JPH06283933A - Fm receiver - Google Patents

Abstract

PURPOSE:To suppress both impulse and non-impulse noises which are dominant with a low level and a high level of the supplied signal respectively by controlling the input signal at a high level and a low level when the signal supplied to an input terminal has a low level and a high level respectively. CONSTITUTION:The input signal supplied to an input terminal 1 is amplified by a variable gain amplifier 3 and undergoes the conversion of frequency through a mixer 4 and a local oscillator 5. Then the converted signal undergoes the band limitation through a filter 6 and then undergoes the FM demodulation through a phase comparator 12, a loop filter 14, and a loop amplifier 15. Thus the demodulated signal is transmitted through an output terminal 2. If the level of the signal supplied to the terminal 1 varies, the level of the signal supplied to a level sensor 8, i.e., the comparator 12 is controlled at the level corresponding to the output voltage of a DC amplifier 10 within a gain control range of the amplifier 3. Thus the signal supplied to the comparator 12 is set at a high level and a low level when the signal supplied to the terminal 1 has a low level and a high level respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver used for receiving satellite broadcasting and the like.

[0002]

2. Description of the Related Art A conventional FM receiver has a structure as shown in FIG. That is, in FIG. 3, reference numeral 1 is an input terminal, and a signal is supplied to the input terminal 1 through an antenna and a frequency converter. Further, the variable gain amplifier 3 is input from the input terminal 1. The amplified output of the variable gain amplifier 3 is input to the mixer 4, and at the same time, the output of the local oscillator 5 is input to and mixed with the mixer 4. The output of the mixer 4 is input to the filter 6, and the output passed through the filter 6 is input to the FM demodulator 7. At the same time, the output of the filter 6 is input to the level detector 8, the magnitude of the average amplitude of the signal is detected, and the detection output of the level detector 8 is used as the comparison side voltage input of the voltage comparator 9. Further, a constant voltage from the reference power source 11 is input to the reference side voltage input of the voltage comparator 9. The output of the voltage comparator 9 is connected and input to the control voltage input terminal of the variable gain amplifier 3. In such a configuration, when the signal level supplied to the input terminal 1 drops, the signal level output from the variable gain amplifier 3 also drops. At this time, the signal level input to the level detector 8 also drops, so the output voltage of the level detector 8 also drops. The voltage comparator 9 compares this voltage with the output voltage of the reference power source 11, and the level detector 8
If the output voltage is higher, the high voltage is output, and if the output voltage is lower, the low voltage is output according to the degree. Since the gain control characteristic of the variable gain amplifier 3 is such that the gain increases as the control voltage decreases, the output voltage of the level detector 8 is low and the output voltage of the voltage comparator 9 is low as described above. Then, the gain of the variable gain amplifier increases until the output voltage of the level detector 8 and the output voltage of the reference power supply 11 match.
Therefore, even if the signal level supplied to the input terminal 1 changes, the signal level input to the level detector 8, that is, the signal level input to the FM demodulator 7 is as shown in FIG. Within the gain control range of, the signal level corresponding to the output voltage of the reference power supply 11 is always kept constant.
In this state, FM demodulation is performed by the FM demodulator 7, and the demodulated signal is output from the output terminal 2.

[0003]

When the signal level supplied to the input terminal 1 is lowered due to such a signal level control characteristic, the signal-to-noise ratio is deteriorated as the signal level is lowered. At that time, the FM receiver is used. Peculiar impulse noise, that is, so-called threshold noise is generated, and the image quality is extremely deteriorated. In order to prevent this, by increasing the loop gain of the phase-locked loop that is performing the FM demodulation operation so that the signal level input to the FM demodulator 7 becomes constant at a high value in advance, the occurrence of impulse noise is prevented. Can be suppressed. However, this increases the loop noise bandwidth of the phase locked loop and increases non-impulse noise. Therefore, in the conventional FM receiver that controls the signal level input to the FM demodulator 7 to be constant regardless of the signal level supplied to the input terminal 1, it is dominant when the signal level supplied to the input terminal 1 is low. However, there is a problem in that it is impossible to simultaneously suppress the impulse noise and the non-impulse noise that is dominant when the signal level is high.

[0004]

In order to solve this problem, the FM receiver of the present invention is one in which the output of this voltage comparator is fed back to the reference voltage input of the voltage comparator.

[0005]

With this configuration, the signal level input to the FM demodulator is controlled to be high when the signal level supplied to the input terminal is low and low when the signal level supplied to the input terminal is high.

By this control, when the signal level supplied to the input terminal is low, the gain of the variable gain amplifier increases, the input signal level of the FM demodulator rises, and the loop gain of the phase locked loop increases. It is possible to suppress the generation of impulse noise. At this time, at the same time, the noise bandwidth of the phase-locked loop is widened, so that non-impulse noise increases and the received image quality deteriorates. However, the improvement of the image quality by suppressing the impulse noise is much more effective, so that the subtraction image quality is improved.

Further, when the signal level supplied to the input terminal is high, impulse noise hardly occurs. Then, since the input signal level of the FM demodulator decreases and the gain of the phase locked loop is reduced, and the noise bandwidth of the phase locked loop is narrowed, non-impulse noise is also reduced.

From the above, it is possible to reduce the influence of noise on the image quality as a whole, regardless of whether the signal level supplied to the input terminal is low or high.

[0009]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an FM receiver according to an embodiment of the present invention. Similarly to the above-mentioned conventional example, the variable gain amplifier 3, the mixer 4, the filter 6, the signal processing order from the input terminal 1 to the output terminal 2,
Phase comparator 12, loop filter 14, loop amplifier 1
5 are connected. Here, the phase demodulator 12, the loop filter 14, and the loop amplifier 15 correspond to the conventional FM demodulator 7. A local oscillator 5 is connected to the mixer 4, and the output of the filter 6 is branched and connected to a control voltage input terminal of the variable gain amplifier 3 via a level detector 8 and a voltage comparator 9. Is the same as. Further, here, the output of the voltage comparator 9 is branched and input to the DC amplifier 10, and the output of the DC amplifier 10 is fed back to the reference voltage input terminal of the voltage comparator 9. Further, the output of the loop amplifier 15 is used as the control input of the voltage controlled oscillator 13, and the output from the voltage controlled oscillator 13 to the phase comparator 12 is controlled.

The operation of the FM receiver configured as above will be described. First, the input signal supplied to the input terminal 1 is amplified by the variable gain amplifier 3 and frequency-converted by the mixer 4 and the local oscillator 5. Further, band limitation is performed by the filter 6, and FM demodulation is performed by the phase comparator 12, the loop filter 14, and the loop amplifier 15, so that a demodulated signal is output from the output terminal 2.

Here, when the signal level supplied to the input terminal 1 is lowered, the signal level input to the level detector 8 is lowered, so that the output voltage of the level detector 8 is also lowered. The voltage comparator 9 compares this voltage with the output voltage of the DC amplifier 10, and outputs a high voltage if the output voltage of the level detector 8 is higher, and outputs a low voltage if the output voltage of the level detector 8 is lower. Here, since the gain control characteristic of the variable gain amplifier 3 is such that the gain increases as the control voltage decreases, the gain gradually increases, and the output voltage of the level detector 8 and the output voltage of the DC amplifier 10 increase. Increases to a value that matches. Furthermore, since the input / output characteristic of the DC amplifier 10 outputs a voltage having a phase opposite to that of the input voltage, when the output voltage of the voltage comparator 9 decreases, the output voltage of the DC amplifier 10 increases.

Therefore, when the signal level supplied to the input terminal 1 changes, the signal level input to the level detector 8, that is, the signal level input to the phase comparator 12 is as shown in FIG. When the signal level is controlled to a signal level corresponding to the output voltage of the DC amplifier 10 within the gain control range of 3, and the signal level supplied to the input terminal 1 is low, it is high, and the signal level supplied to the input terminal 1 is high. Becomes lower.

As described above, according to this embodiment, when the signal level supplied to the input terminal 1 is low, the phase comparator 1
The signal level input to 2 will be kept high.
As a result, the loop gain of the phase locked loop that is performing the FM demodulation operation in the next stage can be increased, and the generation of impulse noise can be suppressed. At this time, at the same time, the noise bandwidth of the phase-locked loop is widened, so that non-impulse noise increases and the received image quality deteriorates. However, the deterioration of image quality due to impulse noise is very conspicuous, and the deterioration of image quality due to non-impulse noise has a smaller effect than that.Therefore, when the impulse noise disappears, the image quality is Improve.

On the contrary, when the signal level supplied to the input terminal 1 is high, the signal level input to the phase comparator 12 is kept low. As a result, non-impulse noise can be suppressed by reducing the loop gain of the phase-locked loop that is performing the FM demodulation operation of the next stage and narrowing the loop noise bandwidth. Input terminal 1
When the level of the signal supplied to is high, impulse noise hardly occurs, and in this case, the reception image quality is simply improved by the amount of suppression of non-impulse noise.

As described above, in this embodiment, the signal level input to the FM demodulator 7 is changed to detect the detection sensitivity of the phase comparator 12, which is a part of the phase-locked loop shown in FIG. By controlling the loop gain of the phase locked loop by controlling
By controlling according to the magnitude of the input level from the input terminal 1, impulse noise that becomes dominant when the signal level supplied to the input terminal 1 is low and non-impulse that becomes dominant when the signal level is high Noise suppression can be realized at the same time. Further, when the signal level supplied to the input terminal 1 is high, the signal level input to the mixer 4 is controlled to be low, so that there is also an effect of suppressing distortion such as intermodulation.

(Embodiment 2) FIG. 6 is a block diagram of an FM receiver in a second embodiment of the present invention. Description of the same numbers as in FIG. 1 is omitted. In FIG. 6, the second variable gain amplifier 16 is interposed between the filter 6 and the phase comparator 12, and the input from the filter 6 is amplified and output to the phase comparator 12. The gain control voltage of the second variable gain amplifier 16 is obtained by branching the output of the voltage comparator 9. It is assumed that when the output of the voltage comparator 9 becomes a low voltage, the gain of the second variable gain amplifier 16 increases.

The signal from the input terminal 1 has exactly the same characteristics as the above-described conventional example up to the output of the filter 6, and maintains a constant signal level within the gain control range of the first variable gain amplifier 3. . That is, the output level of the filter 6 becomes a curve similar to that of FIG. 4 described above with respect to the input signal level.
However, the second variable gain amplifier 16 connected to the latter stage has a large gain when the input signal is small, and a large gain when the input signal is large, according to the control voltage from the voltage comparator 9. Work to get smaller. As a result, the second
The output of the variable gain amplifier 16, that is, the detection input of the phase comparator 12 has a curve similar to that of FIG. 2 with respect to the signal level of the input terminal 1. For such an input, the operation of the subsequent stage after the phase comparator 12 is the same as that described in the first embodiment.

In this way, also in this embodiment, the influence of impulse noise and non-impulse noise can be reduced.

(Third Embodiment) FIG. 7 is a block diagram of an FM receiver according to a third embodiment of the present invention. Here, the output of the voltage comparator 9 is branched and used as an input for controlling the gain of the loop amplifier 15. When the input signal level is low, the output of the voltage comparator 9 outputs a low voltage. At this time, the gain of the loop amplifier can be increased to increase the loop gain of the phase locked loop, and the generation of impulse noise can be suppressed. Conversely, when the input signal level is high, the loop gain decreases, the noise bandwidth narrows, and non-impulse noise can be suppressed. This mechanism is the same as in the first and second embodiments.

(Fourth Embodiment) FIG. 8 is a block diagram of an FM receiver according to a fourth embodiment of the present invention. Here, the output of the voltage comparator 9 is branched and used as an input for adjusting the oscillation frequency control sensitivity of the voltage controlled oscillator 13. As a result, similarly to the third embodiment, the effect of impulse noise and non-impulse noise can be reduced by increasing or decreasing the loop gain of the phase locked loop according to the level of the input signal level of the input terminal 1.

It should be noted that the functions of the level detector 8 and the voltage comparator 9 may be simultaneously performed by a single circuit, and the functions of the loop filter 14 and the loop amplifier 15 may be also integrated. It is clear from the description.

[0022]

As described above, according to the present invention, when the signal level supplied to the input terminal of the FM receiver is low, the signal level input to the FM demodulator is high and the signal level supplied to the input terminal is high. When the signal level supplied to the input terminal is low, the signal level input to the FM demodulator is controlled to be low and the loop gain of the phase-locked loop is controlled to prevent the deterioration of the demodulated signal. Simultaneous suppression of dominant impulse noise and non-impulse noise that is dominant when the signal level supplied to the input terminal is high, and mutual interference that occurs when the signal level supplied to the input terminal is high It is possible to provide an excellent FM receiver that improves deterioration of a demodulated signal due to distortion such as modulation.

[Brief description of drawings]

FIG. 1 is a block diagram of an FM receiver according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the FM receiver according to the embodiment of the present invention.

FIG. 3 is a block diagram of a conventional FM receiver.

FIG. 4 is a characteristic diagram for explaining the operation of a conventional FM receiver.

FIG. 5 is a block diagram of a phase locked loop forming an FM demodulator.

FIG. 6 is a block diagram of an FM receiver according to a second embodiment of the present invention.

FIG. 7 is a block diagram of an FM receiver according to a third embodiment of the present invention.

FIG. 8 is a block diagram of an FM receiver according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1 Input Terminal 2 Output Terminal 3 First Variable Gain Amplifier 4 Mixer 5 Local Oscillator 6 Filter 7 FM Demodulator 8 Level Detector 9 Voltage Comparator 10 DC Amplifier 11 Reference Power Supply 12 Phase Comparator 13 Voltage Controlled Oscillator 14 Loop Filter 15 Loop amplifier 16 Second variable gain amplifier

Claims (4)

[Claims] 1. A signal from an input terminal is input to a first variable gain amplifier, an output from this first variable gain amplifier and an output from a local oscillator are input to a mixer, and the output of this mixer is input. Is input to a phase comparator through a filter, the output of the filter is compared with the output of the voltage controlled oscillator in the phase comparator, and the output of the phase comparator is input to a loop amplifier through a loop filter. The output of the amplifier is taken out to the output terminal, the output of the loop amplifier is branched and used as the control input of the voltage controlled oscillator, and the output from the filter to the phase comparator is branched and input to the level detector. , The output of the level detector is input to a voltage comparator, the output of the voltage comparator is branched, and one of them is used as a gain control voltage input of the first variable gain amplifier, An FM receiver configured to feed back the other to the reference input of this voltage comparator. 2. A signal from an input terminal is input to a first variable gain amplifier, an output from this first variable gain amplifier and an output from a local oscillator are input to a mixer, and the output of this mixer is input. Is input to a phase comparator through a filter and a second variable gain amplifier, the phase comparator compares the output of the filter with the output of the voltage controlled oscillator, and the output of the phase comparator is looped through a loop filter. The output of the loop amplifier is output to the output terminal, and the output of the loop amplifier is branched and used as the control input of the voltage controlled oscillator, and the output of the filter is branched and input to the level detector. Then, the output of the level detector is input to the voltage comparator, the output of the voltage comparator is branched, and one of them is used as the gain control voltage input of the first variable gain amplifier. , An FM receiver configured such that the other is used as a gain control voltage input of the second variable gain amplifier. 3. A signal from an input terminal is input to a first variable gain amplifier, an output from this first variable gain amplifier and an output from a local oscillator are input to a mixer, and the output of this mixer is input. Is input to the phase comparator through the filter, the phase comparator compares the output of the filter with the output of the voltage controlled oscillator, and the output of the phase comparator is input to the loop amplifier through the loop filter. The output of the amplifier is taken out to the output terminal, the output of the loop amplifier is branched and used as the control input of the voltage controlled oscillator, and the output of the filter is branched and input to the level detector. Is input to the voltage comparator, the output of this voltage comparator is branched, and one is used as the gain control voltage input of the first variable gain amplifier,
An FM receiver in which the other is used as a control voltage input of the loop amplifier. 4. A signal from an input terminal is input to a first variable gain amplifier, an output from this first variable gain amplifier and an output from a local oscillator are input to a mixer, and the output of this mixer is input. Is input to the phase comparator through the filter, the phase comparator compares the output of the filter with the output of the voltage controlled oscillator, and the output of the phase comparator is input to the loop amplifier through the loop filter. The output of the loop amplifier is branched and used as the control input of the voltage controlled oscillator, and the output of the filter is branched and input to the level detector. The output is input to a voltage comparator, the output of this voltage comparator is branched and one is used as the gain control voltage input of the first variable gain amplifier, and the other is used for the voltage control generator. An FM receiver configured to input the frequency sensitivity control voltage of the shaker.