JPH08298528A - Digital satellite receiver - Google Patents

Abstract

(57) [Summary] [Composition] A means for controlling the oscillation frequency of the oscillator 5 is provided at random based on the measurement result of the frequency measurement means 18 which measures the oscillation frequency of the oscillator 9 in a predetermined cycle. Alternatively, the conversion output frequency of the mixer 4 is matched with the intermediate frequency by intermittent control at regular intervals. Further, a means for storing the control process or the oscillation frequency of the oscillator 5 is provided, and the oscillation frequency before being out of synchronization is used as the oscillation frequency of the oscillator 5 in the resynchronization pull-in process. [Effect] The center frequency of the digital modulation signal input to the bandpass filter 7 can be stabilized with respect to the fluctuation of the local oscillation frequency of the outdoor unit, and quick carrier re-pull-in for loss of synchronization can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital satellite broadcasting receiver suitable for stable reception of digitally modulated digital satellite broadcasting.

[0002]

2. Description of the Related Art In order to effectively utilize a limited number of channels such as terrestrial broadcasting, satellite broadcasting, and communication satellites, high efficiency digital compression technology and digital modulation are applied to one program service for one channel of conventional analog television broadcasting. By using the technology, multi-channel digital television broadcasting is planned in which a plurality of program services are provided on one channel in the analog transmission band. Quadrature digital modulation such as QPSK modulation or MSK modulation is used for these digital modulations.

FIG. 7 shows a main part of a digital satellite broadcasting receiver for receiving quadrature digital modulation. 1 is a high pass filter, 2 is a preamplifier, 3 is a tunable filter, 4 is a mixer, 5 is an oscillator, 6 is a frequency synthesizer, 7 is a band pass filter, 8 is an intermediate frequency amplifier, 9 is an oscillator,
Reference numeral 10 is a frequency divider, and 15 is a quadrature detector, which constitutes the front end of 12. Reference numeral 11 is an intermediate frequency amplifier, 12 is a 90-degree phase shifter, 13A and 13B are multipliers, and 14A and 14B are amplifiers, which constitute 15 quadrature detectors. Reference numeral 16 is an analog-digital converter. 17 is a carrier reproducing means,
Reference numeral 18 is a frequency measuring means and 19 is a clock reproducing means.
0 digital demodulating means. 21 is a control microcomputer, 100 is an input terminal, 101 is a power supply terminal of an outdoor unit, 102 is a tuning power supply terminal, 103 is a frequency divider output terminal,
104 is a carrier control terminal, 105 is a power supply terminal, 106
Is an I signal output terminal of the quadrature detector, 108 is an analog-digital converted I signal output, 110 is a digitally demodulated I signal output, 107 is a quadrature detector Q signal output, and 109 is analog-digital converted Q signal output, 111 is digitally demodulated Q signal output, 112
Is a digitally demodulated clock signal, and 113 is a control signal for the frequency synthesizer 6. Front end 12
Is a digital modulated signal of 1 GHz band input from an input unit 100 from an outdoor unit (not shown), a high-pass filter 1 removes unnecessary low-frequency waves, and a preamplifier 2
After being amplified by, the image band is removed by the variable tuning filter 3, the desired channel is converted to an intermediate frequency of 400 MHz band by the frequency conversion means consisting of the mixer 4 and the oscillator 5, and the output of the mixer 4 is converted by the bandpass filter 7. Unwanted waves are removed, amplified by the amplifier 8, and the quadrature detection means 15 generates two 90 ° different carrier signals from the output of the oscillator 9 by the 90 ° phase shifter 12 and the multiplier 13.
Multiplied by A and B, the I signal of the quadrature detection signal is output from the output terminal 106 and the Q signal is output through the amplifiers 14A and 14B.
It outputs from 07. I obtained from the front end 12
The signal and the Q signal are converted into digital signals I signal 108 and Q signal 109 by the analog-digital converter 16, respectively, and the carrier reproducing means 17 of the digital demodulating means 20 reproduces the carrier to control the oscillator 9. The clock reproduction means 19 reproduces the clock I
And Q demodulated signals 110 and 111 and a clock signal 112 are obtained. The frequency measuring means 18 measures the frequency of the signal obtained by dividing the oscillation frequency of the oscillator 9 by the frequency divider 10 into 1 / n at a predetermined cycle. The oscillation frequency of the oscillator 5 is controlled by the control synthesizer 6 by the frequency synthesizer 6. An example of the frequency digital demodulation means is described in Technical Report of the Institute of Electronics, Information and Communication Engineers, RCS 91-37 (October 31, 1991), pages 19 to 24. FIG. 8 is an operation flowchart of the carrier pull-in process after tuning the digital satellite broadcast receiver. For example, when a tuning button (not shown) is pressed to generate a tuning interrupt 30, the control microcomputer 21 and the frequency synthesizer 6 set the oscillation frequency corresponding to the selected transponder frequency in the oscillator 5 to select the transponder channel 31. Since the pull-in range of the closed loop composed of the carrier regenerating means 17 and the oscillator 9 is very narrow, the oscillator 9 is controlled by the carrier control signal of the carrier regenerating means 17 in order to facilitate pulling in to the local oscillation frequency shift of the outdoor unit.
A carrier sweep 33 for sweeping the frequency of is performed from one end of the band of the bandpass filter 7. When the oscillation frequency of the oscillator 9 is pulled to the input frequency and the synchronization of the digital demodulation means 20 is established 34, the carrier sweep is stopped 35, and the oscillator 9 becomes the carrier follower 36 that follows the input frequency. The frequency measuring means 18 in the digital demodulating means 20 is used to measure the oscillation frequency of the oscillator 9 such as the carrier sweep 33. Once the carrier tracking 36 is entered, it is possible to follow the local oscillation frequency fluctuation of the outdoor unit, and stable reception can be obtained. If the synchronization is lost for some reason, the carrier sweep 33 is performed again.

[0004]

In the above-mentioned conventional example, the oscillation frequency of the oscillator 9 is made to follow the fluctuation of the local oscillation frequency of the outdoor unit to prevent the loss of synchronization. However, if the frequency of the outdoor unit fluctuates, the bandpass filter 7
Since the center frequency of the digitally modulated signal that passes through fluctuates, the lower or upper end of the signal spectrum is attenuated by the shoulder characteristics of the bandpass filter, and the symmetry of the signal spectrum is impaired, resulting in deterioration of the digital demodulation characteristics and bit error. There was a drawback that the rate increased. Further, there is a drawback that it takes time to carry out the carrier sweep again from the edge of the band out of synchronization. The object of the present invention is to stabilize the center frequency of the digital modulation signal input to the bandpass filter 7 against the fluctuation of the local oscillation frequency of the outdoor unit, and to obtain the carrier re-pull-in quickly even if the synchronization is lost. A receiver for digital satellite broadcasting is provided.

[0005]

The above-mentioned object is based on the measurement result of the frequency measuring means 18 which measures the oscillation frequency of the oscillator 9 in a predetermined cycle.
It is achieved by matching the converted output frequency of the mixer 4 with the intermediate frequency by means of intermittent control of random or fixed intervals.

Further, for quick carrier re-pull-in for loss of synchronization, a means for storing the control process or oscillation frequency of the oscillator 5 is provided, and oscillation before the loss of synchronization with the oscillation frequency of the oscillator 5 during the re-synchronization pull-in process is provided. This is achieved by using frequency.

[0007]

[Operation] When the local oscillation frequency of the outdoor unit changes,
The converted output frequency of the mixer 4 also changes accordingly, and the oscillation frequency of the oscillator 9 also follows and changes. The change in the oscillating frequency of the oscillator 9 is measured by the frequency measuring means 18 which measures the frequency at a predetermined cycle, and the mixer 4 is compared by comparing the measurement result with the correct intermediate frequency.
It is possible to know the deviation of the conversion output frequency of. Mixer 4
The oscillation frequency of the oscillator 5 is controlled so as to cancel the shift of the conversion output frequency of. The oscillation frequency of the oscillator 5 is controlled by random control or intermittent control at regular intervals so that the oscillation frequency of the oscillator 5 is not excessively changed. The random or constant interval can be either the timing of reading the measurement result of the frequency measuring means 18 or the timing of controlling the oscillator 5.

With respect to carrier re-pull-in for loss of synchronization, the control process or oscillation frequency of the oscillator 5 is stored, and the frequency of the oscillator 5 at the time of occurrence of loss of synchronization is used so that the band-pass filter band is almost equalized during carrier sweep. It is possible to re-pull in the center, which makes it possible to re-pull faster than before. Also, the start point of the carrier sweep can be selected to be the center frequency of the bandpass filter, and the pull-in can be performed more quickly. When the synchronization is lost, the control of the oscillator 9 is erroneously operated. As a result, the oscillator 5 is erroneously controlled and the converted output frequency of the mixer 4 largely deviates from the correct intermediate frequency. By storing the frequencies up to n, it is possible to know the correct control process or oscillation frequency of the oscillator 5 that avoids erroneous control due to loss of synchronization. The determination as to whether or not the control process or the oscillation frequency of the erroneously controlled oscillator 5 is achieved by selecting m control processes or oscillation frequencies and selecting the one with the smallest change.

[0009]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 114 is a signal line through which the control microcomputer 21 reads out the measurement result of the frequency measuring means 18 which measures the oscillation frequency of the oscillator 9 in a predetermined cycle. FIG. 2 is an embodiment of a flow chart showing the synchronization establishment using the configuration of FIG. 1 and control of the oscillator 5 after carrier tracking. After the carrier follow-up 36, the control microcomputer 21 reads out the measurement result of the frequency measuring means 18, carries out the carrier frequency read-out 37, and the control microcomputer 21 carries out a comparison 38 between the carrier frequency read-out and the correct intermediate frequency, which is correct. If the frequency matches the intermediate frequency, the carrier frequency reading 37 is repeated. However, when the result of the carrier frequency reading 37 does not match the correct intermediate frequency, the frequency difference is calculated by the control microcomputer 21, a new oscillation frequency of the oscillator 5 is calculated in order to cancel the frequency difference, and the frequency synthesizer 6 The new oscillation frequency information is sent to, and the local oscillation frequency of the oscillator 5 is corrected 3
9 is executed, and the carrier frequency reading 37 is repeated. Due to the correction 39 of the local oscillation frequency, the frequency conversion output of the mixer 4 can obtain a stable and correct intermediate frequency signal even if the local oscillation frequency of the external unit fluctuates, and the signal deviates from the band of the bandpass filter 7. FIG. 3 is another embodiment of the flowchart showing the synchronization establishment and the control of the oscillator 5 after carrier tracking using the configuration of FIG. 3 is different from FIG. 2 in that the carrier frequency reading 37 by the control microcomputer 21 after the carrier tracking 36 is performed.
Is a carrier frequency reading 40 that is not continuous but is random or at regular intervals. This prevents an excessive change in the oscillation frequency of the oscillator 5 because the variation of the local oscillation frequency of the external unit is gentle based on the temperature.

FIG. 4 is a block diagram showing another embodiment of the present invention. Reference numeral 115 is a signal line through which the control microcomputer 21 reads whether the carrier reproduction is in the synchronous state or not. FIG. 5 is an embodiment of a flow chart showing the control of the oscillator 5 after establishment of synchronization and carrier tracking using the configuration of FIG. If the carrier reproducing means 17 is out of synchronization for some reason while the control of FIG. 3 is being performed, the control microcomputer 21 is interrupted by the signal line 115 and interrupted by the interruption 41. When the out-of-synchronization interrupt 41 is generated, the control microcomputer 21 holds 42 the local oscillation frequency of the oscillator 5 at the time of out-of-synchronization with respect to the frequency synthesizer 6.
The carrier sweep start 32 is performed again, and the re-carrier pull-in process starts. By selecting the oscillation frequency when the oscillation frequency of the oscillator 5 is out of synchronization, the recarrier pull-in is performed at a substantially correct intermediate frequency, that is, the center of the bandpass filter 7, and the recarrier pull-in time can be shortened. Further, by setting the start point of the recarrier sweep near the center of the bandpass filter 7, it becomes possible to pull in the recarrier faster.

FIG. 6 is another embodiment of a flow chart showing the synchronization establishment and the control of the oscillator 5 after carrier tracking using the configuration of FIG. 5 is different from FIG. 5 in that the local oscillation frequency is stored in the oscillator 5 after the local oscillation frequency is corrected 39.
3 and 44 for selecting the frequency setting of the oscillator 5 after the out-of-synchronization interrupt 41 from the memory 43 of the local oscillation frequency.
In the present embodiment, when the synchronization is lost, the control of the oscillator 9 is erroneously operated, and as a result, the oscillator 5 is also erroneously controlled and the converted output frequency of the mixer 4 largely deviates from the correct intermediate frequency. In order to prevent the local oscillation frequency 42 from being held 42, the local oscillation frequency immediately before being out of synchronization is used instead of the local oscillation frequency immediately before being out of synchronization. Therefore, the local oscillation frequency of the oscillator 5 after the correction of the local oscillation frequency 39 is sequentially stored in n pieces, and the n pieces of storage are updated every time the correction of the local oscillation frequency 39 is performed, and the local oscillation frequency at the beginning is the newest. Is. When the out-of-synchronization interrupt 41 is generated, the frequency change for every m from the beginning of the n storages is calculated, and the frequency of the oscillator 5 is selected from the frequency group having a small change near the beginning. By selecting from a frequency group that is close to the beginning and has a small change, it is possible to remove the local oscillation frequency that greatly fluctuates due to loss of synchronization, and select the newest local oscillation frequency excluding it. As a result, recarrier pull-in is performed at a substantially correct intermediate frequency, that is, at the center of the bandpass filter 7 without being affected by malfunction of the oscillator 5 due to loss of synchronization, and the recarrier pull-in time can be shortened. Further, by setting the start point of the recarrier sweep near the center of the bandpass filter 7, it becomes possible to pull in the recarrier faster.

[0013]

The oscillator 9 is provided with a means for controlling the oscillation frequency of the oscillator 5 on the basis of the measurement result of the frequency measuring means 18 which measures the oscillation frequency of the oscillator 9 in a predetermined cycle. By making the converted output frequency of the mixer 4 coincident with the intermediate frequency by the intermittent control, the center frequency of the digital modulation signal input to the bandpass filter 7 can be stabilized against the fluctuation of the local oscillation frequency of the outdoor unit. Further, a means for storing the control process or the oscillation frequency of the oscillator 5 is provided, and by using the oscillation frequency before being out of synchronization as the oscillation frequency of the oscillator 5 in the resynchronization pulling process, fast carrier re-pulling for loss of synchronization can be realized. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the second embodiment of the present invention.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the second embodiment of the present invention.

FIG. 6 is a flowchart showing the operation of the third embodiment of the present invention.

FIG. 7 is a block diagram showing a conventional example.

FIG. 8 is a flowchart showing the operation of a conventional example.

[Explanation of symbols]

 1 ... High-pass filter, 2 ... Preamplifier, 3 ... Variable tuning filter, 4 ... Mixer, 5 ... Oscillator, 6 ... Frequency synthesizer, 7 ... Bandpass filter, 8 ... Intermediate frequency amplifier, 9 ... Oscillator, 10 ... Division , 15 ... Quadrature detector, 12 ... Front end, 11 ... Intermediate frequency amplifier, 12 ... 90 degree phase shifter, 15 ... Quadrature detector, 16 ... Analog-digital converter, 17 ... Carrier regeneration means, 18 ... Frequency measurement Means, 19 ... Clock reproducing means, 20 ... Digital demodulating means, 21 ... Control microcomputer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Adachi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd. Hitachi, Ltd. multimedia system development headquarters

Claims (7)

[Claims] 1. A frequency conversion means including a first oscillator, a mixer and a variable gain amplifier, a frequency synthesizer, a bandpass filter, and a quadrature detection means including a second oscillator, a multiplier and a variable gain amplifier. A divider for dividing the output of the second oscillator, an analog-digital converter,
It comprises a digital demodulator and a control microcomputer, and the desired signal of the digital modulated wave is frequency-converted into an intermediate frequency signal by the frequency control of the first oscillator by the frequency synthesizer, and the quadrature detection means is passed through the band pass filter. Is input to the digital demodulator, and the output of the frequency divider and the output of the quadrature detection means subjected to analog-to-digital conversion are input to the digital demodulator, and the synchronization pull-in control and the synchronization holding control of the second oscillator are performed by the digital demodulator. A digital satellite broadcast receiver for measuring an oscillation frequency, comprising a means for controlling the oscillation frequency of the first oscillator based on the oscillation frequency measurement of the second oscillator by the digital demodulator. Broadcast receiver. 2. The frequency conversion according to claim 1, wherein the oscillation frequency of the first oscillator is controlled based on the oscillation frequency measurement of the second oscillator by the digital demodulator after the synchronization of the second oscillator is pulled in. A digital satellite broadcast receiver comprising means for matching the output frequency of the means with an intermediate frequency. 3. The digital control according to claim 1, wherein the control of the oscillation frequency of the first oscillator based on the measurement of the oscillation frequency of the second oscillator by the digital demodulator is random or intermittent control at equal intervals. Satellite receiver. 4. The digital satellite according to claim 1, 2 or 3, wherein, in the resynchronization pull-in process of the second oscillator after the loss of synchronization, the oscillation frequency before the loss of synchronization is used as the oscillation frequency of the first oscillator. Broadcast receiver. 5. The control of the oscillation frequency of the first oscillator based on the oscillation frequency measurement of the second oscillator by the digital demodulator or the oscillation frequency from the present or ( A digital satellite broadcast receiver equipped with a means for storing the current number of -1) to the number n before. 6. The oscillation frequency of the first oscillator according to claim 4 or 5, wherein the oscillation frequency of the first oscillator is controlled in the resynchronization pull-in process of the second oscillator after being out of synchronization. A digital satellite broadcasting receiver which is carried out based on the stored information of means for storing control or oscillation frequencies up to n. 7. The oscillation frequency of the first oscillator according to claim 4, 5 or 6, wherein the oscillation frequency of the first oscillator is controlled during the resynchronization pull-in process of the second oscillator after being out of synchronization. From the stored information of the means for storing the frequency control or the oscillation frequencies up to n, the number of consecutive m (m ≧ 2)
A digital satellite broadcast receiver based on a group of frequencies with the smallest frequency change between.