JP2007184693A - Fm tuner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FM tuner for applying optimizing control to a variable band width of an IF filter so as to be capable of improving the S/N ratio by emphasizing reception sensitivity in the case of a weak electric field input and for applying optimizing control to the variable band width of the IF filter so as to be capable of efficiently receiving a desired wave at elimination of disturbance in the case of a medium or strong electric field input. <P>SOLUTION: The FM tuner includes: the IF filter 1 whose band width is controllable; an IF limiter amplifier 2; an FM detector 3; an adjacent disturbance level detector 4; a modulation degree detector 5 for detecting an FM modulation degree; a weak electric field detector 7 for discriminating whether or not an FM reception signal is received at the weak electric field input; a switching circuit 8 for receiving an output of an adjacent disturbance detector and an output of the modulation degree detector switching and selecting the outputs on the basis of a discrimination output of the weak electric field detector; a controller 9 for receiving the selected output of the switching circuit and applying a prescribed coefficient control to the selection output to output a first control signal; and a variable band width control circuit 10 for receiving the first control signal to convert the first control signal into a second control signal for controlling the band width of the IF filter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an FM (frequency modulation) tuner, and more particularly to an IF (intermediate frequency) band control system, which is used for mobile object reception such as car audio.

  The conventional FM tuner has (1) a function of controlling the bandwidth of the IF filter based on the level of the adjacent jamming radio wave to suppress the adjacent jamming to a predetermined level when a strong electric field is input in the FM received radio wave, and (2 ) In a weak electric field, it has a function of controlling the bandwidth of the IF filter based on the modulation degree of the FM signal, and improving the reception sensitivity and thus the signal-to-noise ratio (S / N) of the FM detection signal.

  For example, in the FM tuner shown in Patent Document 1, an IF filter, an IF limiter amplifier, an FM detector, an adjacent interference detector that detects adjacent interference from the FM detection output, a modulation degree detector that detects the modulation degree from the FM detection output, An electric field detector for detecting the intensity of the input electric field from the output of the IF limiter amplifier, a weak electric field detector for determining whether or not a weak electric field is being input (medium or strong electric field input), and a controller are provided. Then, the adjacent interference detection output and the modulation degree detection output are switched according to the electric field detection output and input to the controller, and the bandwidth of the IF filter is changed by the control output of the controller.

In the above conventional configuration, the controller is shared for the adjacent interference detection output and the modulation degree detection output, so the IF filter band control range is the same. For this reason, the variable range of the bandwidth of the IF filter must be set to be the same for the weak electric field, the medium electric field, and the strong electric field. However, regarding the bandwidth of the IF filter at the time of super narrow, the signal component of the FM detection output at the time of controlling to improve the S / N with emphasis on the reception sensitivity at the time of weak electric field input, and at the time of adjacent interference of the middle electric field There is a trade-off relationship with the case where it is desired to control so as to efficiently receive the desired wave while suppressing the loss. Therefore, it is difficult to optimally control the setting of the IF filter band variable width so as to satisfy both demands for the IF filter band at the time of weak electric field and adjacent interference.
JP 2004-312077 A

  The present invention has been made to solve the above-described conventional problems. When a weak electric field is input, the reception sensitivity is emphasized to improve the S / N. An object of the present invention is to provide an FM tuner capable of optimizing and controlling the setting of the variable bandwidth of the IF filter so as to receive a desired wave.

  An FM tuner according to a first aspect of the present invention extracts an intermediate frequency signal converted from an FM reception signal, amplifies an intermediate frequency filter having a bandwidth controllable characteristic, and an output signal of the intermediate frequency filter An intermediate frequency limiter amplifier, an FM detector for FM detecting the output of the intermediate frequency limiter amplifier, an adjacent disturbance detector for detecting a signal level of an adjacent interference wave, and detecting an FM modulation degree from the output of the FM detector A modulation degree detector, an electric field detector that detects the electric field strength of the FM reception signal based on the output of the intermediate frequency limiter amplifier, and a weakness that determines whether or not a weak electric field is input from the detection output of the electric field detector An electric field detector, an output of the adjacent disturbance detector and an output of the modulation degree detector, and a switching circuit that selects and switches these based on the determination output of the weak electric field detector; A selection output of the switching circuit is input, a controller that performs a predetermined coefficient control and outputs a first control signal, and a first control signal is input and a second for controlling the bandwidth of the intermediate frequency filter A variable bandwidth control circuit for outputting a control signal.

  An FM tuner according to a second aspect of the present invention extracts an intermediate frequency signal converted from an FM reception signal, amplifies an intermediate frequency filter having a characteristic whose bandwidth can be controlled, and an output signal of the intermediate frequency filter An intermediate frequency limiter amplifier, an FM detector for FM detecting the output of the intermediate frequency limiter amplifier, an adjacent disturbance detector for detecting a signal level of an adjacent interference wave, and detecting an FM modulation degree from the output of the FM detector A modulation degree detector, an electric field detector that detects the electric field strength of the FM reception signal based on the output of the intermediate frequency limiter amplifier, and a weakness that determines whether or not a weak electric field is input from the detection output of the electric field detector An electric field detector, a first controller that receives an output of the adjacent disturbance detector, performs a predetermined coefficient control, and outputs a first control signal; and an output of the modulation degree detector A second controller that performs predetermined coefficient control and outputs a second control signal, and switches and selects the first control signal and the second control signal based on the determination output of the weak electric field detector. And a switching circuit that outputs a control signal for controlling the bandwidth of the intermediate frequency filter.

  According to the present invention, when a weak electric field is input, the S / N is improved with an emphasis on reception sensitivity, and the IF filter band is variable so that a desired wave can be received efficiently when interference is removed when a strong electric field is input. It is possible to provide an FM tuner capable of optimizing the width setting.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this description, common parts are denoted by common reference numerals throughout the drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a first embodiment of the FM tuner of the present invention. All or most of the components in FIG. 1 are formed together with other circuits on the same semiconductor chip, and are used for a mobile receiver such as a car audio.

  In FIG. 1, an intermediate frequency (IF) filter (filter) 1 extracts an IF signal obtained by frequency conversion from an RF signal amplified at a high frequency stage, for example, an FM signal having a center frequency of 450 kHz. The IF filter 1 has a characteristic capable of changing the -3 dB bandwidth in the range of about 30 kHz to about 200 kHz by the control signal C2. The IF limiter amplifier (limit amplifier) 2 amplifies the output signal (IF signal) of the IF filter. This IF limiter amplifier 2 has an amplitude limiting function. The FM detector 3 performs FM detection on the output of the IF limiter amplifier 2 and generates a detection output, in this example, an audio signal.

  The adjacent interference detector 4 detects the signal level (noise) of the adjacent interference wave. In this example, the carrier component of the adjacent interfering wave, for example, 100 to 200 kHz is extracted from the detection output of the FM detector 3 by a filter (not shown). However, the present invention is not limited to this, and adjacent interference waves can be detected even if they are inserted on the output side of the electric field detector 6 described later, for example. The modulation degree detector 5 detects the FM modulation degree from the output of the FM detector 3.

  The electric field detector 6 detects the electric field strength of the FM reception signal. In this example, the electric field strength is detected based on the intermediate stage output of the IF limiter amplifier 2, but not limited to this, based on a signal between the output end of the IF filter 1 and the input end of the FM detector 3. The electric field strength may be detected.

  The weak electric field detector 7 determines from the detection output of the electric field detector 6 whether or not a weak electric field is input. The switching circuit 8 receives the output of the adjacent disturbance detector 4 and the output of the modulation degree detector 5 and selects them based on the determination output of the weak electric field detector 7.

  The bandwidth control controller 9 receives the selection output of the switching circuit 8, performs predetermined coefficient control (coefficient calculation), and outputs a DC control signal C1. Further, the band variable width control circuit 10 receives the control signal C1 and converts the control signal C1 into a DC control signal C2 for changing the filter band. In order to prevent the above-described circuit oscillation of the FM tuner, it is desirable to provide an integrator in the controller 9, for example, to give the control of the IF filter 1 a predetermined time constant.

  In the FM tuner having the above configuration, the IF signal extracted by the IF filter 1 is subjected to FM detection by the FM detector 3 after noise is removed by the IF limiter amplifier 2. The output signal of the FM detector 3 is input to the adjacent interference detector 4 to detect the level of the adjacent interference wave. Further, the output signal of the FM detector 3 is input to the modulation degree detector 5 to detect a desired audio signal level. On the other hand, the level of the output signal of the IF limiter amplifier 2 is detected by the electric field detector 6, and this detected level is input to the weak electric field detector 7, and whether the received signal of the FM tuner is a weak electric field input (medium, strong electric field input). ) Is determined. Then, the switching circuit 8 switches between the output of the adjacent disturbance detector 4 and the output of the modulation degree detector 5 according to the determination output of the weak electric field detector 7, and then is input to the controller 9 to perform coefficient control. A control signal C1 is output.

  Here, the basic operation of the controller 9 will be described. When the level input from the adjacent disturbance detector 4 is large, that is, when the desired wave and the adjacent disturbance wave are not close to each other, the controller 9 widens the bandwidth of the IF filter 1 so as to receive the desired wave widely. The control signal C1 is generated. On the other hand, when the level input from the adjacent interference detector 4 is small, that is, when the desired wave and the adjacent interference wave are close to each other, the bandwidth of the IF filter 1 is narrowed to block the adjacent interference wave. A control signal C1 is generated.

  In addition, the controller 9 increases the detection sensitivity of the adjacent disturbance detector 4 by making the bandwidth of the IF filter 1 wide when the electric field is weak, based on the output of the weak electric field detector 7, and effectively makes the adjacent disturbance wave effective. The IF filter 1 can be adjusted by detection.

  Further, the controller 9 generates the control signal C1 so that the bandwidth of the IF filter 1 is increased when the modulation degree of the desired wave input from the modulation degree detector 5 is large, that is, when the sound level is high. Thereby, the defect | deletion with respect to the modulation degree of a desired wave is suppressed as much as possible, and FM detection characteristics (total harmonic distortion etc.) can be improved.

  As described above, the bandwidth of the IF filter 1 is appropriately set via the controller 9 based on the information obtained by the adjacent disturbance detector 4, the modulation degree detector 5, and the weak electric field detector 7 from the received FM signal. Can be controlled. As a result, the bandwidth of the IF filter 1 is not excessively narrowed while the desired wave is being received, and it is possible to change the stable bandwidth of the IF filter 1 during adjacent interference.

  Further, in the present embodiment, the control signal C1 output from the controller 9 is input to the band variable width control circuit 10 and converted to the filter band variable control signal C2. In this case, the relationship between the input and output of the band variable width control circuit 10 is switched as shown in FIG. 2, for example, according to the determination output of the weak electric field detector 7. Then, when the control signal C2 is input to the IF filter 1, the bandwidth of the IF filter 1 is controlled to a desired value according to characteristics as shown in FIG. 3, for example.

  FIG. 2 is a characteristic diagram showing an example of the relationship between the input (control signal C1) and the output (control signal C2) of the bandwidth variable width control circuit 10 in FIG. When a weak electric field is input, as shown by characteristic A in FIG. 2, the level of the control signal C2 is a constant value in a range where the level of the control signal C1 is low. If the level of the control signal C1 increases from this range, It changes so that the level of the control signal C2 increases in proportion to the signal C1. When the level of the control signal C1 exceeds a certain threshold value VT1, the level of the control signal C2 is limited to a constant value.

  On the other hand, when a strong electric field is input, the level of the control signal C2 is a constant value in a range where the level of the control signal C1 is low as shown by the characteristic B in FIG. When the level increases, the level of the control signal C2 changes in proportion to the control signal C1. When the level of the control signal C1 exceeds a certain threshold value VT2 (> VT1), the level of the control signal C2 is limited to a constant value.

  FIG. 3 is a characteristic diagram showing an example of the relationship between the input (control signal C2) of the IF filter 1 in FIG. 1 and the bandwidth BW. The bandwidth of the IF filter 1 is controlled in accordance with the level of the input (control signal C2) of the IF filter 1, the bandwidth is controlled to, for example, 20 to 120 kHz when a weak electric field is input, and the bandwidth when a medium or strong electric field is input. The width is controlled to 40 to 180 kHz, for example. That is, compared with the variable bandwidth of the IF filter 1 when a weak electric field is input, the variable bandwidth of the IF filter 1 when removing interference when a strong electric field is input is shifted to a higher side and the bandwidth is wide.

  FIG. 4 is a characteristic diagram showing how the bandwidth of the IF filter 1 in FIG. 1 is controlled according to the characteristic shown in FIG. Control is performed so that the bandwidth of the IF filter 1 is optimized when a weak electric field is input, when a weak electric field is input, and when a strong electric field is input.

  According to the FM tuner according to the first embodiment described above, by controlling the bandwidth of the IF filter 1 according to the characteristics as shown in FIG. By performing optimization control so that the width is narrowed to, for example, 20 to 120 kHz, S / N can be improved with emphasis on reception sensitivity. On the other hand, at the time of interference removal when a strong electric field is input, the loss of the signal component of the FM detection output is suppressed by performing optimization control so that the band variable width of the F filter 1 is expanded to, for example, 40 to 180 kHz. The desired wave can be received efficiently.

<Second Embodiment>
FIG. 5 is a block diagram showing a second embodiment of the FM tuner of the present invention. Compared with the FM tuner described above with reference to FIG. 1, the FM tuner shown in FIG. 5 omits the bandwidth variable width control circuit 10, and the first tuner to which the output of the adjacent disturbance detector 4 is input as a controller. A controller 9-1 and a second controller 9-2 to which the output of the modulation degree detector 5 is input are provided. The output signals C1-1 and C1-2 of the two controllers 9-1 and 9-2 are switched and selected by the switching circuit 8 in response to interference removal at the time of medium or strong electric field input and at the time of weak electric field input. Thus, the control signal C3 is changed to be input to the IF filter 1.

  The first controller 9-1 is capable of optimizing control so as to widen the variable bandwidth of the IF filter 1 to, for example, 40 to 180 kHz based on the output of the adjacent interference detector 4. Is output. Here, the first control signal C1-1 is the same signal as the second control signal C2 at the time of strong electric field input in the first embodiment described above.

  Based on the output of the modulation degree detector 5, the second controller 9-2 generates a second control signal C1-2 that can be optimized and controlled to narrow the variable bandwidth of the IF filter 1 to, for example, 20 to 120 kHz. Has output characteristics. Here, the second control signal C1-2 is the same signal as the second control signal C2 when the strong electric field is input in the first embodiment described above.

  Also in the second embodiment described above, basically the same effects as those in the first embodiment described above can be obtained.

<Third Embodiment>
FIG. 6 is a block diagram showing a third embodiment of the FM tuner of the present invention. The FM tuner shown in FIG. 6 has a desired wave / undesired wave (DU ratio) detector 61 to which the output of the FM detector 3 is input and the DU ratio compared to the FM tuner described above with reference to FIG. The difference is that an adder 62 that adds the output of the detector 61 to the output of the modulation degree detector 5 and inputs the sum to the second controller 9-2 is added.

  The DU ratio detector 61 detects the amount of deviation from the midpoint potential of the FM detection characteristic (S curve) of the output of the FM detector 3 to generate a DC control signal, and the S / N deteriorates. A signal can be reliably generated even when a weak electric field is input. Thus, the second controller 9-2 narrows the variable bandwidth of the IF filter 1 to, for example, 20 to 120 kHz based on the output of the modulation degree detector 5 and the output of the DU ratio detector 61 when a weak electric field is input. It is possible to output a control signal that can be optimized and controlled.

  Also in the third embodiment described above, basically the same effect as in the first embodiment described above can be obtained.

<Fourth Embodiment>
FIG. 7 is a block diagram showing a fourth embodiment of the FM tuner of the present invention. The FM tuner shown in FIG. 7 subtracts the output of the modulation degree detector 5 from the output of the adjacent interference detector 4 and inputs it to the first controller 9-1 as compared with the FM tuner described above with reference to FIG. The difference is that a subtracter 71 is added.

  By changing in this way, when the signal strength of the FM signal input from the weak electric field detector 7 is small, the bandwidth of the IF filter 1 is controlled to be widened, and further input from the modulation degree detector 5. When the modulation degree of the desired wave is large, that is, when the sound level is high, the IF filter 1 can be controlled to increase the bandwidth. In this way, the controller 9-1, 9- controls the received FM signal from the information obtained by the detectors 4, 5, 7, 61 to determine the optimum bandwidth of the IF filter 1. Can do.

  Also in the fourth embodiment described above, basically the same effects as in the first embodiment described above can be obtained.

1 is a block diagram showing a first embodiment of an FM tuner of the present invention. The characteristic view which shows an example of the input-output relationship of the band variable width control circuit in FIG. The characteristic view which shows an example of the relationship between the input of IF filter in FIG. 1, and a bandwidth. FIG. 4 is a characteristic diagram showing how the bandwidth of the IF filter in FIG. 1 is controlled according to the characteristic as shown in FIG. 3. The block diagram which shows 2nd Embodiment of the FM tuner of this invention. The block diagram which shows 3rd Embodiment of the FM tuner of this invention. The block diagram which shows 4th Embodiment of the FM tuner of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... IF filter, 2 ... IF limiter amplifier, 3 ... FM detector, 4 ... Adjacent disturbance detector, 5 ... Modulation degree detector, 6 ... Electric field detector, 7 ... Weak electric field detector, 8 ... Switching circuit, 9 ... Controller, 10 ... Bandwidth control circuit.

Claims (5)

An intermediate frequency filter having a characteristic capable of controlling the bandwidth by extracting an intermediate frequency signal converted from the FM reception signal;
An intermediate frequency limiter amplifier for amplifying the output signal of the intermediate frequency filter;
An FM detector for FM detecting the output of the intermediate frequency limiter amplifier;
An adjacent disturbance detector for detecting the signal level of the adjacent disturbance wave;
A modulation degree detector for detecting an FM modulation degree from the output of the FM detector;
An electric field detector for detecting the electric field strength of the FM reception signal based on the output of the intermediate frequency limiter amplifier;
A weak electric field detector for determining whether or not a weak electric field is input from the detection output of the electric field detector;
A switching circuit that receives the output of the adjacent disturbance detector and the output of the modulation degree detector, and switches and selects them based on the determination output of the weak electric field detector;
A controller that receives a selection output of the switching circuit, performs a predetermined coefficient control, and outputs a first control signal;
An FM tuner comprising: a bandwidth variable bandwidth control circuit that receives the first control signal and outputs a second control signal for bandwidth control of the intermediate frequency filter. An intermediate frequency filter having a characteristic capable of controlling the bandwidth by extracting an intermediate frequency signal converted from the FM reception signal;
An intermediate frequency limiter amplifier for amplifying the output signal of the intermediate frequency filter;
An FM detector for FM detecting the output of the intermediate frequency limiter amplifier;
An adjacent disturbance detector for detecting the signal level of the adjacent disturbance wave;
A modulation degree detector for detecting an FM modulation degree from the output of the FM detector;
An electric field detector for detecting the electric field strength of the FM reception signal based on the output of the intermediate frequency limiter amplifier;
A weak electric field detector for determining whether or not a weak electric field is input from the detection output of the electric field detector;
A first controller that receives an output of the adjacent disturbance detector, performs a predetermined coefficient control, and outputs a first control signal;
A second controller that receives an output of the modulation degree detector, performs a predetermined coefficient control, and outputs a second control signal;
A switching circuit for selecting and switching the first control signal and the second control signal based on the determination output of the weak electric field detector and outputting the control signal for bandwidth control of the intermediate frequency filter; FM tuner characterized by.   The second controller further includes a DU ratio detector for detecting a desired wave / undesired wave, and the second controller outputs a signal obtained by adding the output of the DU ratio detector and the output of the modulation degree detector as the modulation degree. 3. The FM tuner according to claim 2, wherein the FM tuner is inputted instead of the output of the detector.   The said 1st controller is replaced with the output of the said adjacent disturbance detector instead of the output of the said adjacent disturbance detector, and the signal which the output of the said modulation degree detector was subtracted from the output of the said adjacent disturbance detector is characterized by the above-mentioned. FM tuner.   Compared to the variable bandwidth of the IF filter at the time of weak electric field input, the variable bandwidth of the IF filter at the time of interference removal at the time of strong electric field input is shifted to a higher side and the bandwidth is wide. The FM tuner according to any one of claims 1 to 4.

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