JP2010124154A - Demodulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a demodulator without beat disturbance and with fewer circuit components. <P>SOLUTION: A reception part 10 includes a binarizing part 14 and a sampling part 15, and a demodulator part 20 includes a phase difference extraction part 21, a virtual IF signal generation/correction part 22 and a demodulation signal generation part 23. The binarizing part 14 and the sampling part 15 determine the polarity of IF signals, perform sampling by a fixed clock and generate digital signals. The phase difference extraction part 21 extracts a phase difference between the digital signals of the sampling part 15 and virtual IF signals supplied from the virtual IF signal generation/correction part 22 and delivers extracted results to the virtual IF signal generation/correction part 22 and the demodulation signal generation part 23. The virtual IF signal generation/correction part 22 generates the virtual IF signals whose frequency and phase are variable by operation, and corrects the frequency and phase of the virtual IF signals on the basis of the results extracted from the phase difference extraction part 21. The demodulation signal generation part 23 generates demodulation signals on the basis of the results extracted from the phase difference extraction part 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a demodulation device.

  A conventional technique for binarizing an FM-modulated input signal, sampling the binarized binary signal, and performing demodulation based on the sampling result is disclosed in Patent Document 1 below.

  The demodulating circuit of Patent Document 1 samples a binary signal obtained by binarizing an input signal with a limiter amplifier at a frequency that is an integral multiple of the frequency of the input signal, and the continuity of the sign of the sampled value determines the frequency. The demodulated signal is formed based on the discrimination result.

JP-A-3-30503

  In the above-mentioned Patent Document 1, it is necessary that the sampling frequency is an exact multiple of the center frequency of the input signal. However, in general, the sampling clock of the signal processing unit is often generated from the master clock for each device, and a frequency shift occurs between the transmission side and the reception side. Even if this deviation is very small, it will accumulate to an error of one clock. When the demodulated signal is unmodulated, the demodulated signal should not be output. However, when the deviation is accumulated in the error of one clock, a demodulated signal that should not have existed originally is generated. This becomes intermittent noise and is mixed in the demodulated signal.

FIGS. 5A to 5H are diagrams for explaining a conventional problem, and a state in which intermittent noise is generated will be described with reference to FIGS.
As shown in FIG. 5A, when an unmodulated intermediate frequency signal (IF signal) of 450 KHz, for example, is input as an input signal, the rectangular wave (binarized IF signal in FIG. 5B) is obtained by binarization. )become. Here, when the sampling frequency is set to 2.7 MHz, which is an integral multiple of 450 KHz, and sampling is performed six times per wavelength of the intermediate frequency signal as shown in FIG. 5C, the sampling result (sampling IF signal) is as shown in FIG. As shown in 5 (d), the frequency is uniform.

  On the other hand, as shown in FIG. 5E, when the frequency of the intermediate frequency signal (IF signal) is slightly shifted and increased, the binarized rectangular wave (binarized IF signal) is changed to that shown in FIG. However, if the sampling frequency is 2.7 MHz as shown in FIG. 5G, the sampling result (sampling IF signal) is as shown in FIG. In contrast, a portion having a higher frequency is periodically generated.

  When FM demodulation is performed based on the sampling result having a portion having a higher frequency with respect to the surroundings, the portion having a higher frequency with respect to the surroundings is naturally output as a demodulated signal. Originally, when an unmodulated signal is demodulated, an output signal should not be output. However, in FIG. 5 (h), an intermittent signal is output and included in the demodulated signal as noise. This is a beat failure that occurs when the modulated signal is sampled with an asynchronous clock.

  In this way, when the sampling timing is not synchronized with the intermediate frequency signal and the sampling frequency is not an integral multiple of the frequency of the intermediate frequency signal, a beat sound is generated. Since the intermediate frequency signal also includes a shift in the transmission frequency of the communication partner, in order to always synchronize the intermediate frequency signal and the sampling timing, a circuit that makes the internal clock that sets the sampling period follow the frequency change of the input signal is required. There is a problem that the number of parts of the apparatus increases because it is required separately.

  The present invention has been made in view of the above situation, and a demodulator that does not generate beat sound even if the average frequency of the modulated signal is not an integer ratio with the sampling clock on the receiving side is provided as a circuit component. The goal is to achieve without increasing.

In order to achieve the above object, a demodulator according to an aspect of the present invention provides:
A demodulator that receives an intermediate frequency signal obtained by converting the frequency of the carrier wave modulated by the modulation signal into an intermediate frequency, periodically samples the intermediate frequency signal as a binary signal, and demodulates the sampled result by calculation Because
A computing means for computing data of a virtual intermediate frequency signal which is a periodic wave independent of the intermediate frequency and has a variable frequency and phase;
Extraction means for extracting the difference between the intermediate frequency signal and the virtual intermediate frequency signal by the sampling;
Correction means for correcting the virtual intermediate frequency signal to approach the intermediate frequency signal based on the extracted difference;
A demodulated signal generating means for generating a demodulated signal based on the correction amount of the virtual intermediate frequency signal by the correcting means;
It is characterized by providing.

  The extraction unit may extract the difference from a time difference in timing when the polarities of the intermediate frequency signal and the virtual intermediate frequency signal change.

  The difference may be a frequency or a phase.

  Further, the correction means corrects the frequency of the virtual intermediate frequency signal so as to approach the average frequency of the intermediate frequency signal based on a value obtained by accumulating the difference over a long period of time than the maximum period of the modulation signal. Also good.

  The correcting means may correct the phase of the virtual intermediate frequency signal so as to approach the phase of the intermediate frequency signal based on the difference in a shorter period than the minimum period of the intermediate frequency signal.

  Further, the demodulated signal generation means may generate the demodulated signal based on a phase correction amount of the intermediate frequency signal.

  According to the present invention, a demodulator that does not generate a beat sound even if the average frequency of the modulated input signal is not an integer ratio with the sampling clock on the receiving side can be realized with a small number of circuit components.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a receiver according to an embodiment of the present invention.

The receiver includes a receiving unit 10 and a demodulating device unit 20.
The receiving unit 10 selects an FM modulated wave of a desired station from the received signal given from the antenna 11, and generates an intermediate frequency signal (hereinafter referred to as an IF signal) in which the frequency of the FM modulated wave is reduced, An amplification circuit 13 that is connected to the output side of the front end 12 and amplifies the IF signal, a binarization unit 14 that converts the amplified IF signal into a binary signal (hereinafter referred to as a binarized IF signal), A sampling unit 15 that samples the valued IF signal with a clock having a constant frequency is provided.

  The demodulation device unit 20 includes a phase difference extraction unit 21, a virtual IF signal generation / correction unit 22, and a demodulation signal generation unit 23. The demodulating device unit 20 can be configured by a DSP (Digital Signal Processor), for example.

The binarization unit 14 is connected to the output side of the amplifier circuit 13, determines the level of the IF signal input from the amplifier circuit 13, and outputs a binary IF signal whose polarity alternately changes in synchronization with the IF signal. Generate.
The sampling unit 15 samples the binarized IF signal with a clock having a constant frequency, and generates a binary digital signal (hereinafter referred to as a sampling IF signal) synchronized with the operation clock of the demodulating device unit 20.

  The phase difference extraction unit 21 is connected to the output side of the sampling unit 15 and the virtual IF signal generation / correction unit 22. The sampling IF signal provided from the sampling unit 15 and the virtual IF signal provided from the virtual IF signal generation / correction unit 22 are connected to the phase difference extraction unit 21. And the phase difference is extracted.

The phase difference extraction result extracted by the phase difference extraction unit 21 is passed to the virtual IF signal generation / correction unit 22 and the demodulated signal generation unit 23. The virtual IF signal generation / correction unit 22 generates a virtual IF signal based on the phase difference extraction result extracted by the phase difference extraction unit 21 and corrects its frequency and phase.
The demodulated signal generator 23 generates a demodulated signal based on the phase difference extraction result extracted by the phase difference extractor 21.

Next, the principle of the virtual IF signal in the receiver of this embodiment will be described.
FIG. 2 is a diagram illustrating a relationship among the IF signal, the sampling IF signal, and the virtual IF signal.

  Originally, it would be desirable to directly demodulate the IF signal of FIG. 2 (a), but the input to the demodulator 20 that performs the demodulation is the sampling IF signal of FIG. 2 (c) obtained by the sampling of FIG. 2 (b). . If this sampling IF signal is demodulated as it is, an intermittent demodulated signal is generated even if the original IF signal is not modulated.

  Therefore, the virtual IF signal shown in FIG. 2D assuming the original IF signal is generated in the demodulator unit 20, and the virtual IF signal is demodulated. Since this virtual IF signal is generated by signal processing calculation, it is possible to realize very fine resolution (for example, 1 / 10,000 of the sampling period) without being limited by the resolution of the sampling period as hardware. It is a problem of the resolution of the sampling period that a large frequency fluctuation occurs in the sampling IF signal even when there is no modulation. If the resolution is very fine, the frequency fluctuation can be ignored. Therefore, if the virtual IF signal is demodulated, it can be avoided that the demodulated signal is periodically generated when the original IF signal is not modulated.

  The virtual IF signal is always compared with the input signal (sampling IF signal) and corrected based on the comparison result. As a result, the modulation signal component of the original IF signal is also reflected in the virtual IF signal. This correction amount increases or decreases in proportion to the modulation amount, and the sum of the correction amounts can be considered as a demodulated signal.

  Incidentally, in the case of FIG. 2, since the polarities of the sampling IF signal and the virtual IF signal match at all sampling points, no correction is made and no demodulated signal is generated.

Next, the principle of the demodulation operation in the receiver of this embodiment will be described.
Consider a case where the IF signal is sampled at a frequency slightly higher than 450 kHz and sampled at a frequency of 2.7 MHz, as in the example of FIG.
In this case, the sampling IF signal has a constant waveform as shown in FIG. 5D in many time zones, and sometimes the fluctuation as shown in FIG. 5H appears.

  The virtual IF signal needs to be continuously corrected in accordance with the input sampling IF signal. However, when the correction of the frequency of the virtual IF signal is completed during this fixed waveform period, the frequency of the virtual IF signal is exactly 450 kHz. Should be. Thereafter, when a fluctuation as shown in FIG. 5H appears, it is necessary to largely correct the fluctuation portion. The modulation amount of the original IF signal and the correction amount of the virtual IF signal corrected so as to always match are equivalent contents, and as a result, fluctuations as shown in FIG. 5H appear as modulation signals. End up.

  Therefore, in order not to directly demodulate the fluctuation as shown in FIG. 5 (h) that occurs at the time of no modulation, it is necessary to make the correction of the frequency of the virtual IF signal very gentle. In addition, the frequency of the virtual IF signal and the average frequency of the input IF signal must match. As a result, the frequency of the virtual IF signal is set to the long-term average frequency of the input IF signal.

  When trying to compare signals, there are two elements, “frequency” and “phase”. When the frequency of the virtual IF signal is changed only very slowly, the frequency fluctuation does not include the component of the modulation signal. For this reason, demodulation uses the phase change of the virtual IF signal.

The frequency and the wavelength are in an inversely proportional relationship, and the wavelength of the FM modulation signal varies as much as the frequency. The phase change is the same as the wavelength change.
When a virtual IF signal having a constant frequency is corrected locally according to the modulated input signal, the phase of the virtual IF signal changes in accordance with the frequency fluctuation of the input signal. If this phase fluctuation is extracted, FM demodulation can be performed.

Next, details of the demodulator unit 20 that performs the demodulation will be described.
FIG. 3 is a functional block diagram showing details of the interior of the demodulator 20 in FIG.

The phase difference extraction unit 21 extracts the phase difference between the sampling IF signal from the reception unit 10 and the virtual IF signal from the virtual IF signal generation / correction unit 22. Specifically, the time shift of the displacement point of each signal is calculated.
The output of the phase difference extraction unit 21 is a deviation time at each sampling time point, but the resolution of this time is not a sampling interval but can be a very fine resolution in arithmetic processing.

  If the phase shift times from the phase difference extraction unit 21 are accumulated, the phase change can be found. The phase change is equivalent to the frequency change, and this accumulated phase change can be considered as an FM demodulated output. Therefore, the demodulated signal generator 23 accumulates the phase shift times to generate a demodulated signal.

  When the phase shift time includes a certain element (such as direct current in terms of current), there is a risk that the phase shift time is accumulated during the calculation of the total and causes overflow. In order to prevent this, a high-pass filter (HPF) is inserted in the demodulated signal generator 23 in FIG.

The virtual IF signal generation / correction unit 22 controls the frequency and phase of the generated virtual IF signal.
Both the frequency and the phase are corrected based on the phase shift time from the phase difference extraction unit 21, but the phase correction is executed every time the phase shift occurs, whereas the frequency correction calculates a long-term average value. After that, correction is performed based on the average value.

First, the frequency correction method is explained.
Since the frequency correction needs to be performed very slowly, the phase shift is averaged over a longer period than the longest period of the modulation signal, and the frequency is corrected based on this. The phase shift changes in accordance with the modulation signal, but if the long-term average is viewed, the change due to the modulation is canceled and only the average frequency is obtained.

Here, it is assumed that when the phase of the virtual IF signal is advanced with respect to the sampling IF signal, the output of the phase difference extraction unit 21 becomes a positive value, for example.
If the frequency of the virtual IF signal is slightly higher than the input IF signal, the phase of the virtual IF signal advances with respect to the sampling IF signal. That is, the total output of the phase difference extraction unit 21 is shifted in the positive direction. In the case where the long-term phase accumulation with little influence of modulation is positive, if the frequency of the virtual IF signal is lowered, the long-term phase accumulation changes in the negative direction. On the other hand, when the long-term phase total is negative, conversely, if the frequency of the virtual IF signal is increased, the total changes in the positive direction. In this way, if the frequency of the virtual IF signal is corrected so that the total of the long-term phase becomes 0, it can be made to coincide with the average value of the frequency of the input IF signal.

Next, the phase correction method will be described.
FIG. 4 is a diagram illustrating an example of phase difference correction.
The phase difference extraction unit 21 matches the sampling IF signal (FIG. 4B) with the virtual IF signal (FIGS. 4C to 4F) at each sampling timing (FIG. 4A). Compare.

  As shown in FIGS. 4C and 4D, when the sign of the sampling IF signal and the virtual IF signal at each sampling timing coincide, the phase difference extraction unit 21 determines that the sampling IF signal and the virtual IF signal are virtual. The phase difference from the IF signal is within an allowable range.

  As shown in FIG. 4E, when there is a mismatch in the sign of the sampling IF signal and the virtual IF signal and the polarity of the virtual IF signal has changed first (the phase has advanced), the phase difference extraction unit 21 Outputs a positive numerical value corresponding to the phase difference of FIG. When the virtual IF signal generation / correction unit 22 receives this positive numerical value, the virtual IF signal generation / correction unit 22 corrects the phase by delaying the time of the virtual IF signal by a time corresponding to this numerical value.

As shown in FIG. 4F, when there is a mismatch in the sign of the sampling IF signal and the virtual IF signal and the polarity of the virtual IF signal is changed later (the phase is delayed), the phase difference extraction unit 21 , A negative numerical value corresponding to the phase difference in FIG.
When the virtual IF signal generation / correction unit 22 receives this negative numerical value, it corrects the phase by advancing the time of the virtual IF signal by a time corresponding to this numerical value.

  As described above, in the receiver of the present embodiment, the virtual IF signal is set internally, the virtual IF signal is corrected, the original IF signal is followed, and a demodulated signal is generated based on the correction amount. Yes. As a result, a circuit for synchronizing the timing for sampling the received FM modulated wave becomes unnecessary.

  In addition, since the average frequency of the IF signal for a sufficiently long period is used as the frequency of the virtual IF signal, beat failure can be prevented even if the sampling frequency and the IF signal are not synchronized.

In addition, the virtual IF signal does not need to be actually generated by the oscillator, and only the signal polarity and the change time are used for the determination, so that the signal processing amount is also reduced.
Further, the binarization unit 14 and the sampling unit 15 of the receiving unit 10 determine the polarity of the IF signal to make a binary signal, and generate a digital signal synchronized with the demodulator unit 20, so that the analog IF signal is converted into a digital signal. An A / D circuit or the like for converting to a signal is not necessary.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible.
For example, the sampling frequency of the binarized IF signal is arbitrary and may be set according to the frequency of the FM modulated wave or IF signal.
In the present invention, the received signal may be a phase-modulated wave. The receiver in this case can also be realized with the same configuration as in the above embodiment.

It is a figure which shows the receiver which concerns on embodiment of this invention. It is a figure which shows the relationship between IF signal, sampling IF signal, and virtual IF signal. It is a figure which shows the detail of a demodulation apparatus part. It is a figure which shows the example of a phase difference. It is explanatory drawing for demonstrating the conventional subject.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Receiving part 11 Antenna 12 Front end 13 Amplifying circuit 14 Binarization part 15 Sampling part 20 Demodulator part 21 Phase difference extraction part 22 Virtual IF signal generation / correction part 23 Demodulation signal generation part

Claims (6)

A demodulator that receives an intermediate frequency signal obtained by converting the frequency of the carrier wave modulated by the modulation signal into an intermediate frequency, periodically samples the intermediate frequency signal as a binary signal, and demodulates the sampled result by calculation Because
A computing means for computing data of a virtual intermediate frequency signal which is a periodic wave independent of the intermediate frequency and has a variable frequency and phase;
Extraction means for extracting the difference between the intermediate frequency signal and the virtual intermediate frequency signal by the sampling;
Correction means for correcting the virtual intermediate frequency signal to approach the intermediate frequency signal based on the extracted difference;
A demodulated signal generating means for generating a demodulated signal based on the correction amount of the virtual intermediate frequency signal by the correcting means;
A demodulating device comprising:   2. The demodulator according to claim 1, wherein the extraction unit extracts the difference from a time difference between timings at which polarities of the intermediate frequency signal and the virtual intermediate frequency signal change.   The demodulator according to claim 1, wherein the difference is a frequency or a phase.   The correction means corrects the frequency of the virtual intermediate frequency signal so as to approach the average frequency of the intermediate frequency signal based on a value obtained by accumulating the difference over a longer period than the maximum period of the modulation signal. The demodulator according to claim 3.   The correction means corrects the phase of the virtual intermediate frequency signal so as to approach the phase of the intermediate frequency signal based on the difference in a shorter period than the minimum period of the intermediate frequency signal. 5. The demodulator according to 3 or 4.   6. The demodulator according to claim 3, wherein the demodulated signal generating unit generates the demodulated signal based on a phase correction amount of the intermediate frequency signal.

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