JPS59141856A - Fs modulating and demodulating system - Google Patents

Abstract

PURPOSE:To reduce greatly characteristic variance depending on the environmental condition including the humidity, etc. by securing the mutual shifts among three working loops in accordance with the presence or absence of a data transmission request signal and the logical value of the transmission data. CONSTITUTION:The 1st and 2nd working loops function to generate digitally and repetitively the sine waves of frequencies fa and fz corresponding to the 1st and 2nd logical values in a cycle of 0-360 deg.. While the 3rd working loop demodulates and delivers repetitively the received FS modulated signal in the form of the 1st or 2nd logical value in accordance with themodulation frequency fa or fz. Thus the data can be shifted mutually among these three working loops in accordance with the presence or absence of a data transmission request and the logical value of the transmission data.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides for transmitting meter reading data to a telephone line when performing centralized meter reading of various meters installed in each home, business office, etc. from a center using a telephone line or the like. Alternatively, it relates to an FS (frequency shift type) modulation/demodulation method used to extract the take from a telephone line.

This type of modulation/demodulation system is required not only to have stable operation, but also to be inexpensive and mass-producible because it is a general-purpose product that can be installed in many demand locations.

FIG. 1 is a block diagram showing a conventional FS modulation/demodulation system. In the same figure, 101 is a hybrid transformer, 10
2 is a band pass filter (BPF), 103 is an amplifier, 1
04 is an amplitude limiter, 105 is a frequency discriminator, 106 is a waveform shaper, 107 is a low pass filter (LPF), 10
8 is a frequency modulator.

As can be seen in Figure 1, in the conventional FS modified appeal system,
The received signal is transmitted from the transmitting/receiving end T to the hybrid transformer 10.
1, bandpass filter 102, amplifier 103, amplitude limiter 104, frequency discriminator 105, waveform shaper 10
Demodulated reception by 6 etc.

The transmission signal is subjected to FS modulation via the frequency modulator 108, the low-pass filter 107, and the hybrid transformer 101, and then transmitted from the transmitting/receiving end T.

Here, the bandpass filter 102 is for removing noise in the signal transmission path. The amplifier 103 is for amplifying the input signal to an appropriate size. The amplitude limiter 104 is a type of nonlinear amplifier that prevents its output from changing even if the magnitude of the input signal changes, and is a limiter that uses saturation characteristics. The frequency discrimination circuit 105 is a Foster Schiele type (Foster 5
eeley), detuned type (two-tuned circuit type), counter type (digital processing type), ratio detector (ratio de
vector), etc., but a two-tuned circuit type is often used for frequency discrimination of FS waves.

The two-tuned frequency discrimination circuit has a circuit configuration as shown in FIG. In the figure, 201 to 204 are resistors, 205 to 212 are capacitors, and 213'
, 214 are transformers, 215, 216 are chokes, 217 to 224 are diodes, 2
25 is a transistor, 226 is a variable resistor, and 227 is a waveform shaping circuit.

In Figure 2, one of the two tuned circuits has a tuning point on the higher side of the carrier frequency, and the other has a tuning point on the lower side, and rectifier circuits in opposite directions (217~220, 221~
224), a smoothing circuit is connected. The output of the discriminator is then corrected for waveform distortion by a waveform shaping circuit 227 to become a rectangular wave signal, and the waveform shaping circuit is constructed of a Schmitt circuit, a slip-flop, a slicer, or the like.

The above-mentioned two-tuned circuit type frequency discriminator circuit (demodulator) adjusts the linearity of the detector by combining tuning circuits in a Foster Schiele type. Since the linearity of the detector greatly affects the detection efficiency, it is not easy to adjust the tuner due to temperature characteristics, element fluctuations, etc. Furthermore, since an inductance is used, it is completely unsuitable for IC implementation.

Further, the frequency modulator 108 in FIG. 1 receives logic "1" as DC serial data from the data terminal to be transmitted
This is where "0" is subjected to FS modulation and output.The low-pass filter 107 is used to prevent high-frequency modulation distortion contained in the output of the modulator 108 from being transmitted to the line.

The FS modulation method uses Winbridge CR as shown in Figure 3.
Oscillators are often used. In FIG. 3, 301 is an operational amplifier, 302. '303 is analog suikte, 304Fi voltage controlled resistor element, 305-309.3
11 is a resistor, 310 is a variable resistor, 312 to 31
4 are capacitors, and 315 is a diode.

In this oscillator, in order to reduce the distortion factor of the oscillation frequency and the level fluctuation of the amplitude, it is necessary to use capacitors and resistors with high precision and little temperature change. The circuit also requires a sufficient rise time for its oscillating output to reach a stable amplitude level.

The present invention has been made in view of the above-mentioned conventional technical circumstances, and therefore, an object of the present invention is to avoid the use of inductance, high-precision capacitors, resistors, etc., and to solve the problem due to environmental conditions such as humidity. A digital FS modulation/demodulation method that minimizes characteristic fluctuations, is suitable for IC circuits, and is suitable for no-adjustment and mass production.More specifically, it is a half-duplex data transmission method that allows reception during transmission and transmission during reception. The purpose of the present invention is to provide a FS modulation/demodulation method.

In order to achieve the above object, the FS modulation/demodulation method according to the present invention digitally converts a sine wave of frequency fa corresponding to the first logical value of the data to be transmitted into a digital signal, with one cycle of the phase angle from 0° to 360°. a first operation loop that operates to repeatedly generate a sine wave of a frequency fz corresponding to a second logical value of the data, and digitally repeats a sine wave of a frequency fz corresponding to a second logical value taken by the data, with one period from the phase angle O0 to 360 degrees. A second operation loop that operates to generate and receive FS
It consists of a third operation loop that periodically repeats the operation of demodulating the K-tone signal as a second logical value according to whether the modulation frequency is fa or fz, and outputting the demodulated signal as a second logic value. It is possible to switch between each operation loop depending on the presence or absence of a transmission request signal and the logical value of transmission data.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. In the figure, 401 is a hybrid transformer having a line coupling function of receiving an FS reception signal from a line and sending an FS transmission signal to the line side. 402 is a band pass filter (BPF) for removing noise in the transmission path other than the received signal. This is an amplifier that amplifies the 403-digit received signal to a suitable amplitude. 404 reception F
This is a waveform shaping circuit that sufficiently amplifies the SS signal, converts it to a binary value at the zero point level, converts it into an amplitude-independent rectangular wave pulse, and outputs the signal. The operation up to this stage during demodulation is almost the same as that of the conventional FS demodulation method explained in FIG.

By the way, 405 is a digital demodulator that digitally processes and demodulates the input FS signal after waveform shaping and outputs it as received data RD, and is also a digital modulator/demodulator that also performs V modulation as described later. be. In this embodiment, the waveform shaper 106 after frequency discrimination shown in FIG. 1 is not required. 406 is a digital modulator/demodulator 40
The oscillator used to generate a clock, which is the basis of the timing of the operation in step 5, is, for example, a crystal oscillator. 408 is for converting this digital signal into an analog waveform, while the digital modulator 405 outputs a digital signal represented by a multi-bit numerical value as an FS transmission wave when performing modulation operation. D/
It is an A converter.

407 removes high-frequency distortion from the output of the D/A converter 408 and transmits only the specified FS modulated wave to the no-brid transformer 4.
01 to the line.

The modulation/demodulation method of the digital FS modulator/demodulator 405, which is the main part of the present invention, will be explained below.

FIG. 5 is an explanatory diagram showing the operating states and transitions of the half-duplex digital FS modem modulator 405 in FIG. 4. This digital F'S post-modulator has three main operating loops. That is, when the transmission request signal (SR) from a data terminal (not shown) is "1", that is, when there is a transmission request and the transmission data (SD) is 1#, when the transmission request signal (SR) is "1", the logic Value ゛1
A first operation loop (fa generation operation loop) operates to digitally repeatedly generate a sine wave with a frequency fa corresponding to # with one cycle of phase angle from 0° to 360°, and ) is 0'', the second operation operates to digitally repeatedly generate a sine wave with a frequency fz corresponding to the logical value ``O'', with the phase angle from 0° to 360° as one cycle. loop (fz generation operation loop) and transmission request signal (SR) is “0”
The answer is that there is no transmission request and the demodulation state is V? - Demodulation operation loop at a certain time, that is, the received F'S modulated signal is 1'' depending on whether the modulated wave is fa or fz.
3 of the third operation loop (demodulation operation loop) that periodically repeats the operation of demodulating and outputting as 0''.
It is one.

Then, at each phase of 90° and 270° in the first operation loop, that is, the fa generation operation loop, the presence or absence of the data transmission request signal SR is checked, and if there is no data transmission request signal SR, the fa
Transitioning from the generation operation loop to the third operation loop, that is, the demodulation operation loop, performs the demodulation operation, checks the transmission data SD, and changes it from a logical value corresponding to the frequency fa to a logical value corresponding to the frequency fzvC. , the fa generation operation loop shifts to the fz generation operation loop and operates to generate a predetermined sine wave, and even in the fz generation operation loop, data is transmitted at each phase of 90' and 270°. The presence or absence of the request signal SR is checked, and if there is no request signal, the fz generation operation loop shifts to the demodulation operation loop to perform the demodulation operation. When the frequency changes to a logical value corresponding to fa, the fz generation operation loop shifts to the fa generation operation loop and operates to generate a predetermined sine wave, and also in the demodulation operation loop, the 90° and The presence or absence of the data transmission request signal SR is checked at each phase of 270°, and if it is present, the demodulation operation loop shifts to the fa generation operation loop (or fz generation operation loop).

When mutually transitioning between the fa generation operation loop and the fz generation operation loop, in order to ensure phase continuity between the generated wave before the transition and the generated wave after the transition, the phases of both loops are the same. We are planning to make the transition at this point.

By the way, it will be explained why the transmission data SD and the transmission request signal SR are checked at each phase of 90° and 270° in each operation loop.

This digital FS modulation/demodulation method has a waveform as shown in Fig. 6 during modulation (however, the solid line waveform is fz, and the broken line waveform is fz).
a) is expressed by a multi-bit digital value and expressed as D
/A converter 408. This approximate sine waveform is maximally approximated by selecting and adding the required number of bits (therefore, the step width of the stairs) as appropriate. By doing so, there is no need to increase the performance of the low-pass filter 407 added at the subsequent stage. In such digital processing, the magnitude of the numerically constant time width Δt indicates how busy the digital FS modulator/demodulator 405 is. From this point of view, 90
Numerical constant time width Δ at the valley phase point of ° or 270°
Since t is the maximum, it is convenient for the digital FSi demodulator 405 to check the transmission request signal SR1 and the transmission data SD at this time when it is least busy.

In Fig. 6, the vertical axis shows numerical values (digital values) and the horizontal axis shows time.
Since both the wave and fa shown by the broken line have the shape of a periodically repeating sine wave, the starting point of one period is the phase O0, and the ending point is 360°.

Returning to the main topic, for example, when the transmission request signal SR is "1", that is, in the modulated state, the transmission data SD is "1".
'', the operation switches to the fz generation operation loop, and the output of the D/A converter 408 generates a step-like approximate sine wave as shown as fz in FIG. 6.The fz generated at this time At the 90° (or 270°) phase of the wave, if there is no change in the state of the transmission request signal SR1 and the transmission data SD, an approximate sine wave of the ifz wave is sent out.If the transmission request signal SR is 1 ”, send data S
When D; 6rO'', a transition is made from the fz generation operation loop to the fa generation operation loop, and an approximate sine wave of fa is sent out.

During this transition, in order to maintain the continuity of the waveform, fz
If the data change is detected at the 90° (270°) phase point of the generation operation loop, then the data change is detected at the 90° (270°) phase point of the fa generation operation loop.
270°). If the transmission request signal SR is "0", there is no transmission request and the reception operation is performed, so the transition to the demodulation operation loop is made unconditionally. The transition from the fa generation operation loop to the fz generation operation loop is also performed in the same manner as the case from fz to fa.

In the demodulation operation loop, the FS received signal is demodulated using the method shown in FIGS. 7 and 8.

This method will be explained below.

Signal (a) in FIG. 7 shows the output of the waveform shaping circuit 404. The digital FS modulator/demodulator first detects the rising point (first, the 0° phase point) of the signal (A).

From this 00 phase point, the timer function in the modulator/demodulator 405 measures a fixed time tO as shown in (b). There is generally a relationship fa)fz between frequencies fa and fz.

The fixed time to is selected to be slightly shorter than 1/2 f &. In this way, the fixed time t.

By determining , other processing can be executed within this to time. After the fixed time to has elapsed, the modem 40
The counter ■ in 5 is started as shown in (c).

Then, the counter measures the time from that point to the next falling point (180° phase point) of the signal (A).

Simultaneously with the detection of the 180° phase point, the timer function within the modulator/demodulator 405 again measures 10 fixed times. Within this second fixed time tO, the modulator/demodulator 405 calculates the count value accumulated in the counter (i), that is, the first fixed time length t from the time length of 00 to 18000 in the signal (A).
By comparing the count value corresponding to the remaining time after subtracting o with the count value corresponding to fa or the count value corresponding to fz, the incoming signal (a) from 0° to It is determined whether the data corresponding to the period of a half cycle of 180° is fa or fz. According to this result, -1 is added to the counter (2) in the modulation/demodulation device 405 if it is fa, and +1 is added if it is fz.

By the way, this counter (2) has an upper limit and a lower limit for the count value, and is designed to prevent the count value from exceeding the upper limit or below the lower limit. (See how this count looks)
Shown below.

Next, as shown in FIG. 8, the modem 405 determines whether the value of the counter () is above or below the center value between the upper and lower limits of the counter (2). The data "1" and "o" information are restored and output as shown in (e). After the above processing, the counter (2) is reset (FIG. 7). Subsequently, the transmission request signal SR is checked, and if it is 1'', a transition is made from the demodulation operation loop to the modulation operation loop.If it is 0'', the demodulation operation loop is maintained.

The processing described above is shown for the phase range of 00 to 180 degrees of received waves, but the same processing is performed for the phase range of 180 degrees to 360 degrees.

However, in the phase range of 180° to 360°, the rising and falling points are interchanged. Demodulation is performed by continuously performing the above operations every half period of the received wave.

In addition, in FIGS. 7 and 8, e + indicated by a wavy line
Waveforms such as f + gr d represent noise.

According to the present invention, in the demodulation method, it is determined whether the received wave is an fa wave or an fz wave every half cycle, so the number of samplings counted by the counter increases, and reception due to noise is Even if an abnormal phenomenon such as wave cracking occurs, its influence is kept to a minimum range, and signal cracking or the like does not occur in the final demodulated data.

′! In the i: modulation method, by changing the required number of bits (therefore, the step width that takes the same value) to maximize the approximation of the generated sine wave, it is possible to lower the order of the next-stage low-pass filter. . Further, phase distortion can be minimized by checking the transmitted signal at the 90° or 270° phase point of the operating loop, changing the generated frequency, and making the phase of the generated wave continuous when changed.

The digital FS modulation/demodulation method according to the present invention performs demodulation and modulation by using a clock generated by one basic oscillator, and only this oscillator is a stable one, such as a crystal oscillator. As a result, changes in the receiving frequency and modulation frequency can be minimized without using other components with high precision and high stability. At the same time, the adjustment remains unchanged. In addition, by performing modulation digitally, compared to conventional analog methods,
Almost no time is required for the oscillator output to stabilize after issuing a transmission request (SR).

Adopting digital processing methods such as those mentioned above is
This is an extremely practical and effective method when implementing the present invention using a program element such as a bit microcomputer, and satisfies the purpose of the invention.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional modulation/demodulation system, Fig. 2 is a circuit diagram showing a two-tuned frequency discriminator circuit, Fig. 3 is a circuit diagram showing a wine bridge CR oscillator, and Fig. 4 is a circuit diagram showing a frequency discrimination circuit of the two-tuned circuit type. A block diagram showing one embodiment, FIG. 5 is an explanatory diagram showing the operating state and transition status of the digital FS modem 405 in FIG. 4, and FIG. FIG. 7 is an explanatory diagram showing the waveforms of the wave and fz wave, and FIG. 7 is an operational waveform of each part showing the operation of the modulator/demodulator 405 in FIG. 4 to identify whether the incoming signal corresponds to frequency fa or fz. Similarly, FIG. 8 is a waveform diagram showing operation waveforms of each part when the modulator/demodulator 405 performs demodulation operation. Description of symbols 401...Hybrid transformer, 402...Band pass filter, 403...Amplifier, 404...Waveform shaping circuit, 405...Digital FSi demodulator, 406
...Crystal oscillator, 407...Low pass filter, 4
08...D/A converter Fig. 1) ) 707 708 Fig. 2 Fig. 3 Fig. 4

Claims (1)

[Scope of Claims] 1) A half that cannot receive when transmitting and cannot transmit when receiving.
FS (frequency shift type) for data transmission using multiplex method
In the modulation/demodulation method, a sine wave of frequency fa corresponding to the first logical value of the data to be transmitted is transmitted at its phase angle O0.
a first operation loop that operates to digitally repeatedly generate a period from
A second operation loop operates to digitally repeatedly generate the phase angle from 0° to 360° as one cycle, and the received FS modulation signal is processed according to whether the modulation frequency is f'a or fz. and a third operation loop that periodically repeats the operation of demodulating and outputting as the first or second logical value, and checks the presence or absence of a data transmission request signal at a specific phase in the first operation loop. , when there is no data, the first operation loop shifts to the third operation loop to perform demodulation operation;
The operation loop shifts from the operation loop to the second operation loop and operates to generate a predetermined sine wave. In the second operation loop, the presence or absence of a data transmission request signal is checked at that specific phase, and if there is no data transmission request signal, the The second operation loop shifts to the third operation loop to perform one demodulation operation, and if the transmission data is data that takes the first logical value, the second operation loop moves to the third operation loop. It moves to operation loop 1 and operates to generate a predetermined sine wave, and! Also in the third operation loop, the presence or absence of a data transmission request signal is checked in that specific phase, and if there is, the third operation loop shifts to the first or second operation loop. FS modulation/demodulation method characterized by: 2. The FS modulation and demodulation method according to claim 1, wherein the specific phase is 90° or 270°. 3) FS as stated in claim 1 or 2
In the modulation/demodulation method, the received FS modulation signal is converted into a train of rectangular waves with a pulse width corresponding to the modulation frequency and input, and a predetermined fixed time is measured and secured from the rising or falling edge of the rectangular wave. Then, measure the time length from the end of the fixed time to the next falling or rising edge, and check whether the measured value of this time length corresponds to the frequency fa.
Determine whether it corresponds to z at the next fixed time,
The count value of the counter is increased or decreased according to the judgment result, and while repeating the above, when the count value of the counter is above the specified value, it is used as the first logical value, and when it is below, it is demodulated as the second logical value. An FS modulation/demodulation method, characterized in that the third operation loop consists of an operation loop that repeatedly outputs an output.