JP5767170B2 - 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 via a terminal. From the received modulated wave, an in-phase component (I (t)) and a quadrature component (Q (t)) are extracted 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 generates a detection signal by adding the in-phase component (I (t)) and the quadrature component (Q (t)) instead of the above-described phase difference detection / frequency detector. It has been known. According to this demodulator, the determination circuit determines Hi if the signal level of the detection signal exceeds the threshold, and determines Lo if it does not exceed the threshold. Usually, the threshold value for determining the signal level is the median value of the detection signal value at the past time and the detection signal value at the current time. 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 through 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 indicated by the one-dot chain line in FIG. 5, when the phase difference θ is ± 90 °, the phase difference is determined to be one value from the value of the detection signal. For this reason, the determination circuit can perform positive / negative determination correctly. On the other hand, when the phase difference θ is other than ± 90 °, the phase difference θ cannot be set to one value from the value of the detection signal v (t). For example, when the phase difference θ is 30 ° and 150 °, both sin θ = 0.5 and the value of the detection signal v (t) is the same. When the phase difference θ is not determined, the determination circuit may make a positive / negative determination error.

  Therefore, there is an FSK demodulator that employs a logic circuit that changes the calculation formula of the detection signal v (t) based on the phase difference between the modulated wave at the current time and the modulated wave at the past time. This logic circuit includes an inner product (conditional expression A) of a modulated wave s (tp) at a past time and a modulated wave s (t) at a current time, and a 90 ° phase rotation of the modulated wave at the past time. The inner product (conditional expression B) of the rot (90 °) s (tp) and the modulated wave s (t) at the current time is stored. Conditional expression A and conditional expression B are shown by the following (Expression 9) and (Expression 10).

Then, the logic circuit changes the calculation formula for obtaining the detection signal v (t) based on the positive / negative of the conditional expression A and the positive / negative of the conditional expression B as shown in the following (Expression 11) to (Expression 13). Let

The determination result of the phase difference θ that can be obtained based on the positive / negative of the conditional expression A and the positive / negative of the conditional expression B is as follows.

(Condition O) When conditional expression A ≧ 0 and conditional expression B ≧ 0, 0 ° ≦ phase difference θ ≦ 90 °.
(Condition P) When conditional expression A <0 and conditional expression B ≧ 0, 90 ° <phase difference θ ≦ 180 °.
(Condition Q) When conditional expression A <0 and conditional expression B <0, −180 ° <phase difference θ <−90 °.

(Condition R) When conditional expression A ≧ 0 and conditional expression B <0, −90 ° ≦ phase difference θ <0 °.
From (Equation 11) to (Equation 13), the relationship between the phase difference θ and the detection signal v (t) is represented by a solid line graph in FIG. As indicated by a solid line in FIG. 5, the phase difference is determined to be one value from the value of the detection signal v (t) in the range where the phase difference θ is less than ± 180 °. For this reason, even if the detection signal v (t) has a center frequency offset and the phase difference θ is other than 90 °, the determination circuit is less likely to make a positive / negative determination error.

  However, in the determination circuit, the threshold value for determining the signal level is the median value of the detection signal value at the past time and the detection signal value at the current time. Therefore, for example, when the phase difference between the modulated wave at the past time and the modulated wave at the current time exceeds 180 ° and below −180 °, the positive / negative of the detection signal at the past time and the current The sign of the detection signal at the time is reversed. That is, the determination circuit erroneously determines the signal level.

  The present invention has been made in view of such a situation, and its purpose is to generate an FSK signal that generates a detection signal that is less likely to be erroneously determined whether the phase difference θ is less than ± 180 ° or more than ± 180 °. It is to provide a demodulator.

  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 determination threshold of a signal level, wherein the logic circuit includes the modulated wave at the first time and the first The detected signal has a unique value with respect to the first phase difference from the modulated wave at the second time different from the time, and is different from the modulated wave at the second time and the first and second times. The detection signal is generated based on the first and second phase differences so that the difference between the second phase difference from the modulated wave at the third time and the first phase difference does not exceed 180 °. The calculation formula for And it is required to further.

  In the conventional FSK demodulator, the calculation formula for generating the detection signal based only on the first phase difference is changed regardless of the difference between the first phase difference and the second phase difference. For this reason, for example, even when the first phase difference is 200 °, the logic circuit determines that the phase difference is −160 °, and generates a detection signal using the calculation formula in the case of −160 °. It was. As can be seen from this example, when the second phase difference exceeds 180 ° or falls below −180 ° with respect to the first phase difference, the positive and negative of the detection signal at the second time, The sign of the detection signal at the time was reversed. As a result, the determination circuit erroneously determines the signal level. Since data is normally assigned according to the signal level, the determination circuit takes out erroneous data if the determination of the signal level is incorrect.

  In this regard, according to the configuration, the logic circuit is configured to detect the detection based on the first and second phase differences so that a difference between the second phase difference and the first phase difference does not exceed 180 °. The calculation formula for generating the signal is changed. Thereby, it is possible to suppress erroneous determination of the signal level in the determination circuit.

  According to a second aspect of the present invention, in the FSK demodulator according to the first aspect, the logic circuit has a normal calculation mode and an extended calculation mode having different calculation formulas, and the logic circuit in the normal calculation mode is When the first phase difference is greater than 90 ° and less than or equal to 180 °, and the second phase difference is greater than −180 ° and less than −90 °, the modulated wave at the second time is The inner product of the modulated wave at the first time with the phase rotated by a predetermined amount, the square of the magnitude of the modulated wave at the first time, or the magnitude of the modulated wave at the second time Or a division value that is the product of the magnitudes of the modulated waves at the first time and the second time, and a calculation formula is set by subtracting the result of the division from minus 2. Switch to extended calculation mode When the first phase difference is greater than −180 ° and less than −90 ° and the second phase difference is greater than 90 ° and less than or equal to 180 °, the modulated wave at the second time is A calculation formula is set by dividing the inner product of the phase rotated by a predetermined amount and the modulated wave at the first time by the division value, and subtracting the division result from 2; The logic circuit in the extended calculation mode is configured such that the first phase difference is greater than 90 ° and equal to or less than 180 °, and the second phase difference is greater than −180 ° and −90 °. If it is less than the result, the inner product of the modulated wave at the first time and the modulated wave at the first time is divided by the division value, and the result of the division Set a formula that subtracts 2 from 2. In both cases, when the mode shifts to the normal calculation mode, the first phase difference is greater than −180 ° and less than −90 °, and the second phase difference is greater than 90 ° and less than or equal to 180 °, A calculation obtained by dividing the inner product of the modulation wave at the second time by a predetermined amount of phase rotation and the modulation wave at the first time by the division value and subtracting the division result from minus 2. The gist is to set an equation and shift to the normal calculation mode.

  According to the configuration, even when the second phase difference exceeds 180 ° or less than −180 ° with respect to the first phase difference, the detection signal becomes a unique value with respect to the first phase difference. The detection signal has a continuous value with respect to the change in the first phase difference. Therefore, the determination circuit can easily determine the signal level of the detection signal.

  According to a third aspect of the present invention, in the FSK demodulator according to the first or second aspect, the logic circuit includes positive / negative of an inner product of the first modulated wave and the second modulated wave, The positive / negative of the inner product of the modulated wave rotated by 90 ° and the first modulated wave, the positive / negative of the inner product of the second modulated wave and the third modulated wave, and the third modulated wave The gist of the invention is to determine the first and second phase differences based on the positive / negative of the inner product of the second modulated wave that has been rotated by 90 °.

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 fourth aspect of the present invention, in the FSK demodulator according to any one of the first to third aspects, the logic circuit outputs a modulated wave acquired one sample before the first modulated wave. The gist is to obtain the detection signal using the second modulated wave as a third modulated wave, and the modulated wave acquired one sample before the second modulated wave as the third modulated wave.

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 a fifth aspect of the present invention, in the FSK demodulator according to any one of the first to fourth 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.

  According to the present invention, it is possible to provide an FSK demodulator that generates a detection signal that is less likely to make a determination error, whether the phase difference θ is less than ± 180 ° or more than ± 180 °.

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 the detection signal of this example. 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 having 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 modulates the modulated wave at the current time, the modulated wave at the past time that is one time before the current time, and the modulation at the most past time that is one time before the past time. Based on the sign of the next four inner products calculated from the wave, a detection signal to be described later is output. The four inner products are the inner product (conditional expression A) of the modulated wave at the past time and the modulated wave at the current time, the phase obtained by rotating the phase of the modulated wave at the past time by 90 °, and the modulated wave at the current time. Product (conditional expression B), inner product (conditional expression A ′) of the modulated wave at the past time and the modulated wave at the past time, and the phase of the modulated wave at the past time rotated by 90 ° This refers to the inner product (conditional expression B ′) with the modulated wave at the past time.

  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 past time is k-p, and the major past time acquired one time before the past time is k-2p. Thus, the modulated waves s (k), s (kp), and s (k-2p) at the current time, the past time, and the past time are expressed by the following (Expression 14) to (Expression 16). It is represented by

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 the following (Expression 17), and the modulated wave at the most past time. The inner product of s (k−2p) and the modulated wave s (k−p) at the past time, that is, the conditional expression A ′ is expressed by the following (Expression 18), respectively.

Also, rot (90 °) s (k−p) obtained by rotating the modulated wave s (k−p) at the past time by 90 ° is the following (Equation 19), and the modulated wave s ( rot (90 °) s (k-2p) obtained by rotating the phase of k-2p) by 90 ° is expressed by the following (Equation 20).

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 21). Further, the inner product of rot (90 °) s (k−2p) obtained by rotating the modulated wave s (k−2p) at the past time by 90 ° and the modulated wave s (k−p) at the past time, That is, the conditional expression B ′ is expressed by the following (Expression 22).

The logic circuit 70 has a normal calculation mode and an extended calculation mode, and switches between the two modes based on the sign of the conditional expressions A, B, A ′, and B ′. When the logic circuit 70 is in the normal calculation mode, the logic circuit 70 determines whether the positive / negative of the conditional expressions A, B, A ′, B ′ corresponds to the condition S to the condition V, and is assigned to the corresponding condition. The detection signal v (t) is calculated using the following calculation formula, that is, (Formula 23) to (Formula 27) shown below.

Further, when the logic circuit 70 is in the extended calculation mode, the logic circuit 70 determines whether the positive / negative of the conditional expressions A, B, A ′, B ′ corresponds to the condition W to the condition Z, and assigns them to the corresponding condition. The detected signal v (t) is calculated using the calculated formula, that is, the following (Formula 28) to (Formula 31).

In the normal calculation mode, the logic circuit 70 generates the detection signal v (t) when (Condition T-2) or (Condition U-2) is satisfied, that is, using (Expression 25) or (Expression 27). If this happens, the extended calculation mode is switched. Further, the logic circuit 70 generates the detection signal v (t) using (Expression 28) or (Expression 31) when (Condition W) or (Condition Z) is satisfied in the extended calculation mode. Switch to normal calculation mode.

  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. The signal level determination threshold is the median value of the detection signal value at the past time and the detection signal value at the current time.

<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. Similarly, the positive / negative of the inner product (conditional expression A ′) of the modulated wave s (k−2p) at the past time and the modulated wave s (k−p) at the past time, and the modulated wave s at the past time. From the positive / negative of the inner product (conditional expression B ′) of the (k−2p) phase rotated by 90 ° and the modulated wave s (k−p) at the past time, the modulated wave s (k at the most past time −2p) and the range of the phase difference θ ′ between the modulated wave s (k−p) at the past time can be easily obtained. The determination results of the phase differences θ and θ ′ are as follows.

Determination 1: When conditional expression A ≧ 0 and conditional expression B ≧ 0, 0 ° ≦ phase difference θ ≦ 90 °.
Determination 2: When conditional expression A <0 and conditional expression B ≧ 0, 90 ° <phase difference θ ≦ 180 °.
Judgment 3 ... When conditional expression A <0 and conditional expression B <0, −180 ° <phase difference θ <−90 °.

Determination 4: When conditional expression A ≧ 0 and conditional expression B <0, −90 ° ≦ phase difference θ <0 °.
Determination 5: When conditional expression A ′ ≧ 0 and conditional expression B ′ ≧ 0, 0 ° ≦ phase difference θ ′ ≦ 90 °.
Determination 6: When conditional expression A ′ <0 and conditional expression B ′ ≧ 0, 90 ° <phase difference θ ′ ≦ 180 °.

Determination 7: When conditional expression A ′ <0 and conditional expression B ′ <0, −180 ° <phase difference θ ′ <− 90 °.
Determination 8: When conditional expression A ′ ≧ 0 and conditional expression B ′ <0, −90 ° ≦ phase difference θ ′ <0 °.

Accordingly, the determination results of the phase differences θ and θ ′ under each condition are as follows.
(Condition S) When conditional expression A ≧ 0 and conditional expression B ≧ 0, 0 ° ≦ phase difference θ ≦ 90 °.
(Condition T-1) When conditional expression A <0 and conditional expression B ≧ 0 and conditional expression A ′ <0 and conditional expression B ′ <0 are not satisfied, 90 ° <phase difference θ ≦ 180 °, − 90 ° ≦ phase difference θ ′ ≦ 180 °.

  (Condition T-2) When the conditional expression A <0 and the conditional expression B ≧ 0 and the conditional expression A ′ <0 and the conditional expression B ′ <0 are satisfied, 90 ° <phase difference θ ≦ 180 °, −180 ° <phase difference θ ′ <− 90 °.

  (Condition U-1) When conditional expression A <0 and conditional expression B <0 and conditional expression A ′ <0 and conditional expression B ′ ≧ 0 are not satisfied, −180 ° <phase difference θ <−90 ° , −180 ° <phase difference θ ′ ≦ 90 °.

  (Condition U-2) When the conditional expression A <0 and the conditional expression B <0 and the conditional expression A ′ <0 and the conditional expression B ′ ≧ 0 are satisfied, −180 ° <phase difference θ <−90 °, 90 ° <phase difference θ ′ ≦ 180 °.

(Condition V) When conditional expression A ≧ 0 and conditional expression B <0, −90 ° ≦ phase difference θ <0 °.
(Condition W) When conditional expression A <0 and conditional expression B ≧ 0 and conditional expression A ′ <0 and conditional expression B ′ <0 are satisfied, 90 ° <phase difference θ ≦ 180 °, −180 ° < Phase difference θ ′ <− 90 °.

(Condition X) When conditional expression A <0 and conditional expression B ≧ 0 and conditional expression A ′ <0 and conditional expression B ′ ≧ 0 are satisfied, 90 ° <phase difference θ ≦ 180 °, 90 ° <position Phase difference θ ′ ≦ 180 °.
(Condition Y) When the conditional expression A <0 and the conditional expression B <0 and the conditional expression A ′ <0 and the conditional expression B ′ <0 are satisfied, −180 ° <phase difference θ <−90 °, −180 ° <phase difference θ ′ <− 90 °.

(Condition Z) When Conditional Expression A <0 and Conditional Expression B <0 and Conditional Expression A ′ <0 and Conditional Expression B ′ ≧ 0 are satisfied, −180 ° <Phase Difference θ <−90 °, 90 ° <Phase difference θ ′ ≦ 180 °.
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, the determination circuit 80 can accurately determine the signal level of the detection signal v (t). Further, the difference between the phase difference θ and the phase difference θ ′ is less than 180 °, and the detection signal v (t) has a continuous value with respect to the change in the phase difference θ. In particular, even when the phase difference θ exceeds 180 ° and below −180 °, the detection signal v (t) becomes a continuous value, and when the phase difference θ exceeds 180 °, the detected value is larger than the previous value. Also, when it falls below -180 °, it decreases from the previous value. The detection signal v (t) in this example is positive when the phase difference θ exceeds 0 °, and negative when it falls below. That is, the positive / negative of the detection signal v (t) does not change when the phase difference θ is 180 ° and −180 °. Therefore, the determination circuit 80 can easily determine the signal level of the detection signal v (t).

  The above (Formula 21) is equal to the above (Formula 6-1). In other words, the numerator terms of (Expression 23) to (Expression 31) 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).

  Further, the magnitude of the modulated wave s (t) at the current time is expressed by the following (Equation 32).

If the right side of the (formula 32) is squared, it is equal to the denominator terms of the above (formula 23) to (formula 31). That is, the denominator terms of (Expression 23) to (Expression 31) 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 normal calculation mode, the logic circuit 70 of the present example rotates rot (90 °) obtained by rotating the modulated wave s (tp) at the past time by 90 ° in the case of the condition S and the condition V. The detected signal v (t) is obtained 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. ). In the case of the condition T-1, 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. Is obtained by dividing the inner product with the square of the magnitude of the modulated wave s (t) at the current time, and subtracting the whole from 2 to output as a detection signal v (t). In the case of the condition T-2, 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. Is obtained by dividing the inner product by the square of the magnitude of the modulated wave s (t) at the current time, and subtracting the whole from minus 2 is output as the detection signal v (t). After that, the process proceeds to the extended calculation mode. In the case of the condition U-1, 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. Is obtained by dividing the inner product by the square of the magnitude of the modulated wave s (t) at the current time, and subtracting the whole from minus 2 is output as the detection signal v (t). In the case of the condition U-2, 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. Is obtained by dividing the inner product with the square of the magnitude of the modulated wave s (t) at the current time, and subtracting the whole from 2 to output as a detection signal v (t). After that, the process proceeds to the extended calculation mode.

  Further, in the extended calculation mode, the logic circuit 70 of the present example, in the case of the condition W, rot (90 °) s (t−t) obtained by rotating the modulated wave s (tp) at the past time by 90 ° p) obtained by dividing the inner product of 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 subtracting the whole from 2 It outputs as a detection signal v (t). After that, the normal calculation mode is entered. 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 whole from minus 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. A product obtained by dividing the inner product by the square of the magnitude of the modulated wave s (t) at the current time and subtracting the whole from 2 is output as the detection signal v (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 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 whole from minus 2 is output as the detection signal v (t). After that, the normal calculation mode is entered.

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) The phase difference θ between the modulated wave s (tp) at the past time and the modulated wave s (t) at the current time, and the modulated wave s (t-2p) at the past time and the past 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 ′ with respect to the modulation wave s (tp) in FIG. Further, the logic circuit 70 is assembled so as to switch between the normal calculation mode and the extended calculation mode based on the phase differences θ and θ ′. By changing the calculation formula of the detection signal v (t) output in accordance with the phase differences θ and θ ′, the detection signal v (t) becomes a unique value with respect to the change in the phase difference θ. Therefore, the determination circuit 80 can accurately determine the signal level of the detection signal v (t). Further, the detection signal v (t) has a continuous value with respect to changes in the phase differences θ and θ ′. In particular, even when the phase difference θ exceeds 180 ° and below −180 °, the detection signal v (t) becomes a continuous value, and when the phase difference θ exceeds 180 °, the detected value is larger than the previous value. Also, when it falls below -180 °, it decreases from the previous value. The detection signal v (t) in this example is positive when the phase difference θ exceeds 0 °, and negative when it falls below. That is, the positive / negative of the detection signal v (t) does not change when the phase difference θ is 180 ° and −180 °. Therefore, the FSK signal can be demodulated even when the phase difference θ exceeds ± 180 °, which has been difficult in the past.

  (2) The logic circuit 70 determines whether the inner product of the modulated wave s (kp) at the past time and the modulated wave s (k) at the current time is positive or negative, and the modulated wave s (kp) at the past time. From the positive / negative of the inner product of the phase wave rotated 90 ° and the modulated wave s (k) at the current time, the modulated wave s (k−p) at the past time and the modulated wave s (k) at the current time Is obtained. Further, the logic circuit 70 determines whether the inner product of the modulated wave s (k−2p) at the past time and the modulated wave s (k−p) at the past time is positive or negative, and the modulated wave s (k (k) at the past time. -2p) is 90 ° phase rotated and the positive / negative of the inner product of the modulated wave s (kp) at the past time, the modulated wave s (k-2p) at the past time and the modulation at the past time A phase difference θ ′ with the wave s (k−p) is obtained. Then, the logic circuit 70 changes the calculation formula of the detection signal v (t) based on the obtained phase differences θ and 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. Further, the modulated wave acquired by the logic circuit 70 at the past time k-2p is acquired two times before the modulated wave acquired at the current time k. The logic circuit 70 performs processing using the modulated wave acquired one and the second before the modulated 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 one and three times before the modulation wave acquired at the current time k, the logic circuit 70 includes the logic circuit 70 at the current time k. Since the modulation wave two before the acquired modulation wave is input, a circuit for temporarily stopping the processing of this modulation wave needs to be incorporated in the logic circuit 70. Thus, the logic circuit 70 can suppress a load on the logic circuit 70.

  (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, in any of the conditions S to Z, the logic circuit 70 determines the denominator of the detection signal v (t), that is, the division value, the magnitude of the modulation wave s (t) at the current time. 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 conditions S and V is expressed by the following (Expression 33).

From the relationship of (Expression 6-2) and (Expression 33), the detection signal v (t) of the condition S and the condition V is expressed by the following (Expression 34).

As shown in (Expression 34), the detection signal v (t) is represented only by the frequency component. In other words, in the (formula 34), 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. Although only the detection signal v (t) of the condition S and the condition V is shown, it can be applied to the detection signal v (t) in any of the conditions S to Z.

  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.

  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 embodiment, the first time is the current time k, the second time is the past time k-p, and the third time is the great past time k-2p. The application of is not limited to this relationship. For example, the past time may be k-2p, and the past time may be k-4p.

-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 10 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 (5)

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 has a unique value for the detected signal with respect to a first phase difference between a modulated wave at a first time and a modulated wave at a second time different from the first time. So that the difference between the second phase difference between the modulated wave at the time 2 and the modulated wave at the third time different from the first and second times does not exceed 180 °. An FSK demodulator that changes a calculation formula for generating the detection signal based on the first and second phase differences. The FSK demodulator according to claim 1, wherein
The logic circuit has a normal calculation mode and an extended calculation mode with different calculation formulas,
When the first phase difference is greater than 90 ° and less than or equal to 180 ° and the second phase difference is greater than −180 ° and less than −90 °, the logic circuit in the normal calculation mode is The inner product of the modulated wave at the first time and the modulated wave at the first time is the square of the magnitude of the modulated wave at the first time, or the first Divide by the square of the magnitude of the modulated wave at time 2 or the division value which is the product of the magnitude of the modulated wave at the first time and the second time, and subtract the result from minus 2. Set the calculated formula and shift to the extended calculation mode,
When the first phase difference is greater than −180 ° and less than −90 °, and the second phase difference is greater than 90 ° and less than or equal to 180 °, the modulated wave at the second time is The inner product of the phase rotated by a predetermined amount and the modulated wave at the first time is divided by the division value, and a calculation formula is set by subtracting the result of division from 2, and the extended calculation mode is set. Is a transition,
When the first phase difference is greater than 90 ° and less than or equal to 180 ° and the second phase difference is greater than −180 ° and less than −90 °, the logic circuit in the extended calculation mode is A calculation formula in which the inner product of the modulated wave at the first time and the modulated wave at the first time is divided by the division value and the result of the division is subtracted from 2 And move to the normal calculation mode,
When the first phase difference is greater than −180 ° and less than −90 °, and the second phase difference is greater than 90 ° and less than or equal to 180 °, the modulated wave at the second time is The inner product of the phase rotated by a predetermined amount and the modulated wave at the first time is divided by the division value, and a calculation formula is set by subtracting the divided result from minus 2. The normal calculation mode FSK demodulator transitioning to The FSK demodulator according to claim 1 or 2,
The logic circuit is positive / negative of an inner product of the first modulated wave and the second modulated wave, and is positive / negative of an inner product of the first modulated wave rotated by a phase of 90 ° and the first modulated wave. , Based on the positive / negative of the inner product of the second modulated wave and the third modulated wave, and the positive / negative of the inner product of the second modulated wave obtained by rotating the third modulated wave by 90 °, An FSK demodulator for determining the first and second phase differences; The FSK demodulator according to any one of claims 1 to 3,
The logic circuit uses the modulation wave acquired one sample before the first modulation wave as the second modulation wave, and uses the modulation wave acquired one sample before the second modulation wave as the third modulation wave. An FSK demodulator for obtaining the detection signal as a wave. In the FSK demodulator according to any one of claims 1 to 4,
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.