JPH11205176A - Receiver for digital satellite broadcasting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate influences of an adjacent channel and to perform excellent reception without degradation of a bit error rate while lowering a cost. SOLUTION: Digital satellite broadcasting signals of received RF signals are converted to IF signals so as to turn a desired channel to have a prescribed frequency and are supplied to an orthogonal detection means 5 by a tuner part 4. In the orthogonal detection means 5, the IF signals are multiplied with a carrier from a local oscillator 17 in a multiplier 15a and converted to demodulation I signals of a base band on one hand, and multiplied with the one for which the carrier is phase shifted by 90 deg. in a phase shifter 16 in a multiplier 15b and converted to demodulation Q signals of the base band on the other hand. The demodulation I and Q signals are demodulated in a digital demodulation means after base band signals of the digital satellite broadcasting signals of adjacent channels are eliminated in LPFs 18 and 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiver used for, for example, a satellite broadcast front end, and more particularly to a digital satellite broadcast receiver provided with at least frequency conversion means and quadrature detection means. .

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing an example of a conventional digital satellite broadcasting receiver, wherein 1 is an input terminal for a high-frequency signal, 2 is an output terminal for an I signal, 3 is an output terminal for a Q signal, 4 is a tuner unit, 5 is a quadrature detection means, 6 is a preamplifier, 7 is a tunable filter, 8 is a gain control circuit, 9 is a mixer, 10 is an IF (intermediate frequency) amplifier, 11 is a local oscillator, and 12 is a frequency. Synthesizers, 13 and 14 are input terminals, 15a and 15b are multipliers, 16 is a 90-degree phase shifter, 1
7, a local oscillator; and 26, an IF filter.

In FIG. 1, a high-frequency signal (ie, RF (radio frequency) signal) of a digital satellite broadcast signal received and input from an input terminal 1 to a tuner section 4 is supplied to a preamplifier 6 and a tunable filter 7. After processing such as unnecessary wave removal and amplification is performed, the level is adjusted by the gain control circuit 8 and supplied to the mixer 9.

In the mixer 9, a local oscillator 11 and a frequency synthesizer 12 form frequency conversion means. The frequency synthesizer 12 operates by a clock supplied from a control microcomputer (not shown) via an input terminal 13, and controls the local oscillator 11 in accordance with information data supplied from the control microcomputer via an input terminal 14. , So that the oscillation frequency becomes a frequency corresponding to the desired channel. As a result, in the mixer 9, the supplied RF signal is frequency-converted from the RF signal of the digital satellite broadcast signal of the desired channel to an IF signal of, for example, 479.5 MHz.

The IF signal output from the mixer 9 is I
After being amplified by the F amplifier 10, the signal is supplied to an IF filter 23 as a band-pass filter. The unnecessary signal such as a digital satellite broadcast signal of an adjacent channel is removed and supplied to the quadrature detector 5.

In the quadrature detection means 5, the IF signal from the IF filter 23 is supplied to the multipliers 15a and 15b, respectively. In the multiplier 15a, the IF signal is supplied to the local oscillator 1
7 is converted to a baseband signal by multiplication with a fixed carrier at a frequency equal to the above-mentioned intermediate frequency 479.5 MHz from the output terminal 2 and output from the output terminal 2 as a demodulated I signal. In the multiplier 15b,
The IF signal is multiplied by the carrier from the local oscillator 17 that has been phase-shifted by 90 degrees by the 90-degree phase shifter 16 to be converted into a baseband signal and output from the output terminal 3 as a demodulated Q signal.

Incidentally, in such a digital satellite broadcasting receiver, the IF filter 26 is provided to prevent the reception state from being deteriorated due to the interference of the adjacent channel signal. The interference will be described below.

Normally, in digital satellite broadcasting, as shown in FIG. 7, frequency bands of digital satellite broadcasting signals of respective channels are arranged at equal intervals by frequency division multiplexing. FIG.
In the digital satellite broadcast receiver shown in FIG. 1, a tuner section 4 selects a digital satellite broadcast signal of an arbitrary desired channel from these channels and converts it into an IF signal. Because there is no provision for suppressing digital satellite broadcast signals on the channel,
The output includes, in addition to the digital satellite broadcast signal of the desired channel converted to the intermediate frequency, the digital satellite broadcast signal of the adjacent channel similarly converted to the intermediate frequency.
It is included as an F signal.

Therefore, the IF output from the tuner unit 4
When the signal is directly supplied to the quadrature detection means 5, as shown in FIG. 8, the output signal of the quadrature detection means 5 includes, in addition to the baseband signal of the digital satellite broadcast signal of the desired channel whose center frequency is 0, The digital satellite broadcast signal of the adjacent channel arranged adjacent thereto is also included as a baseband signal at a frequency position separated from the digital satellite broadcast signal of the desired channel by the signal interval. The digital satellite broadcast signal of the adjacent channel converted in the same manner as the digital satellite broadcast signal of the desired channel adversely affects the demodulation characteristics of the digital demodulation means (not shown in FIG. 6) connected at the subsequent stage, This degrades the bit error rate, which is the most important characteristic in transmission, to cause deterioration in image quality and the like.

In order to reduce the adverse effect of such a digital satellite broadcast signal of an adjacent channel, in a conventional digital satellite broadcast receiver, as shown in FIG. An IF filter 26 is arranged in the RF signal so as to suppress the digital satellite broadcast signal of the adjacent channel included in the IF signal from the tuner unit 4, whereby deterioration of the bit error rate due to the digital satellite broadcast signal of the adjacent channel is suppressed. Had been prevented.

[0011]

However, in order to remove a digital satellite broadcast signal of an adjacent channel, I.
If an IF filter consisting of a band-pass filter is used at the stage of the F signal, the components constituting the IF filter must have excellent high-frequency characteristics.
Generally, surface acoustic waves (S
AW) filters are used, which are also very expensive because they are also high frequency components.

[0012] For example, when an IF filter is formed using individual elements such as a capacitor and a coil, design difficulty is high because of high frequency, which is a factor that hinders cost reduction and design efficiency of a receiver. .

It is an object of the present invention to provide a digital satellite broadcast receiver which solves such a problem and enables cost reduction and improvement in design efficiency.

[0014]

According to the present invention, a low-pass filter is provided at an output stage of a detector for outputting a baseband digital satellite broadcast signal.
The low-pass filter removes a digital satellite broadcast signal of an adjacent channel at a baseband stage in a low frequency band.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a digital satellite broadcast receiver according to the present invention.
Reference numeral 19 denotes a low-pass filter, and portions corresponding to those in FIG.

In this embodiment, in this embodiment, a tuner unit 4 is used in the conventional digital satellite broadcast receiver shown in FIG.
A low-pass filter (hereinafter referred to as an LPF) is connected to each of two output terminals of the quadrature detection unit 5 except for the IF filter 26 provided between the quadrature detection unit 5 and the quadrature detection unit 5.
18 and 19 are provided. Therefore, tuner unit 4
The IF signal amplified by the IF amplifier 10 is supplied directly to the quadrature detection means 5 and converted into baseband signals by multipliers 15a and 15b, respectively.

The baseband signal from the multiplier 15a is L
The signal is supplied to the PF 18 to remove the digital satellite broadcast signal of the adjacent channel, and only the detection output of the digital satellite broadcast signal of the desired channel is extracted and output from the output terminal 2 as a demodulated I signal. The baseband signal from the multiplier 15b is also supplied to the LPF 19 to remove the digital satellite broadcast signal of the adjacent channel, and only the detection output of the digital satellite broadcast signal of the desired channel is extracted and output from the output terminal 2 as a demodulated Q signal. Is output.

Here, the passing characteristics of the LPFs 18 and 19 will be described.

The cutoff frequencies of these LPFs 18 and 19 need to be set in accordance with the bandwidth of the signal to be transmitted, and as shown in FIG.
Set to 2. For example, when the transmission bandwidth BW normally defined by the 3 dB bandwidth is 27 MHz, these LPFs
The pass bandwidth of 18, 19 is set to 13.5 MHz.

In the first embodiment, as described above,
The tuner 4 and the quadrature detector 5 have no means for suppressing a digital satellite broadcast signal of an adjacent channel, and an IF filter 26 as shown in FIG. As shown in FIG. 8, the output signal of the quadrature detection means 5 includes a baseband signal of a digital satellite broadcast signal of a desired channel whose center frequency is 0 and a signal adjacent to the baseband signal. The baseband signal of the digital satellite broadcast signal of the adjacent channel is included in a frequency position separated by the signal interval from the baseband signal of the digital satellite broadcast signal of the desired channel. Therefore, when the output signals of the mixers 15a and 15b are supplied to digital demodulation means (not shown) as they are,
The digital satellite broadcast signal of the adjacent channel has an adverse effect on the demodulation characteristics of the digital demodulation means, causing the bit error rate, which is the most important characteristic in digital signal transmission, to deteriorate, thereby deteriorating image quality and the like.

However, in the first embodiment, the LPFs 18, 19 whose cutoff frequencies are set between the quadrature detection means 5 and the output terminals 2, 3 according to the transmission bandwidth BW of the baseband signal of the desired channel. Is provided to suppress the digital satellite broadcast signal of the adjacent channel, so that good reception without adverse effects from the digital satellite broadcast signal of the adjacent channel becomes possible.

Further, in the first embodiment, since the digital satellite broadcast signal of the adjacent channel is suppressed in the baseband frequency band, the intermediate frequency of the conventional digital satellite broadcast receiver shown in FIG. There is no need to suppress this in the band, and this makes it possible to suppress digital satellite broadcast signals in adjacent channels without using high-frequency components, which is effective in reducing the cost of the receiver and improving the design efficiency.

Further, by constructing the LPFs 18 and 19 by surface mounting components, productivity can be improved.
Further cost reduction is possible.

FIG. 2 is a block diagram showing a second embodiment of a digital satellite broadcast receiver according to the present invention, in which reference numeral 20 denotes an analog-digital conversion circuit, reference numeral 21 denotes a digital demodulation circuit, and reference numeral 22 denotes an output terminal. The same reference numerals are given to the portions corresponding to 1 and the duplicate description will be omitted.

In the figure, an A / D conversion circuit 20 converts an I signal supplied from the quadrature detector 5 via the LPF 18 and a Q signal supplied from the quadrature detector 5 via the LPF 19 into binary numbers, respectively. Digital demodulation circuit 2
1 digitally demodulates the binary-coded signal and also performs error correction processing. This digital demodulated signal is output from the output terminal 22.

Other configurations and operations have the same effects as those of the first embodiment shown in FIG.

FIG. 3 is a block diagram showing a third embodiment of a digital satellite broadcast receiver according to the present invention. Reference numeral 23 denotes an integrated circuit (IC), and portions corresponding to those in FIG. And a duplicate description will be omitted.

In this figure, the third embodiment has the same configuration and performs the same operation as the second embodiment shown in FIG. 2, but the quadrature detection means 5 and the LPF 1
8 and 19 are integrated to form an integrated circuit 23 enclosed in the same package.

The third embodiment is different from the second embodiment shown in FIG.
The same effect as that of the embodiment is obtained, and the quadrature detection means 5
And LPFs 18 and 19 are packaged in one,
The size of the receiver can be reduced, and the space can be spared and the degree of freedom in design can be increased. The LPF in the integrated circuit 23
As the elements 18 and 19, any desired characteristics can be obtained by connecting some elements to the outside of the integrated circuit 23. For example, if a desired cut-off frequency is low and a large-capacity capacitor that cannot be accommodated in a package is required, it is possible to obtain desired characteristics by connecting the capacitor outside the package.

In the first embodiment shown in FIG. 1, the quadrature detection means 5 and the LPFs 18 and 19 are similarly provided.
Can be packaged into one, and the same effect can be obtained.

FIG. 4 is a block diagram showing a fourth embodiment of a digital satellite broadcast receiver according to the present invention. Reference numeral 24 denotes an integrated circuit (IC), and portions corresponding to those in FIG. And a duplicate description will be omitted.

In the figure, the fourth embodiment has the same configuration and performs the same operation as the second embodiment shown in FIG. 2, but the LPFs 18, 19 and the A / D
The conversion circuit 20 is integrated into an integrated circuit 24 enclosed in the same package.

The fourth embodiment is different from the second embodiment shown in FIG.
The same effect as that of the embodiment is obtained, and the quadrature detection means 5
And the A / D conversion circuit 20 are integrated into one package, so that the size of the receiver can be reduced, a space can be provided, and the degree of design freedom can be increased. Also, as in the embodiment shown in FIG. 3, the LPFs 18 and 19 formed in the integrated circuit 24 can have any desired characteristics by connecting some of the elements to the outside of the integrated circuit 23. You can also get it.

FIG. 5 is a block diagram showing a fifth embodiment of the digital satellite broadcast receiver according to the present invention, wherein reference numeral 25 denotes an integrated circuit (IC), and portions corresponding to those in FIG. And a duplicate description will be omitted.

In this figure, the fifth embodiment has the same configuration and performs the same operation as the second embodiment shown in FIG. 2, but the LPFs 18 and 19 and the A / D
The conversion circuit 20 and the digital demodulation circuit 21 are integrated to form an integrated circuit 25 enclosed in the same package.

The fourth embodiment is different from the second embodiment shown in FIG.
The same effect as that of the embodiment is obtained, and the quadrature detection means 5
And the A / D conversion circuit 20 and the digital demodulation circuit 21 are integrated into one package, so that the size of the receiver can be reduced, a space can be provided, and the degree of design freedom can be increased. FIG.
Similarly to the embodiment described in the above, the LPF configured in the integrated circuit 25 can obtain any desired characteristics by connecting some of the elements to the outside of the integrated circuit 25.

[0038]

As described above, according to the present invention,
Since an LPF is provided at the output of the quadrature detection means to suppress the signal of the adjacent channel, it is possible to prevent the bit error rate from deteriorating due to the signal of the adjacent channel and to perform a good reception. Compared with a conventional digital satellite broadcast receiver that suppresses the signal of the adjacent channel, it is excellent in cost and has good detection characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a digital satellite broadcast receiver according to the present invention.

FIG. 2 is a block diagram illustrating a digital satellite broadcast receiver according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a digital satellite broadcast receiver according to a third embodiment of the present invention.

FIG. 4 is a block diagram illustrating a digital satellite broadcast receiver according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a fifth embodiment of the digital satellite broadcast receiver according to the present invention.

FIG. 6 is a block diagram showing an example of a conventional digital satellite broadcast receiver.

FIG. 7 is a diagram showing a signal arrangement of each channel in digital satellite broadcasting.

FIG. 8 is a diagram illustrating an output signal of a detection unit of a digital satellite broadcast receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal of high frequency signal 2 Output terminal of I signal 3 Output terminal of Q signal 4 Tuner part 5 Quadrature detection means 6 Preamplifier 7 Variable tuning filter 8 Gain control circuit 9 Mixer 10 Intermediate frequency amplifier 11 Local oscillator 12 Frequency synthesizer 15a , 15b Multiplier 16 90-degree phase shifter 17 Local oscillator 18, 19 Low-pass filter 20 Analog-digital conversion circuit 21 Digital demodulation circuit 22 Digital demodulation signal output terminal 23-25 Integrated circuit

Claims (5)

[Claims] 1. A frequency conversion means for frequency-converting a received digitally modulated signal of a plurality of channels such that a signal of a desired channel becomes an intermediate frequency signal of a predetermined frequency, and an output signal of the frequency conversion means. On the one hand, it directly mixes with the local oscillation signal, and on the other hand, it mixes the local oscillation signal with a signal whose phase has been shifted by 90 degrees to obtain respective detection outputs. From the respective detection outputs of the detection means, A low-pass filter for extracting I and Q signals of the signal of the desired channel. 2. A frequency conversion means for converting a received digitally modulated signal of a plurality of channels so that a signal of a desired channel becomes an intermediate frequency signal of a predetermined frequency, and an output signal of the frequency conversion means. On the one hand, it directly mixes with the local oscillation signal, and on the other hand, it mixes the local oscillation signal with a signal whose phase has been shifted by 90 degrees to obtain respective detection outputs. From the respective detection outputs of the detection means, A low-pass filter for extracting I and Q signals of the signal of the desired channel; binary encoding means for encoding each of the I and Q signals from the low-pass filter into a binary number; Digital demodulation means for digitally demodulating and error-correcting an output signal of the converting means and outputting a digital demodulated signal. 3. The digital satellite broadcast receiver according to claim 1, wherein said low-pass filter is integrated with said detection means. 4. The digital satellite broadcast receiver according to claim 1, wherein the low-pass filter is integrated together with the binary encoding means. 5. The digital satellite broadcasting receiver according to claim 1, wherein the low-pass filter is integrated with the binary encoding unit and the digital demodulation unit.