JPH0799514A - Fs modulator-demodulator - Google Patents

Abstract

PURPOSE:To relieve the distortion of a bit time by changing the oscillation frequency of a voltage signal in response to the phase difference of both frequencies by a predetermined filter means. CONSTITUTION:A phase comparator 5 outputs a voltage signal corresponding to a phase difference between a selection frequency fr0 and a reference frequency f0 to a LPF 6 and its output is applied to a voltage controlled oscillator 8. When the level of transmission data is changed from 0 to 1, since the voltage signal corresponding to the level change is not applied to the voltage controlled oscillator 8, a pass band of a band pass filter 10 and a received frequency are yet unchanged. Since the LPF 6 has a predetermined time constant till the voltage signal corresponding to a change in the transmission data reaches the oscillator 8, a predetermined time delay is produced. Thus, even when the level of the transmission data changes from 0 to 1, a frequency change in the band pass filter 10 and a transmission line is moderated and the difference between the frequency change and the transmission time becomes very small, resulting that distortion in a bit time is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FS modulator / demodulator which can be used, for example, for data transmission of a remote monitoring device.

[0002]

2. Description of the Related Art In a general remote monitoring device, a remote controlled station and a control station are connected via a communication line, and both data terminal devices are connected to each other.
The modulator / demodulator has a modulator that modulates transmission data into an analog signal suitable for a communication line at the time of transmission and sends the analog signal, and a demodulator having a demodulator that demodulates an analog signal from the communication line into digital data at the time of reception.

Generally, an analog signal can be expressed by three kinds of parameters such as frequency, phase and amplitude. As one method for modulating transmission data, a frequency shift keying method (FSK) is used in which the frequency of a carrier wave is changed and modulated. : Frequenc
y shift keying).

FIG. 8 shows a conventional modulation device (hereinafter, referred to as "FSC") that uses a frequency shift keying method (hereinafter, also referred to as FS modulation).
(A FS modulator) is shown. This FS
Modulator has a frequency generated by the oscillator 1 respectively dividing in two dividers 2,3 to 1 / m _o, 1 / m _1,
The two divided frequencies are supplied to the frequency switching circuit 4. The frequency switching circuit 4 selects one frequency corresponding to the value (0, 1) of the transmission data represented by "0" and "1",
The selected frequency is input to the bandpass filter 15. The bandpass filter 15 is composed of a high-order filter for removing unnecessary band noise outside the transmission band, and FS-modulates the carrier wave at the frequency F ₀ or F ₁ that has passed through the bandpass filter 5.

In the FS modulation, the frequency of the carrier wave is instantly switched in correspondence with 0 or 1 of the data, but the bandpass filter and the transmission line have the characteristic that the transmission time changes with the frequency. For this reason, the bit time of the data changes due to the difference in transmission time, the rate of occurrence of distortion in the bit time increases, and a problem occurs in which data errors increase.

Further, as the order of the bandpass filter increases, the difference in individual characteristics increases. Therefore, since the error rate changes depending on the combination of the transmitting side and the receiving side, in order to reduce the error rate, select the combination of bandpass filters used on the transmitting side and the receiving side,
Or it was necessary to make fine adjustments.

As described above, in the conventional FS modulator, there is a problem that a data error occurs due to a change in transmission time of a transmission line corresponding to a change in frequency, or it is necessary to select a bandpass filter combination or perform fine adjustment. there were.

FIG. 9 shows a conventional demodulation device for demodulating a signal modulated by FS modulation (hereinafter referred to as FS demodulation device).
2 shows a schematic configuration of. This FS demodulation device removes noise in an unnecessary band outside the transmission band from a received signal of the frequency F ₀ or F ₁ of FS modulation by a band pass filter 22 composed of a high-order filter, and this band pass filter 22 Is output to the phase comparator 23. Then, the phase comparator 23 compares the phases of the output of the bandpass filter 22 and the output of the voltage controlled oscillator 33, and a voltage signal corresponding to this phase difference is generated. This voltage signal is sent to the low pass filter 27, smoothed, and sent to the voltage controlled oscillator 33 as a control voltage. A pulse signal having a frequency corresponding to the control voltage is generated from the voltage control oscillator 33, is sent to the phase comparator 23, and the above is repeated, and finally the pulse signal of the voltage control oscillator 33 is generated. Frequency is bandpass filter 2
It becomes the same as the frequency of the output of 2. At this time, the output of the low-pass filter 27 has a value corresponding to the frequency of the output of the band-pass filter 22, that is, the frequency of the carrier wave.
The output of the low-pass filter 27 is used as a reference voltage and voltage comparator 3
5, the data "0" and "1" are demodulated. The pass band characteristic of the low pass filter is shown in FIG.
As shown in, the characteristics are such that the frequency F ₀ or F ₁ of the FS modulation is not significantly attenuated.

In such a conventional demodulator, when the received data changes from "0" to "1" or from "1" to "0", that is, the frequency of FS modulation is from F ₀ to F.
_When it changes from ₁ or F ₁ to F ₀ , the amplitude level of the output signal of the bandpass filter 22 becomes low due to the difference in the transmission time in the transmission side bandpass filter and the transmission line, which corresponds to the frequency change, and The frequency of the output signal of the bandpass filter 22 may fluctuate due to the influence of noise or the like having a frequency in the passband of the pass filter 22. At this time, the voltage controlled oscillator 33
When it tries to lock, it takes time to return to a steady state (for example, when F ₀ is changed to F ₁ and F _{1 is} blocked), the data demodulated by the voltage comparator 35 is erroneous. There was a problem of becoming.

The present invention has been made in consideration of the above circumstances, and a first object thereof is to provide an FS modulator and a demodulator capable of preventing data errors as much as possible.

[0011]

An FS modulator according to a first aspect of the present invention comprises a reference frequency generating means for generating a reference frequency and a reference frequency generated by the reference frequency generating means divided by a plurality of frequency division values. Frequency dividing means for generating a plurality of frequencies having different frequencies, a frequency switching means for selecting a frequency corresponding to the value of transmission data from the plurality of frequencies generated by the frequency dividing means, and a frequency switching means for selecting the frequency. And a phase comparison means for detecting a phase difference between the frequency and the reference frequency and outputting a voltage signal corresponding to the phase difference, and a phase transition means having a transit transient characteristic in which the transmission time changes according to the frequency. Filter means through which the voltage signal passes, and the voltage signal passed through the filter means is applied, the oscillation frequency changes in accordance with the applied voltage, and this oscillation frequency is used as the reference frequency. A voltage controlled oscillation means for outputting to the serial phase comparing means, characterized in that and an FS signal output means for generating the FS modulated wave for transmission based on the oscillation frequency of the voltage controlled oscillation means.

The first aspect of the FS demodulator according to the second invention
In this mode, the first filter means that has a single-peaked pass characteristic in which the pass center frequency changes according to the operation clock and that receives the FS modulated wave signal, and the pulse signal with the oscillation frequency according to the control voltage are provided. Voltage-controlled oscillation means for outputting, frequency-dividing means for dividing the output pulse signal of the voltage-controlled oscillation means,
Phase comparison means for comparing the phase of the output signal of the first filter means and the output signal of the frequency divider and outputting a voltage signal according to the phase difference, and smoothing the output voltage of this phase comparison means, A second filter means for outputting to the voltage controlled oscillator means as a control voltage; and a voltage comparator means for demodulating the received data by comparing the output voltage of the second filter means with a reference voltage. The first filter means uses the output pulse signal of the voltage controlled oscillating means as an operation clock, and the second filter means has a frequency f _D or less corresponding to the transit time difference T ₁ of the FS modulation frequencies F ₀ and F _{1 on} the transmission line. corresponding to the data transmitted with the pass without attenuating the frequency signal frequency f _t and the highest sensitivity (<f _D), the predetermined frequency signal from the frequency f _D to F ₀ or F ₁ level Characterized in that it has a pass characteristic which attenuates.

The second aspect of the FS demodulation device according to the second invention
In this mode, the first filter means that has a single-peaked pass characteristic in which the pass center frequency changes according to the operation clock and that receives the FS modulated wave signal, and the pulse signal with the oscillation frequency according to the control voltage are provided. Voltage-controlled oscillation means for outputting, frequency-dividing means for dividing the output pulse signal of the voltage-controlled oscillation means,
Phase comparison means for comparing the phase of the output signal of the first filter means and the output signal of the frequency divider and outputting a voltage signal according to the phase difference, and smoothing the output voltage of this phase comparison means, Second filter means for outputting to the voltage controlled oscillation means as a control voltage, third filter means for smoothing the output voltage of the phase comparison means, and comparison of the output voltage of the third filter means with a reference voltage. Voltage comparison means for demodulating received data by
Filter means uses the output pulse signal of the voltage controlled oscillator means as an operation clock, and the second filter means uses FS.
A frequency signal equal to or lower than the frequency f _D corresponding to the transmission time difference T ₁ of the transmission paths of the modulation frequencies F ₀ and F ₁ is allowed to pass without being attenuated, and the frequency signal from the frequency f _D to F ₀ or F ₁ is set to a predetermined level. The third filter is a low-pass filter having a pass characteristic of attenuating and having the highest sensitivity at a frequency f _t corresponding to data transmission.

[0014]

According to the FS modulator of the first aspect of the present invention, the reference frequency generated by the reference frequency generating means is divided by the frequency dividing means into a plurality of frequencies corresponding to the number of values (0, 1, etc.) of the transmission data. To be done. A frequency corresponding to the value of the transmission data is selected by the frequency switching means, and the selected frequency is given to the phase comparison means. When the phase comparison means detects the phase difference between the frequency from the frequency switching means and the reference frequency from the voltage controlled oscillation means, it outputs a voltage signal corresponding to the phase difference to the voltage controlled oscillation means via the signal path. In the voltage controlled oscillation means, the oscillation frequency is changed by the voltage signal, and as a result, the oscillation frequency of the voltage control means is stabilized by the frequency from the frequency switching means.

When the frequency selected by the frequency switching means changes in accordance with the value of the transmission data, the voltage signal is generated from the phase comparing means so that the phase difference between the two signals disappears.
As a result, the oscillation frequency of the voltage controlled oscillation means is stabilized by the frequency from the frequency switching means. The stabilized oscillation frequency is converted into an FS signal by the FS signal output means and then input to, for example, a bandpass filter.

As described above, since the voltage signal corresponding to the phase difference between the two frequencies is passed through the filter means having a predetermined passage transient characteristic and then input to the voltage controlled oscillation means to change the oscillation frequency, the FS signal output means. The frequency change of the FS signal output from the device becomes gradual, and the bit time distortion is reduced.

According to the first aspect of the FS demodulator of the second invention, the first filter for receiving the received FS modulated signal changes the pass center frequency with the output of the voltage controlled oscillation means as an operation clock. It has the characteristic of passing through the second
Filter has the highest sensitivity at a frequency f _t, the frequency f _D
Does not attenuate frequency signals up to. This makes it possible to prevent data errors during demodulation as much as possible even if the received data changes.

According to the second aspect of the FS demodulating device of the second invention, the first clock for receiving the received FS modulated signal has a single peak in which the passing center frequency changes with the output of the voltage controlled oscillation means as the operating clock. The second filter passes the frequency signals up to the frequency f _D without attenuating, and the third filter has the highest sensitivity at the frequency f _t . This makes it possible to prevent data errors during demodulation as much as possible even when the received data changes.

[0019]

FIG. 1 shows the configuration of an embodiment of the FS modulator according to the first invention. The FS modulator of this embodiment includes a reference frequency oscillator 1, frequency dividers 2 and 3, and a frequency switching circuit 4.
1, a phase comparator 5, a low pass filter 6, a voltage controlled oscillator 8, a frequency divider 9, and a band pass filter 10.

The reference frequency fr oscillated by the reference frequency oscillator 1 composed of a crystal oscillator is 1 / m by the two frequency dividers 2 and 3.
Each of ₀ and 1 / m _{1 is} divided, and the two divided frequencies are input to the frequency switching circuit 4. Frequency switching circuit 4
Is provided with transmission data of "0" and "1", and when the provided data is "0", the output fr of one frequency divider 2 is output.
_{When 0} is selected and the given data is “1”, the output fr ₁ of the other frequency divider 3 is selected. This frequency switching circuit 4
The output terminal of is connected to one input terminal of the phase comparator 5. The phase comparator 5 indicates the selected frequency (fr ₀ or fr ₁ ) of the frequency switching circuit 4 and the oscillation frequency f ₀ or f _{1 of the} voltage controlled oscillator 8 (the oscillation frequency given from the voltage controlled oscillator 8 to the phase comparator 5). (Referred to as a reference frequency), and outputs a voltage signal according to the phase difference between the selection frequency and the reference frequency. The voltage signal generated by the phase comparator 5 is applied to the voltage controlled oscillator 8 through the low pass filter 6. The voltage controlled oscillator 8 is an oscillator whose oscillation frequency changes according to the applied voltage, and the oscillation frequency is initially set near the selected frequency. The oscillation frequency of the voltage controlled oscillator 8 is given to the phase comparator 5 as a reference frequency, and the same oscillation frequency is given to the frequency divider 9. Divide the oscillation frequency of the voltage controlled oscillator 8 with the frequency divider 9 to 1 / N
The frequency divided by is input to the bandpass filter 10,
The output of the bandpass filter 10 is used as an FS modulated wave for transmission. The bandpass filter 10 has a single-peak characteristic with a low filter order, and the pass band changes depending on the operation clock. Specifically, the bandpass filter 10
Is a switched capacitor system, the oscillation frequency of the voltage controlled oscillator 8 is given as an operation clock, and the frequency of 1 / N of the operation clock is used as the pass frequency.

Next, the operation of this embodiment configured as described above will be described.

In the FS modulator of this embodiment, the reference frequency fr from the reference frequency oscillator 1 is divided by the two frequency dividers 2 and 3, and the frequency fr corresponding to "0" or "1" of the transmission data is obtained. ₀ and fr ₁ are generated and the reference frequency is sent from the voltage controlled oscillator 8 to the phase comparator 5.

When the transmission data is given to the frequency switching circuit 4, the frequencies fr ₀ and fr ₁ corresponding to “0” and “1” of the transmission data are selected by the frequency switching circuit 4 and given to the phase comparator 5. .

In the case of transmission data "0", the frequency fr ₀
Is the selected frequency. In the phase comparator 5, the phases of the selected frequency fr ₀ and the reference frequency f ₀ are compared to detect the phase difference, and the voltage signal corresponding to the detected phase difference is output to the low pass filter. The voltage signal passes through the low pass filter 6 and is applied to the voltage controlled oscillator 8.
The voltage controlled oscillator 8 changes the oscillation frequency according to the applied voltage corresponding to the phase difference. When the selected frequency fr ₀ and the reference frequency f ₀ match and there is no phase difference between them, the applied voltage becomes 0, and the oscillation frequency f of the voltage controlled oscillator 8 becomes
₀ is stabilized at the selected frequency fr ₀ . By setting the selected frequency fr ₀ and the reference frequency f ₀ before stabilization to values that are close to each other to some extent, the phase difference becomes a frequency difference, and by matching the phases, the frequencies also match.

The oscillation frequency f ₀ of the voltage controlled oscillator 8 is given to the frequency divider 9 and the bandpass filter 10. The frequency divider 9 divides the oscillation frequency f ₀ into 1 / N to generate a square wave. The frequency-divided square wave of frequency f ₁₀ is applied to bandpass filter 10.

In the switched capacitor type band pass filter 10, the relationship between the pass band and the operating clock is 1: N.
Therefore, the frequency f ₁₀ divided into 1 / N by the frequency divider 9 passes. The harmonic components of the square wave obtained by the frequency divider 9 when passing through the bandpass filter 10 are removed,
An FS modulated wave F _{0 of the} carrier wave is generated.

On the other hand, when the transmission data supplied to the frequency switching circuit 4 changes from "0" to "1", the selected frequency in the frequency switching circuit 4 is immediately switched from fr ₀ to fr ₁ and the data "1" is output. The selected frequency fr ₁ corresponding to is supplied to the phase comparator 5. At this time, the voltage controlled oscillator 8 oscillates at the reference frequency f ₀ which has been stabilized at the selection frequency fr ₀ . As a result, in the phase comparator 5 to which the reference frequency f ₀ is input, the selected frequency f
A voltage signal corresponding to the phase difference between r ₀ and the reference frequency f ₀ is generated.

Then, by the same operation as in the above case, the oscillation frequency f ₁ of the voltage controlled oscillator 8 becomes the selected frequency f _1.
It is stabilized to r ₁ and the same frequency, band-pass filter 1
Passband of 0 is changed to correspond to the frequency f _1, the frequency obtained by dividing the oscillation frequency f ₁ to 1 / N is outputted to the transmission path is converted to FS modulated wave of a carrier to remove the harmonics.

Here, when the transmission data changes from "0" to "1", the voltage signal corresponding to the data change is not applied to the voltage controlled oscillator 8, so that the pass band of the band pass filter 10 and The input frequency has not changed yet. In addition, since the low-pass filter 6 has a constant time constant until the voltage signal generated corresponding to the change of the transmission data “0” or “1” reaches the voltage controlled oscillator 8, a constant time delay occurs. .

As a result, the transmission data is "0" to "1".
Even if it changes to, the frequency change in the bandpass filter 10 and the transmission path becomes gentle, the difference in the transmission time with respect to the frequency change becomes extremely small, and the bit time distortion becomes small.

In the present embodiment, the difference in transmission time in the transmission path (bandpass filter 10 and transmission path) of the transmission signal due to the difference between the frequencies F ₀ and F ₁ is T ₁ , and the data transmission speed is v (bit / bit / sec), the time constant T of the low pass filter 6 is set to a value in the range of T ₀ <T <1 / v. As a result, it is possible to reduce the distortion of the bit time due to the difference in transmission time with respect to the frequency change, and it is possible to prevent the data error due to the FS modulation as much as possible.

In the present embodiment in which the low-pass filter 6 set to the time constant as described above is provided, the transmission data is "0".
When changing from “1” to “1”, the oscillation frequency of the voltage controlled oscillator 8 changes from the frequency f ₀ to the frequency f ₁ due to the change dominated by the pass transient characteristics of the low pass filter 6. This means that, as mentioned above,
This means that there are few transients at the time of switching, which makes it difficult for the transmission signal to be affected by the distortion generated on the transmission path.

As described above, according to this embodiment, it is possible to generate a carrier wave in which the carrier wave of the transmission signal is less likely to be distorted in the bit time due to the difference in the transmission time with respect to the frequency change, and to reduce the data error when the transmission signal is received. Yes, the reliability of the data can be improved. Moreover, since the modulation is performed while comparing the reference frequency and the reference frequency, the frequency accuracy and stability of the carrier can be set to high values.

Further, the low-pass filter 6, the voltage-controlled oscillator 8 and the band-pass filter 10 can be constituted by a logic circuit, and the voltage-controlled oscillator 8 and the band-pass filter 10 can be integrated into a circuit. Since 6 can realize the function by the CR filter, the device can be realized with a simple configuration.

By changing the division ratio of the reference frequency,
Since the frequency of the carrier wave can be changed, it is possible to support multiple channels with the same circuit component.

Since the bandpass filter 10 for removing harmonics uses the switched capacitor type, it is possible to use a filter having a single-peak characteristic and a small order. As a result, it is not necessary to select the filter to be used or to finely adjust the filter to be used depending on the combination of the transmitting side and the receiving side, because the difference in individual filter characteristics is smaller than that of the high-order filter.

The configuration of the first embodiment of the FS demodulator according to the second invention is shown in FIG. The FS demodulator of this embodiment has a bandpass filter 21, a phase comparator 23, a lowpass filter 24, a voltage controlled oscillator 31, and a frequency divider 32.
It has and. The bandpass filter 21 has a single-peak characteristic with a low filter order, and its passband changes depending on the operation clock (output pulse of the voltage controlled oscillator 31). Specifically, the bandpass filter 21 is configured by a switched capacitor method, and has a frequency of 1 / N of the operation clock (frequency division ratio of the frequency divider 25) as a center pass frequency. The phase comparator 23 compares the phase of the output of the bandpass filter 21 with the signal obtained by dividing the output pulse of the voltage controlled oscillator 31 into 1 / N by the frequency divider 32, and outputs a voltage signal corresponding to this phase difference. Occur. The low-pass filter 24 smoothes the output signal of the phase comparator 23, and its pass band characteristic is as shown in FIG. That is, the frequency depending on the data transmission rate is f _t (=
Data transmission rate (bits / sec) / 2) Letting f _D be the frequency due to the difference in passage time of the transmission signals of the modulation frequencies F ₀ and F ₁ when passing through the bandpass filter and the transmission path on the modulator side, A signal whose frequency is less than f _D (> f _t ) is passed through without being attenuated, sensitivity is improved at f _t (for example, 3 dB), and a signal of a frequency from f _D to F ₀ or F _{1 is} attenuated by, for example, 6 dB. It was made.
Since the frequency when the transmission data changes is f _t ,
The low-pass filter 24 can detect a change in transmission data sensitively.

The voltage controlled oscillator 31 is a low pass filter 2
A pulse signal having a frequency corresponding to the output voltage of 4 is generated.
The voltage comparator 35 compares the output voltage of the low-pass filter 24 with the reference voltage, thereby receiving data "0",
Demodulate to "1".

Next, the operation of this embodiment will be described. The output pulse of the voltage controlled oscillator 31 is sent to the frequency divider 32, and 1 /
It is divided into N and sent to the phase comparator 23. The output pulse of the voltage controlled oscillator 31 is also sent to the bandpass filter 21 as an operation clock. At this time, the bandpass filter 21 has a passband characteristic corresponding to the operation clock, and the signal of the frequency F ₀ or F ₁ which is FS-modulated corresponding to the transmission data “0” or “1” is the bandpass filter. When input to 21, the signal of the frequency matching the pass band is taken out. Now, assume that the transmission data is “0”, that is, the frequency of the transmission signal is F ₀ , and the frequency of the output pulse of the voltage controlled oscillator 31 is close to N · F ₀ . Then, the data signal of frequency F ₀ passes through the bandpass filter 21 and is sent to the phase comparator 23.
Then, the phase of this data signal is compared with the output pulse of the frequency divider 32 in the phase comparator 23, and a voltage signal corresponding to the phase difference is sent to the low pass filter 24. This voltage signal is smoothed by the low pass filter 24 and sent to the voltage controlled oscillator 31 as a voltage control signal. Then, a pulse signal having a frequency corresponding to this voltage control signal is generated from the voltage controlled oscillator 31. The voltage control signal also changes when the phase difference between the output of the bandpass filter 21 and the output of the frequency divider 32 disappears, that is, when the frequency of the output pulse of the voltage controlled oscillator 31 becomes f ₀ (= N · F ₀ ). Without, the frequency of the output pulse of the voltage controlled oscillator 31 is stabilized at N · F ₀ . Then, the output of the low-pass filter 24 is compared with the reference voltage value in the voltage comparator 35, and the received transmission data is demodulated to "0".

In such a case, the bandpass filter 21
It is assumed that the transmission data input to is changed from "0" to "1". At this time, the frequency of the transmission data input to the bandpass filter 21 is F ₁ , but the frequency of the output pulse of the voltage controlled oscillator 24 is N · F ₀ , so the passband of the bandpass filter 21 matches F ₀ . It remains as it is. Therefore, although the transmission data of frequency F ₁ is attenuated by the bandpass filter 21, it is sent to the phase comparator 23. Then, the phase comparator 23 compares the phase with the output pulse of the frequency divider 32, and a voltage signal corresponding to the phase difference is sent to the low-pass filter 24. On the other hand, the low-pass filter 24 is set to have the highest sensitivity at f _t as shown in FIG. 6 and attenuates the signal from the frequency f _D to F ₀ or F _1. Sensitively detect the difference in the transit time of the modulation frequency,
The frequency of the output pulse of the voltage controlled oscillator 31 is f ₀ (= N
Generate a control voltage from F ₀ ) to f ₁ (= N · F ₁ ). Then, the oscillation frequency is changed based on the control voltage, and the output pulse is output to the bandpass filter 21.
To the phase comparator 23 via the frequency divider 32.

The operation clock is set to the band pass filter 2
When 1 is received, the center frequency of passage is changed to F ₁ . Then, the output amplitude of the bandpass filter 21 increases more than before. Then, the phases are compared in the phase comparator 23, the above is repeated, and finally the oscillation frequency of the voltage controlled oscillator 31 becomes NF ₁ . When the transmission data changes in this way, the bandpass filter 21
The change of the pass center frequency of can be made almost equal to the difference between the pass times of the modulation frequencies F ₀ and F ₁ by the pass characteristic of the low pass filter 24. Further, at that time, since the pass characteristic of the band pass filter 21 is unimodal, noise can be reduced, and further, the low pass filter 24.
Thus, it is possible to sensitively detect a change in transmission data. This makes it possible to eliminate data errors during demodulation as much as possible.

Next, FIG. 3 shows the configuration of a second embodiment of the demodulation device according to the second invention. The demodulation device of this embodiment is shown in FIG.
In the demodulator of the first embodiment shown in FIG. 3, low pass filters 25 and 26 are provided instead of the low pass filter 24. The low-pass filter 25 is the phase comparator 23.
The voltage signal output from the circuit is smoothed and sent to the voltage controlled oscillator 31 as a control voltage. Also low pass filter 2
Reference numeral 6 smoothes the output voltage of the phase comparator 23 and sends it to the voltage comparator 35.

The low pass filter 25 has the pass band characteristic shown in FIG. That is, a signal having a frequency equal to or lower than f _D is passed through without being attenuated, and f _D to F ₀
Alternatively, the frequency signal up to F _{1 is} attenuated by 6 dB and passed. As a result, the frequency signal corresponding to the difference T ₁ between the passing times of the modulation frequencies F ₀ and F ₁ is passed without being significantly attenuated. Therefore, when the transmission data changes, the passing center frequency of the bandpass filter 21 changes. Changes to about T ₁ , noise is removed, and the phase comparator 23, the low-pass filter 25, the voltage-controlled oscillator 3
1 and a PLL circuit (a phase
Locked loop circuit) will operate stably.

The low-pass filter 26 is shown in FIG.
It has the pass band characteristic shown in. That is, without attenuating the frequency signal of up to f _t, f _t, for example 3d
B sensitivity is improved. As a result, it is possible to detect a change in transmission data sensitively and to eliminate data errors during demodulation as much as possible.

As can be seen from the above description, the low-pass filter 24 shown in FIG. 2 has the combined characteristics of the low-pass filters 25 and 26 shown in FIG.

Next, the configuration of the third embodiment of the demodulation device according to the second invention is shown in FIG. The demodulation device of this embodiment is shown in FIG.
In the demodulator of the first embodiment shown in FIG.
8, a control voltage generator 29, and a changeover switch 30 are newly provided. The amplitude detector 28 detects the amplitude of the output of the bandpass filter 21 and outputs a changeover command signal to the changeover switch 30 when the amplitude exceeds a predetermined value. In the control voltage generator 29, the oscillation frequency of the voltage controlled oscillator 31 is from f ₀ (= N · F ₀ ) to f ₁ (= N · F ₁ ).
Then, for example, a control voltage signal of a triangular wave that changes from f ₁ to f ₀ is generated. The changeover switch 30 is normally
The voltage controlled oscillator 31 is connected to the control voltage generator 29, and when the switching command signal from the amplitude detector 28 is received, the voltage controlled oscillator 31 is connected to the low pass filter 24.

The demodulator of this embodiment uses the FS of the received signal.
1 / N of frequency of modulation and frequency of voltage controlled oscillator 31
When the frequencies are distant from each other, a control voltage is generated from the control voltage generator 29 and sent to the voltage controlled oscillator 31, the oscillation frequency is changed to change the pass frequency of the bandpass filter 21, and the FS for reception is changed. By extracting the modulated frequency signal, the received FS modulated frequency signal cannot pass through the bandpass filter 21.
Is not working. And FS of reception
When the modulated frequency signal is allowed to pass through the bandpass filter 21 and the phase comparison operation is enabled, the amplitude detector 28 issues a changeover command to the changeover switch 30 to switch the connection. The PLL circuit operates as described above. It goes without saying that this embodiment also has the same effect as that of the first embodiment.

Next, the configuration of the fourth embodiment of the demodulation device according to the second invention is shown in FIG. The demodulation device of this embodiment is shown in FIG.
In the demodulation device of the second embodiment shown in FIG. 5, the amplitude detector 28 and the control voltage generator 29 are the same as in the case of the third embodiment.
And a changeover switch 30 are newly provided. The change-over switch 30 normally connects the control voltage generator and the voltage-controlled oscillator 31, and connects the low-pass filter 25 and the voltage-controlled oscillator 31 when the changeover command is received from the amplitude detector 28. This fourth embodiment is also the third
It goes without saying that the same effect as that of the above embodiment can be obtained.

In the first to fourth embodiments, a switched capacitor type filter is used as the bandpass filter 21, so that the bandpass filter 21 has a single peak characteristic and a low order, and a high order. Compared to the case of using a filter, the characteristics of each filter are smaller, and it becomes unnecessary to select the filter to be used by the combination of the transmitting side and the receiving side or to finely adjust it.

[0050]

As described above, according to the present invention, data errors can be prevented as much as possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a modulator according to the first invention.

FIG. 2 is a block diagram showing a configuration of a first embodiment of a demodulation device according to the second invention.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the demodulation device according to the second invention.

FIG. 4 is a block diagram showing the configuration of a third embodiment of the demodulation device according to the second invention.

FIG. 5 is a block diagram showing the configuration of a fourth embodiment of the demodulation device according to the second invention.

FIG. 6 is a graph showing pass characteristics of the low-pass filter according to the first embodiment shown in FIG.

FIG. 7 is a graph showing the pass characteristic of the low pass filter according to the second embodiment shown in FIG.

FIG. 8 is a block diagram showing a configuration of a conventional modulator.

FIG. 9 is a block diagram showing the configuration of a conventional demodulation device.

FIG. 10 is a graph showing pass characteristics of a low-pass filter according to a conventional demodulation device.

[Explanation of symbols]

 1 reference frequency oscillator 2, 3 frequency divider 4 frequency switching circuit 5 phase comparator 6 low pass filter 8 voltage controlled oscillator 9 frequency divider 10 band pass filter 21 band pass filter 23 phase comparator 24, 25, 26 low pass filter 28 amplitude Detector 29 Control voltage generator 30 Changeover switch 31 Voltage controlled oscillator 32 Frequency divider 35 Voltage comparator

Claims (5)

[Claims] 1. A reference frequency generating unit for generating a reference frequency, and a frequency dividing unit for dividing the reference frequency generated by the reference frequency generating unit by a plurality of frequency dividing values to generate a plurality of different frequencies. , A frequency switching means for selecting a frequency corresponding to a value of transmission data from a plurality of frequencies generated by the frequency dividing means, and a phase difference between the frequency selected by the frequency switching means and a reference frequency is detected. A phase comparison means for outputting a voltage signal according to the phase difference; a filter means having a passage transient characteristic in which the transmission time changes according to the frequency and a voltage signal output from the phase comparison means passing therethrough; A voltage-controlled oscillator that applies the passed voltage signal, changes the oscillation frequency in accordance with the applied voltage, and outputs the oscillation frequency as the reference frequency to the phase comparator. FS modulation apparatus characterized by comprising a, and the FS signal output means for generating the FS modulated wave for transmission based on the oscillation frequency of the voltage controlled oscillation means. 2. The FS signal output means is provided with a frequency divider for dividing the oscillation frequency of the voltage controlled oscillation means into 1 / N, and the oscillation frequency of the voltage controlled oscillation means is given as an operation clock to obtain a filter frequency / The clock frequency ratio is 1 / N
The FS modulator according to claim 1, wherein the FS modulator is a switched capacitor type band pass filter. 3. A first filter means having a unimodal pass characteristic in which a pass center frequency changes in accordance with an operation clock and receiving an FS modulated wave signal, and a pulse signal having an oscillation frequency in accordance with a control voltage. To compare the phases of the output signal of the first filter means and the output signal of the frequency divider. , A phase comparison means for outputting a voltage signal according to the phase difference, a second filter means for smoothing the output voltage of the phase comparison means and outputting it as a control voltage to the voltage controlled oscillation means, and the second filter Voltage comparing means for demodulating received data by comparing the output voltage of the means with a reference voltage, the first filter means using the output pulse signal of the voltage controlled oscillating means as an operating clock. Said second filter means FS modulation frequency F _0, the frequency corresponding to the data transmitted with the pass without attenuating the frequencies below the signal frequency f _D, corresponding to the transit time difference T ₁ of the transmission path F ₁ f _t ( <F _D ) maximizes sensitivity and frequency f
An FS demodulator having a pass characteristic for attenuating a frequency signal from _D to F ₀ or F ₁ to a predetermined level. 4. A first filter means having a unimodal pass characteristic in which a pass center frequency changes according to an operation clock and receiving an FS modulated wave signal, and a pulse signal having an oscillation frequency according to a control voltage. To compare the phases of the output signal of the first filter means and the output signal of the frequency divider. A phase comparison means for outputting a voltage signal according to the phase difference, a second filter means for smoothing the output voltage of the phase comparison means and outputting it as a control voltage to the voltage controlled oscillation means, and a phase comparison means for the phase comparison means. A first filter means for smoothing the output voltage; and a voltage comparison means for demodulating the received data by comparing the output voltage of the third filter means with a reference voltage. The means uses the output pulse signal of the voltage controlled oscillating means as an operation clock, and the second filter means uses a frequency signal of a frequency f _D or less corresponding to the passage time difference T ₁ of the FS modulation frequencies F ₀ and F _{1 on} the transmission path. The third filter has a pass characteristic that allows the signals of frequencies f _D to F ₀ or F ₁ to be attenuated by a predetermined level while allowing the signals to pass without being attenuated. The third filter has the highest sensitivity at the frequency f _t corresponding to data transmission. An FS demodulator, which is a low-pass filter having the same. 5. An amplitude detection means for detecting the amplitude level of the output of the first filter means and outputting a switching command signal when the amplitude level is a predetermined value or more, a control voltage generation means for generating a control voltage signal, In this case, the input terminal of the voltage controlled oscillation means and the output terminal of the control voltage generation means are connected, and when the switching command signal is received, the connection is switched to connect the input terminal of the voltage controlled oscillation means to the second filter. The FS demodulator according to claim 3 or 4, wherein the FS demodulator is connected to an output terminal of the means.