception channel (hereinafter also referred to as reception frequency), and F2 is the frequency of the spurious signal (hereinafter also referred to as spurious interference frequency).

  Referring to FIG. 2C, the signal level of the spurious interference frequency F2 reaching the detection circuit 9 of the mixer oscillator PLL_IC 10 becomes the signal level of the reception frequency F1 due to the attenuation characteristics of the single tuning filter 2 and the double tuning filter 4. On the other hand, it is lower by (A1-A4).

  Here, in the state where the spurious interference frequency is F2, the level adjustment of the RF_AGC circuit 3 is operating at the optimum point, that is, the C / N deterioration in the RF_AGC circuit 3 and the crossing in the RF_AGC circuit 3 and the mixer oscillator PLL_IC10. It is assumed that the degradation of the tuner reception performance due to modulation distortion is minimized.

  When the spurious interference frequency F2 is shifted in the direction of the reception frequency F1, as shown in FIG. 2C, the signal level of the spurious interference frequency F2 reaching the detection circuit 9 becomes higher than A4. Then, since the level of the IF signal detected by the detection circuit 9 is increased, the gain of the RF_AGC circuit 3 is lowered, so that the level adjustment is deviated from the optimum point, and reception performance is greatly deteriorated due to C / N deterioration.

  On the other hand, when the spurious interference frequency F2 is shifted in the opposite direction to the reception frequency F1, the level reaching the detection circuit 9 is smaller than A4 as shown in FIG. Then, since the level detected by the detection circuit 9 becomes small, the gain of the RF_AGC circuit 3 rises, so that it deviates from the optimum point for level adjustment, and reception performance is greatly deteriorated due to cross modulation distortion.

  Therefore, when the spurious interference frequency changes, the level at which the spurious interference signal reaches the detection circuit 9 varies, so that the RF_AGC circuit 3 does not operate stably at the optimum level adjustment level, and reception performance deteriorates.

  In this tuner, the adjustment contents of the single-tuned filter 2 and the double-tuned filter 4 are different for each tuner due to manufacturing variations of the circuits including the single-tuned filter 2 and the double-tuned filter 4. The frequency characteristics of the 2 and double-tuned filter 4 often vary from tuner to tuner.

  Here, in the tuner according to the first embodiment of the present invention, the filter circuit 15 that performs band limitation for the purpose of suppressing the interference signal output to the IF amplifier 8 and the detection circuit 9 is provided after the mixer circuit 5. However, if the filter circuit 15 is designed to have a steep frequency characteristic in order to reduce the influence of the spurious signal and to cope with the variation in the frequency characteristic of the single tuning filter 2 and the double tuning filter 4, The IF signal, which is the main signal, is excessively attenuated, and reception performance deteriorates due to variations in the filter circuit 15 and temperature drift.

  As described above, in the tuner according to the first embodiment of the present invention, when the frequency of the interference wave varies, the AGC circuit does not operate stably at the optimum point of level adjustment, and the reception performance deteriorates. There is.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to a tuner in which the position of the filter circuit is changed with respect to the first embodiment. Configurations and operations other than those described below are the same as those of the tuner according to the first embodiment.

FIG. 3 is a functional block diagram of a tuner according to the second embodiment of the present invention.
With reference to the figure, this tuner includes a detection filter 21 instead of the filter circuit 15 with respect to the tuner according to the first embodiment.

IF amplifier 8 amplifies the IF signal received from mixer circuit 5.
The detection filter 21 attenuates the component outside the predetermined band among the frequency components of the IF signal received from the IF amplifier 8.

The detection circuit 9 detects the level of the IF signal received from the detection filter 21.
By the way, in the tuner according to the first embodiment of the present invention, when the frequency of the interference wave fluctuates, the AGC circuit does not operate stably at the optimum level adjustment level, and the reception performance deteriorates. is there. However, in the tuner according to the second embodiment of the present invention, since the detection filter 21 is not provided on the main signal line, the IF signal is attenuated by designing the frequency characteristic of the detection filter 21 sharply. However, the reception performance does not deteriorate. Even if the detection filter 21 varies and the temperature drifts, the IF signal of the main signal line is not directly affected, so that the reception performance does not deteriorate. For this reason, the detection filter 21 can be freely designed without considering the influence on the main signal.

  Therefore, in the tuner according to the second embodiment of the present invention, the interference filter output to the detection circuit 9 is provided by providing the detection filter 21 on a line different from the main signal line and before the detection circuit 9. Since the signal can be further suppressed, the AGC circuit can be operated at the optimum level adjustment level regardless of the frequency fluctuation of the interference wave, and the reception performance of the tuner according to the first embodiment is deteriorated. Furthermore, it can be prevented.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Third Embodiment>
The present embodiment relates to a tuner that can change the frequency characteristics of the detection filter with respect to the second embodiment. Configurations and operations other than those described below are the same as those of the tuner according to the second embodiment.

FIG. 4 is a functional block diagram of a tuner according to the third embodiment of the present invention.
With reference to the figure, the tuner includes a detection filter 22 instead of the detection filter 21 with respect to the tuner according to the second embodiment, and includes an SW circuit 41, a tuner external terminal 42, and Is further provided.

  The SW circuit 41 outputs a control signal for changing the frequency characteristic of the detection filter 21 based on the control signal from the tuner external terminal 42.

  The detection filter 22 changes frequency characteristics such as a bandwidth and a cutoff frequency based on the control signal received from the SW circuit 41.

  Therefore, in the tuner according to the third embodiment of the present invention, the frequency characteristic of the detection filter 22 can be changed according to the reception state of the tuner, such as the level of the interference wave, so the detection result of the detection circuit 9 Can be achieved and good reception performance can be obtained.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Fourth embodiment>
The present embodiment relates to a tuner in which the input method of the control signal from the outside of the tuner to the SW circuit is changed with respect to the third embodiment. Configurations and operations other than those described below are the same as those of the tuner according to the third embodiment.

FIG. 5 is a functional block diagram of a tuner according to the fourth embodiment of the present invention.
With reference to the figure, the tuner includes a tuner external terminal 43 instead of the tuner external terminal 42 with respect to the tuner according to the third embodiment.

  The tuner external terminal 43 is a terminal for the mixer oscillator PLL_IC 10 to transmit / receive signals to / from the tuner using the I2C bus.

  The SW circuit 41 outputs a control signal for changing the frequency characteristic of the detection filter 21 based on a control signal received from the outside of the tuner via the mixer oscillator PLL_IC 10.

  Therefore, in the tuner according to the fourth embodiment of the present invention, the frequency characteristic of the detection filter 22 can be changed according to the reception state of the tuner, such as the level of the interference wave, so the detection result of the detection circuit 9 Can be achieved and good reception performance can be obtained. Further, the control for the detection filter 22 can be easily performed from the outside via the I2C bus.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Fifth embodiment>
The present embodiment relates to a tuner that can output the detection result of the detection circuit to the outside of the tuner with respect to the second embodiment. Configurations and operations other than those described below are the same as those of the tuner according to the second embodiment.

FIG. 6 is a functional block diagram of a tuner according to the fifth embodiment of the present invention.
With reference to the figure, the tuner includes a detection circuit 45 instead of the detection circuit 9 and further includes a tuner external terminal 42 with respect to the tuner according to the second embodiment.

  The detection circuit 45 detects the level of the IF signal received from the detection filter 21, and outputs the detection result to the outside of the tuner via the RF_AGC circuit 3 and the tuner external terminal 42.

  The level determination circuit 44 is provided outside the tuner and determines the reception level of the tuner based on the detection result received from the detection circuit 45 via the tuner external terminal 42.

  Therefore, in the tuner according to the fifth embodiment of the present invention, the reception level of the tuner can be confirmed outside the tuner, and the direction of the antenna of the receiving device including the tuner is adjusted based on the reception level of the tuner. And good reception performance can be obtained.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Sixth Embodiment>
The present embodiment relates to a tuner in which the method of outputting the detection result of the detection circuit to the outside of the tuner is changed with respect to the fifth embodiment. Configurations and operations other than those described below are the same as those of the tuner according to the fifth embodiment.

FIG. 7 is a functional block diagram of a tuner according to the sixth embodiment of the present invention.
With reference to the figure, the tuner includes a tuner external terminal 43 instead of the tuner external terminal 42 and further includes a level determination circuit 46 with respect to the tuner according to the fifth embodiment.

  The tuner external terminal 43 is a terminal for the mixer oscillator PLL_IC 10 to transmit / receive signals to / from the tuner using the I2C bus.

  The level determination circuit 46 is provided in the mixer oscillator PLL_IC 10, determines the reception level of the tuner based on the detection result received from the detection circuit 45, and outputs the determination result to the outside of the tuner via the tuner external terminal 43. Further, for example, a read register connected with an I2C bus is provided outside the tuner, and a determination result is read from the read register.

  Therefore, in the tuner according to the sixth embodiment of the present invention, the reception level of the tuner can be confirmed outside the tuner, and the direction of the antenna of the receiving device including the tuner is adjusted based on the reception level of the tuner. And good reception performance can be obtained. In addition, the determination result can be easily output to the outside of the tuner via the I2C bus.

  Note that the detection circuit 45 may include a level determination circuit 46 and output the determination result of the level determination circuit 46 to the outside of the tuner as a detection result.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Seventh embodiment>
The present embodiment relates to a tuner including a plurality of RF_AGC circuits as compared to the second embodiment. Configurations and operations other than those described below are the same as those of the tuner according to the second embodiment.

  FIG. 8 is a functional block diagram of a tuner according to the seventh embodiment of the present invention. FIG. 9 is a diagram showing the contents of the delay control performed by the delay circuit 48.

  With reference to the figure, the tuner further includes an RF_AGC circuit 47 and a delay circuit 48 in addition to the tuner according to the second embodiment.

  The delay circuit 48 outputs the detection result of the detection circuit 9 to the RF_AGC circuit 3, and then outputs the detection result of the detection circuit 9 to the RF_AGC circuit 47.

  The RF_AGC circuit 47 adjusts the level of the RF signal input from the input terminal 1 based on the detection result received from the delay circuit 48.

  The single tuning filter 2 attenuates a component outside the predetermined band among the frequency components of the RF signal whose level is adjusted by the RF_AGC circuit 47.

  The RF_AGC circuit 3 adjusts the level of the RF signal that has passed through the single tuning filter 2 based on the detection result received from the delay circuit 48.

  Here, as described above, in the tuner according to the embodiment of the present invention, when the level of the IF signal detected by the detection circuit 9 is equal to or higher than a predetermined level, the RF_AGC circuit 3 adjusts the level of the RF signal. It is. That is, when the received radio wave is a strong electric field, the gain of the RF_AGC circuit is lowered to prevent the output signal of the RF_AGC circuit from being distorted and the reception performance from being deteriorated. However, NF usually deteriorates when the gain of the RF_AGC circuit is lowered. Further, the deterioration of NF is larger when the output signal level of the preceding circuit is lowered than when the output signal level of the latter circuit is lowered.

  Therefore, in the tuner according to the seventh embodiment of the present invention, when the received radio wave is a strong electric field, the delay circuit 48 outputs the detection result to the RF_AGC circuit 3 subsequent to the RF_AGC circuit 47 first. Thus, as shown in FIG. 9, the gain of the RF_AGC circuit 3 at the subsequent stage is lowered before the gain of the RF_AGC circuit 47 at the previous stage. As described above, by appropriately controlling the gain of each RF_AGC circuit, it is possible to suppress the deterioration of NF due to the decrease in the gain of the RF_AGC circuit and to obtain good reception performance in a strong electric field.

  Although the tuner according to the seventh embodiment of the present invention includes the RF_AGC circuit 3 and the RF_AGC circuit 47, the present invention is not limited to this, and three or more connected in series on the main signal line. The RF_AGC circuit can be provided. In this case, the delay circuit 48 sequentially outputs detection results from the last RF_AGC circuit to the previous RF_AGC circuit.

  In addition, the delay control of the detection result of the delay circuit 48 is not limited to the above-described content, and by setting the timing for outputting the detection result to each RF_AGC circuit according to the reception state of the tuner, it is possible to achieve good reception. Performance can be obtained. In other words, the delay circuit 48 outputs a detection result to at least one of the AGC circuits at a timing different from that of the other AGC circuits. Also, the delay circuit 48 may be configured to delay and output the detection result to at least one of the AGC circuits, and to output the detection result as it is without delaying to other AGC circuits. Good.

  In the tuners according to the first to seventh embodiments of the present invention, the frequency of the RF signal input from the input terminal 1 is set to the UHF band and the 1BAND configuration. However, the VHF band and the CATV band may be used. It may be 2BAND and 3BAND.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

FIG. 3 is a functional block diagram of a tuner according to the first embodiment of the present invention. (A) is a graph showing the frequency characteristics of the single tuning filter 2. (B) is a graph showing the frequency characteristics of the double-tuned filter 4. (C) is a graph showing the combined frequency characteristics of the single-tuned filter 2 and the double-tuned filter 4. It is a functional block diagram of the tuner which concerns on the 2nd Embodiment of this invention. It is a functional block diagram of the tuner which concerns on the 3rd Embodiment of this invention. It is a functional block diagram of the tuner which concerns on the 4th Embodiment of this invention. It is a functional block diagram of the tuner which concerns on the 5th Embodiment of this invention. It is a functional block diagram of the tuner which concerns on the 6th Embodiment of this invention. It is a functional block diagram of the tuner which concerns on the 7th Embodiment of this invention. It is a figure which shows the content of the delay control which the delay circuit 48 performs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Input terminal (reception part), 2 Single tuning filter, 3,47 RF_AGC circuit, 4 Double tuning filter, 5 Mixer circuit, 6 Local oscillation circuit, 7 PLL circuit, 8 IF amplifier, 9,45 Detection circuit, 10 Mixer oscillator PLL_IC, 11 SAW filter, 12 IF_AGC circuit, 13 IF amplifier, 14 OFDM demodulation IC (demodulation circuit), 15 filter circuit, 21, 22 filter for detection, 41 SW circuit, 42, 43 tuner external terminal, 44, 46 level judgment Circuit, 48 delay circuit.

Claims (5)

A receiver for receiving a radio signal;
An AGC circuit for adjusting the level of the received radio signal;
A mixer circuit for frequency-converting the level-adjusted radio signal into an IF signal by multiplying the level-adjusted radio signal and a local oscillation signal;
A demodulation circuit for demodulating the IF signal;
A detection filter for attenuating a component outside a predetermined band among the frequency components of the IF signal;
A detection circuit that detects the level of the IF signal that has passed through the detection filter;
The AGC circuit is a tuner that performs the level adjustment based on a detection result of the detection circuit.   The tuner according to claim 1, wherein the detection filter can change a frequency characteristic.   The tuner according to claim 1, wherein the detection circuit outputs the detection result to the outside. The tuner is
A plurality of the AGC circuits connected in series;
The detection result received from the detection circuit is output to each AGC circuit, and the detection result is output to at least one of the AGC circuits at a timing different from that of the other AGC circuits. The tuner according to claim 1, further comprising a circuit.   5. The tuner according to claim 4, wherein the delay circuit sequentially outputs the detection results from the AGC circuit at the last stage toward the AGC circuit at the preceding stage.

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