JP2005151120A - Demodulation method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a demodulation method and a demodulation device for preventing the quality of a reception signal from deteriorating and for miniaturizing a circuit. <P>SOLUTION: The demodulation method includes a step for performing first filtering to an analog reception signal in which a signal for each of a plurality of channels is demodulated, a step for converting a signal obtained by the first filtering step to a digital signal, and a step for simultaneously demodulating the signal for each of the plurality of channels by performing mathematical computation for each channel to the digital signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to signal processing, and more particularly to demodulation of a signal in which a plurality of channels such as a television and a radio are multiplexed. The present invention is suitable for receiving, for example, a multi-channel color television signal.

  Conventionally, in order to transmit information to an unspecified number of viewers, broadcasting via wire or wireless has been widely performed. The transmission side modulates a signal such as video or audio and broadcasts it by superimposing it on a high frequency carrier wave. On the other hand, the receiving side demodulates the video signal and the audio signal by selectively amplifying the frequency band corresponding to the selected channel among the received signals. Here, the frequency band used for television broadcasting is, for example, 90 MHz to 108 MHz, 170 MHz to 222 MHz in the case of VHF, and 470 MHz to 770 MHz in the case of UHF. This frequency band is slightly different depending on the country or region.

  FIG. 13 shows a block diagram of a conventional television receiver 1. The modulated / multiplexed received signal is excited by the antenna 10, and the distributor 20 distributes the received signal to the tuner 30A and the tuner 30B. The distributor 20 is generally composed of a transformer. Assuming that the power of the input signal is Pi, the powers Pi0 and Pi1 of the received signal distributed from the distributor 20 to the tuners 30A and 30B decrease as follows. In the following equation, 2 corresponds to the number of tuners (or channels), and Pi / n if the number of tuners is n.

  The signal distributed by the distributor 20 enters the high frequency amplifier circuit 32 through the input circuit 31 of each tuner. The received high-frequency signal amplified through the high-frequency amplifier circuit 32 is output by the channel selection circuit 34 at a frequency corresponding to the channel selection signal indicating the channel selected by the local transmitter 35.

  FIG. 14 shows an example of TV broadcast channel arrangement. Each channel is arranged every 6 MHz, and a video signal, a color signal, and an audio signal are modulated by each carrier signal in the channel.

  Next, in order to facilitate the subsequent processing of the circuits 36 and 37, the mixer 33 mixes the local oscillation frequency signal and the input signal of the local oscillator 35 to obtain a predetermined intermediate frequency (fv = 58.75 MHz, fs = 54.25 MHz). For example, in the case of channel 1, since the video carrier (or carrier) is 91.25 MHz, a local oscillation frequency signal of 150 MHz (91.25 + 58.75) is added. In the case of channel 2, since the video carrier wave is 97.25 MHz, a local transmission frequency signal of 156 MHz (97.25 + 58.75) is superimposed.

  The converted intermediate frequency signal is amplified by the video intermediate frequency amplifier 36 and converted into a color television signal by the video detection circuit 37.

As described above, the multi-channel receiver 1 using the conventional electronic tuner has a configuration in which the tuner selectively extracts the signal of one channel, and therefore, the multi-channel receiver 1 is received by using a plurality of these receivers. Other conventional electronic tuners are disclosed in Patent Document 1, for example. The channel frequency and the configuration of the receiving circuit are also disclosed in Non-Patent Document 1.
JP 11-298346 A NHK, Television Technical Textbook [top], Japan Broadcasting Corporation, pages 22, 121-151

  In the conventional demodulation technique, a tuner is prepared for each channel to be received, and a distributor is arranged in the preceding stage to distribute the received signal for each tuner. For this reason, the signal received by the antenna is attenuated by the number of tuners, and there is a problem that the S / N ratio deteriorates due to the inherent noise of the tuner.

  Further, in the conventional tuner, the transmission frequency of the local oscillator is adjusted in accordance with a specific channel desired to be demodulated, the received signal is converted into a predetermined intermediate frequency signal, and demodulation is performed for each channel. For this reason, when trying to demodulate multiple channels simultaneously from a received signal in which multiple channels are multiplexed, an input circuit, a high frequency amplifier circuit, a local oscillator circuit, a mixer, a video intermediate amplifier circuit, and a video detector circuit are required for the channels to be demodulated. there were. More specifically, the tuners 30A and 30B are housed in separate housings in order to prevent noise generation due to interference, and the circuits 32 and 35 in each tuner are separated in order to prevent noise generation in principle. It is stored in. For this reason, in order to simultaneously demodulate a plurality of channels, there has been a problem that the circuit becomes large and the cost increases.

  Accordingly, an object of the present invention is to provide a demodulating apparatus and method capable of preventing the quality deterioration of a received signal and reducing the circuit size.

  A demodulation method as one aspect of the present invention includes a step of performing a first filter process on an analog reception signal in which a signal for each of a plurality of channels is modulated, and a signal obtained by the first filter process step. The method includes a step of converting into a digital signal and a step of performing a numerical operation on the digital signal for each channel and demodulating the signals for the plurality of channels simultaneously. Since analog processing is not performed for each channel as in the prior art, but digital processing is performed for each channel, there is no attenuation of the received signal and no signal degradation. In addition, since digital processing can be performed by hardware or software processing using a single digital signal processor (DSP), for example, miniaturization can be achieved.

  The demodulation method further includes the step of converting the frequency of the analog reception signal to a lower frequency, and the first filtering step includes the first filtering step for the analog reception signal having the lower frequency. Filter processing may be performed. An inexpensive A / D converter with a small bandwidth can be used by low-frequency processing.

  The demodulating step includes, for example, a step of reproducing a carrier wave synchronized with the received signal from the digital signal, and a step of performing a second filter process for extracting a signal corresponding to a target channel in the plurality of channels from the digital signal. And a step of superimposing the carrier wave on the signal obtained by the second filter processing step, and a step of generating a signal of the target channel by performing a third filter processing on the signal after the superposition step; Have Alternatively, the demodulation step includes a step of performing a second filtering process for extracting a signal corresponding to a target channel from the digital signal, and a component of the signal obtained by the second filtering process. , With respect to the absolute value 0, a step of performing a third filtering process for removing the carrier wave of the target channel from the signal obtained by the folding step, and a signal obtained as a result of the third filtering process And generating a signal of the target channel. The analog reception signal is, for example, a signal obtained by multiplexing the signal for each of the plurality of channels by performing amplitude modulation, frequency modulation, or phase modulation.

  A demodulator according to another aspect of the present invention includes a filter circuit that performs a filtering process on an analog reception signal in which a signal for each of a plurality of channels is modulated, and an A / A that converts an output of the filter circuit into a digital signal. A D converter; and a demodulator that performs a numerical operation for each channel on the A / D converter and simultaneously demodulates the signals for the plurality of channels. The demodulator further includes a conversion unit that converts the frequency of the analog reception signal to a lower frequency, and the A / D converter converts the analog reception signal having the lower frequency into the digital signal. May be. These demodulating devices have the same effects as the above-described demodulation method.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  ADVANTAGE OF THE INVENTION According to this invention, the demodulation apparatus and method which can aim at size reduction of a circuit while preventing the quality deterioration of a received signal can be provided.

  Hereinafter, a receiver 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 3. Here, FIG. 1 is a schematic block diagram of the receiver 100. The receiver 100 demodulates a video signal simultaneously from a modulation signal in television broadcasting by a plurality of channels. The modulation method used in television broadcasting is an amplitude modulation method for video signals and a frequency modulation method for audio signals.

  As shown in FIG. 1, the receiver 100 is connected to an antenna 102, an input circuit 104, a high frequency amplifier 106, a filter 108, an analog / digital (A / D) converter 110, and channels 1 and 2. Tuners 120A and 120B that respectively perform demodulation processing (note that reference numeral “120” is a sum of these).

  The antenna 102 receives a signal from a transmitter (not shown). In the present embodiment, the received signal input from the antenna 102 is an analog video signal in which signals for a plurality of channels are modulated and multiplexed. The input circuit 104 is a circuit to which a reception signal is input. The input circuit matches the impedance of the feeder that supplies the received signal from the antenna and the input impedance of the high-frequency amplifier circuit over all channels. The high frequency amplifier circuit 106 amplifies the signal level of the received signal to an appropriate level that can be processed by the A / D converter 110. The filter 108 limits the frequency of the received signal to be equal to or lower than the Nyquist frequency of the A / D converter 110. The A / D converter 110 converts the received signal into a digital signal.

  The tuner 120 performs a numerical operation on the digital signal, performs a numerical operation for each channel, and simultaneously demodulates the signals for the plurality of channels. Each tuner 120 includes a bypass filter (BPF) processing unit 122 and an envelope detection processing unit 124. The BPF processing unit 122 performs band pass filter processing on the digital signal and extracts only a signal of a predetermined channel. The output of the BPF processing unit 122 is, for example, a signal g (t) shown in FIG.

  The envelope detection processing unit 124 reproduces the original video signal from the received AM signal of the selected channel. The envelope detection processing unit 124 includes, for example, an absolute value processing unit 125, a low-pass filter (LPF) processing unit 126, and a conversion processing unit 127, as shown in FIG. Here, FIG. 2 is a schematic block diagram of the envelope detection processing unit 124. The absolute value processing unit 125 loops back the negative signal portion and converts it to only a positive signal. The output of the absolute value processing unit 125 is, for example, the signal h (t) in FIG. 3C corresponding to the negative signal portion of the signal g (t) folded with respect to the absolute value 0 in FIG. It becomes. The LPF processing unit 126 performs low pass filter processing on the output signal of the absolute value processing unit 125 to remove the carrier wave of the target channel, and obtains the signal k (t) in FIG. The conversion processing unit 127 inverts the signal processed so far and reproduces the video signal v (t) in FIG. 3E, which is the signal of the target channel. The conversion processing unit 127 can be realized by, for example, subtracting k (t) from the reference DC signal. FIG. 3 is a signal waveform diagram by the envelope detection processing unit 124.

  Hereinafter, a receiver 100A according to a second embodiment of the present invention will be described with reference to FIGS. Here, FIG. 4 is a schematic block diagram of the receiver 100A. Similarly to the receiver 100, the receiver 100A can simultaneously demodulate a video signal from a modulated signal in a television broadcast, and an audio signal can be simultaneously demodulated with respect to a plurality of channels with the same configuration.

  As shown in FIG. 4, the receiver 100 </ b> A is connected to the antenna 102, the input circuit 104, the high frequency amplifier 106, the filter 108, the analog / digital (A / D) converter 110, and the channels 1 and 2. Tuners 130A and 130B that perform demodulation processing (referred to as “130” collectively). The same members as those in FIG. 1 are denoted by the same reference numerals, and a duplicate description is omitted.

  The tuner 130 performs a numerical operation on the digital signal, performs a numerical operation for each channel, and simultaneously demodulates the signals for the plurality of channels. Each tuner 130 includes a filter processing unit 131, a carrier reproduction processing unit 132, a multiplier 133, and a filter processing unit 134.

  The filter processing unit 131 performs band pass filter processing on the digital signal and extracts only a signal of a predetermined channel. The carrier reproduction processing unit 132 reproduces a carrier synchronized with the received signal. As shown in FIG. 5, the carrier reproduction processing unit 132 includes a carrier extraction processing unit 141, a reference signal generation unit 142, a phase comparison processing unit 143, a phase calculation processing unit 144, and a carrier reproduction processing unit 145. . Here, FIG. 5 is a schematic block diagram of the carrier reproduction processing unit 132.

The carrier extraction processing unit 141 extracts the intersection by comparing with the 0 level. This intersection indicates the phase of the extracted carrier signal. An example of the extracted carrier signal is shown in FIG. The reference signal generation unit 142 divides the sampling clock by the A / D converter 110 to generate a signal having a frequency closest to the carrier signal as a reference (square wave) signal, and this square wave signal is generated by the phase comparison processing unit 143. output to, and outputs a reference sine wave sin .omega _{S t} synchronized with the square wave carrier reproduction processing unit 145. An example of the reference square wave signal is shown in FIG. The phase comparison processing unit 143 performs phase comparison between the extracted carrier signal and the reference square wave signal. The phase comparison result is shown in FIG. The LPF processing unit 144 performs low-pass filter processing on the phase comparison result. The phase selection processing unit generates a sine wave signal synchronized with the carrier signal by advancing or delaying the phase of the reference sine wave signal according to the output level of the LPF processing unit. In this example, the phase is advanced when the level is high, and the phase is delayed when the level is low.

  Multiplier 133 multiplies the reception signal selected by filter processing section 131 with the carrier reproduction signal. The filter processing unit 134 extracts the original video signal before the desired modulation.

  An example of amplitude modulation (AM) signal demodulation processing is shown below. When the original signal is v (t) and the modulation signal is g (t), the modulation signal is expressed as follows.

Here, when f ₀ is the carrier frequency of the modulation signal, ω ₀ = 2πf ₀ and {1 + k × v (t)}> 0.

The A / D converted received signal g (t) is multiplied by the reproduced carrier signal sin ω ₀ t by a multiplier 503, and the following signal is obtained.

From this signal, the high frequency signal portion cos2ω ₀ t is removed by the filter processing unit 134, and the following signal is obtained.

Further, the original signal v (t) is reproduced by solving the following equation.

Here, A ₀ and k are constants and are calculated based on the DC level of the synchronization signal.

  Of course, the demodulation processing shown here can be performed alternately by, for example, doubling the processing clock, and can also be programmed using a processor.

  Hereinafter, a receiver 100B according to a third embodiment of the present invention will be described with reference to FIGS. Here, FIG. 7 is a schematic block diagram of the receiver 100B. Similarly to the receiver 100, the receiver 100B can simultaneously demodulate a plurality of channels of video signals from a modulation signal in television broadcasting, and can also perform simultaneous demodulation of a plurality of channels of audio signals with the same configuration.

  As shown in FIG. 7, the receiver 100B includes an antenna 102, an input circuit 104, a high frequency amplifier 106, a filter 108, an analog / digital (A / D) converter 110A, a mixer 112, and a local oscillator. 114 and tuners 130A and 130B that perform demodulation processing on channels 1 and 2, respectively. The same members as those in FIG. 4 are denoted by the same reference numerals, and a duplicate description is omitted.

  The receiver 100B is different from the receiver 100A in that it includes a mixer 112 and a local oscillator 114. The mixer 112 mixes the output signal from the high frequency amplifier 106 and the output signal of the local oscillator 114 and outputs the result to the filter 108. In the demodulation method of the present embodiment, the mixer 112 uses the signal of the local transmitter 114 to convert the frequency of the analog reception signal to a lower frequency, and the A / D converter 110A has an analog signal having a lower frequency band. A / D conversion can be performed on the received signal. As a result, the A / D converter 110A is different from the A / D converter 110 in that the A / D converter 110A has a smaller bandwidth than the A / D converter 110. Thus, the A / D converter 110A performs the A / D conversion. It can be configured at a lower cost than the device 110.

  Specifically, in the receiver 100A, the A / D converter 110 normally requires twice as much bandwidth as the channel bandwidth shown in FIG. A bandwidth of 101.75 MHz × 2, that is, a bandwidth of 203.5 MHz is required. On the other hand, in the receiver 100B, the local oscillator 114 outputs a signal having a frequency of 90 MHz, for example, and the mixer 112 subtracts this from the output signal from the high frequency amplifier 106. In FIG. 14, this means that the start frequency of channel 1 is 0 MHz, and the end frequency of channel 2 is from 102 MHz to 12 MHz. As a result, the A / D converter 110A only needs to have a bandwidth of 24 MHz. Such a situation is shown in FIG. Here, FIG. 8 is a waveform diagram shown in FIG.

  Next, a demodulation method of a frequency modulation (FM) modulation signal will be described with reference to FIGS. When the original signal is m (t) and the modulation signal is g (t), the FM modulation signal is expressed as follows.

Here, f _d is called a modulation index. The instantaneous phase is obtained as follows.

  FIG. 9 shows an FM signal demodulation processing unit. FIG. 9 shows a modification of 124 in FIG. As shown in the figure, the demodulation processing unit is connected to the BPF processing unit 122 in FIG. 1 and includes a differentiation processing unit 160 and an envelope detection processing unit 124. When the received signal is expressed by Equation 8, the differentiating circuit 160 outputs the following signal.

For example, as shown in FIG. 10, the differentiation processing unit 123 includes a register 162 and a calculation unit 164, and is realized by differential processing with respect to a signal delayed in units of samples. In general, the register 162 indicates that the input is simply delayed. If the delay is expressed as z ⁻¹ , its output is g (t) × z ⁻¹ . From the differential signal, the envelope detection processing unit 124 converts the negative signal into the positive signal by the absolute value processing in the same manner as the AM demodulation processing, and then the LPF processing removes the sine wave portion of the mathematical formula 10. 11 is extracted as a signal.

  Thereafter, the conversion processing unit 127 demodulates m (t).

  Next, a method of demodulating a phase modulation (PM) modulation signal will be described with reference to FIGS. If the original signal is m (t) and the modulation signal is p (t), the PM modulation signal is expressed as follows.

  FIG. 11 shows a PM signal demodulation processing unit. As shown in the figure, the demodulation processing unit includes an integration processing unit 170, a differentiation processing unit 160, and an envelope detection processing unit 124. When the received signal is expressed by Equation 13, the differentiating circuit 160 outputs the following signal.

  For example, as shown in FIG. 12, the integration processing unit 170 includes a calculation unit 172 and a register 174, and is realized by an accumulation process of input samples. The integrated signal is output to the differentiation processing unit 160, and the differentiation circuit 160 outputs the following signal.

  The output of the differentiation circuit 160 is supplied to the envelope detection processing unit 124, and the negative signal is converted into a positive signal by the absolute value processing similarly to the AM demodulation processing, and then the sine wave portion of Expression 10 is removed by the LPF processing, It is taken out as a signal shown in Equation 16.

  Thereafter, the conversion processing unit 127 demodulates m (t). Thus, after the received signal is once integrated, the same processing as the FM signal demodulation processing is performed.

  As described above, according to the present invention, signals of a plurality of channels can be demodulated simultaneously. Therefore, when storing signals of a plurality of channels in a home server or the like, a plurality of tuners are not required. Since it can be configured as a digital signal processor (DSP), downsizing and cost reduction can be achieved. Further, in digital processing, since reception signals are not attenuated, high-quality demodulation can be performed.

  As mentioned above, although preferable embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. For example, the modulation signal is not limited to amplitude modulation, frequency modulation, and phase modulation, and is not limited to amplitude phase modulation, spread modulation, complementary code or complementary code keying (CCK) modulation, or orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing). : OFDM) modulation and other modulation schemes. Here, “CCK” refers to a modulation scheme used in a wireless LAN using the 2.4 GHz band conforming to IEEE 802.11b and realizing a data transmission rate of 11 Mbps at the maximum. “OFDM” is a digital modulation scheme that multiplexes multiple orthogonal carrier signals.

It is a schematic block diagram of the receiver of the 1st Embodiment of this invention. FIG. 2 is a schematic block diagram illustrating a configuration example of an envelope detection processing unit of the receiver illustrated in FIG. 1. It is a signal waveform diagram by the envelope detection processing unit shown in FIG. It is a schematic block diagram of the receiver of the 2nd Embodiment of this invention. FIG. 2 is a schematic block diagram illustrating a configuration example of a carrier reproduction processing unit of the receiver illustrated in FIG. 1. It is a signal waveform diagram by the carrier reproduction | regeneration processing part shown in FIG. It is a schematic block diagram of the receiver of the 3rd Embodiment of this invention. FIG. 8 is a signal waveform diagram showing an example of television broadcast channel arrangement that has been low-frequency converted by the mixer of the receiver shown in FIG. 7. It is a schematic block diagram which shows the demodulation process part of a frequency modulation (FM) signal. It is a figure which shows the structure of the differential process part of the demodulation process part shown in FIG. It is a schematic block diagram which shows the demodulation process part of an amplitude modulation (PM) signal. It is a figure which shows the structure of the integration process part of the demodulation process part shown in FIG. It is a schematic block diagram which shows the structure of the conventional receiver. It is a signal waveform diagram which shows the example of a channel arrangement | positioning of normal television broadcasting.

Explanation of symbols

100, 100A, 100B Receiver 108 Filter 110 A / D converter 112 Mixer 114 Local transmitter 120A, 120B Tuner 122 BPF processing unit 124 Envelope detection processing unit 130A, 130B Tuner 131 Filter processing unit 132 Carrier regeneration processing unit 133 Multiplication unit 134 Filter processing unit

Claims (7)

First filtering the analog received signal in which the signals for each of the plurality of channels are modulated;
Converting the signal obtained by the first filtering step into a digital signal;
Demodulating the digital signal for each channel and demodulating the signals for each of the plurality of channels simultaneously. The demodulation method further includes the step of converting the frequency of the analog reception signal to a lower frequency,
The demodulation method according to claim 1, wherein the first filter processing step performs the first filter processing on the analog reception signal having the lower frequency. The demodulation step includes
Regenerating a carrier wave synchronized with the received signal from the digital signal;
Performing a second filtering process for extracting a signal corresponding to a target channel in the plurality of channels from the digital signal;
Superimposing the carrier wave on the signal obtained by the second filtering step;
The demodulation method according to claim 1, further comprising: performing a third filter process on the signal after the superimposing step to generate a signal of the target channel. The demodulation step includes
Performing a second filtering process for extracting a signal corresponding to a target channel in the plurality of channels from the digital signal;
Folding back the component of the signal obtained by the second filter processing with respect to an absolute value of 0;
Performing a third filtering process for removing the carrier wave of the target channel from the signal obtained by the folding step;
3. The demodulation method according to claim 1, further comprising the step of generating a signal of the target channel by inverting a signal obtained as a result of the third filter processing. 4.   2. The demodulation method according to claim 1, wherein the analog reception signal is a signal obtained by multiplexing the signal for each of the plurality of channels by amplitude modulation, frequency modulation, or phase modulation. A filter circuit that performs a filtering process on an analog reception signal in which a signal for each of a plurality of channels is modulated;
An A / D converter for converting the output of the filter circuit into a digital signal;
A demodulating device comprising: a demodulator that performs a numerical operation for each channel on the A / D converter and simultaneously demodulates the signals for the plurality of channels. The demodulator further includes a conversion unit that converts the frequency of the analog reception signal to a lower frequency,
The demodulator according to claim 6, wherein the A / D converter converts the analog received signal having the lower frequency into the digital signal.