JPH0434583Y2 - - Google Patents

Description

[Detailed explanation of the idea] <Industrial application field of this invention> The present invention relates to a pulse modulation circuit.

<Prior art> (Figures 1 and 2) Conventional pulse modulation circuits include pulse amplitude modulation PAM that modulates the amplitude of the pulse, pulse width modulation PWM that modulates the width of the pulse, and pulse phase modulation that modulates the phase of the pulse. There are PPM etc. In both of these methods, the instantaneous amplitude value of a modulated wave input signal is extracted at regular intervals, and the pulse train is modulated in accordance with the instantaneous amplitude value.

For example, in an optical space transmission device that emits and transmits a light beam into space, information is transmitted by driving a light emitting element with a pulse-modulated signal. However, in optical space transmission devices, PPM modulation is mainly used because external noise easily enters because light is propagated in space.

FIG. 1 shows a pulse phase modulation circuit in a conventional optical space transmission device of this type.

In FIG. 1, 1 is a rectangular wave oscillator that outputs a rectangular wave at a predetermined frequency, and 2 is a sawtooth generator that integrates a rectangular wave input and outputs a sawtooth signal. 3 is a comparator that compares the modulated wave input signal and the sawtooth wave signal, and produces an output while the level of the sawtooth wave signal exceeds the modulated wave input signal; 4 is a comparator that compares the modulated wave input signal and the sawtooth wave signal, and produces an output while the level of the sawtooth wave signal exceeds the modulated wave input signal; and 4, when it receives the output pulse of comparator 3, it It is a monostable multivibrator that outputs pulses of constant width.

Note that 5 is a light emitting element, and 6 is a drive transistor that is conductive while a pulse signal is output from the monostable multivibrator 4 to drive the light emitting element 5.

The circuit of FIG. 1 operates as shown in the timing chart of FIG.

The rectangular wave oscillator 1 outputs a rectangular wave output signal with a constant period (shown in Fig. 2A), and the sawtooth wave generator 2
The signal is converted into a synchronized sawtooth signal (shown in B of the same figure).
It is input to the non-inverting input terminal of comparator 3.

On the other hand, the modulated wave input signal inputted from the input terminal A is applied with a bias voltage V and inputted to the inverting input terminal of the comparator 3 (FIG. 3).

The comparator 3 compares both input voltages, and produces an output while the voltage of the sawtooth signal is greater (as shown in Figure D). When the output of the comparator 3 rises, the monostable multivibrator 4 outputs a pulse signal of a constant width (shown in E of the figure).

In this way, the monostable multivibrator 4
The pulse train E outputted from the pulse train E has the phase of each one changed in accordance with the change in the amplitude of the modulated wave input signal C.

The drive transistor 6 is operated by the pulse signal from the monostable multivibrator 4, and while the pulse signal is being output, the light emitting element 5 is driven and light is emitted into space.

On the receiving side, this light is collected and received by a light receiving element, and the received light signal is demodulated.

<Problems to be Solved by the Present Invention> However, since the PPM modulation shown in FIG. 1 modulates the phase of the pulse, the output level decreases in proportion to the decrease in the frequency of the modulated wave input signal.

For this reason, when the band of the transmitted signal becomes wider, such as when transmitting audio and FSK signals simultaneously through optical space transmission, the influence of noise increases, and the SN ratio of the audio signal in the low frequency region deteriorates. There was a problem that satisfactory transmission could not be achieved.

In addition, in the PPM modulation shown in Figure 1, phase modulation is performed in response to each sawtooth signal generated at each fixed period, so the modulation frequency component is very small, so it can be used for demodulation on the receiving side as it is. Demodulation cannot be performed simply by applying a range filter. For this reason, the PPM signal must be converted into a PAM or PWM signal and then applied to a low-pass filter, posing the problem of complicating the configuration of the demodulation circuit on the receiving side.

The present invention solves the above-mentioned problems and provides a pulse modulation circuit that sufficiently enables signal transmission in the low frequency region of a modulated wave input signal and eliminates the need for complicating the configuration of the demodulation circuit. It is an object.

<Means for solving the above problems> In order to solve the above problems, the pulse modulation circuit of the present invention includes a sawtooth signal generating means 10 for generating a sawtooth signal, and a sawtooth wave signal and a modulated wave input signal. and a first pulse signal having a constant pulse width when the output from the comparing means 11 is generated. a first pulse signal generating means 12 that generates the first pulse signal of the first pulse signal generating means 12;
When it receives a pulse signal, it outputs a second pulse signal with a predetermined pulse width, and when it receives the next first pulse signal before the end of the pulse width of the second pulse signal, it outputs a second pulse signal with a predetermined pulse width. a second pulse signal generating means 15 for generating a second pulse signal having the predetermined pulse width and outputting a second pulse signal having the predetermined pulse width;
a rectangular wave oscillating means 16 that stops oscillating the rectangular wave signal upon receiving the second pulse signal of the pulse signal generating means 15; each time it receives the first pulse signal from the first pulse signal generating means 12,
During the stop period of the pulse signal generation of the first pulse signal generation means 12, the rectangular wave oscillation means 1
Resetting means 17 for resetting the sawtooth wave signal of the sawtooth wave signal generating means at the beginning of each of the first pulse signals or the rectangular wave signal and restarting it at the end each time the sawtooth wave signal of No. 6 is received; It is equipped with

<Function> Because of this configuration, if there is no abnormality in the modulated wave input signal, when the sawtooth signal from the sawtooth signal generation means 10 reaches the same level as the modulated wave input signal, the comparison output from the comparison means 11 is arise.

When this comparison output occurs, the first pulse signal generating means outputs a first pulse signal having a constant width.

For each first pulse signal, the sawtooth signal is reset by the reset means 17 at the beginning of the first pulse signal and restarts at the end. Therefore, the sawtooth signal is reset and restarted each time it reaches the level of the modulated input signal.
The generation interval of the sawtooth signal changes in accordance with the level change of the modulated wave input signal, and a modulated output is generated from the pulse generation means in response to the reset of this sawtooth signal, so the pulse train of the modulated output changes according to the modulated wave input signal. The interval changes in response to a change in signal level.

If the level of the modulated wave input signal becomes lower than the level of the sawtooth signal due to noise or overmodulation to the negative side, and the generation of the first pulse signal stops, the sawtooth signal is not reset and becomes linear. Therefore, even if the modulated wave input signal returns to normal, the normal first pulse signal generation operation may become impossible. However, in this case, the second pulse signal from the second pulse generation means 15 stops, and as a result, the square wave oscillation means 16 oscillates a rectangular wave,
The reset means 17 resets the sawtooth signal at the beginning of this rectangular wave signal to prevent it from increasing linearly, and restarts it at the end. Therefore, when the modulated wave input signal returns to normal, the first pulse signal generation operation is started. will automatically return to normal.

<Configuration of an Embodiment of the Present Invention> (FIG. 3) FIG. 3 shows an embodiment of the pulse modulation circuit of the present invention applied to an optical space transmission device.

In FIG. 3, 10 is an integrator constituting a sawtooth signal generating means for generating a sawtooth signal.

Reference numeral 11 denotes a comparator (comparison means) which inputs the modulated wave input signal from the terminal A to a non-inverting input terminal, inputs the output signal of the integrator 10 to an inverting input terminal, and generates an output.

12 receives the output of the comparator 11, and outputs Q
The first pulse signal with a predetermined width is High level “H”.
This is a monostable multivibrator (first pulse signal generating means) that outputs.

13 is a light emitting element, and 14 is a driving transistor that drives the light emitting element 13 when it receives a pulse output "H" from the output Q of the monostable multivibrator 12.

15 receives a pulse output low level "L" from the inverted output of the monostable multivibrator 12, and generates a negative pulse (second pulse signal) of a predetermined width.
This is a monostable multivibrator that outputs to the Q output, and if the next first pulse signal is input within the end time T _C of this pulse width, from that point onwards, the same time width T _C continues. This is a retriggerable monostable multivibrator (second pulse signal generation means) that outputs a second pulse signal.

16 outputs a rectangular wave signal "L" with a pulse width Td ₂ at intervals of Td ₁ as shown on the right side of d in FIG. 4B, and receives a negative pulse output from the monostable multivibrator 15. As shown on the left side of d in FIG. 4B or on the right side of d in FIG. 4A, this is a rectangular wave oscillator in which this oscillation operation is stopped and the output is held at "H".

A NAND circuit (17) receives the inverted output of the monostable multivibrator 12 and the output of the square wave oscillator 16, outputs a logic output from both outputs to the integrator 10, resets the sawtooth signal, and restarts it immediately. (resetting means), which generates a single signal every time it receives the first pulse signal of the monostable multivibrator (first pulse signal generating means) 12 during the period when the oscillation of the rectangular wave signal of the rectangular wave oscillator 16 is stopped. During the period when the stable multivibrator (first pulse signal generation means) 12 stops generating the pulse signal, each time it receives a rectangular wave signal from the rectangular wave oscillator 16, the sawtooth signal of the integrator (sawtooth signal generation means) 10 is activated. This is a NAND circuit (resetting means) that outputs a reset signal that resets the wave signal at the beginning of each of the first pulse signals or the rectangular wave signal and restarts the wave signal at the end.

Note that V _B is the bias voltage, V _C is the power supply voltage of the drive transistor 14, and R ₁ , R ₂ , R ₃ are the comparator 11
, R ₄ is the base resistance of the drive transistor 14, and R ₅ is the collector resistance.

<Operation of the above embodiment> Next, the operation of the above embodiment will be explained with reference to the timing chart shown in FIG.

First, in the initial state when the power is turned on, no pulse is output from the Q output of the monostable multivibrator 12, and the Q output is "L" and the output is "H".

Therefore, since "H" is input to the monostable multivibrator 15, the monostable multivibrator 15 does not produce an output. At this time, the Q output of the monostable multivibrator 15 is "H". Therefore, the rectangular wave oscillator 16 starts oscillating the rectangular wave signal "L" (pulse width Td ₂ ) every interval Td ₁ .

When the rectangular wave rises and becomes "H" at time _t1 (see d in FIG. 4A), all the inputs of the NAND circuit 17 become "H", so they become "L" as shown in e in FIG. 4A. "become. The integrator 10 starts the integration operation from this time, and as shown in f of FIG. 4A,
The voltage increases linearly with a constant slope.

The comparator 11 compares the voltage of the modulated wave input signal (indicated by h in FIG. 4A) input to the non-inverting terminal with the output voltage of the integrator 10 input to the inverting terminal,
An output is produced when the output voltage of integrator 10 reaches the voltage of the modulated wave input signal (as indicated by t ₂ at g in FIG. 4A).

Due to the output of the comparator 11, the Q output of the monostable multivibrator 12 outputs a pulse "H" with a predetermined width, and therefore, the drive transistor 1
4, the light emitting element 13 is driven to emit light.

Also, at this time, the monostable multivibrator 12
Since the output becomes "L", the monostable multivibrator 15 generates a negative pulse output with a predetermined width T _C and becomes "L".

Therefore, as shown in d of FIG. 4A, the output from the vibrator 15 is "L" during the pulse interval Td ₁ , so the oscillation of the rectangular wave oscillator 16 is stopped and the "H" level is reached. will be retained. Therefore, while the output of the monostable multivibrator 12 is inverted to "L", the NAND circuit (resetting means) 17
The output of becomes "H". As a result, integrator 10 is reset.

Then, when the output of the monostable multivibrator 12 returns to "H" after a predetermined time, the output of the NAND circuit 17 becomes "L" again. Therefore, the integrator 10 starts the integration operation again.

Then, as shown at f in FIG. 4A, the integrator 1
When the output of 0 reaches the level of the modulated wave input signal
At t ₃ , an output is produced from comparator 11. As a result, the monostable multivibrator 12
A pulse with a predetermined width is output from the light emitting element 13.
is driven and emits light again.

At this time, the output of the monostable multivibrator 12 becomes "L". Monostable multivibrator 1
If the width of the output pulse 5 is set to a sufficiently large value T _C , the Q output “L” of the monostable multivibrator 12 occurs before this pulse width T _C ends. Therefore, the monostable multivibrator 15
is triggered from time t ₃ and again width T _C
produces a negative pulse of

In this way, monostable multivibrator 1
The output of No. 5 remains at "L" thereafter. Therefore, the square wave oscillator 16 also remains stopped,
The output is kept at "H" as shown at d in FIG. 4A.

Therefore, from now on, the output of the NAND circuit 17 becomes "H" every time the output of the monostable multivibrator 12 becomes "L". Therefore, an output is generated from the comparator 11, and at the beginning of the pulse "L" from the Q output of the monostable multivibrator 12, the integrator 10
is reset and restarts the integration operation again at the end of this pulse "L".

Note that, as shown in FIG. 4B, when the integrator 10 is released from the reset state and starts integrating, the level h of the modulated wave input signal is lowered by the integration due to noise or overmodulation on the negative side. When a state [h<f] smaller than the level f of the output pulse signal of the device 10 occurs, the voltage of the level f of the output pulse signal increases linearly, so that the level h of the modulated wave input signal is then normal. Even if you return to the level, always h
<f, and the operation of the sawtooth wave signal repeating in response to the level change of the modulated wave input signal is no longer performed.

In such a state, the first pulse signal is not output from the monostable multivibrator (first pulse signal generating means) 12, so the monostable multivibrator (second pulse signal generating means) 1
The output of the monostable multivibrator 12 becomes "H" after a time T _C from the last pulse of the output of the monostable multivibrator 12, as shown in c of FIG. 4B.

As a result, the rectangular wave oscillator 16 starts oscillating a rectangular wave signal of "L" level with a pulse width Td ₂ as shown in d of FIG. 4B. During the time width Td ₂ in which the output of the rectangular wave oscillator 16 is at "L", the output of the NAND circuit (reset means) 17 is at "H" as shown in e of FIG. 4B. Therefore, integrator 1
The sawtooth signal of 0 is the output “H” of this NAND circuit 17.
It is reset at the rising edge of , the linear increase is prevented, and the integration operation is restarted at the falling edge. As shown in FIG. As shown on the right side of f in B, as soon as the modulated wave input level returns to normal, the normal first pulse signal generation operation is resumed.

In this way, the monostable multivibrator 15,
Due to the functions of the square wave oscillator 16 and the NAND circuit 17, even when the first pulse signal generation operation stops due to noise etc., it also has an automatic recovery function to immediately return to normal operation. .

<Effects of the present invention> As explained above, in the conventional pulse modulation circuit shown in FIG. 1, as shown in FIG.
The sawtooth signal is generated at a constant period synchronized with the rectangular wave oscillator 1, whereas in the present invention, the sawtooth signal has a generation interval that changes according to the level change of the modulated wave input signal. The first pulse signal generating means 12 outputs a pulse train whose intervals change in response to changes in the level.

In this way, in the pulse modulation circuit of the present invention, the interval rather than the phase of the pulse is modulated, so
The frequency characteristics of the pulse output become flat, making it easier to use a low-frequency modulated wave input signal like the conventional circuit shown in Figure 1.
There is no deterioration in the SN ratio, and even audio signals can be transmitted satisfactorily.

In addition, in the conventional circuit shown in Fig. 1, the modulated wave input signal is modulated by a sawtooth signal at regular intervals, but in the present invention, the next comparison operation starts immediately every time a comparison output is generated. Therefore, the modulated output (a in FIG. 4A) is large, and the modulation frequency component is large, as is clear when compared with the conventional modulated output (a in FIG. 2). Therefore, demodulation on the receiving side does not require conversion to PAM or PWM signals as in the past, and can be easily demodulated by simply applying a low-pass filter.

Further, as explained in FIG. 4B, the second pulse signal generating means 15, the rectangular wave signal oscillating means 16,
By the action of the reset means 17, even if the pulse interval modulation is stopped due to noise or the like, it can be immediately and automatically restored.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional pulse modulation circuit, and FIG. 2 is a timing chart showing signal waveforms of the main parts of FIG. 1. FIG. 3 is a diagram showing an embodiment of the present invention, and FIGS. 4A and 4B are timing charts showing signal waveforms of the main parts of FIG. 3. 10... Integrator (sawtooth wave generation means), 11... Comparator, 12... Monostable multivibrator (first
pulse signal generating means), 13... light emitting element, 1
4... Drive transistor, 15... Monostable multivibrator (second pulse signal generation means), 1
6... Square wave oscillator, 17... NAND circuit (reset means).

Claims (1)

[Claims for Utility Model Registration] A sawtooth signal generating means 10 that generates a sawtooth signal compares the sawtooth signal with a modulated wave input signal, and the sawtooth signal reaches the same level as the modulated wave input signal. a first pulse signal generating means 12 that generates a first pulse signal having a constant pulse width when the output from the comparing means 11 occurs; The first signal generating means 12
When it receives a pulse signal, it outputs a second pulse signal with a predetermined pulse width, and when it receives the next first pulse signal before the end of the pulse width of the second pulse signal, it outputs a second pulse signal with a predetermined pulse width. a second pulse signal generating means 15 for generating a second pulse signal having the predetermined pulse width and outputting a second pulse signal having the predetermined pulse width;
a rectangular wave oscillating means 16 that stops oscillating the rectangular wave signal upon receiving the second pulse signal of the pulse signal generating means 15; each time it receives the first pulse signal from the first pulse signal generating means 12,
During the stop period of the pulse signal generation of the first pulse signal generation means 12, the rectangular wave oscillation means 1
Resetting means 17 for resetting the sawtooth wave signal of the sawtooth wave signal generating means at the beginning of each of the first pulse signals or the rectangular wave signal and restarting it at the end each time the sawtooth wave signal of No. 6 is received; A pulse modulation circuit with