JPH0646353A - High frequency receiver - Google Patents

Abstract

PURPOSE:To make it possible to receive all satellite broadcasting reception signals having different degrees of modulation in an optinum condition and to obtain a superior demodulation output signal. CONSTITUTION:After a reception high frequency signal supplied from an input terminal 1 is converted into an intermediate frequency signal by a tuner part 3 and a band limit is performed for it in a band pass filter part 4, the signal is converted into a base band signal (for instance, an FM demodulation) by a demodulation part 5 and it is outputted from an output terminal 2. The base band signal is also supplied to a detection part 6, DC voltage in accordance with the amplitude is generated, thereafter this is compared with a reference signal in a comparison circuit part and a switch control signal switching the band width of the band pass filter part 4 is generated. By this switching control signal, the band width of the band pass filter part 4 is switched to be wide when the amplitude of the base band signal is large (the degree of modulation is large) and is switched to be narrow when the amplitude is small (the degree of modulation is small).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency receiver such as a satellite broadcast front end, and more particularly to a high frequency receiver capable of receiving a plurality of signals having different modulation degrees.

[0002]

2. Description of the Related Art Conventionally, as a method for receiving an FM wave signal having a different degree of modulation in a good state in a satellite broadcast receiving apparatus for receiving a satellite broadcast, for example, Japanese Patent Laid-Open No. 2-8948.
As described in Japanese Patent No. 5 or the like, a plurality of band pass filters having different pass band widths are provided, and a band pass filter having a band width matching a desired broadcast wave is selected by an external control signal. , Are known to be able to receive the desired broadcast wave satisfactorily.

[0003]

However, in the above-mentioned conventional satellite broadcast receiving apparatus, since the bandwidth of the band limiting circuit is selected by the control signal arbitrarily given from the outside, the broadcast signals having different degrees of modulation are transmitted. When receiving, the bandwidth must be set in advance or the user must perform a switching operation for each setting each time, and it is insufficient to support a plurality of broadcast signals with different modulation degrees. It was

An object of the present invention is to provide a high frequency receiver which solves the above problem and is capable of automatically supporting a plurality of broadcast signals having different modulation degrees.

[0005]

In order to achieve the above object, the present invention provides a frequency conversion means for selecting a desired signal from a plurality of input signals, amplifying it, and converting it to an intermediate frequency signal. In a high frequency receiver provided with band limiting means for band limiting the intermediate frequency signal to a plurality of different bandwidths, and demodulation means for demodulating the intermediate frequency signal band limited by the band limiting means into a base band signal, A detection means for detecting the amplitude value of the band signal and outputting the detection signal, and a comparison means for comparing the detection signal with a reference signal to generate a control signal are provided, and the bandwidth of the band limiting means by the control signal. To control.

Further, according to the present invention, a frequency converting means for selecting a desired signal from a plurality of input signals, amplifying it and converting it into an intermediate frequency signal, and band limiting the intermediate frequency signal to a plurality of different bandwidths. In a receiver equipped with a band limiting means for controlling and a demodulating means for demodulating the band limited intermediate frequency signal into a baseband signal, a detection means for detecting an amplitude value of the baseband signal and outputting a detected signal, Comparing means for comparing the detected signal with a reference signal to generate a control signal, and variable gain amplifying means to which the baseband signal is supplied are provided. And controlling the gain of the amplification means.

Further, according to the present invention, a frequency converting means for selecting a desired signal from a plurality of input signals, amplifying it and converting it into an intermediate frequency signal, and band limiting the intermediate frequency signal to a plurality of different bandwidths. In a high-frequency receiver equipped with a band limiting unit that performs the above and a demodulating unit that demodulates the band-limited intermediate frequency signal into a baseband signal, a signal outside the band of the baseband signal is detected and a detection signal is output. A detection means and a comparison means for comparing the detected signal with a reference signal to generate a control signal are provided, and the control signal controls the bandwidth of the band limiting means.

Still further, according to the present invention, a frequency converting means for selecting a desired signal from a plurality of input signals, amplifying it, and converting it into an intermediate frequency signal, and the intermediate frequency signal into a plurality of different bandwidths. In a high frequency receiver equipped with a band limiting unit for limiting and a demodulating unit for demodulating the band limited intermediate frequency signal into a baseband signal, a selecting unit for selecting a horizontal synchronizing signal in the baseband signal, The horizontal sync signal is subtracted from the sync signal delayed by a predetermined period, the differential signal is output by a delay subtraction means, and the differential signal is accumulated for a certain period, and the set reference value and the accumulated value are compared. And a calculation means for generating a control signal, and the bandwidth of the band limiting means is controlled by the control signal.

[0009]

The amplitude of the baseband signal output from the demodulation means differs depending on the modulation degree of the input intermediate frequency signal of the demodulation means. Further, the amount of the signal (noise) outside the baseband signal band of the output signal of the demodulation means is larger as the bandwidth of the band limiting means is wider. Therefore, the modulation factor of the FM wave can be detected from the amplitude of the baseband signal, the level of the noise component outside the band, and the amount of noise (count value) superimposed on the horizontal synchronization signal, and the band can be detected according to the detection result. The bandwidth can be automatically selected by controlling the bandwidth of the limiting means. Therefore, even when receiving signals with different modulation factors, it is possible to properly receive a plurality of signals with different modulation factors in an appropriate state without setting the bandwidth in advance or performing a switching operation by the user. it can.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a high frequency receiver according to the present invention, in which 1 is a high frequency signal input terminal and 2 is a high frequency signal input terminal.
Is a baseband signal output terminal, 3 is a tuner section, 4 is a bandpass filter section, 5 is a demodulation section, 6 is a detection section, and 7 is a comparison circuit section.

In FIG. 1, a high frequency signal which is a received broadcast signal from a satellite, for example, is input from an input terminal 1, a tuner 3 selects a desired high frequency signal and converts it into an intermediate frequency signal. The intermediate frequency signal is band-limited by the band-pass filter unit 4 in which a plurality of bandwidths can be selectively set, and then supplied to the demodulation unit 5, converted into a baseband signal by, for example, FM demodulation, and output terminal. It is output from 2.

Further, the baseband signal output from the demodulation section 5 is also supplied to the detection section 6 for detection, and a DC detection voltage corresponding to the amplitude of the baseband signal is generated.
The DC detection voltage is compared with the reference voltage in the comparison circuit unit 7, and a signal corresponding to the difference between them is output as a switching control signal of the band pass filter unit 4.

Here, the intermediate frequency signal having a large modulation degree is a wider band signal than the intermediate frequency signal having a small modulation degree, and when demodulated, an intermediate frequency signal having a larger amplitude than the intermediate frequency signal having a small modulation degree is demodulated. The signal is obtained. The bandwidth of the bandpass filter unit 4 is switched and controlled by the control signal from the comparison circuit unit 7. When the baseband signal has a large amplitude (intermediate frequency signal having a large modulation degree), the wideband width has a small bandwidth, and the baseband signal has a small amplitude. In the case of (intermediate frequency signal with small modulation degree), narrow bandwidths are set respectively.

The bandwidth control operation of the band pass filter section 4 will be described in more detail. Now, a certain control signal from the comparison circuit section 7 causes a certain bandwidth in the band pass filter section 4. If it is set, it is assumed that an intermediate frequency signal having a large degree of modulation is supplied thereto, and the bandwidth set for this intermediate frequency signal is not yet sufficient. In this case, the band pass filter unit 4 passes only a part of the frequency components of the intermediate frequency signal over the entire set bandwidth, whereby the control signal output from the comparison circuit unit 7 is It will be bigger than ever. As a result, the bandwidth of the band pass filter unit 4 is widened. In this way, the bandwidth of the bandpass filter unit 4 is sequentially switched in the expanding direction until the entire band of the intermediate frequency signal is included, and when the bandwidth becomes wider than the band of the intermediate frequency signal. Stabilize to bandwidth. Therefore, after that, when an intermediate frequency signal having a wider band is received, this can be detected by the increase in the difference between the DC detection voltage and the reference voltage in the comparison circuit unit 7, and by the switching control signal at this time, The bandpass filter unit 4 can switch to a wider bandwidth. vice versa,
When the intermediate frequency signal with a small modulation degree is supplied, the difference between the DC detection voltage and the reference voltage becomes small in the comparison circuit unit 7, and thus the switching control signal causes the bandpass filter unit 4 to have a narrower bandwidth. Can be switched to.

In this way, the bandwidth of the band-pass filter unit 4 is automatically switched so as to follow the band of the supplied intermediate frequency signal, and the bandwidth that best fits the band of the intermediate frequency signal is always available. Will be set. Therefore, it is possible to prevent the characteristic deterioration (impulse noise, S / N, etc.) due to the different modulation of the received signal, and the user does not need to perform a troublesome operation.

FIG. 2 is a block diagram showing another embodiment of the high-frequency receiver according to the present invention, in which 8 is a variable gain amplifier (hereinafter referred to as AGC amplifier), and the parts corresponding to those in FIG. 1 are the same. A reference numeral is given and a duplicate description is omitted.

In the figure, in this embodiment, an AGC amplifier 8 is added to the embodiment shown in FIG. 1, and the baseband signal output from the demodulation unit 5 is output from the output terminal 2 via the AGC amplifier 11. It was done like this.

That is, the baseband signal output from the demodulator 5 is amplified by the AGC amplifier 8 and then output from the baseband output terminal 2. The gain of the AGC amplifier 8 is controlled by the DC detection voltage from the detector 6. As a result, when the amplitude of the baseband signal output from the demodulation unit 5 is small, the gain of the AGC amplifier 8 is set to be large, and a baseband signal whose amplitude level is always constant is obtained at the output terminal 2.

As described above, when the modulation degree of the received signal is different, the bandwidth of the bandpass filter section 4 changes according to the modulation degree as described above, so that the baseband output from the demodulation section 5 is changed. Although there is a difference in the magnitude of the signal amplitude,
In this embodiment, the gain control of the AGC amplifier 8 eliminates the difference in the amplitude. Therefore, in this embodiment, in addition to the effect of the embodiment shown in FIG. 1, a baseband signal of a constant amplitude level is always obtained regardless of the modulation degree of the received signal, and the subsequent processing circuit (not shown) It can also be simplified.

FIG. 3 is a block diagram showing still another embodiment of the high-frequency receiver according to the present invention. The parts corresponding to those in FIG. 2 are designated by the same reference numerals and their duplicate description will be omitted.

In the figure, the baseband signal output from the demodulation unit 5 is amplified by the AGC amplifier 8. The baseband signal output from the AGC amplifier 8 is supplied to the detection unit 6 and the baseband signal is output. A DC detection voltage according to the amplitude of the signal is generated, and the bandwidth of the bandpass filter unit 4 and the gain of the AGC amplifier 8 are controlled according to the DC detection voltage as in the embodiment shown in FIG. It

Also in this case, as in the embodiment shown in FIG. 2, when the modulation degree of the received signal changes, the amplitude of the baseband signal output from the demodulation section 5 changes and is output from the AGC amplifier 8. The amplitude of the baseband signal changes, and the detection unit 6 detects this and controls the bandwidth of the bandpass filter unit 4 and the gain of the AGC amplifier 8. Therefore, in this embodiment, the same effect as that of the embodiment shown in FIG. 2 can be obtained, and further, the effect that the level variation due to the temperature of the AGC amplifier 8 is less likely to be obtained.

FIG. 4 is a block diagram showing still another embodiment of the high-frequency receiver according to the present invention, in which 9 is a band-pass filter, and the portions corresponding to those in FIG. Is omitted.

In FIG. 4, in this embodiment, a bandpass filter 9 is added to the embodiment shown in FIG. 1, and the baseband signal output from the demodulation unit 5 is detected by the detection unit 6 via this bandpass filter 9. It is intended to be supplied to. Here, the center frequency of the bandpass filter 8 is set higher than the band of the baseband signal output from the demodulation unit 5 (that is, in the noise region, for example, 4.5 MHz or more in the case of the NTSC system). , Noise components are extracted and supplied to the detection unit 6. The detection unit 6 detects this noise level, and the comparison circuit unit 7 compares the magnitude of the detected output with the reference level to determine. When the bandwidth of the band-pass filter unit 4 is wider than the band of the intermediate frequency signal input thereto, the wider the bandwidth, the higher the noise level becomes. When the bandwidth is less than the band of the intermediate frequency signal, the noise level becomes less than a predetermined value. Becomes Therefore, when the noise level detected by the detection unit 6 is higher than a predetermined value (the above-mentioned reference level), the band width of the band pass filter unit 4 becomes too wide. Filter section 4
When the noise level is high, the band-pass filter unit 4 selects the narrower band width by switching the band width of. Further, when the detected noise level is equal to or lower than the reference level, the bandwidth of the band pass filter unit 4 may be narrower than the band of the intermediate frequency signal. Therefore, when the noise level is low, the band pass filter unit 4 reduces the bandwidth. Try to choose a wider one.

As a result, the S / N of the baseband signal due to the change of C / N (carrier signal to noise ratio) of the intermediate frequency signal
It is possible to reduce N (signal-to-noise ratio) deterioration and the generation of impulse noise (so-called medaka noise, hereinafter referred to as medaka noise) that occurs when the C / N is low, and when the received signal deteriorates (low C / N). Even at N hours), it is possible to operate under optimum conditions. Moreover, since the bandwidth of the bandpass filter unit 4 is automatically switched in accordance with the received signal, a troublesome switching operation by the user is unnecessary.

FIG. 5 is a block diagram showing still another embodiment of the high frequency receiver according to the present invention, in which 10 is a bandpass filter, 11 is a delay circuit, 12 is a subtraction circuit, and 13 is a counting circuit. The same reference numerals are given to the parts corresponding to 1.

The baseband signal output from the demodulation unit 5 is supplied to the bandpass filter 10 to extract a signal component having a predetermined cycle, and this signal component is delayed by the delay circuit 11 having a delay time equal to this cycle. The output signal of the bandpass filter 10 and the output signal of the delay circuit 11 are supplied to the subtraction circuit 12, and if there is a difference between these, the counting circuit 1 outputs the difference signal output from the subtraction circuit 12 every certain period.
3, the count value is compared with the reference value, a switching control signal is formed according to the result, and the bandwidth of the bandpass filter unit 4 is switched by this switching control signal. Here, as the signal component of the above-mentioned predetermined period, a signal that is not affected by the information content of the signal is good,
From this, for example, a horizontal synchronizing signal is preferable. Therefore, in the case of the horizontal synchronizing signal, the bandpass filter 10
Is for extracting only the horizontal synchronizing signal, and the delay circuit 1
The delay time of 1 is one horizontal scanning period.

When the degree of modulation of the input intermediate frequency signal with respect to the set bandwidth of the band pass filter unit 4 increases, the signal level increases and the S / N increases, but the degree of modulation of the band pass filter is increased. When the bandwidth is increased, a signal loss occurs, and impulse noise is generated due to the signal loss. On the other hand, when the modulation factor decreases with respect to the bandwidth of the bandpass filter, the above-mentioned signal loss is unlikely to occur, but the signal level decreases, so the S / N decreases. In this way, in any case, noise is generated when the modulation degree of the intermediate frequency signal is not optimal with respect to the set bandwidth of the bandpass filter unit 4. Also,
Even when the C / N (input signal to noise ratio) of the input signal drops,
Noise and medaka noise are generated due to deterioration of S / N (output signal to noise ratio).

Therefore, when the above noise is generated,
The noise superimposed on the horizontal synchronizing signal is extracted by the subtraction circuit 12, and when the count value of the counting circuit 13 at a certain time is equal to or greater than a predetermined value, the bandwidth set by the bandpass filter unit 4 is not optimum. If there are two settable bandwidths of the bandpass filter 4, the bandwidth is switched to the other bandwidth.

When the bandwidth that can be set by the band pass filter unit 4 is 3 or more, first, one of the two (for example,
The bandwidth is switched in the increasing direction, and when the count value of the counting circuit 13 does not change or increases, the bandwidth is switched in the opposite direction (for example, decreasing direction).

As a result, it is possible to prevent the characteristic deterioration (impulse noise, S / N, etc.) due to the different modulation of the input signal. In addition, S due to a decrease in C / N of the input signal
/ N deterioration and medaka noise generated at low C / N can also be reduced. Further, since the bandwidth of the bandpass filter unit 4 is automatically switched following the received signal, the user's troublesome operation is unnecessary.

Although the horizontal sync signal is selected from the baseband signal by the bandpass filter, the same effect can be obtained even if it is selected by the video processing circuit (sync separation circuit) connected in the subsequent stage. can get.

[0033]

As described above, according to the present invention,
Demodulation operation (filter selection) according to the signal state of the received signal
Since it can be automatically performed, a good operation can be obtained without deterioration of image quality due to a change in received signal. Further, since the received signal is automatically switched to follow the received signal, the user's troublesome operation becomes unnecessary.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing another embodiment of the high frequency receiver according to the present invention.

FIG. 3 is a block diagram showing another embodiment of the high frequency receiver according to the present invention.

FIG. 4 is a block diagram showing another embodiment of the high-frequency receiver according to the present invention.

FIG. 5 is a block diagram showing another embodiment of the high-frequency receiver according to the present invention.

[Explanation of symbols]

 1 Input terminal for high frequency signal 2 Output terminal for baseband signal 3 Tuner section 4 Bandpass filter section 5 Demodulation section 6 Detection section 7 Comparison circuit section 8 Variable gain amplifier (AGC amplifier) 9,10 Bandpass filter 11 Delay circuit 12 Subtraction Circuit 13 Counting circuit

Claims (6)

[Claims] 1. A frequency conversion means for selecting a desired signal from a plurality of input signals, amplifying it and converting it to an intermediate frequency signal, and a band limiting means for band limiting the intermediate frequency signal to a plurality of different bandwidths. And a demodulation means for demodulating the intermediate frequency signal band-limited by the band limiting means into a baseband signal, a detection means for detecting the amplitude value of the baseband signal and outputting the detected signal. And a comparison means for generating a control signal by comparing the detected signal with a reference signal, and controlling the bandwidth of the band limiting means by the control signal. 2. The high frequency receiving device according to claim 1, further comprising: a variable gain amplifying means for amplifying the baseband signal from the demodulating means, and controlling the gain of the amplifying means by the control signal. Machine. 3. The high frequency receiver according to claim 2, wherein the baseband signal output from the demodulating means is supplied to the detecting means after being amplified by the amplifying means. 4. A frequency conversion means for selecting a desired signal from a plurality of input signals, amplifying it and converting it into an intermediate frequency signal, and a band limiting means for band limiting the intermediate frequency signal to a plurality of different bandwidths. And a demodulating means for demodulating the intermediate frequency signal band-limited by the band limiting means into a baseband signal, in which a signal outside the band of the baseband signal is detected and a detected signal is output. A high-frequency receiver comprising: a detection means and a comparison means for outputting a control signal by comparing the detection signal with a reference signal, and controlling the bandwidth of the band limiting means by the control signal. 5. A frequency conversion means for selecting a desired signal from a plurality of input signals, amplifying it and converting it into an intermediate frequency signal, and a band limiting means for band limiting the intermediate frequency signal to a plurality of different bandwidths. And a demodulation means for demodulating the intermediate frequency signal band-limited by the band limiting means into a baseband signal, a selecting means for selecting a horizontal synchronizing signal in the baseband signal, A synchronization signal delayed by a predetermined period is subtracted from the synchronization signal, and delay subtraction means for outputting the difference signal and the difference signal are accumulated for a certain period, and a set reference value and an accumulated value are compared. And a calculation means for generating a control signal,
A high frequency receiver characterized in that the bandwidth of the band limiting means is controlled by the control signal. 6. The high frequency receiver according to claim 1, wherein all the means are constituted by an integrated circuit.