JPH06284100A - Multiplex communication method, multiplexing device, and multiplex separator - Google Patents

Abstract

PURPOSE:To easily and surely execute time division multiplexing using pulse width modulation(PWM) by setting a pulse width modulation signal non-sending period on a transmission side, and detecting the period as synchronous information on a reception side. CONSTITUTION:The state of a ring counter 18 is changed inn synchronizing with a sawtooth wave start signal, and one time out of four times of state change is assigned to the period where no timing signals 1-3 are generated. The period is the PWH signal non-sending period. The signals 1-3 are supplied to NANDs 16-1 to 16-3, and PWM signals 1-3 are outputted, and they are inputted to an OR 20. The output of the OR 20 becomes a signal in which the PWM signal is multiplexed. A level conversion circuit 22 converts the signal level of multiplexed output into a level adaptive for universal serial interface. The signal level is converted into the one adaptive for RS-422 by comprising the circuit 22 of a TTL, and it is sent out to a transmission line, and is sent to a reception circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for time division multiplexing a plurality of analog signals, and more particularly to a method and apparatus using pulse width modulation (PWM).

[0002]

2. Description of the Related Art In the case of transmitting a plurality of analog signals through a single transmission line, it is necessary to multiplex the analog signals on the transmission line. When attempting to realize such analog multiplexing by a method as simple as possible, conventionally, prescriptions such as frequency division multiplexing and PCM time division multiplexing have been used.

Frequency division multiplexing is a method in which a plurality of channels to which different frequencies are assigned are formed on a single transmission line and a plurality of analog signals can be transmitted using the plurality of channels. is there. However, this method has a problem in that the circuit configuration becomes complicated and sophisticated. That is, since a carrier wave oscillator, a multiplier, and many other filters having steep characteristics are required according to the number of multiplexed signals, the circuit must be technically sophisticated.

On the other hand, also in the case of PCM time division multiplexing, the circuit configuration must be complicated and sophisticated. That is, a sophisticated A / D conversion circuit is required when performing quantization and encoding, and since one analog amount is represented by multiple bits, synchronization / separation can be managed with high accuracy during multiplexing. Since it must be done, sophistication of the circuit will occur.

Since frequency division multiplexing and PCM time division multiplexing require technically advanced circuits as described above,
In terms of cost, it is not suitable for relatively simple applications.
That is, it is difficult to use such a multiplexing method which causes a great waste in terms of cost when transmitting an audio signal in various audio devices or performing voice communication over a relatively short distance.

Focusing on such a problem, as a method developed to realize analog multiplexing with a simpler circuit,
There is pulse width modulation time division (PWM time division). This time division method is a method in which a plurality of analog signals to be transmitted are pulse-width modulated and then assigned to a plurality of channels formed on a single transmission path for transmission. By using such a method, it is possible to multiplex-transmit an analog signal without making the circuit configuration complicated and sophisticated. That is, analog multiplexing can be realized with a relatively inexpensive and simple circuit configuration.

[0007]

However, the conventional pulse width modulation time division multiplexing has problems such as the need for a clock recovery circuit and weakness in the distortion of the transmission waveform.

Generally, when performing time division multiplex transmission,
It is necessary to ensure synchronization between the sender and the receiver. When a method of sending out a transmission signal in which a clock component and a synchronization signal are mixed to a transmission line is used as a synchronization method in pulse width modulation time division multiplexing, the receiving side reproduces this clock component and uses this as a reference. Recognize the synchronization signal and ensure synchronization.

Therefore, in this method, since a clock recovery circuit is required on the receiving side, there is a limit to simplification of the circuit configuration. In addition, since the relationship between the timing of the reproduced clock and the timing of the synchronization signal included in the received waveform is strict, the signal cannot be demodulated properly when the transmission waveform is distorted.

The present invention has been made to solve the above-mentioned problems, and it is necessary for the receiving side to reproduce the clock component and to recognize the synchronizing signal based on the clock component without transmitting the clock component. It is an object of the present invention to provide a multiplex communication method capable of ensuring time division synchronization between a receiver and a receiver and a device suitable for the method.

[0011]

In order to solve the above-mentioned problems, the multiplex communication method of the present invention has the following features:
While circulating the transmission timing of the pulse width modulated signal on the transmission path at a number of timings greater than the number of analog signals to be transmitted, transmit a plurality of pulse width modulated signals whose rising timing is controlled at a constant timing. It is characterized in that it is sent out on the road and the receiving side detects the period during which the pulse width modulation signal is not sent out as synchronization information.

Further, the multiplexing device of the present invention comprises a pulse width modulating means for modulating the pulse width of each of a plurality of analog signals so that the rising timing is constant, and an analog signal for transmitting the transmission timing on the transmission line. And a time division transmission means for transmitting this pulse width modulation signal on a single transmission line in a time division manner at a corresponding transmission timing while circulating at a timing larger than the number of It is characterized in that signals are time-division multiplexed.

The multiplexing device of the present invention further comprises sawtooth wave generation means for generating a sawtooth wave, the pulse width modulation means generates a pulse width modulated signal in synchronization with the sawtooth wave, and the time division transmission means The pulse width modulation signal is sent out on the transmission line in synchronization with the sawtooth wave.

The multiplexing device of the present invention is further characterized in that the sawtooth wave generating means generates a sawtooth wave by smoothing a digitally generated stepwise sawtooth wave.

The multiplexing device of the present invention is characterized in that the pulse width modulation means generates the pulse width modulation signal by comparing the analog signal with the sawtooth wave.

Further, the demultiplexing device of the present invention includes a synchronization detecting means for detecting, as synchronization information, a period during which the pulse width modulated signal is not transmitted, from the signal received via the single transmission line, and the detected synchronization. And demultiplexing means for demultiplexing a plurality of pulse width modulation signals from the received signal based on the information, and demultiplexing the time division multiplexed signal in the time division multiplexing apparatus of the present invention.

In the demultiplexer of the present invention, the synchronization detecting means further detects the rising edge of the pulse width modulation signal included in the received signal, and detects the rising edge of the pulse width modulation signal in accordance with the detected rising edge and uses the synchronization signal as a reference. When the transmission timing is reproduced, if it does not occur again within the predetermined time of rising, it is considered that it is a period in which the pulse width modulation signal is not transmitted, and the synchronization signal is generated, and the demultiplexing means sets the reproduced transmission timing. The pulse width modulation means is demultiplexed accordingly.

The demultiplexing device of the present invention is characterized by further comprising means for low-pass filtering the demultiplexed pulse width modulated signal to demodulate an analog signal.

Further, the multiplexer or demultiplexer of the present invention, when transmitting the pulse width modulated signal to the transmission line or receiving the pulse width modulated signal from the transmission line, conforms the signal level to the general-purpose serial interface standard. It is characterized in that it is provided with a means for converting to the above level or for inverse conversion.

[0020]

In the multiplex communication method of the present invention, a plurality of analog signals to be transmitted are pulse width modulated.
At this time, the rising timing of each pulse width modulation signal is controlled to be constant. The resulting pulse width modulated signal is
The signals are transmitted onto a single transmission line at a predetermined transmission timing, whereby a plurality of analog signals are time-division multiplexed on the transmission line. At that time, the transmission timing of the pulse-width modulated signal on the transmission path is circulated at a timing larger than the number of analog signals to be transmitted, and the pulse-width modulated signal is transmitted on the transmission path according to the corresponding transmission timing. Sent out. Therefore, a pulse width modulation signal non-transmission period occurs on the transmission path.

On the receiving side, such a pulse width modulation signal non-transmission period is detected as synchronization information. When the synchronization information is detected in this way, a plurality of pulse width modulation signals are demultiplexed from the received signal based on the synchronization information. Therefore, in the present invention, it is possible to synchronize the time division timings on the transmitting side and the receiving side with a simple method and circuit configuration.

The multiplexing device of the present invention provides a multiplexing device that can be used as a transmitting device in such a multiplex communication method. The demultiplexing device of the present invention realizes a demultiplexing device that can be used as a receiving side device in the multiplex communication method of the present invention.

When the sawtooth wave generating means is provided in the multiplexer of the present invention, the operations relating to pulse width modulation and time division transmission are executed in synchronization with this sawtooth wave. That is, the rising timing of the pulse width modulation signal is generated in synchronization with this sawtooth wave, and the transmission timing of the pulse width modulation signal is generated in synchronization with this sawtooth wave, so that the synchronization information is not transmitted in the pulse width modulation signal. The function of the present invention that is added as is realized by a relatively simple circuit configuration.

If the sawtooth wave is generated by smoothing a digitally generated stepwise sawtooth wave, the standard is set and the accuracy is relatively high without using a high technology. You can get a sawtooth wave. That is, when a sawtooth wave that is a reference when performing pulse width modulation is generated by an analog circuit, a sawtooth wave with a uniform standard is required for distortionless transmission and time division multiplexing / demultiplexing. Advanced technology is used. On the other hand, when a sawtooth wave is generated by the method according to the present invention, a sawtooth wave with a uniform standard can be obtained with a relatively simple circuit configuration. Specifically, a counter that generates a stepwise sawtooth wave,
By using a simple circuit such as a CR circuit for smoothing this, the sawtooth waveform standard can be easily unified, and a signal quality with no practical problems can be obtained.

Further, when the pulse width modulation signal is generated by comparing an analog signal with a sawtooth wave or the like in the multiplexer of the present invention, a relatively simple circuit configuration is used, for example, by using a comparator or the like. Therefore, it becomes possible to easily and surely execute the pulse width modulation.

As described above, the rising edge of the pulse width modulation signal included in the received signal is controlled to be constant.
It is possible to demultiplex the pulse width modulated signal by detecting this rising edge in the synchronization detecting means of the demultiplexing device and reproducing the transmission timing of the pulse width modulated signal based on this. This synchronization information can be detected by detecting the rising edge of the pulse width modulation signal. When the pulse width modulation signal does not occur again within a predetermined time after the rising edge of the pulse width modulation signal, the synchronization detecting means regards it as a period in which the pulse width modulation signal is not transmitted and generates the synchronization signal. This synchronization signal is used as a reference when reproducing the output signal of the pulse width modulation signal. This allows
The demultiplexing device according to the present invention can be realized by using a simple circuit configuration such as a counter.

As means for modulating the analog signal from the demultiplexed pulse width modulated signal, means for low pass filtering the pulse width modulated signal can be used. That is, the analog signal can be demodulated by inputting the demultiplexed pulse width modulation signal to the low pass filter.

The signal level of the pulse width modulated signal is converted into a level suitable for a general-purpose serial interface standard (for example, RS-422) or inverse conversion is performed as an interface of a transmission line such as a multiplexer or demultiplexer of the present invention. By providing such means, it becomes possible to improve the transmission performance of the pulse width modulation signal.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a transmission circuit according to an embodiment of the present invention. The transmitting circuit shown in this figure has a function of pulse-width-modulating and analogizing three analog inputs 1 to and sending them to a transmission line. In the case of this embodiment, the transmission circuit, which is supposed to have a length of several hundred meters or less, has a binary counter 10. Two
The advance counter 10 counts a clock of a predetermined frequency supplied from the clock generation circuit 12, and outputs counting results Q1 to Q5. Q1 of this output excluding most significant bit Q5
.About.Q4 are synthesized by the ladder resistor R, and thereby a stepped sawtooth wave is digitally generated. The generated staircase sawtooth wave is smoothed by the capacitor C provided at the subsequent stage of the ladder resistor R and input to the-input terminals of the comparators 14-14.

Analog inputs ~ are input to the + input terminals of the comparators 14 to 14 via a capacitor together with a DC voltage obtained by dividing the power supply voltage Vcc. Therefore, the signals output from the comparators 14 to 14 are signals showing the result of comparing the analog inputs to with the sawtooth wave obtained as described above. As described above, since the stepwise sawtooth wave is generated in synchronization with the counting operation of the binary counter 10, the sawtooth wave supplied to the comparators 14 to 14 is synchronized with the clock as shown in FIG. The waveform becomes This sawtooth wave has multiple analog inputs,
For example, when compared with an analog input, a signal shown by a PWM signal in this figure is output from the comparator 14.

The PWM signals ~ output from the comparators 14 to 14 are NAND 16 to 16 respectively.
Entered in. The NANDs 16 to 16 are gates for supplying the corresponding PWM signals or to the circuits in the subsequent stages. Timing signals ~ indicating the sending timing of the PWM signal ~ are input to the other input terminals of the NANDs 16 ~ 16, respectively.

The timing signals ~ are generated by the ring counter 18. The ring counter 18 inputs the output Q5 of the binary counter 10 as a sawtooth wave start signal,
In response to this, the counting operation is executed. Ring counter 18
Of the outputs Q0 to Q4, Q3 is output as a timing signal, Q2 is output as a timing signal, and Q1 is output as a timing signal. The output Q4 is input to the clear terminal CL of the ring counter 18. Therefore,
Since the state of the ring counter 18 changes in synchronization with the sawtooth wave start signal, one of the four state changes of the ring counter 18 is assigned to a period in which none of the timing signals ~ is generated. This period is called a PWM signal non-transmission period.

When the timing signal ~ generated in this way is supplied to the NAND 16 ~, the NA
A PWM signal ~ is output from the ND 16 ~ and input to the OR 20 in the subsequent stage. The output of OR20 is therefore
The PWM signal is a multiplexed signal, for example, a signal shown as a multiplexed output in FIG. The level conversion circuit 22 provided at the subsequent stage of the OR 20 is a circuit that converts the signal level of the multiplexed output into a level suitable for a general-purpose serial interface. That is, when the circuit shown in this figure is configured by TTL, the level conversion circuit 2
Reference numeral 2 converts a TTL level signal into a signal level suitable for a general-purpose serial interface, for example, RS-422, and sends it out on a transmission line.

FIG. 2 shows the configuration of the receiving circuit according to this embodiment. The circuit shown in this figure is a circuit that separates the multiplexed output sent on the transmission path by the transmission circuit and demodulates analog to.

The circuit shown in this figure includes a level conversion circuit 24. Contrary to the level conversion circuit 22 described above, the level conversion circuit 24 is a circuit that converts a signal level suitable for RS-422 to a TTL signal level.
The signal input / level-converted by the level conversion circuit 24 is a signal having a waveform as shown as a PWM input in FIG. The rising edge detection circuit 26 provided in the subsequent stage of the level conversion circuit 24 detects the rising edge of this PWM input and supplies the detected edge to the ring counter 28 as a rising edge detection pulse.

The ring counter 28 has a rising edge detection circuit 2
6 is a circuit that counts the rising detection pulses supplied from 6 and generates the timing signals ~. That is, of the outputs Q0 to Q3 of the ring counter 28, Q1 to Q3 are input to the ANDs 30 to 30 as timing signals. The timing signal ~ is therefore synchronized with the rising edge detection pulse, as shown in FIG.

A PWM input is supplied from the level conversion circuit 24 to the other input terminals of the ANDs 30 to 30. Therefore, the PWM supplied from the level conversion circuit 24
The inputs are gated by the timing signals ~ in ANDs 30-30. For example, gating the PWM input with a timing signal results in a PWM signal having a waveform as shown in FIG.

PW output from AND30 to 30
The low-pass filters (LPFs) 32 to 32 having a simple structure filter the M signal ~ in the low-pass range, whereby an analog output ~ is obtained. That is, as shown in FIG. 3, the PWM obtained by AND30
By low-pass filtering the signal, the analog input
It will be demodulated as an analog output.

The operation of the ring counter 28 is as follows.
Cleared by sync signal. This synchronization signal is generated by the clock generation circuit 34 and the binary counter 36. The clock generation circuit 34 and the binary counter 36
Constitutes a so-called watchdog timer.

The clock generation circuit 34 generates a clock having a predetermined frequency and supplies it to the binary counter 36. The binary counter 36 counts the clocks supplied from the clock generation circuit 34 and outputs the counting result. Outputs Q4 and Q5 of the binary counter are both NAND38
The output of the NAND 38 is inverted by the NAND 42 and then supplied to the clear terminal CL of the ring counter 38 as a synchronization signal.

The count value incremented by the binary counter 36 is set so as to correspond to a time longer than the clock interval in the transmission circuit and shorter than twice the clock interval. Therefore, when the binary counter 36 counts up, it can be considered that the PWM signal non-transmission period has arrived at that time.

For example, if the multiplexed output of the transmission circuit is PWM
It is assumed that the signal transmission period, the PWM signal transmission period, the PWM transmission period, the PWM signal non-transmission period, ... Are cyclically time-divided in this order. When time division multiplexing is performed in this way, the rising edge of the PWM signal included in the PWM input is detected before the binary counter 36 counts up. Similarly, the rising edge of the PWM signal included in the PWM input is detected before the binary counter 36 counts up. The rising detection pulse is 2 through OR42.
It is input to the clear terminal CL of the binary counter 36. Therefore, when the rising edge of the PWM signal or is detected, the binary counter 36 executes the counting operation again from the initial state.
Therefore, the binary counter 36 does not count up.

On the other hand, when the rising edge of the PWM signal included in the PWM input is detected by the rising edge detection circuit 26, the PW comes after the sending period of the PWM signal.
Since it is the M signal non-transmission period, the binary counter 36 is counted up because it is not cleared by the rising edge detection pulse. When the binary counter 36 counts up, the ring counter 28 is cleared by the synchronizing signal as described above. The output Q0 of the ring counter 28 is supplied to the clear terminal CL of the binary counter 36, so that the ring counter 28 is cleared and the binary counter 36 is also cleared.

Therefore, according to this embodiment, one of the time-division transmission timings is assigned to the PWM signal non-transmission period in the transmission circuit, and the reception circuit detects the PWM signal non-transmission period to secure the synchronization. Therefore, it is possible to time-division multiplex-transmit multiple analog signals with a simple and inexpensive circuit configuration. Such a circuit is particularly useful for signal transmission inside various audio devices and voice communication over a relatively short distance.

[0046]

As described above, according to the present invention, the transmission side sets the pulse width modulation signal non-transmission period, and the reception side detects the pulse width modulation signal non-transmission period as synchronization information. The configuration of the multiplexer and the multiplexer / demultiplexer can be simplified and the price can be reduced. Further, since the circuit configuration is simple and no high technology is adopted, it is possible to reduce the development cost / capacity and the capability / cost required for dealing with a failure. Further, for example, the audio signal and the control signal can be multiplexed with a simple circuit configuration, or the two-terminal audio output can be multiplexed on a single transmission path, so that the audio transmission having monaural / stereo compatibility. Can be realized.
In such an application, a monaural audio signal can be received when the receiving side does not have the configuration according to the present invention.

Further, according to the present invention, when the pulse width modulation is executed with reference to the sawtooth wave, the pulse width modulated signal generating operation and the pulse width modulated signal sending operation are executed in synchronization with the sawtooth wave. Therefore, the addition of the pulse width modulation signal non-transmission period on the transmission side can be realized with a simple circuit configuration.

Further, according to the present invention, since the sawtooth wave is generated by smoothing the stepwise sawtooth wave that is digitally generated, the sawtooth wave standard can be easily unified, and the application is simple. If so, a sawtooth wave with sufficient accuracy can be generated.

Further, according to the present invention, since the pulse width modulation signal is generated by comparing the analog signal and the sawtooth wave, the pulse width modulation can be executed by a relatively simple means such as a comparator.

According to the present invention, the rising edge of the pulse-width modulated signal that is constantly controlled during transmission is detected and the rising interval is monitored to detect the pulse-width modulated signal non-transmission period. The detection of information can be realized by a simple means such as a counter or a timer.

Further, according to the present invention, since the analog signal is time-division multiplexed by pulse width modulation, the analog signal can be easily demodulated by low-pass filtering the demultiplexed pulse width modulated signal. be able to.

According to the present invention, when the pulse width modulated signal is transmitted / received, the signal level is converted so that the signal is transmitted at a level conforming to the general-purpose serial interface standard (RS-422 etc.). Or a means for performing inverse conversion is provided, so that the transmission capacity on the transmission path can be secured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a transmission circuit of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a receiving circuit of the device according to the present embodiment.

FIG. 3 is a timing chart showing the operation of this embodiment.

[Explanation of symbols]

 10,36 Binary counter 12,34 Clock generation circuit 14,14,14 Comparator 16,16,16 NAND 18,28 Ring counter 20,42 OR 22,24 Level conversion circuit 26 Rise detection circuit 30,30,30 AND 32 , 32, 32 low-pass filter (LPF)

Claims (9)

[Claims] 1. A plurality of analog signals to be transmitted are respectively pulse-width modulated and time-division multiplexed, the multiplexed pulse-width modulated signals are transmitted by a single transmission line, and signals are received from the transmission lines. In the multiplex communication method that multiplexes multiple pulse-width modulated signals from the received signal based on the detected synchronization information based on the detected synchronization information. While circulating at a timing that is greater than the number of signals, send multiple pulse-width modulated signals whose rise timing is controlled to a constant level on the transmission path at the corresponding sending timing, and A multiplex communication method characterized by detecting as synchronization information. 2. A pulse width modulation means for pulse-width-modulating each of a plurality of analog signals, and a time-division transmission means for time-divisionally transmitting the obtained plurality of pulse-width modulation signals on a single transmission path. In a multiplexing device that time-division-multiplexes multiple analog signals by pulse-width modulation, the pulse-width modulation means generates the pulse-width modulation signal so that the rising timing is constant, and the time-division transmission means transmits on the transmission line. A multiplexing device, wherein the pulse width modulated signal is sent to the transmission line at the corresponding sending timing while circulating the sending timing to the number of analog signals to be transmitted. 3. The multiplexing device according to claim 2, further comprising a sawtooth wave generating means for generating a sawtooth wave, wherein the pulse width modulation means generates a pulse width modulated signal in synchronization with the sawtooth wave, and transmits the signal in a time division manner. A multiplexing device, wherein the means outputs the pulse width modulated signal to the transmission line in synchronization with the sawtooth wave. 4. The multiplexing device according to claim 3, wherein the sawtooth wave generating means generates a sawtooth wave by smoothing a stepwise sawtooth wave generated digitally. 5. The multiplexing device according to claim 3, wherein the pulse width modulation means generates a pulse width modulation signal by comparing the analog signal with a sawtooth wave. . 6. A synchronization detecting means for detecting synchronization information from a signal received through a single transmission path, and a multiplexing device for demultiplexing a plurality of pulse width modulation signals from the received signal based on the detected synchronization information. A demultiplexing device for demultiplexing a plurality of time-division-multiplexed pulse-width modulated signals, wherein the synchronization detection means provides synchronization information during a period in which no pulse-width modulated signal is transmitted in the received signal. 6. The demultiplexing device, wherein the demultiplexing device receives the signal from the time division multiplexing device according to claim 2 through a transmission line and demultiplexes the signal. 7. The demultiplexing device according to claim 6, wherein the synchronization detecting means detects a rising edge of the pulse width modulation signal included in the received signal, and the pulse width modulation is performed according to the detected rising edge and with the synchronization signal as a reference. Reproduce the signal transmission timing, and if the rising edge does not occur again within the predetermined time, consider that it is the period during which the pulse width modulation signal is not transmitted and generate the synchronization signal, and the demultiplexing means reproduces the reproduced signal. A demultiplexing device, which demultiplexes a pulse width modulation signal according to timing. 8. The demultiplexer according to claim 7, further comprising means for low-pass filtering the demultiplexed pulse width modulated signal to demodulate an analog signal. 9. The apparatus according to claim 2, wherein when the pulse width modulation signal is transmitted to or received from the transmission line, the signal level thereof is a level conforming to a general-purpose serial interface standard. An apparatus comprising means for converting into or converting into.