JP5801764B2 - FSK demodulator - Google Patents

Description

  The present invention relates to an FSK demodulator that demodulates a modulated wave (modulated signal) modulated by FSK (Frequency Shift Keying).

  Conventionally, the FSK demodulator disclosed in Patent Document 1 is well known. This FSK demodulator receives a modulated wave (s (t)) that has been FSK modulated at a terminal. The received modulated wave extracts the in-phase component (I (t)) and the quadrature component (Q (t)) from the modulated wave through two sets of mixers and a low-pass filter (LPF). The in-phase component (I (t)) and the quadrature component (Q (t)) are expressed by the following (Expression 1) and (Expression 2).

These in-phase component (I (t)) and quadrature component (Q (t)) are sent to a determination circuit via a phase difference detection / frequency detector that performs edge detection. The determination circuit determines a threshold value of the detection signal based on the results of phase difference detection and frequency detection. However, in this demodulator, the demodulation characteristic is defined by the appearance frequency of the edge. Therefore, an FSK demodulator that employs a logic circuit that outputs a detection signal by adding the in-phase component (I (t)) and the quadrature component (Q (t)) in place of the above-described phase difference detection / frequency detector. Are known. The determination circuit determines Hi when the signal level of the detection signal exceeds the threshold, and determines Lo when it does not exceed the threshold. For the signal level, for example, 1 is assigned to Hi and 0 is assigned to Lo. Through the determination, the determination circuit extracts data included in the modulated wave.

Japanese Patent Laid-Open No. 8-204764 (FIG. 4)

  The modulated wave received at the terminal may contain noise due to reflection by, for example, a building. When noise is included in the modulated wave, the amplitudes of the in-phase component and the quadrature component change. Therefore, the detection signal obtained by adding these also includes noise. Depending on the magnitude of the noise included in the detection signal, the determination circuit may cause a determination error, for example, as indicated by a circle in FIG. In other words, there is a risk that it is determined to be the Hi level even though it is originally at the Lo level.

  On the other hand, it is generally known that the phase change is equal to the frequency. That is, the frequency can be obtained by differentiating the phase. Therefore, instead of a logic circuit that outputs a detection signal obtained by simply adding the in-phase component (I (t)) and the quadrature component (Q (t)), the detection signal shown in the following (Equation 3) is used. An FSK demodulator that employs an output logic circuit is known.

If the current time is k and the past time is k−p, the differential value of the in-phase component I (t) (in the formula, (dot) is added on I (t)), and the quadrature component Q (t ) Is a difference value between the detection signal at the current time and the detection signal at the past time, that is, the following (Expression 4). And it is known that it can be approximated by (Equation 5).

From the relationship of (Equation 4) and (Equation 5), the numerator term of the detection signal shown in the above (Equation 3) is (Equation 6-2) shown below, and the denominator term is (Equation 7) shown below.

From the relationship of (Expression 6-2) and (Expression 7), the detection signal is expressed by the following (Expression 8).

From (Equation 8), the relationship between the phase difference θ and the detection signal v (t) is represented by the graph of FIG. As shown in FIG. 5, when the phase difference θ is around ± 90 °, the change in the value of the detection signal v (t) is small. Therefore, if the detection signal v (t) includes noise, the determination circuit determines whether the detection signal is positive or negative. Is easy to make mistakes.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an FSK demodulator that outputs a detection signal that is not easily affected by noise.

In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that an in-phase component and a quadrature component of an FSK-modulated modulated wave are input, and a logic circuit that generates a detection signal based on both components, A determination circuit that demodulates data included in the modulated wave through a comparison between a detection signal and a signal level determination threshold; and the logic circuit includes a predetermined amount of the modulated wave at a first time. The inner product of the phase rotated and the modulated wave at the second time different from the first time is the square of the magnitude of the modulated wave at the first time or the modulated wave at the second time Divide by the square of the magnitude or the division value which is the product of the magnitude of the modulated wave at the first time and the second time, and detect the result by raising the result of division to a positive integer power of 2 or more. Generate signal The gist of the Rukoto.

According to this configuration, a term including a trigonometric function is raised to a positive integer power of 2 or more . For this reason, compared with the case where the term including the trigonometric function is not raised to a positive integer power of 2 or more , the detection signal changes linearly with respect to the phase difference. For this reason, even if noise or the like is included in the detection signal, the determination circuit can easily determine whether the signal level of the detection signal is positive or negative. As a result, the data included in the modulated wave can be accurately extracted.

  According to a second aspect of the present invention, in the FSK demodulator according to the first aspect, the logic circuit is configured such that the modulated wave at a first time and a modulated wave at a second time different from the first time. The gist is to change a calculation formula for generating the detection signal based on the phase difference so that the detection signal has a unique value with respect to the phase difference.

  According to this configuration, the detection signal has a unique value with respect to the phase difference. That is, the phase difference is determined from the value of the detection signal. Thus, the determination circuit can accurately determine the signal level. As a result, the data included in the modulated wave can be accurately extracted.

According to a third aspect of the present invention, in the FSK demodulator according to the second aspect, when the phase difference is not less than 0 ° and not more than 90 °, the calculation formula indicates that the modulation wave at the first time is The inner product of the phase rotated by a predetermined amount and the modulated wave at the second time is divided by the division value, and the result of division is multiplied by a positive integer greater than or equal to 2 , and the phase difference Is greater than 90 ° and less than or equal to 180 °, the inner product of the modulated wave at the first time and the modulated wave at the second time is calculated by dividing the inner product of the modulated wave at the second time. If the phase difference is greater than −180 ° and less than −90 °, the result obtained by dividing the result obtained by dividing the result of division by 2 to a positive integer power is less than −90 °. A phase wave rotated by a predetermined amount with respect to the modulated wave and the second time The inner product of the definitive modulated wave, divided by the division value, those two or more positive integer power taking the absolute value of the dividing result, which plus to minus 2, the phase difference is -90 If it is not less than 0 ° and less than 0 °, the inner product of the modulated wave at the first time and the modulated wave at the second time is divided by the division value. The gist is that the absolute value of the result of the division is taken as a positive integer power of 2 or more and a minus sign is added.

  According to this configuration, the detection signal has a unique value with respect to the phase difference, and the detection signal has a continuous value with respect to a change in the phase difference. For this reason, even if there is an influence of noise or the like, the determination circuit can easily determine the signal level of the detection signal.

The invention described in claim 4 is the FSK demodulator according to claim 3, wherein the positive integer power of 2 or more is a square.
According to this configuration, the detection output with the highest linearity can be obtained.

  According to a fifth aspect of the present invention, in the FSK demodulator according to the third or fourth aspect, the logic circuit includes positive / negative of an inner product of the modulated wave at the first time and the modulated wave at the second time, And the modulation of the first time and the modulation of the second time based on the positive or negative of the inner product of the modulation wave of the first time rotated by 90 ° and the modulation wave of the second time The gist is to determine the phase difference from the wave.

According to this configuration, the phase difference between the modulated wave at the first time and the modulated wave at the second time can be obtained with a simple circuit configuration called an inner product arithmetic circuit.
According to a sixth aspect of the present invention, in the FSK demodulator according to any one of the first to fifth aspects, the logic circuit includes the modulated wave at the first time and the modulated at the second time. The gist is to obtain the modulated waves at the first and second times so that the phase difference from the wave is 90 °.

  According to the configuration, the inner product of the modulated wave at the first time and the modulated wave at the second time different from the first time becomes the maximum value or the minimum value. Therefore, the value of the detection signal is also the maximum value or the minimum value. For this reason, the determination circuit can perform more accurate positive / negative determination.

  According to a seventh aspect of the present invention, in the FSK demodulator according to any one of the first to sixth aspects, the logic circuit obtains a modulated wave acquired immediately before the modulated wave at the second time. To obtain the detection signal as a modulated wave at the first time.

According to this configuration, when obtaining a detection signal, since there are few modulation waves (data) to be processed in the logic circuit, the load on the logic circuit can be suppressed.
According to an eighth aspect of the present invention, in the FSK demodulator according to any one of the first to seventh aspects, the logic circuit is a digital circuit that processes a digital signal, and is a modulated wave that is an analog signal. The analog-to-digital converter converts the in-phase component and the quadrature component into a digital signal, and the analog-digital converter inputs the in-phase component and the quadrature component of the modulated wave converted into the digital signal to the logic circuit.

  Logic circuits that process analog signals have different outputs depending on component variations. Therefore, the accuracy of the output detection signal is low. On the other hand, in the case of a logic circuit that processes a digital signal, the accuracy of a detection signal to be output can be increased by increasing the number of bits of data to be processed.

  The present invention can provide an FSK demodulator that outputs a detection signal that is not easily affected by noise.

The block diagram which shows schematic structure of the FSK demodulator in this embodiment. (A) is a graph showing the relationship between the phase difference between the modulated wave at the past time rotated by 90 ° and the modulated wave at the current time and the positive / negative of these inner products, and (b) the past time. The graph which shows the relationship between the phase difference of the modulated wave in and the modulated wave in the present | current time, and the positive / negative of these inner products. The graph which shows the relationship between a phase difference and this example, ie, the relationship between the detection signal which squares the term of sin, and the relationship between the phase difference and the detection signal which does not square the term of sin. The figure which shows the determination error in the conventional FSK demodulator. The graph which shows the relationship between a phase difference and the conventional detection signal.

Hereinafter, an embodiment embodying the FSK demodulator of the present invention will be described with reference to FIGS.
<Configuration of FSK demodulator>
As shown in FIG. 1, the FSK demodulator 1 includes an antenna 10, a local oscillator 20, a phase shifter 30, first and second mixers (mixers) 41 and 42, and first and second low-pass signals. Filters (LPF) 51 and 52, first and second analog / digital converters (A / D converters) 61 and 62, a logic circuit 70, and a determination circuit 80 are provided.

  The antenna 10 receives a modulated wave (analog signal) subjected to FSK modulation. This modulated wave is a signal having two different types of predetermined frequencies. The antenna 10 is connected to the first and second mixers 41 and 42, respectively, and sends the received modulated waves to the first and second mixers 41 and 42.

  The first and second mixers 41 and 42 mix signals of two different frequencies and output a signal having a frequency different from the input signal. The first mixer 41 is directly connected to the local oscillator 20. The second mixer 42 is connected to the local oscillator 20 via the phase shifter 30. The local oscillator 20 oscillates at a frequency obtained by adding two different types of frequencies included in the modulated wave and dividing by two. The oscillation signal generated by the local oscillator 20 is sent to the first mixer 41 and the phase shifter 30. The phase shifter 30 shifts the phase of the oscillation signal sent from the local oscillator 20 by 90 °, and sends the oscillation signal whose phase is shifted to the second mixer 42. The first and second mixers 41 and 42 are connected to the first and second LPFs 51 and 52, respectively. The first mixer 41 mixes the oscillation signal directly input from the local oscillator 20 and the modulated wave, and sends the mixed signal to the first LPF 51. The second mixer 42 mixes the oscillation signal whose phase is shifted by 90 ° by the phase shifter 30 and the modulated wave, and sends the mixed signal to the second LPF 52.

  The first and second LPFs 51 and 52 remove high frequency components of the input signal. The first and second LPFs 51 and 52 are connected to the first and second A / D converters 61 and 62. The first and second LPFs 51 and 52 send signals from which the high frequency components have been removed to the first and second A / D converters 61 and 62. The signal that has passed through the first LPF 51 is the in-phase component (I (t)) of the modulated wave s (t), and the signal that has passed through the second LPF 52 is the quadrature component (Q (t) of the modulated wave s (t). ). The in-phase component (I (t)) and the quadrature component (Q (t)) are expressed by the above (Formula 1) and (Formula 2).

  The first A / D converter 61 converts the in-phase component I (t) of the input modulated wave s (t) into a digital signal. The second A / D converter 62 converts the orthogonal component Q (t) of the input modulated wave s (t) into a digital signal. The first and second A / D converters 61 and 62 are connected to the logic circuit 70. The first and second A / D converters 61 and 62 send the in-phase component I (t) and the quadrature component Q (t) of the modulated wave s (t) converted into a digital signal to the logic circuit 70.

  The logic circuit 70 is an electronic circuit that generates a detection signal v (t) by performing a logical operation based on the in-phase component I (t) and the quadrature component Q (t). The logic circuit 70 calculates the positive / negative of the inner product (conditional expression A) of the modulated wave at the past time and the modulated wave at the current time, and the modulated wave at the current time by rotating the phase of the modulated wave at the past time by 90 °. Is configured to output a detection signal to be described later based on the positive / negative of the inner product (conditional expression B).

  Here, a time interval (sampling period) at which the logic circuit 70 acquires a modulated wave (more precisely, an in-phase component and a quadrature component of the modulated wave) is a time p. Therefore, if the current time is k, the previous time acquired immediately before is k−p. Thus, the modulated wave s (t) at the current time and the past time is expressed by the following (Equation 9) and (Equation 10).

Therefore, the inner product of the modulated wave s (kp) at the past time and the modulated wave s (k) at the current time, that is, the conditional expression A is expressed by the following (Expression 11).

Further, rot (90 °) s (k−p) obtained by rotating the modulated wave s (k−p) at the past time by 90 ° is expressed by the following (formula 12).

Therefore, the inner product of rot (90 °) s (kp) obtained by rotating the modulated wave s (kp) at the past time by 90 ° and the modulated wave s (k) at the current time, that is, the condition Formula B is expressed by the following (Formula 13).

Moreover, the calculation formulas of the detection signal v (t) that change based on the positive and negative of the conditional expressions A and B are expressed by the following (Expression 14) to (Expression 17).

Note that a determination circuit 80 is connected to the logic circuit 70. The determination circuit 80 generates a data signal indicating data included in the modulated wave through a comparison between the detection signal output from the logic circuit 70 and a signal level determination threshold value.

<Operation of logic circuit>
Next, the operation of the logic circuit 70 will be described. It is well known that when the inner product of two vectors is positive, the angle formed by both vectors is within 90 °, and when the inner product of two vectors is negative, the angle formed by both vectors is greater than 90 °. . That is, as shown in FIG. 2B, the positive / negative of the inner product (conditional expression A) of the modulated wave s (kp) at the past time and the modulated wave s (k) at the current time, and FIG. As shown in a), from the positive / negative of the inner product (conditional expression B) of the modulated wave s (k−p) at the past time rotated by 90 ° and the modulated wave s (k) at the current time It is possible to easily determine in which range the phase difference θ between the modulated wave s (kp) at the past time and the modulated wave s (k) at the current time is. The determination result of the phase difference θ is as follows.

(Condition W) When conditional expression A ≧ 0 and conditional expression B ≧ 0, 0 ° ≦ phase difference θ ≦ 90 °.
(Condition X) When conditional expression A <0 and conditional expression B ≧ 0, 90 ° <phase difference θ ≦ 180 °.
(Condition Y) When conditional expression A <0 and conditional expression B <0, −180 ° <phase difference θ <−90 °.

(Condition Z) When conditional expression A ≧ 0 and conditional expression B <0, −90 ° ≦ phase difference θ <0 °.
From the above, the relationship between the phase difference θ and the detection signal v (t) is represented by the graph of FIG. As shown in FIG. 3, the detection signal v (t) has a unique value with respect to the phase difference θ. Therefore, for example, even when the detection signal v (t) is affected by noise, the determination circuit 80 can accurately determine the signal level of the detection signal v (t). Further, as indicated by a solid line in FIG. 3, the detection signal v (t) of this example changes linearly over the entire range of the phase difference θ. This is because the term of sin is squared as shown in (Expression 8) and (Expression 14) to (Expression 17). Therefore, the detection signal v (t) changes more linearly, especially when the phase difference θ is around ± 90 °, compared to the case where the sin term indicated by the alternate long and short dash line in FIG. 3 is not squared. Therefore, even if the detection signal v (t) includes noise, the determination circuit 80 can easily determine the signal level of the detection signal v (t). Furthermore, as shown in FIG. 3, the detection signal v (t) has a continuous value with respect to the change in the phase difference θ. For this reason, even if there is an influence of noise, the determination circuit 80 can easily determine the signal level of the detection signal v (t).

  The above (Formula 13) is equal to the above (Formula 6-1). In other words, the numerator terms of (Expression 14) to (Expression 17) described above are the rot (90 °) s (tp) obtained by rotating the modulated wave s (tp) at the past time by 90 ° and the present. (A) is an inner product with the modulated wave s (t) at the time of (A).

  The magnitude of the modulated wave s (t) at the current time is expressed by the following (Equation 18).

If the right side of the (formula 18) is squared, it is equal to the denominator term of the above (formula 9). That is, the denominator terms in (Expression 14) to (Expression 17) are equal to the square of the magnitude of the modulated wave s (t) at the current time (B).

  As described above, the following can be understood from the descriptions of (A) and (B). That is, in the case of condition W, the logic circuit 70 modulates rot (90 °) s (tp) obtained by rotating the modulated wave s (tp) at the past time by 90 ° and the current time. The inner product of the wave s (t) is divided by the square of the magnitude of the modulated wave s (t) at the current time, and the result obtained by squaring the result is output as the detection signal v (t). To do. In the case of the condition X, rot (90 °) s (tp) obtained by rotating the modulated wave s (tp) at the past time by 90 ° phase and the modulated wave s (t) at the current time. The inner product is divided by the square of the magnitude of the modulated wave s (t) at the current time, and the result obtained by subtracting the square of the divided result from 2 is output as the detection signal v (t). In the case of the condition Y, rot (90 °) s (tp) obtained by rotating the modulated wave s (tp) at the past time by 90 ° and the modulated wave s (t) at the current time. The detection signal v is obtained by dividing the inner product by the square of the magnitude of the modulated wave s (t) at the current time, and taking the absolute value of the result of the division and adding the square to minus 2. Output as (t). In the case of the condition Z, rot (90 °) s (tp) obtained by rotating the modulated wave s (tp) at the past time by 90 ° phase and the modulated wave s (t) at the current time. The detection signal v is obtained by dividing the inner product by the square of the magnitude of the modulated wave s (t) at the current time, taking the absolute value of the result of division, and adding the minus sign to the square. Output as (t).

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) A logic circuit so that the calculation formula of the detection signal v (t) changes based on the phase difference θ between the modulated wave s (tp) at the past time and the modulated wave s (t) at the current time. 70. More specifically, when the condition W, that is, 0 ° ≦ phase difference θ ≦ 90 °, the logic circuit 70 rotates rot (90 °) by 90 ° phase rotation of the modulated wave s (tp) at the past time. By dividing the inner product of s (tp) and the modulated wave s (t) at the current time by the square of the magnitude of the modulated wave s (t) at the current time, and square the result of the division What is obtained is output as a detection signal v (t). When the condition X, that is, 90 ° <phase difference θ ≦ 180 °, the logic circuit 70 rotates the modulated wave s (tp) at the past time by rot (90 °) s (t−) by 90 °. p) and the inner product of the modulated wave s (t) at the current time is divided by the square of the magnitude of the modulated wave s (t) at the current time, and the squared result of the division is subtracted from 2. Is obtained as a detection signal v (t). When the condition Y, that is, −180 ° <phase difference θ <−90 °, the logic circuit 70 rotates the modulated wave s (tp) at the past time by rot (90 °) s (90 °). The inner product of tp) and the modulated wave s (t) at the current time is divided by the square of the magnitude of the modulated wave s (t) at the current time, and the absolute value of the result of the division is squared. Then, the signal obtained by adding to minus 2 is output as the detection signal v (t). When the condition Z, that is, −90 ° ≦ phase difference θ <0 °, the logic circuit 70 rotates rot (90 °) s (t) obtained by rotating the modulated wave s (tp) at the past time by 90 °. -P) and the inner product of the modulated wave s (t) at the current time divided by the square of the magnitude of the modulated wave s (t) at the current time, and squared as the absolute value of the result of the division What is obtained by attaching a minus sign to is output as a detection signal v (t). In this way, by changing the calculation formula of the detection signal v (t) output in accordance with the phase difference θ, the detection signal v (t) becomes a unique value with respect to the phase difference θ. Therefore, for example, even if the detection signal v (t) is affected by noise, the determination circuit 80 can accurately determine the signal level of the detection signal v (t) even if there is an influence of noise or the like. it can. Further, the detection signal v (t) becomes a continuous value with respect to the change in the phase difference θ. For this reason, even if there is an influence of noise, the determination circuit 80 can easily determine the signal level of the detection signal v (t). Furthermore, as shown in (Equation 8) and (Equation 14) to (Equation 17), since the term of sin is squared, as shown in FIG. 3, the detection signal v (t) has a phase difference θ. It changes linearly over the entire range. In particular, when the phase difference θ is around ± 90 °, the detection signal v (t) changes more linearly than in the case where the sin term is not squared, so that noise is present in the detection signal v (t). Even if included, the determination circuit 80 can easily determine the signal level of the detection signal v (t).

  (2) The positive / negative of the inner product of the modulated wave s (kp) at the past time and the modulated wave s (k) at the current time, and the modulated wave s (kp) at the past time by 90 ° phase rotation The phase difference θ between the modulated wave s (k−p) at the past time and the modulated wave s (k) at the current time is calculated from the positive / negative of the inner product of the generated wave and the modulated wave s (k) at the current time. The logic circuit 70 is assembled so that the calculation formula of the detection signal v (t) changes based on the phase difference θ. That is, the phase difference can be obtained with a simple circuit configuration called an inner product arithmetic circuit.

  (3) The logic circuit 70 acquires a modulated wave every time p. In other words, the modulated wave acquired by the logic circuit 70 at the past time k-p is acquired immediately before the modulated wave acquired at the current time k. The logic circuit 70 performs processing using the modulation wave acquired immediately before the modulation wave acquired at the current time k. For this reason, when obtaining the detection signal v (t), the modulation wave (data) processed in the logic circuit 70 is less than in other cases. For example, when the logic circuit 70 performs processing using the modulation wave acquired two times before the modulation wave acquired at the current time k, the logic circuit 70 includes the modulation acquired at the current time k. Since the previous modulated wave is input, it is necessary to build a circuit in the logic circuit 70 that temporarily stops the processing of the modulated wave. From this, the logic circuit 70 performs processing using the modulation wave acquired immediately before the modulation wave acquired at the current time k, so that the load on the logic circuit 70 can be suppressed. .

  (4) The logic circuit 70 is a digital circuit that processes digital signals. For this reason, the logic circuit 70 can easily increase the number of bits of data to be processed, and as a result, the accuracy of the detection signal to be output can be increased.

In addition, you may change the said embodiment as follows.
In the above embodiment, the logic circuit 70 determines whether the phase difference θ corresponds to the condition W to the condition Z, and changes the calculation formula of the detection signal v (t) to be output based on the determination. However, it does not have to be changed. For example, the calculation formula of the detection signal v (t) is fixed to the formula of the condition W. Even in such a configuration, when the phase difference θ is around ± 90 °, the detection signal v (t) changes more linearly than when the sin term is not squared. Even if the noise is included in t), the determination circuit 80 can easily determine the signal level of the detection signal v (t).

  In the above embodiment, the logic circuit 70 outputs the detection signal v (t) that squares the sin term, but is not limited to the one that squares the sin term. For example, the power may be N (N is an integer). Even when configured in this manner, the same effects as those of the above-described embodiment can be obtained.

  In the above embodiment, in any of the conditions W to Z, the logic circuit 70 uses the magnitude of the modulated wave s (t) at the current time as the denominator of the detection signal v (t), that is, the division value. However, it may be the square of the magnitude of the modulated wave s (tp) at the past time. Even when configured in this manner, the same effects as those of the above-described embodiment can be obtained. Further, it may be a product of the magnitude of the modulated wave s (t) at the current time and the magnitude of the modulated wave s (tp) at the past time. In this case, for example, the denominator term of the detection signal v (t) under the condition W is expressed by the following (Equation 19).

From the relationship of (Expression 6-2) and (Expression 19), for example, the detection signal v (t) of the condition W and the condition Z is expressed by the following (Expression 20).

As shown in (Expression 20), the detection signal v (t) is represented only by the frequency component. In other words, in the (Equation 20), a term indicating an amplitude that changes under the influence of noise is excluded. Therefore, the determination circuit 80 can determine the signal level of the detection signal v (t) that is not easily affected by noise. For this reason, the determination circuit 80 is less likely to make an error in determining the signal level. Further, when the denominator term of the absolute value of the detection signal v (t) under the condition W is (Expression 18), the calculation of the square root required in (Expression 19) becomes unnecessary. Thereby, the detection signal v (t) can be obtained more easily. Although only the detection signal v (t) of the condition W is shown, the detection signal v (t) of the condition X, the condition Y, and the condition Z can also be applied.

  In the above embodiment, the logic circuit 70 acquires the modulated wave every time p. However, for example, the logic circuit 70 may acquire the modulated wave every time n different from the time p. Even in this case, the same effect as the effect (1) of the above embodiment can be obtained. Even in this case, if the time interval (sampling period) at which the logic circuit 70 acquires the modulated wave is set to 90 ° with respect to the previous modulated wave, the logic circuit 70 outputs the signal. The detected signal value is the maximum value or the minimum value. Therefore, the determination circuit 80 can perform more accurate signal level determination.

  In the above embodiment, the first and second A / D converters 61 and 62 may be omitted. In this case, the logic circuit 70 is a logic circuit that processes an analog signal. Even in this case, the same effect as the effect (1) of the above embodiment can be obtained.

  In the above-described embodiment, the relationship is described in which the first time is the past time (kp) and the second time is the current time k, but this relationship may be reversed. In this case, when the modulated wave s (k) at the current time k is rotated by −90 °, the same effect as that of the above embodiment can be obtained.

-The formula shown in the above embodiment may be changed to a different form as long as the solution is found equivalently.
In the above embodiment, the modulated wave at the past time is rotated by 90 °. However, the phase is not necessarily limited to 90 °.

  In the above embodiment, the detection signal v (t) is changed according to the four types of conditions. However, the present invention is not limited to this, and the types of conditions may be appropriately increased or decreased. Further, the condition determination formula and the calculation formula of the detection signal v (t) may be appropriately changed.

DESCRIPTION OF SYMBOLS 1 ... FSK demodulator, 10 ... Antenna, 20 ... Local oscillator, 30 ... Phaser, 41 ... 1st mixer, 42 ... 2nd mixer, 51 ... 1st low pass filter (LPF), 52 ... 1st 2 low-pass filters (LPF), 61... First analog-digital converter (A / D converter), 62... Second analog-digital converter (A / D converter), 70.

Claims (8)

An in-phase component and a quadrature component of an FSK-modulated modulated wave are input and included in the modulated wave through a comparison between a logic circuit that generates a detection signal based on both components and the detection signal and a signal level determination threshold value. An FSK demodulator comprising a decision circuit for demodulating
The logic circuit calculates an inner product of a modulated wave at a second time different from the first time and a modulated wave at the first time by rotating the modulated wave at a first time by a predetermined amount of phase and the modulated wave at a second time different from the first time. Divided by the square of the magnitude of the modulation wave, the square of the magnitude of the modulated wave at the second time, or the product of the magnitude of the modulated wave at the first time and the second time. An FSK demodulator that generates a detection signal by multiplying the result of division by a positive integer of 2 or more . The FSK demodulator according to claim 1, wherein
The logic circuit uses the phase difference so that the detection signal has a unique value with respect to the phase difference between the modulated wave at the first time and the modulated wave at the second time different from the first time. An FSK demodulator that changes a calculation formula for generating the detection signal based on the FSK demodulator. The FSK demodulator according to claim 2,
When the phase difference is not less than 0 ° and not more than 90 °, the calculation formula indicates that the modulation wave at the first time is rotated by a predetermined amount of phase and the modulation wave at the second time. The inner product is divided by the division value, and the divided result is raised to a positive integer power of 2 or more ,
If the phase difference is greater than 90 ° and less than or equal to 180 °, the inner product of the modulated wave at the second time and the modulated wave at the second time obtained by rotating the modulated wave at the first time by a predetermined amount, Dividing by the division value, and subtracting the result of division by a positive integer power of 2 or more from 2.
If the phase difference is greater than −180 ° and less than −90 °, the inner product of the modulated wave at the first time and the modulated wave at the second time is obtained by rotating the modulated wave at the first time by a predetermined amount. , Dividing by the division value, taking the absolute value of the result of division and adding a positive integer greater than or equal to 2 to minus 2,
When the phase difference is not less than −90 ° and less than 0 °, the inner product of the modulation wave at the first time and the modulation wave at the second time is obtained by calculating the inner product of the modulation wave at the second time and the modulation wave at the second time. An FSK demodulator that divides by a division value, adds the absolute value of the result of division, and adds a minus sign to a positive integer of 2 or more . The FSK demodulator according to claim 3,
The FSK demodulator, wherein the positive integer power of 2 or more is a square. The FSK demodulator according to claim 3 or 4,
The logic circuit includes positive and negative signs of inner products of the modulated wave at the first time and the modulated wave at the second time, and the second modulated wave at the first time rotated by 90 ° and the second An FSK demodulator that determines a phase difference between the modulated wave at the first time and the modulated wave at the second time based on the sign of the inner product with the modulated wave at the time. In the FSK demodulator according to any one of claims 1 to 5,
The logic circuit acquires FSK at the first and second times so that a phase difference between the modulated wave at the first time and the modulated wave at the second time is 90 °. Demodulator. In the FSK demodulator according to any one of claims 1 to 6,
The FSK demodulator, wherein the logic circuit obtains the detection signal using a modulation wave acquired immediately before the modulation wave at the second time as the modulation wave at the first time. The FSK demodulator according to any one of claims 1 to 7,
The logic circuit is a digital circuit for processing a digital signal,
An analog-to-digital converter that converts in-phase and quadrature components of a modulated wave that is an analog signal into a digital signal
The analog-digital converter is an FSK demodulator that inputs an in-phase component and a quadrature component of a modulated wave converted into a digital signal to the logic circuit.