Mutual conversion method of binary data and multilevel signal, its communication method, and its receiving device

What is claimed is:

1. A conversion method of binary data constituted by n bits per data into a multilevel signal comprising the steps of:

setting a basic period to have m (m=2.sup.n) time slots ranging from 0 to m-1;

setting m+1 multilevels constituted by 0th to m-1th levels and an upper standard level above said m-1th level;

defining said basic period as A type basic period and B type basic period alternately in series;

constituting m data per group in accordance with said basic period;

defining a value of index data appearing kth from the beginning of said group as time index value T and defining values of m-1 normal data j except said index data as level value L.sub.j ;

converting said index data into said multilevel signal in Tth time slot of said basic period, said multilevel signal having 0th level when said basic period is said A type period and having said upper standard level when said basic period is said B type period;

allocating respective said normal data j to each of corresponding said time slots except one for said index data, and

converting respective said normal data j into said multilevel signal in corresponding respective said time slot of said basic period, said multilevel signal having respective L.sub.j +1 level shifting up said level value L.sub.j by one level when said basic period is said A type period and having respective L.sub.j level without being shifted when said basic period is said B type period.

2. A conversion method of binary data constituted by n bits per data into a multilevel signal comprising the steps of:

setting a basic period to have m (m=2.sup.n) time slots ranging from 0 to m-1;

setting m+1 multilevels constituted by 0th to m-1th levels and an lower standard level below said 0th level;

defining said basic period as A type basic period and B type basic period alternately in series;

constituting m data per group in accordance with said basic period;

defining a value of index data appearing kth from the beginning of said group as time index value T and defining values of m-1 normal data j except said index data as level value L.sub.j ;

converting said index data into said multilevel signal in Tth time slot of said basic period, said multilevel signal having m-1th level when said basic period is said A type period and having said lower standard level when said basic period is said B type period;

allocating respective said normal data j to each of corresponding said time slots except one for said index data, and

converting respective said normal data j into said multilevel signal in corresponding respective said time slot of said basic period, said multilevel signal having respective L.sub.j -1 level shifting down said level value L.sub.j by one level when said basic period is said A type period and having respective L.sub.j level without being shifted when said basic period is said B type period.

3. A inverse conversion method of a multilevel signal into binary data constituted by n bits per data comprising the steps of:

setting a basic period to have m (m=2.sup.n) time slots ranging from 0 to m-1;

setting m+1 multilevels constituted by 0th to m-1th levels and an upper standard level above said m-1th level;

constituting m data per group in accordance with said multilevel signal per said basic period;

defining said basic period as A type basic period and B type basic period alternately in series;

detecting a minimum value of said multilevel signal in said A type basic period and detecting a maximum value of said multilevel signal in said B type basic period;

generating m+1 standard levels based on a difference between said minimum value and said maximum value so as to quantize said multilevel signal;

deciding each level value L.sub.j of said multilevel signal in respective said time slot based on said m+1 standard levels;

detecting a time slot number T of said minimum value in said basic period when said basic period is said A type basic period and detecting a time slot number T of said maximum value in said basic period when said basic period is said B type basic period;

defining said time slot number T as a value of said index data;

converting said index data into said binary data which is located at kth position from a beginning of a group; and

converting respective said level value L.sub.j of said multilevel signal except said Tth time slot in said basic period into respective said binary data which is located at respective position of said group corresponding to said respective time slot, said binary data having value L.sub.j -1 given by shifting down said level value L.sub.j of said multilevel signal by one level when said basic period is said A type period and having value L.sub.j without shifting when said basic period is said B type period.

4. A inverse conversion method of a multilevel signal into binary data constituted by n bits per data comprising the steps of:

setting a basic period to have m (m=2.sup.n) time slots ranging from 0 to m-1;

setting m+1 multilevels constituted by 0th to m-1th levels and a lower standard level below said 0th level;

constituting m data per group in accordance with said multilevel signal per said basic period;

defining said basic period as A type basic period and B type basic period alternately in series;

detecting a maximum value of said multilevel signal in said A type basic period and detecting a minimum value of said multilevel signal in said B type basic period;

generating m+1 standard levels based on a difference between said minimum value and said maximum value so as to quantize said multilevel signal;

deciding each level value L.sub.j of said multilevel signal in respective said time slot based on said m+1 standard levels;

detecting a time slot number T of said maximum value in said basic period when said basic period is said A type basic period and detecting a time slot number T of said minimum value in said basic period when said basic period is said B type basic period;

defining said time slot number T as a value of said index data;

converting said index data into said binary data which is located at kth position from a beginning of a group; and

converting respective said level value L.sub.j of said multilevel signal except said Tth time slot in said basic period into respective said binary data which is located at respective position of said group corresponding to said respective time slot, said binary data having value L.sub.j +1 given by shifting up said level value L.sub.j of said multilevel signal by one level when said basic period is said A type period and having value L.sub.j without shifting when said basic period is said B type period.

5. A conversion method of binary data constituted by n bits per data into a multilevel signal comprising the steps of:

setting a basic period to have m (m=2.sup.n) time slots ranging from 0 to m-1;

setting m+2 multilevels constituted by 0th to m-1th level, an lower standard level below said 0th level, and an upper standard level above said m-1th level;

defining said basic period as A type basic period and B type basic period alternately in series;

constituting m data per group in accordance with said basic period;

defining a value of index data appearing kth from the beginning of said group as time index value T and defining values of m-1 normal data j except said index data as level value L.sub.j ;

converting said index data into said multilevel signal in Tth time slot of said basic period, said multilevel signal having lower standard level when said basic period is said A type period and having said upper standard level when said basic period is said B type period;

allocating respective said normal data j to each of corresponding said time slots except one for said index data, and

converting respective said normal data j into said multilevel signal in corresponding respective said time slot of said basic period, said multilevel signal having respective L.sub.j level without being shifted.

6. A inverse conversion method of a multilevel signal into binary data constituted by n bits per data comprising the steps of:

setting a basic period to have m (m=2.sup.n) time slots ranging from 0 to m-1;

setting m+2 multilevels constituted by 0th to m-1th levels, a lower standard level below said 0th level, and an upper standard level above said m-1th level;

constituting m data per group in accordance with said multilevel signal per said basic period;

defining said basic period as A type basic period and B type basic period alternately in series;

detecting a minimum value of said multilevel signal in said A type basic period and detecting a maximum value of said multilevel signal in said B type basic period;

generating m-2 standard levels based on a difference between said minimum value and said maximum value so as to quantize said multilevel signal;

deciding each level value L.sub.j of said multilevel signals based on said m+2 standard levels;

detecting a time slot number T of said minimum value in said basic period when said basic period is said A type basic period and detecting a time slot number T of said maximum value in said basic period when said basic period is said B type basic period;

defining said time slot number T as a value of said index data;

converting said index data into said binary data which is located at kth position from a beginning of a group; and

converting respective said level value L.sub.j of said multilevel signal except said Tth time slot in said basic period into respective said binary data which is located at respective position of said group corresponding to said respective time slot, said binary data having value L.sub.j without shifting.

7. A communication method utilizing conversion method of claim 1 comprising the steps of;

modulating a carrier of a predetermined frequency by said multilevel signal; and

transmitting a modulated multilevel signal into a transmission line.

8. A communication method utilizing conversion method of claim 2 comprising the steps of;

modulating a carrier of a predetermined frequency by said multilevel signals; and

transmitting a modulated multilevel signal into a transmission line.

9. A communication method utilizing conversion method of claim 5 comprising the steps of;

modulating a carrier of a predetermined frequency by said multilevel signals; and

transmitting a modulated multilevel signal into a transmission line.

10. A communication method utilizing inverse conversion method of claim 3 comprising the steps of;

receiving a modulated multilevel signal from a transmission line; and

demodulating said modulated multilevel signal into said binary data, said modulated multilevel signal being given by modulating a carrier of a predetermined frequency by said multilevel signal.

11. A communication method utilizing inverse conversion method of claim 4 comprising the steps of;

receiving a modulated multilevel signal from a transmission line; and

demodulating said modulated multilevel signal into said binary data, said modulated multilevel signal being given by modulating a carrier of a predetermined frequency by said multilevel signal.

12. A communication method utilizing inverse conversion method of claim 6 comprising the steps of;

receiving a modulated multilevel signal from a transmission line; and

demodulating said modulated multilevel signal into said binary data, said modulated multilevel signal being given by modulating a carrier of a predetermined frequency by said multilevel signal.

13. A receiving device utilizing communication method of claim 7 comprising:

an amplifier so as to receive said multilevel signal transmitted through said transmission line;

a maximum/minimum value detection means detecting a minimum voltage value of said multilevel signal in said A type basic period and a maximum voltage value of said multilevel signal in said B type basic period; and

an amplification factor controller so as to retain a constant voltage difference between said minimum voltage value and said maximum voltage value.

14. A receiving device utilizing communication method of claim 8 comprising:

an amplifier so as to receive said multilevel signal transmitted through said transmission line;

a maximum/minimum value detection means detecting a maximum voltage value of said multilevel signal in said A type basic period and a minimum voltage value of said multilevel signal in said B type basic period; and

an amplification factor controller so as to retain a constant voltage difference between said minimum voltage value and said maximum voltage value.

15. A receiving device utilizing communication method of claim 9 comprising:

an amplifier so as to receive said multilevel signal transmitted through said transmission line;

a maximum/minimum value detection means detecting a minimum voltage value of said multilevel signal in said A type basic period and a maximum voltage value of said multilevel signal in said B type basic period; and

an amplification factor controller so as to retain a constant voltage difference between said minimum voltage value and said maximum voltage value.

16. A receiving device utilizing communication method of claim 7 comprising:

a synchronizing index signal detection means detecting a synchronizing index signal at the timing when said multilevel signal takes a minimum voltage value in said A type basic period and at the timing when said multilevel signal takes a maximum voltage value in said B type basic period;

a synchronizing signal generating means generating a synchronizing signal so as to provide a sampling timing of said multilevel signal in respective said time slots by phase-locking said synchronizing signal to said synchronizing index signal; and

a sampling means sampling said multilevel signal based on said sampling timing provided by said synchronizing signal.

17. A receiving device utilizing communication method of claim 8 comprising:

a synchronizing index signal detection means detecting a synchronizing index signal at the timing when said multilevel signal takes a maximum voltage value in said A type basic period and at the timing when said multilevel signal takes a minimum voltage value in said B type basic period;

a synchronizing signal generating means generating a synchronizing signal so as to provide a sampling timing of said multilevel signal in respective said time slots by phase-locking said synchronizing signal to said synchronizing index signal; and

a sampling means sampling said multilevel signal based on said sampling timing provided by said synchronizing signal.

18. A receiving device utilizing communication method of claim 9 comprising:

a synchronizing index signal detection means detecting a synchronizing index signal at the timing when said multilevel signal takes a minimum voltage value in said A type basic period and at the timing when said multilevel signal takes a maximum voltage value in said B type basic period;

a synchronizing signal generating means generating a synchronizing signal so as to provide a sampling timing of said multilevel signal in respective said time slots by phase-locking said synchronizing signal to said synchronizing index signal; and

a sampling means sampling said multilevel signal based on said sampling timing provided by said synchronizing signal.

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BACK GROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of converting binary data and a multilevel signal, mutually and a communication method employing the mutual conversion. Further, it relates to a receiving device to stabilize amplitude and sampling timing of a received signal.

2. Description of the Prior Art

It has been known for data transmission to modulate a carrier with a predetermined frequency by binary data in amplitude, frequency and phase modulation. However, they are problematic in transmission efficiency. Alternatively, there has been a modulation method to use a multilevel signal converted in three to four bites per unit from binary data. This method increases state number of the carrier and improves the transmission efficiency. However, this method also has following several problems.

When the transmission method is the amplitude modulation by the multilevel signal, it is necessary to quantize a demodulated multilevel signal at multilevels at receiving end. Accordingly, accurate detection of amplitude width and sampling standard from the received multilevel signal are required for accurate inverse conversion from the multilevel signal to the binary data. Since the amplitude width of the received multilevel signal is affected with attenuation of a transmission line, temperature characteristics of an amplifier, aging variation, and so on, an automatic gain control (AGC) is necessary to stabilize the amplitude width. However, it has been difficult to obtain an accurate control voltage stably and constantly when the multilevel random signal is used as a modulation signal. Further, there has been a problem that the timing standard cannot be picked up at the receiving end, because a constant amplitude width continues when same data are successively output.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to obtain level and timing standards accurately from a received signal in mutual conversion between binary data and a multilevel signal.

It is another object of the present invention to stabilize levels of the received multilevel signal so as to obtain accurate standard levels from the received signal at the time of demodulation.

It is further object of the present invention to provide accurate and stabilized sampling timing of the received multilevel signal.

According to the first aspect of the invention, there is provided a conversion method of binary data into a multilevel signal. The binary data is constituted by n bits per data. The multilevel signal has m (m=2.sup.n) time slots per period, or symbol periods per period, and m+1 levels. The time slots range from the 0th to m-1th, and the levels range from the 0th to the m-1th and an upper standard level above the m-1th. Further, consecutive basic periods are defined as A type or B type basic period, alternately.

In the respective A type basic periods, data values are shifted up by one level so as to generate the multilevel signal, and in the respective B type basic periods, data values are not shifted at all.

The binary data has m data per basic group. One of the m data appearing at kth from the beginning of the basic group is defined as an index data. The value of the index data is defined as a time index value T when the binary data is converted into the multilevel signal. The other data, or m-1 data, is defined as normal data j whose level values are defined as L.sub.j.

In order to gain amplitude and timing standards at the time of signal receiving, the index data locating at kth position in the basic group is arranged to take the 0th level in the Tth time slot of the basic period when the basic period is the A type and to take the upper standard level in the Tth time slot of the basic period when the basic period is the B type. The normal data j is allocated to each of the corresponding time slots except the Tth time slot, taking L.sub.j +1 levels being shifted up by one level when the basic period is the A type, and taking L.sub.j levels without being shifted when the basic period is the B type.

According to the second aspect of the invention, there is provided another conversion method of the binary data into the multilevel signal. The multilevel signal is constituted by m+1 levels including 0th to m-1th levels and a lower standard level below the 0th level. The difference between the first and the second aspects of the invention is where to set the standard level, above the m-1th level or below the 0th level. Therefore, the index data locating in the kth position of the basic group is arranged to take the m-1th level in the Tth time slot when the basic period is the A type and to take the lower standard level in the Tth time slot when the basic period is the B type. Further, the normal data j takes L.sub.j -1 level being shifted down by one level when the basic period is the A type, and takes L.sub.j level without being shifted when the basic period is the B type.

According to the third aspect of the invention, there is provided an inverse conversion method, converting the multilevel signal into binary data. Corresponding relation of the ranges between the binary data and the multilevel signal are the same as that described in the first aspect of the invention. The method further includes the steps of:

detecting a minimum value of the multilevel signal in the A type basic periods and detecting a maximum value of the multilevel signal in the B type basic periods;

generating m+1 standard levels based on a difference between the minimum value and the maximum value so as to quantize the multilevel signal;

deciding each level value L.sub.j of the multilevel signal in respective the time slot based on the m+1 standard levels;

detecting a time slot number T of the minimum value in the basic period when the basic period is the A type basic period and detecting a time slot number T of the maximum value when the basic period is the B type;

defining the time slot number T as a value of the index data;

locating the index data at kth position from the beginning of a group; and

converting the respective level value L.sub.j of the multilevel signal except the Tth time slot in the basic period into the respective binary data which is located at respective position of the group corresponding to the respective time slot, the binary data having value L.sub.j -1 given by shifting down the level value L.sub.j of the multilevel signal by one level when the basic period is the A type period and having value L.sub.j without shifting when the basic period is the B type period.

According to the fourth aspect of the invention, there is provided another inverse conversion method. The multilevel signal is constituted by m+1 levels including 0th to m-1th levels and a lower standard level below the 0th level. The difference between the third and the fourth aspects of the invention is which multilevel signal is used for the inverse conversion, the multilevel signal with the upper standard level above the m-1th level or that with the lower standard level below the 0th level. The inverse conversion method further includes the steps of:

detecting a maximum value of the multilevel signal in the A type basic period and detecting a minimum value of the multilevel signal in the B type basic period;

generating m+1 standard levels based on a difference between the minimum value and the maximum value so as to quantize the multilevel signal;

deciding each level value L.sub.j of the multilevel signal in the respective time slot based on the m+1 standard levels;

detecting a time slot number T of the maximum value when the basic period is the A type and detecting a time slot number T of the minimum value when the basic period is the B type;

defining the time slot number T as a value of the index data;

locating the index data at kth position from beginning of a group; and

converting the respective level value L.sub.j of the multilevel signal except the Tth time slot in the basic period into the respective binary data which is located at respective position of the group corresponding to the respective time slot, the binary data having value L.sub.j +1 given by shifting up the level value L.sub.j of the multilevel signal by one level when the basic period is the A type and having value L.sub.j without shifting when the basic period is the B type.

According to the fifth aspect of the invention, there is provided the other conversion method of binary data into the multilevel signal. Two levels, an upper standard level above the m-1th level and a lower standard level below the 0th level, are added to the m levels of the multilevel signal. Namely, the multilevel signal has m+2 levels. Therefore, the index data is defined as the multilevel signal taking the lower standard level in the respective A type basic periods and the upper standard level in the respective B type basic periods. The respective normal data j is allocated into each time slot except for the Tth time slot taking the multilevel signal of respective L.sub.j level without being shifted.

According to the sixth aspect of the invention, there is provided the other inverse conversion method of the multilevel signal into binary data. The inverse conversion method includes the steps of:

detecting a minimum value of the multilevel signal in the A type basic period and detecting a maximum value of the multilevel signal in the B type basic period;

generating m+2 standard levels based on a difference between the minimum value and the maximum value so as to quantize the multilevel signal;

calculating each level value of the multilevel signals based on the m+2 standard levels;

detecting a time slot number T of the minimum value when the basic period is the A type and detecting a time slot number T of the maximum value when the basic period is the B type;

defining the time slot number T as a value of the index data;

locating the index data at kth position from beginning of a group; and

converting the respective level value L.sub.j of the multilevel signal except the Tth time slot in the basic period into the respective binary data which is located at respective position of the group corresponding to the respective time slot, the binary data having value L.sub.j without shifting.

According to the seventh aspect of the invention, there is provided a receiving device utilized in a communication method transmitting the multilevel signal converted by the conversion method described in the first, second, and fifth aspects of the invention. The receiving device is constituted by:

an amplifier so as to receive the multilevel signal transmitted through the transmission line;

a maximum/minimum value detection means of the first and the fifth aspects detecting a minimum voltage value of the multilevel signal in the A type basic period and a maximum voltage value of the multilevel signal in the B type basic period, or a maximum/minimum value detection means of the second aspect detecting a maximum voltage value of the multilevel signal in the A type basic period and a minimum voltage value of the multilevel signal in the B type basic period; and

an amplification factor controller so as to retain a constant voltage difference between the minimum voltage value and the maximum voltage value.

According to the eighth aspect of the invention, there is provided another receiving device utilized in a communication method transmitting the multilevel signal converted by the conversion method described in the first, second, and fifth aspects of the invention. The receiving device is constituted by:

a synchronizing index signal detection means of the first and the fifth aspects detecting a synchronizing index signal at the timing when the multilevel signal takes a minimum voltage value in the A type basic period, and at the timing when the multilevel signal takes a maximum voltage value in the B type basic period, or a synchronizing index signal detection means of the second aspect detecting a synchronizing index signal at the timing when the multilevel signal takes a maximum voltage value in the A type basic period, and at the timing when the multilevel signal takes a minimum voltage value in the B type basic period;

a synchronizing signal generating means generating a synchronizing signal so as to provide a sampling timing of the multilevel signal in respective the time slots by phase-locking the synchronizing signal to the synchronizing index signal; and

a sampling means sampling said multilevel signal based on the sampling timing provided by the synchronizing signal.

The values of the above described 0, 1 . . . , m-1 of the 0th, first . . . , m-1th levels are mere index number labeled thereon and so are the value of the level value L.sub.j. Namely, absolute voltage values corresponding to the lower and upper standard levels and the 0th to m-1th levels are not necessary to have regular intervals each other. As an example, it is acceptable to set irregular voltage intervals only between the lower standard and the 0th levels, and the upper standard and the m-1th levels such as 2, 3/2, folds and so on in contrast to setting a regular interval of each voltage from the 0th to m-1th levels. Since absolute voltage values of the lower and upper standard levels are utilized to generate absolute standard voltage values corresponding to each level, the irregular voltage levels help distinguish the standard levels from the levels of other normal data so as to detect timing of time slots detection and to quantize voltage values of the multilevel signal, accurately.

Therefore, shifting level values up and down by one level means merely shifting up and down by one index regardless of intervals among levels. When level values are shifted up and down by one level, they are respectively described as L.sub.j +1 and L.sub.j +1 which do not mean absolute voltage values but means mere index value.

The conversion methods described in the first, second, and fifth aspects of the invention are designed to ensure detecting the standard for sampling and amplitude without impeding transmission efficiency. For that purpose, a predetermined data, or the index data, is manipulated to contain two pieces of information as the data and the standard for sampling and amplitude. The information as the data is conveyed by a time slot number and the information as the standard for sampling and amplitude is by the level of the index data. The value T of the index data of the multilevel signal, is converted as the multilevel signal in the Tth time slot taking the 0th or upper standard level in the first aspect of the invention, the m-1th or lower standard level in the second aspect, and the lower or upper standard level in the fifth aspect. In the A type basic period, the value L.sub.j of the normal data j except the index data are shifted up by one level in the first aspect and described as L.sub.j +1, or shifted down by one level in the second aspect and described as L.sub.j -1. In the B type basic periods of the first and second aspects, the value L.sub.j of the normal data j become the level value in the respective time slot of the multilevel signal without being shifted. In the fifth aspect of the invention, level shift is not carried out. The A and B type basic periods appear in consecutive basic periods, alternately. The binary data constituted by n bits per data and m data per group is converted into the multilevel signal of m time slots per basic period with m+1 levels in the first and second aspects and m+2 levels in the fifth aspect. Consequently, the transmission efficiency of this invention becomes as same as that of conventional multilevel transmission method of m data ensuring detecting the standard for sampling and amplitude.

In other words, a conventional conversion method of m data may obtain the standard for sampling and amplitude of the multilevel signal by arranging one additional time slot to show the beginning of a data group. However, this arrangement impedes transmission efficiency by the additional time slot without any information as data. In this point of view, conversion method of the present invention has improved transmission efficiency than that of the prior art.

The inverse conversion methods described in the third, fourth, and sixth aspects of the invention are designed to convert the multilevel signal into binary data, accurately. In the alternately appearing A and B type basic periods, detecting the maximum or minimum level value of the multilevel signal per period helps determine maximum amplitude of the multilevel signal and generate standard levels so as to quantize the multilevel signal, accurately. In addition, information where the index signal locates among the m time slots per basic period helps provide the value of the original index data regardless of levels which the index signal are taking.

Further, in the case where several normal data whose values are the same to each other continuously appears in a basic period, the index data which definitely appears in one basic period enables the receiving end to pick up a timing standard periodically and to regenerate carrier wave easily at the time of synchronous demodulation.

As described above, the present invention can transmit amplitude information as the detection standard of multilevels and timing information without redundant data so that accurate inverse conversion of the multilevel signal into binary data can be achieved without impeding transmission efficiency.

In the communication method employing the first aspect of the invention, the multilevel signal regardless of original binary data definitely have the time slot taking the 0th level in the respective A type basic period and the time slot taking the upper standard level in the respective B type basic period. Consequently, the minimum voltage value detected in the A type basic period means the 0th level, and the maximum voltage value detected in the B type basic period means the upper standard level.

In the communication method employing the second aspect of the invention, the multilevel signal regardless of original binary data definitely have the time slot taking the m-1th level in the A type basic period and the time slot taking the lower standard level in the B type basic period. Consequently, the maximum voltage value detected in the A type basic period means the m-1th level, and the minimum voltage value detected in the B type basic period means the lower standard level.

In the communication method employing the fifth aspect of the invention, the multilevel signal regardless of original binary data definitely have the time slot taking the lower standard level in the A type basic period and the time slot taking the upper standard level in the B type basic period. Consequently, the minimum voltage value detected in the A type basic period means the lower standard level, and the maximum voltage value detected in the B type basic period means the upper standard level.

Therefore, controlling gains of the amplifier so as to obtain the constant voltage difference between the maximum and minimum voltage values stabilizes voltage corresponding to the level values of the multilevel signal output by the amplifier. Such stabilized voltage further helps stabilize the standard voltage for quantizing the multilevel signal. Consequently, precision of the conversion into binary data improves.

Further, the synchronizing index signal employed in the first and the fifth aspects is output at the same timing when the minimum voltage in the A type basic period and the maximum voltage in the B type basic period appear. And the synchronizing index signal employed in the second aspect is output at the same timing when the maximum voltage in the A type basic period and the minimum voltage in the B type basic period appear.

Further, the synchronizing signal is generated in synchronize with the synchronizing index signal so as to provide timing of sampling the multilevel signal in each time slot. Then, the multilevel signal is sampled based on the timing by the synchronizing signal.

In the above-described three communication methods, timing information to generate the synchronizing index signal is definitely contained in a certain time slot of each basic period of the multilevel signal. That enables to lock phase corresponding to the synchronizing signal of each basic period and to generate the synchronizing signal stabilized by locking phases of the multilevel signal. Consequently, precision of inverse conversion of the multilevel signal into binary data can be improved.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawings:

FIGS. 1A-1D are timing charts explaining conversion method in the first embodiment;

FIGS. 2A-2C are timing charts explaining conversion method in the second embodiment;

FIGS. 3A and 3B are wave form charts showing a pattern of a multilevel signal which indicates the beginning or end of data frame in the first embodiment;

FIGS. 4A to 4F are wave form charts showing a pattern of a multilevel signal which indicates the beginning or end of data frame in the second embodiment;

FIGS. 5A-5D are timing charts explaining a conversion method as a variation that is described in the first embodiment;

FIG. 6 is a timing chart explaining a conversion method as a variation that is described in the second embodiment;

FIG. 7 is a block diagram showing a constitution of the receiving device that is described in the first and second embodiments;

FIGS. 8A-8M and 9A-9F are timing charts explaining performance of the receiving device that is described in the first and second embodiments;

FIG. 10 is a flowchart of a conversion method according to the present invention; and

FIG. 11 is a flowchart of an inverse conversion method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will be more fully understood by reference to the following examples.

EXAMPLE 1

With reference to FIGS. 1A-1D and steps S10-S17 of FIG. 10, a conversio