JPH0117629B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention enables meter reading data to be sent to the telephone line when performing centralized meter reading of various meters installed in each home, business, etc. from a certain center using a telephone line or the like. , or the FS (Frequency Shift) modulation and demodulation method used to extract the data from the telephone line.

This type of modulation/demodulation system is required not only to have stable operation, but also to be inexpensive and mass-producible due to its nature as 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 figure, 101 is a hybrid transformer, 102 is a band pass filter (BPF),
103 is an amplifier, 104 is an amplitude limiter, 105 is a frequency discriminator, 106 is a waveform shaper, 107 is a low pass filter (LPF), and 108 is a frequency modulator.

As seen in FIG. 1, in the conventional FS modem system, the received signal passes from the transmitting/receiving end T through the hybrid transformer 101 and then passes through the bandpass filter 10.
2. The transmitted signal is demodulated and received by the amplifier 103, amplitude limiter 104, frequency discriminator 105, waveform shaper 106, etc., and the transmitted signal is sent to the frequency modulator 108, low-pass filter 107, and hybrid transformer 10.
1 and then FS modulated and transmitted from the transmitting and 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 of Foster Seeley type,
There are detuned types (two-tuned circuit type), counter types (digital processing type), ratio detectors, etc., but two-tuned circuit types are often used for frequency discrimination of FS waves.

The two-tuned frequency discrimination circuit has a circuit configuration as shown in FIG. In the same figure, 201-2
04 is a resistor, 205 to 212 are capacitors, 213 and 214 are transformers, 215 and 216 are respective chokes, and 217
224 is a diode, 225 is a transistor, 226 is a variable resistor, and 227 is a waveform shaping circuit.

In FIG. 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 the rectifier circuits 217 are oriented in opposite directions.
~220, 221~224, smoothing circuits are connected. The output of the discriminator is then corrected for waveform distortion by a waveform shaping circuit 227 to form a rectangular wave signal, and the waveform shaping circuit is constructed of a Schmitt circuit, a flip-flop, a slicer, or the like.

The above two-tuned circuit type frequency discrimination 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 variations in temperature characteristics and elements. Also, since it uses inductance, it is completely unsuitable for IC implementation.

Further, the frequency modulator 108 in FIG. 1 is a part that performs FS modulation on logic "1" and "0" as DC serial data from a data terminal to be transmitted and outputs the same. Furthermore, the low-pass filter 107 is provided to prevent high-frequency modulation distortion contained in the output of the modulator 108 from being transmitted to the line.

A Winbridge CR oscillator as shown in FIG. 3 is often used in the FS modulation method. In FIG. 3, 301 is an operational amplifier, 302 and 303 are analog switches, 304 is a voltage-controlled resistor element, 305 to 309, and 311 are resistors, and 3
10 is a variable resistor, 312 to 314 are each a capacitor, 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. This circuit also requires a certain amount of rise time for its oscillation output to reach a stable amplitude level.

The present invention has been made in view of the above-mentioned conventional technical circumstances, and therefore, it is an object of the present invention to avoid the use of inductance, high-precision capacitors, resistors, etc., and to reduce environmental conditions such as humidity. A digital FS modulation/demodulation method that minimizes characteristic fluctuations due to The objective is to provide an FS modulation/demodulation method for

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 data to be transmitted into a digital signal with a phase angle of 0° to 360° as one period. a first operation loop that operates to repeatedly generate data, and a frequency fz that corresponds to a second logical value taken by the data.
A second operating loop operates to digitally repeatedly generate a sine wave with a phase angle of 0° to 360° as one cycle, and a second operating loop that operates to digitally repeatedly generate a sine wave with a phase angle of 0° to 360°, and a received FS modulated signal with a modulation frequency of fa or fz. and a third operation loop that periodically repeats the operation of demodulating and outputting it as the first or second logical value depending on the presence or absence of the data transmission request signal and the logical value of the transmission data. It is possible to move between each operation loop.

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 same figure, 401 is the FS from the line.
This is a hybrid transformer that has a line coupling function that receives received signals and sends FS transmission signals to the line side. 402 is a band pass filter (BPF) for removing noise in the transmission path other than the received signal. 403 is an amplifier that amplifies the received signal to an appropriate amplitude. 404 sufficiently amplifies the received FS signal, and at the zero point level 2
This is a waveform shaping circuit that converts it into a value, converts it into an amplitude-independent rectangular wave pulse, and outputs it. The operation up to this stage during demodulation is the same as the conventional one explained in Figure 1.
It is almost the same as that of the FS demodulation method.

By the way, 405 is input after being waveform shaped.
This is a digital demodulator that demodulates the FS signal by digitally processing it and outputs it as received data RD, and also performs modulation as described later. In this embodiment, the waveform shaper 106 after frequency discrimination shown in FIG. 1 is not required. Reference numeral 406 denotes a resonator, such as a crystal resonator, used to generate a clock that is the basis of the timing of the operation of the digital modulator/demodulator 405. 408 is a digital modulator/demodulator 40
5 outputs a digital signal expressed as a multi-bit numerical value as an FS transmission wave when performing modulation operation, while a D/A converter converts this digital signal into an analog waveform. It is. A low-pass filter 407 removes high-frequency distortion from the output of the D/A converter 408 and sends only a specified FS modulated wave to the line via the hybrid transformer 401.

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 state of the digital FS modulator/demodulator 405 using the half-duplex system in FIG. 4 and its transition state. This digital FS modem has three main operation loops. That is, when the transmission request signal (SR) from a data terminal (not shown) is "1", that is, when the transmission request is in the modulated state, and the transmission data (SD) is "1", Logical value “1”
The first special loop (fa generation operation loop) operates to digitally repeatedly generate a sine wave with a frequency fa corresponding to the phase angle from 0° to 360° as one cycle, and the transmission data (SD ) is “0”, the second controller operates to digitally and repeatedly generate a sine wave with a frequency fz corresponding to the logical value “0”, with one cycle of phase angle from 0° to 360°. The operation loop (fz generation operation loop) and the demodulation operation loop when the transmission request signal (SR) is “0”, that is, when there is no transmission request and is in the demodulation state, that is, the received FS modulation signal is converted into its modulated wave. A third operation loop (demodulation operation loop) periodically repeats the operation of demodulating and outputting the signal as "1" or "0" depending on whether it is fa or fz.

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, the fa generation operation loop shifts to the third operation loop, that is, the demodulation operation loop, and demodulation operation is performed. When is changing from a logical value corresponding to frequency fa to a logical value corresponding to frequency fz, the fa generation operation loop shifts to the fz generation operation loop and operates to generate a predetermined sine wave, and fz generation In the operation loop, the presence or absence of the data transmission request signal SR is checked at each phase of 90° and 270°, and if there is no data transmission request signal SR, the corresponding signal is detected.
When the fz generation operation loop shifts to the demodulation operation loop and demodulation operation is performed, the transmission data SD is checked and it changes from a logical value corresponding to the frequency fz to a logical value corresponding to the frequency fa. moves from the fz generation operation loop to the fa generation operation loop and operates to generate a predetermined sine wave, and also in the demodulation operation loop, the data transmission request signal SR is generated at each phase of 90° and 270°. The presence or absence of the signal is checked, and if it is present, the demodulation operation loop shifts to the fa generation operation loop (or the fz generation operation loop).

For mutual transition 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 phase of both loops must be The migration is performed at the same point in time.

By the way, we will explain 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 uses the sixth
A waveform as shown in the figure (where the solid line waveform indicates fz and the broken line waveform indicates fa) is expressed as a multi-bit digital value and is passed to the D/A converter 408. This approximate sinusoidal waveform is maximally approximated by appropriately selecting and determining the required number of bits (and therefore the step width of the staircase). By doing this, 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 is determined by the digital FS modulator/demodulator 4.
This represents the busyness of operations in 05.
From this point of view, since the numerical constant time interval Δt at each phase point of 90° or 270° is maximum,
The transmission request signal is sent at this time when the operation is not the busiest.
Digital checking of SR and transmission data SD
This is convenient for the FS modem 405.

In Figure 6, the vertical axis shows numerical values (digital values) and the horizontal axis shows time, but both the fz wave shown by the solid line and the fa shown by the broken line are sine waves that repeat periodically. Since it is in the form of a wave, the starting point of one cycle is 0° and the ending point is 360°.

Returning to the main topic, for example, the transmission request signal SR is “1”
In other words, in the modulation state, if the transmission data SD is "1", the operation goes to the fz generation operation loop, and the output of the D/A converter 408 is as shown as fz in FIG. Generates a step-like approximate sine wave. At the 90° (or 270°) phase of the fz wave generated at this time, the transmission request signal
Checks the status of SR and transmission data SD, and if there is no change, sends out an approximate sine wave of the fz wave as is.
If the transmission request signal SR is “1” and the transmission data
When SD is “0”, fa is output from the fz generation operation loop.
Transition to the generation operation loop and send out an approximate sine wave of fa. During this transition, in order to maintain the continuity of the waveform, if a data change is detected at the 90° (270°) phase point of the fz generation operation loop, it is Make the transition to the point in time. 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 as described above.
This is done in the same way as 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 of signal A (first, the point at 0° phase). From this 0° phase point, the timer function in the modulator/demodulator 405 measures a fixed time t ₀ as shown in (b). There is generally a relationship of fa>fz between frequencies fa and fz. The fixed time t ₀ is selected to be slightly shorter than 1/2fa. By determining the fixed time t ₀ in this manner, other processing can be executed within this t ₀ time. After the fixed time t ₀ has elapsed, the counter 1 in the modulator/demodulator 405 is started as shown in FIG.

Then, the counter 1 measures the time from that point to the next falling point (180° phase point) of the signal A.
Simultaneously with the 180° phase point detection, the modem 405 again
The fixed time of t ₀ is measured using the timer function inside. Within this second fixed time t _{0 ,} the modulator/demodulator 405 uses the count value accumulated in counter 1, that is, the remaining time obtained by subtracting the first fixed time length t ₀ from the time length from 0° to 180° in signal A. By comparing the corresponding count value with the count value corresponding to fa or the count value corresponding to fz, it is determined that the corresponding count value corresponds to the period of half a cycle from 0° to 180° of the incoming signal A. Determine whether the data is fa or fz. According to this result, the modem 40
If it is fa, add -1 to counter 2 in 5, and if it is fz, add +1.

By the way, this counter 2 is provided with 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. The state of this counting is shown in D.

Next, as shown in FIG. 8, the modem 405 determines whether the value of the counter 2 is above or below the center value L between the upper and lower limits of the counter 2. The "1" and "0" information of the received data is restored and output as shown in E. After the above processing, the counter 1 is reset (FIG. 7C). Next, check the transmission request signal SR, and it is “1”.
If so, a transition is made from the demodulation operation loop to the modulation operation loop. If it is "0", the demodulation operation loop continues.

The processing described above is shown for the phase range of 0° to 180° of the received wave, but the processing is similarly performed for the phase range of 180° to 360°. however,
In the phase range of 180° to 360°, the rising and falling points are interchanged. Modulation is performed by continuously performing the above operations every half period of the received wave.

In addition, in FIGS. 7 and 8, waveforms such as e, f, g, and d shown by broken lines 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 period cycle, so the number of samplings for counting by the counter 2 increases, and the reception due to noise Even if abnormal phenomena such as wave breaking occur,
This effect is kept to a minimum range, and signal cracking does not occur in the final demodulated data.

In addition, in the 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 low-pass filter in the next stage. can. Furthermore, 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 made of a stable device, such as a crystal oscillator. By doing so, 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. Furthermore, by performing modulation digitally, compared to conventional analog systems, almost no time is required for the oscillator output to stabilize after issuing a transmission request (SR).

Furthermore, using the digital processing method as described above is an extremely practical and effective method when implementing the present invention using a program element such as a 4-bit microcomputer, and satisfies the purpose of the invention.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional modulation/demodulation system.
FIG. 2 is a circuit diagram showing a two-tuned frequency discrimination circuit, FIG. 3 is a circuit diagram showing a Winbridge CR oscillator, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. FIG. 6 is an explanatory diagram showing the operating state of the digital FS modem 405 and its transition situation. FIG. 6 is an explanatory diagram showing the waveforms of the fa wave and fz wave output during modulation by the modulation and demodulation method according to the present invention. FIG. 4 is an operation waveform diagram of each part showing the operation of the modem 405 in FIG. 4 to identify whether the incoming signal corresponds to frequency fa or fz, and FIG. FIG. 4 is a waveform diagram showing operation waveforms of each part when performing the operation. Code explanation, 401...hybrid transformer,
402...Band pass filter, 403...Amplifier, 404...Waveform shaping circuit, 405...Digital FS modulator/demodulator, 406...Crystal oscillator, 407
...Low pass filter, 408...D/A converter.

Claims (1)

[Claims] 1. An FS (frequency shift type) modulation/demodulation method for data transmission using a half-duplex method in which reception is possible during transmission and transmission is not possible during reception, and the first logic adopted by the data to be transmitted is The first circuit operates to digitally repeatedly generate a sine wave with a frequency fa corresponding to the value, with one period ranging from its phase angle of 0° to 360°.
and a second operation that operates to digitally repeatedly generate a sine wave with a frequency fz corresponding to the second logical value of the data, with a phase angle of 0° to 360° as one cycle. Loop and check if the received FS modulated signal is whose modulation frequency is fa
fz, and a third operation loop that periodically repeats the operation of demodulating and outputting it as the first or second logical value depending on whether the data is The presence or absence of a transmission request signal is checked, and if there is no transmission request signal, the first operation loop shifts to the third operation loop to perform a demodulation operation, and even if there is a transmission request signal, the transmission data is data that takes the second logical value. At this time, the first operation loop shifts to the second operation loop and operates to generate a predetermined sine wave, and in the second operation loop, the presence or absence of a data transmission request signal is checked at that specific phase. , when there is no, the second operation loop moves to the third operation loop and demodulation operation is performed; The loop shifts to the first operation loop 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 at that specific phase.
1. An FS modulation/demodulation method, characterized in that, when the FS modulation/demodulation method is present, a transition is made from the third operation loop to the first or second operation loop. 2. The FS modulation and demodulation method according to claim 1, wherein the specific phase is 90° or 270°. 3. Claims 1 or 2
In the FS modulation/demodulation method, the received FS modulation signal is converted into a sequence of rectangular waves with a pulse width corresponding to the modulation frequency, and a predetermined fixed time is measured from the rising or falling edge of the rectangular wave. Measure the time length from the end of the fixed time to the next falling or rising edge, and determine whether the measured value of this time length corresponds to the frequency fa or fz at the next fixed time. The count value of a certain counter is increased or decreased according to the determination result, and when the count value of the counter is greater than or equal to a certain specific value, it is set as the first logical value. FS modulation/demodulation method, characterized in that the third operation loop consists of an operation loop that repeatedly outputs a demodulated output as a second logical value.