JPH1155142A - Digital satellite broadcasting receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital satellite broadcasting receiver which is capable of lowering an intermediate frequency and reduced in circuitry scale. SOLUTION: In this digital satellite broadcasting receiver, a reception frequency is bisected into lower and higher frequency components, and the oscillation frequency of a local oscillator 6 composed of a PLL frequency synthesizer is set to the frequency of downside heterodyne with respect to the lower frequency components and set to the frequency of upside heterodyne with respect to the higher frequency components. Thus, the intermediate frequency can be lowered, an intermediate frequency signal can be directly A/D converted, and circuit scale is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital satellite broadcast receiver such as a broadcast satellite (BS) digital broadcast receiver.

[0002]

2. Description of the Related Art In a conventional digital satellite broadcast receiver, for example, a BS digital broadcast receiver, unnecessary low-frequency components are removed by a high-pass filter 1 from a BS-intermediate frequency signal inputted and frequency-converted as shown in FIG. The signal is amplified by the amplifier 2, the level is controlled to be constant by the automatic gain control circuit 3, and the output signal of the automatic gain control circuit 3 is transmitted through the tracking filter 4. The signal transmitted through the tracking filter 4 is multiplied by an oscillation output from a local oscillator 6A composed of a PLL frequency synthesizer in a mixer 5, and frequency-converted.
It is down-converted to an intermediate frequency signal in the Hz band.

In this case, the frequency of the upper heterodyne is adopted as the local oscillation frequency and is set higher than the BS-intermediate frequency signal. The correspondence between the center frequency of the BS-intermediate frequency band and the local oscillation frequency for each channel is as follows. In Japan, this is as shown in FIG. FIGS. 7A and 7B show the frequency relationship of each channel of the BS band and the BS-intermediate frequency signal. The output from the mixer 5 is amplified by the amplifier 7 and then, for example, the SAW band-pass filter 8 extracts only the component of the channel of the desired reception frequency. The output of the SAW band-pass filter 8 is fed back to the automatic gain control circuit 3. It has also been used for gain control.

For example, when the channel {7} (CH = 7) is selected, data for the local oscillation frequency of channel {7} is sent from the control signal bus to the local oscillator 6A. An oscillation output having a local oscillation frequency of 06 MHz is transmitted. The frequency relationship after the frequency conversion is as shown in FIGS. 7C and 7D. FIG. 7C shows an intermediate frequency band whose frequency has been changed.
(D) shows the local oscillation frequency of 1644.06 MHz, that is, the frequency of each of the other frequency-converted channels when channel {7} is selected, and the bandwidth of the SAW band-pass filter 8 is set to 27 MHz.

Note that FIG.
As shown in (d), the frequency spectrum relationship of each channel is inverted, and a line is added to the channel number, and B indicates the bandwidth of the SAW band-pass filter 8. FIG. 7E shows a frequency band when the channel {7} is selected by band limitation by the SAW band-pass filter 8.

The component of the desired channel extracted through the SAW band-pass filter 8 is amplified by an automatic gain control circuit 9 so that the level becomes constant, amplified by an amplifier 10, and then amplified by a quadrature detector 11. After synchronous detection, baseband signals I and Q are output. The baseband signals I and Q have their high-frequency components removed by low-pass filters 12-1 and 12-2 to prevent aliasing noise, and are amplified by amplifiers 13-1 and 13-2.
The signals are converted into digital signals by the converters 14-1 and 14-2 and demodulated by the demodulation unit 15. The signal component extracted from the demodulation unit 15 via the low-pass filter 18 is supplied to the variable gain control circuit 9 to perform automatic gain control.

[0007]

However, in the conventional digital satellite broadcast receiver as described above, when converting to the intermediate frequency, only the upper heterodyne frequency is used as the local oscillation frequency. In order for the frequency to increase and to directly A / D convert the intermediate frequency signal,
There is a problem that it is difficult due to the frequency limit of the A / D converter. Further, when the intermediate frequency is to be lowered, there is a problem in that two sets of frequency conversion circuits are required because the image frequency overlaps with the frequency of the adjacent channel.

Further, the above-mentioned conventional digital satellite broadcast receiver has a problem that a mixer for quadrature detection, a 90-degree phase shifter, and an oscillator are required, and further, an amplifier and a filter for a baseband signal are required. There was also a problem that two sets were required.

In addition, since the quadrature detection is performed by the analog method, the frequency-to-phase characteristics and the frequency-to-amplitude characteristics of the 90-degree phase shifter are not flat characteristics. There has been a problem that an amplitude error occurs, which causes fixed deterioration.

An object of the present invention is to provide a digital satellite broadcast receiver which can reduce the intermediate frequency and requires a small circuit size.

[0011]

A digital satellite broadcast receiver according to the present invention is a digital satellite broadcast receiver comprising:
The receiving frequency is divided into a lower frequency part and a higher frequency part, and the local oscillation frequency is set to the lower heterodyne frequency for the lower frequency part, and the higher frequency part is set. The frequency is set to the upper heterodyne for the portion.

The digital satellite broadcast receiver according to the present invention divides the reception frequency into two parts, a lower frequency part and a higher frequency part, and the local oscillation frequency is lower than the lower frequency part. It is set to the frequency of the side heterodyne, and for the higher frequency part, it is set to the frequency of the upper heterodyne, so that the intermediate frequency can be set low, and is about the same as that used in the conventional method. Digital conversion can be performed by an A / D converter with an upper frequency limit, only one A / D converter is required, and only one circuit for frequency conversion is required. Furthermore, an analog quadrature detection mixer, A transmitter is not required, and since the quadrature detection and subsequent signals are digital signals, no phase error and amplitude error occur in the baseband signals I and Q, and fixed deterioration is reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A digital satellite broadcast receiver according to the present invention will be described below with reference to embodiments. In the embodiment of the present invention, a case of a BS digital broadcast receiver is illustrated. FIG. 1 shows a BS according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a digital broadcast receiver. FIG. 2 shows correspondence between a center frequency and a local oscillation frequency of a BS-intermediate frequency band for each channel of the BS digital broadcast receiver according to one embodiment of the present invention. FIG.

In the BS digital broadcast receiver according to one embodiment of the present invention, the same components as those of the conventional BS digital broadcast receiver shown in FIG. 5 are denoted by the same reference numerals.

Unnecessary low-frequency components are removed from the input BS-intermediate frequency signal by a high-pass filter 1 and an amplifier 2
Then, the level is controlled to be constant by the automatic gain control circuit 3, and the output signal of the automatic gain control circuit 3 is sent out via the tracking filter 4. The signal transmitted through the tracking filter 4 is multiplied by an oscillation output from a local oscillator 6 composed of a PLL frequency synthesizer in a mixer 5 and frequency-converted.
It is down-converted to an intermediate frequency signal in the Hz band.

Here, for conversion into an intermediate frequency signal, all channels are divided into upper and lower halves, and the transmission frequency of the local oscillator 6 is changed to the lower heterodyne frequency for the lower reception frequency channel and to the lower heterodyne frequency for the higher reception frequency. The channel on the side is set to the frequency of the upper heterodyne to perform frequency conversion. By doing so, the frequency of the intermediate frequency signal can be made lower than the frequency of the conventional intermediate frequency signal.

Now, assuming that the number of channels is X and the channel interval is Y (MHz), the minimum intermediate frequency Fif (MHz) obtained by frequency conversion is Fif = Y · X / 4.

When the number of channels X = 8 and the channel interval Y = 38.36 MHz as in BS digital broadcasting,
Fif = 76.72 MHz, and interference with other channels does not occur even if the intermediate frequency is lowered to this frequency.
As described above, the intermediate frequency can be reduced by switching the local oscillation frequency for frequency conversion between the upper heterodyne frequency and the lower heterodyne frequency depending on the channel.

When the oscillation frequency of the local oscillator 6 is set so that the intermediate frequency becomes Fif = 76.72 MHz, the center frequency and the local oscillation frequency of the BS-intermediate frequency band for each channel are as shown in FIG. FIG.
In FIG. 2, the local oscillation frequency in the case of the conventional system (only the upper heterodyne) is shown for reference.

The signal frequency-converted by the mixer 5 is amplified by the amplifier 7 and then, for example, only the component of the channel of the desired reception frequency is extracted by the SAW band-pass filter 8. SAW bandpass filter 8
Is fed back to the automatic gain control circuit 3,
It is also used for gain control. The signal component of the desired channel extracted through the SAW band-pass filter 8 is amplified by the automatic gain control circuit 9 so that the level becomes constant, amplified by the amplifier 10, and then amplified by the A / D converter 14. It is converted into a digital signal, and the quadrature detection / demodulation unit 1
At 6 the signal is detected / demodulated. The signal components extracted from the quadrature detection / demodulation unit 16 via the low-pass filter 18 are supplied to a variable gain control circuit 9 to perform automatic gain control.

Here, in order to set the oscillation frequency of the local oscillator 6 with respect to the channel number, data for setting the frequency division ratio is sent to the PLL frequency synthesizer forming the local oscillator 6 from the control signal bus. Then, data for the demodulation integrated circuit is transmitted to the quadrature detection / demodulation unit 16.

As described above, the frequency of the local oscillator 6 is divided into the lower heterodyne frequency, and the upper heterodyne frequency is divided into the lower reception frequency channel and the higher reception frequency channel. When frequency conversion is performed as follows, for example, if the frequency relationship after frequency conversion is shown, for example, when channel {1} is selected, the frequency of the local oscillator 6 is 972.76 MHz, and FIG.
As shown in (a), only one channel of channel {1} can be selected by SAW filter 8 without overlapping with other channels. Here, FIG.
B indicates the bandwidth of the SAW bandpass filter 8.

If the frequency conversion based on the upper heterodyne frequency is performed on all the channels and the channel {1} is selected, the local oscillation frequency becomes 11
At 26.20 MHz, as shown in FIG. 3 (b), channel 5 loops back at the position of zero frequency, and channel {1} and channel {9} overlap,
Only one channel {1} cannot be selected by the SAW filter 8 without duplication.
However, in the BS digital broadcast receiver according to the embodiment of the present invention, this does not occur as shown in FIG.

As described above, in the BS digital broadcast receiver according to one embodiment of the present invention, since the intermediate frequency can be lowered, the signal selected by the SAW bandpass filter 8 is converted to an A / D converter. A directly by 14
/ D conversion can be performed, and the quadrature detection and the subsequent steps can be performed by a digital method.

Therefore, the analog quadrature detector 11 used in the prior art becomes unnecessary, and the mixer for quadrature detection, 9
The problem of requiring a 0-degree phase shifter and an oscillator is solved, the fixed deterioration due to the phase error and the amplitude error in the baseband signals I and Q is eliminated, and the amplifier and the filter for the baseband signal are further eliminated. Also eliminates the problem that two sets are required.

In the BS digital broadcast receiver according to the embodiment of the present invention configured as described above, the local oscillator 6 oscillates the signal input to the mixer 5 and the signal after frequency conversion by the mixer 5. When the frequency is the lower heterodyne frequency, as shown in FIG. 4A, the frequency spectrum remains unchanged, that is, the upper frequency of the channel is converted in the upper frequency relationship after the frequency conversion. When the oscillation frequency of the local oscillator 6 is the upper heterodyne frequency for the signal input to the mixer 5 and the signal after the frequency conversion by the mixer 5, FIG.
As shown in (1), the frequency spectrum relationship is inverted, that is, the upper frequency of the channel is converted by an inversion relationship in which the frequency is shifted downward after the frequency conversion.

However, even if the frequency relationship is inverted as shown in FIG. 4B, demodulation can be performed by exchanging the I-axis and Q-axis of the baseband signal in the quadrature detection / demodulation unit 16.

In the above example, the case where the number of channels is an even number has been exemplified. However, the present invention can be applied to a case where the number of channels is an odd number and cannot be divided by X / 4. In this case, as a result of the division into two, there is a difference of one channel in the number of channels between the number of lower reception frequency channels and the remaining higher reception frequency channels. The channel may be assigned to the lower receiving frequency channel or to the higher receiving frequency channel.

[0029]

As described above, according to the digital satellite broadcast receiver of the present invention, the intermediate frequency can be lowered, so that the A / D has the same upper limit frequency limit as that used in the conventional system. The digital conversion can be performed by the converter, and an effect that only one A / D converter is required can be obtained.
In addition, only one circuit for frequency conversion is required, so that an analog quadrature detection mixer and transmitter are not required, and the baseband signals I and Q are used for digital signals after quadrature detection.
Thus, there is obtained an effect that the phase deterioration and the amplitude error do not occur and the fixed deterioration is reduced. Further, an effect that an amplifier and a filter for amplifying the baseband signals I and Q become unnecessary is also obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a BS digital broadcast receiver according to one embodiment of the present invention.

FIG. 2 is a diagram showing correspondence between a center frequency and a local oscillation frequency of a BS-intermediate frequency band for each channel of the BS digital broadcast receiver according to one embodiment of the present invention.

FIG. 3 is a frequency relation diagram for explaining channel selection in the case of a BS digital broadcast receiver according to one embodiment of the present invention.

FIG. 4 is a diagram illustrating a frequency relationship for explaining an operation of the BS digital broadcast receiver according to the embodiment of the present invention;

FIG. 5 is a block diagram illustrating a configuration of a conventional BS digital broadcast receiver.

FIG. 6 is a diagram showing a correspondence between a center frequency and a local oscillation frequency of a BS-intermediate frequency band for each channel of a conventional BS digital broadcast receiver.

FIG. 7 is a diagram showing a frequency relationship for explaining the operation of a conventional BS digital broadcast receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High-pass filter 2, 7, and 10 Amplifier 3 and 9 Automatic gain control circuit 4 Tracking filter 5 Mixer 6 Local oscillator 8 SAW band-pass filter 14 A / D converter 15 Quadrature detection / demodulation unit

Claims (1)

[Claims] In a digital satellite broadcast receiver, a reception frequency is divided into a lower frequency portion and a higher frequency portion, and a local oscillation frequency is reduced by a lower heterodyne for the lower frequency portion. A digital satellite broadcast receiver, wherein the frequency is set to a frequency of the upper side and the frequency of the higher side is set to the frequency of the upper heterodyne.