JPS589616B2 - Fukuchiyouhoushiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multiplex modulation and demodulation method, in which one carrier wave is modulated with first and second modulation signals, and width modulation is performed alternately with the first or second modulation signal at every zero cross. It is an object of the present invention to provide a multiplex modulation and demodulation method which is capable of obtaining a modulated wave and demodulating it with a simple circuit configuration, and which is particularly suitable for recording and reproducing the modulated wave.

Conventionally, for example, a method of modulating the high-potential period and low-potential period of the output rectangular wave of an astable multivibrator with two different modulation signals was published on November 28, 1964 as the "Cross-by-cross modulation/demodulation method." It was published in the materials of the TV Society's 3rd Recording Research Committee.

In other words, the conventional method described above modulates the output rectangular wave of an astable multivibrator that alternately has first or second information at each zero cross, and when demodulating this, a general demodulator cannot be used. First, a cello-crossing point of the modulated wave is detected to create a double frequency signal, and demodulation is performed by calculating the sum and difference of this double frequency signal and the modulated wave, respectively.

Therefore, the conventional method described above must always use, as its demodulator, a constant pulse width pulse generator for creating the frequency-doubled signal and a matrix circuit for taking the sum and difference, and the circuit configuration is relatively high. The disadvantage is that it is complicated and expensive.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a block system diagram of one embodiment of the system of the present invention.

In the figure, reference numeral 1 denotes a matrix circuit, which is supplied with a first information signal A and a second information signal B, respectively, and calculates the sum and difference of these two signals.

The sum signal X (=A+B) and the difference signal Y (=A−B) taken out from the matrix circuit 1 are respectively supplied to the modulation circuit 2 as husband and wife modulation signals and are modulated there.

A concrete circuit of the modulation circuit 2 is shown in FIG.

In the figure, 9 is a sum signal input terminal, 10 is a difference signal input terminal, and the sum signal X from input terminal 9 is supplied to the NPN transistor Q4.
N through the emitter follower and diode D4, respectively.
Supplied to the base of PN transistor Q3.

Further, the difference signal Y input from the input terminal 10 is applied to the NPN transistor Q. is supplied to the base of the NPN transistor Q2 through the emitter follower of and the diode D3, respectively.

Here, the diodes D3 and D4 are diodes for clamping the base reverse bias potentials of the transistors Q and Q3 to the input signal.

In addition, diodes D1 and D2 apply a carrier setting bias from a variable resistor VR connected in series between the DC power supply (+Vcc) and ground (GND) to the bases of transistors Q2 and Qa, while input sum signal X and difference signal Y This is a diode to prevent mutual interference.

The above transistors Q2, Q3, trimmer capacitor C
, , capacitor C2, and resistors R1 and R2 constitute an astable multivibrator as is well known.

Here, diodes D5 and D6 connected between the bases and collectors of transistors Q2 and Qs, respectively, are clamp diodes for preventing saturation of transistors Q2 and Q3.

As a result, the modulation circuit 2 changes the reverse base potential of the transistor in the off state of the astable multivibrator to
The off-time is configured to be modulated by clamping to the potential of the modulation signal.

Further, the carrier frequency when the two input signals X and Y are zero is adjusted by the variable resistor VR, and the duty factor of the output rectangular wave at that time is adjusted to approximately 50% by the trimmer capacitor C1.

As a result, as is well known, a rectangular wave whose high potential period and low potential period are modulated by the modulation signals X and Y, respectively, is guided to the output terminal 11 from the collector of the transistor Q2.

To detect the modulated wave, it is supplied to a phase detection circuit (PM demodulation circuit) 5 and a frequency detection circuit (FM demodulation circuit) 6, where it is demodulated and guided to output terminals 7 and 8.

Here, as an example of the PM demodulation circuit 5, a circuit as shown in FIG. 3 is used, and as the FM demodulation circuit 6, for example, a pulse counter type FM demodulation circuit as shown in FIG. 4 is used.

First, when the modulated signals X and Y are both zero (when no modulation is performed), the waveform of the modulated wave transmitted and received is a symmetrical rectangular wave with a pulse width To, as shown in FIG. 5A.

This rectangular wave is input to the input terminal 1 of the phase detection circuit 5 shown in FIG.
2 to a clamp circuit consisting of a capacitor C3 and a diode D7, where its low level is clamped to zero volts, and then supplied to a low-pass filter 13.

For convenience of explanation, the amplitude of the modulated wave shown in FIG.
volts, the amplitude of the demodulated signal extracted from the low-pass filter 13 and guided to the output terminal 14 is as follows.

Next, the carrier wave is modulated by the modulated signals X and Y, and the first information signal A
When modulating with is T
o + A).

Therefore, the amplitude of the demodulated signal taken out from the output terminal 14 is always 0.5 volts regardless of the amplitude of the signal A.

On the other hand, when the carrier wave is modulated with the signals to be demodulated A=0, BkiO, the waveform of the modulated wave is as shown in Figure 5C, and the period is equal to the period 2TO of the modulated wave when no modulation is performed. Equal, but the duty factor changes.

Therefore, what is the amplitude of the demodulated signal taken out from the output terminal 14? Become.

That is, compared to the case where the modulated waves shown in FIGS. 5A and 5B are demodulated, the output signal of the phase detection circuit 5 is (
2) Increases by Eq.

Next, when signals A and B both exist (AkiO, BkiO)
The waveform of the modulated wave at that time is as shown in Figure 6A,
The high potential period is To + A + B, and the low potential period is To + A
-B pulse train.

Therefore, the amplitude of the demodulated signal taken out from the output terminal 14 is ? Become.

In this case, assuming that To>A, a demodulated signal expressed by 0.5+ is obtained as in equation (2).

It can be seen that in this way, only the second information signal B is demodulated by the phase detection circuit 5.

On the other hand, the input terminal 1 of the frequency detection circuit 6 shown in FIG.
The input modulated wave supplied to 5 is differentiated by a resistor R3 and a differential transformer T, and a constant pulse width determined by these time constants is made into a positive and negative pulse with TO, and each rising and falling edge of the carrier wave ( (leading edge and trailing edge) only.

The output differential pulse of this differential transformer T is
8 and D9, where it is double-wave rectified, clamped at zero port, and supplied to the low-pass filter 16.

Here, when the input modulated wave is the unmodulated modulated wave shown in FIG. 5A, a signal as shown in FIG. 5D is added to the input of the low-pass filter 16.

Therefore, the amplitude of the signal integrated by the low-pass filter 16 and guided to the output terminal 17 is 1-T9-.

Furthermore, when the modulated wave shown in FIG. 5B obtained by modulating the carrier wave only with the first information signal A enters the input terminal 15, the low-pass filter 16 supplies the signal shown in FIG. 5E. be done.

Therefore, the amplitude of the signal guided from the low-pass filter 16 to the output terminal 17 is increased by TcA/To (To+A) compared to the case where the modulated wave shown in FIG. 5D is input.

Here, if To > A, the increase in the above output is TOA
/TQ2 can be approximated.

Furthermore, when the modulated wave shown in FIG. 5C enters the input terminal 15, the low-pass filter 16 is supplied with the signal shown in FIG. 5F.

Therefore, the amplitude of the signal guided from the low-pass filter 16 to the output terminal 17 is as follows, which is the same as the amplitude of the output signal when the modulated wave is supplied without modulation as shown in FIG. 5A.

Next, signals A and B are both present, and as shown in FIG.
When the modulated wave shown in FIG. 6 enters the input terminal 15, a pulse train as shown in FIG. 6B is applied to the low-pass filter 16.

Therefore, the amplitude of the demodulated signal guided from the low-pass filter 16 to the output terminal 17 is as follows, which is the same as the equation (4) above.

Therefore, it can be seen that only the first information signal A is demodulated and detected by the frequency variable detection circuit 6 shown in FIG.

It goes without saying that the directions of the diodes D7D8 and D shown in FIGS. 3 and 4 may be reversed.

Furthermore, the detection circuits 5 and 6 are not limited to the circuits shown in FIGS. 3 and 4, but may be other circuits having the same function.

Furthermore, the modulation circuit 2 may be configured to modulate the base bias supply voltages of the transistors Q2 and Q3 of the circuit shown in FIG. 1, and furthermore, other modulation circuits may also be used.

Note that the transmission bands of the first and second information signals A and B are as follows:
It has been experimentally confirmed that the band is about 1/3 of the carrier frequency.

Further, the first and second information signals are, for example, stereo signals of a right channel audio signal and a left channel audio signal, and furthermore, the first information signal A is a stereo signal of a right channel audio signal and a left channel audio signal.
A sum signal of the video signal of the field (odd field) and the video signal of the second field (even field),
It is also conceivable that the second information signal B is a difference signal between the first field video signal and the second field video signal.

In this case, when transmitting and receiving still image signals, A, O, B
=! becomes to.

Furthermore, when the received modulated wave is recorded on a VTR, for example, if the modulated signals A and B of the modulated wave are the sum or difference signal of the first and second fields described above, they are recorded on one track. Since two fields are recorded, tape consumption can be halved compared to a conventional VTR that records one field on one track.

As mentioned above, the multiplex modulation and demodulation method according to the present invention is based on the first
and a multiplex modulation and demodulation method that modulates one carrier wave with a second modulation signal to obtain a modulated wave that is width-modulated with the first or second modulation signal alternately at every zero cross, and demodulates the same,
The first signal to be demodulated as the first and second modulated signals
Since the sum signal and the difference signal of the information signal and the second information signal are used, the modulated wave and the phase detection circuit and the frequency detection circuit are used for separate detection, making it possible to eliminate the need for a conventional matrix circuit and to use a band separation filter. Therefore, the demodulation system circuit can be configured extremely simply and at low cost, and when the side transmitting the modulated wave is a side providing a service such as a broadcasting station, and the receiving side receiving the service is an unspecified number of people. It has many features such as being very economically advantageous.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of one embodiment of the method of the present invention;
The figure is a specific circuit diagram of one embodiment of the modulation circuit in Figure 1,
5 and 4 are circuit diagrams of each embodiment of the demodulation circuit shown in FIG. 1, and FIGS. 5A-F and 6A and 6B are waveform diagrams for explaining the operation of FIGS. 3 and 4, respectively. It is. 1... Matrix circuit, 2... Modulation circuit, 5... Phase detection circuit (PM demodulation circuit),
6... Frequency detection circuit (FM demodulation circuit), 9.
... Sum signal input terminal, 10 ... Difference signal input terminal, 11 ... Modulated wave output terminal, 13, 1
6...Low pass filter, Q, ~Q4...
NPN transistor, T... Differential transformer.

Claims (1)

[Claims] 1 A modulation means for modulating one carrier wave with the sum signal and difference signal of the first and second information signals to obtain a modulated wave whose width is alternately modulated at every zero cross; 1
Alternatively, a multiplex modulation and demodulation method comprising a phase detection circuit that demodulates the second information signal and a frequency detection circuit that is supplied with the modulated wave and demodulates the second or first information signal.