JP2001217714A - Digital communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system capable of securing a sufficient dynamic range. SOLUTION: Corresponding to the compared result of an analog signal and a prescribed level, a transmitter sends out a transmitting signal containing any one of a digital signal, with which the digital conversion of the analog signal is performed, and a digital signal, with which the digital conversion of the analog signal is performed after analog amplification, and a control bit C expressing the compared result. Corresponding to the control bit C contained in the received digital signal, a receiver outputs a signal, with which the received digital signal is converted into an analog signal, or signal, with which the analog amplification of the received digital signal is performed after conversion into the analog signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital communication system for converting an analog signal such as a voice signal input from a microphone into a digital format and transmitting the digital signal. The present invention relates to a digital communication system with a reduced bandwidth.

[0002]

2. Description of the Related Art FIG. 6 shows an outline of a configuration of a wireless microphone system which is one of digital radio communication systems. In order to secure a necessary dynamic range, an A / D converter and an A / D converter having an accuracy corresponding thereto are provided. D /
A converter is used. In FIG. 1, on the transmission side, an audio signal input from a microphone 1 is amplified by a low-frequency amplifier 2 as much as necessary for A / D conversion, and is converted into a digital signal by an A / D converter 3 having a resolution of, for example, 20 bits. Thereafter, the digital signal processing unit 4 performs required signal processing, modulates the signal-processed digital signal by the modulator 5, and transmits it to the receiving side as a 20-bit digital signal. On the receiving side, the received digital signal is amplified by the amplifier 6 and then demodulated to the original digital signal by the demodulator 7 and processed by the signal processing unit 8. The signal is converted into an analog signal by the / A converter 9, further amplified by the low-frequency amplifier 10, and then output from the speaker 11.

In theory, an A / D converter and a D / A
If you use a converter with a resolution of 16 bits,
The dynamic range is about 96 dB.
108 dB for 8 bits, 120 dB for 20 bits, 24
A dynamic range of 144 dB can be secured with bits.

However, in practice, the dynamic range as theoretical cannot be ensured due to the influence of noise or the like, and the A / D converter and the D / A converter having a resolution of 16 bits are not available.
Since the converter can obtain only a dynamic range of about 90 dB, it is necessary to use a more accurate A / D converter and D / A converter in order to secure a sufficient dynamic range. On the other hand, when the number of bits of the A / D converter and the D / A converter is increased, the accuracy is improved, but at the same time, the cost is increased. Therefore, if a D / A converter used for a CD player or the like for mass production can be used, it is extremely advantageous for cost reduction.

Further, in such a wireless communication system, an increase in the number of bits directly leads to an increase in a bit rate,
Since it occupies a wide bandwidth, there is a serious disadvantage that a sufficient number of channels cannot be secured. Therefore, in order to effectively use the frequency band, which is a limited resource, it is important to reduce the bit rate that can be used for communication as much as possible and to narrow the used frequency bandwidth.

[0006] As a measure to avoid an increase in cost due to the use of a high-precision A / D converter, the applicant of the present application filed a patent application entitled "High-precision A / D converter" on May 29, 1998. Patent application has been made, and a method has been proposed in which the dynamic range can be extended even if an inexpensive A / D converter with low accuracy is used (Japanese Patent Laid-Open No. 11-111,1992).
-340831).

FIG. 7 shows an example of the configuration of the above-mentioned "high-precision A / D converter". The analog input signal from the microphone is divided into two systems, and one of the signals is digitally converted by the A / D converter 12. Switcher 1 after converting to signal
3 and the other signal is an amplifier 14 with a gain of 2 ^m .
After that, the signal is converted into a digital signal by an A / D converter 15, further amplified by an amplifier 16 having an amplification factor of 2 ^−m , and added to a switch 13. The output level of the A / D converter 12 is also applied to the level detector 17 and
The output power from the / D converter 12 is detected. As a result, the switching unit 1 starts at a predetermined level as a boundary.
According to 3, the output of the A / D converter 12 is extracted as a digital signal when the analog input signal is large, and the output of the analog amplifier 16 is extracted as the digital signal when the analog input signal is small.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems of the conventional communication system, and an object of the present invention is to provide an A / D converter and a D / A with low accuracy. It is an object of the present invention to provide a communication system capable of securing a sufficient dynamic range even if a converter is used.

[0009]

In order to achieve the above object, according to the present invention, at least one transmitter and at least one receiver for receiving a digital signal transmitted from the transmitter are provided. Wherein the receiver amplifies the analog input signal and a digital signal obtained by digitally converting the analog input signal according to a comparison result between the analog input signal and a predetermined level. And transmitting a transmission signal including one of the converted digital signal and a control bit representing the comparison result, wherein the receiver responds according to the control bit included in the received digital signal. Converting the received digital signal into an analog signal or the received digital signal. To provide a communication system, characterized by outputting a signal analog amplified after converted into analog signals.

According to a second aspect of the present invention, there is provided a communication system comprising at least one transmitter and at least one receiver for receiving a digital signal transmitted from the transmitter. Input means for inputting an analog signal, a first A / D converter for outputting a signal obtained by digitizing the analog signal, and outputting a digitized signal after amplifying the analog signal by a transmission analog amplifier A second A / D converter that selects the output of the first A / D converter when the level of the analog signal is higher than a predetermined level, and the level of the analog signal is higher than the predetermined level. Is also smaller, a selector for selecting the output of the second A / D converter, and the first A selected by the selector.
Either the output of the first A / D converter or the output of the second A / D converter is selected as the digital signal output from the / D converter or the second A / D converter. A transmission output unit for outputting a transmission signal combined with a control bit indicating whether the received digital signal is a digital signal to an analog signal. And a reception output section for outputting an analog signal output from the D / A conversion section directly or after being amplified by a reception analog amplifier in accordance with a control bit included in the received digital signal. A communication system, wherein the amplification factor of the transmission analog amplifier is i decibel, and the amplification factor of the reception analog amplifier is −i decibel (i> 0). Subjected to.

The selection section detects at least one of an output level of the first A / D conversion section and an output level of the second A / D conversion section, and determines that the output level is the predetermined level. Detecting that the output of the second A / D converter has been selected, and informing the transmission output unit that the output of the second A / D converter has been selected. A vessel can be provided.

When the control bit indicates that the second A / D conversion unit has been selected, the reception output unit transmits an analog signal output from the D / A conversion unit to the reception analog amplifier. It is desirable to supply.

In the receiver, the D / A
The conversion unit may include a first D / A converter and a second D / A converter, and in this case, the reception output unit determines that the control bit is selected by the first A / D conversion unit. When the control bit indicates that the second A / D converter is selected, the analog signal output from the first D / A converter is output. An analog signal output from the two D / A converters is output via the reception analog amplifier.

The digital communication system according to the present invention can be realized as a digital radio communication system such as a wireless microphone.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a communication system according to the present invention will be described below with reference to FIGS. FIG. 1 schematically shows a configuration of a transmitter that can be used in the communication system according to the present invention. In FIG. 1, the output of a microphone 21 to which an analog input signal is applied is amplified by an analog amplifier 22 and then divided into two parts, one to a first A / D converter 23 and the other via an analog amplifier 24 to a second. It is applied to the A / D converter 25, respectively. The amplification factor of the analog amplifier 24 is i decibel (for example, 24 dB), and the first A / A
The resolution of the D converter 23 and the second A / D converter 25 is j bits (for example, 16 bits).

Since an A / D converter manufactured for stereo signal processing is available, the left channel of the A / D converter for stereo is connected to the first A / D converter.
When the right channel is used for the D / D converter 23 and the second A / D converter 25, components can be used efficiently.

A first A / D converter 23 and a second A / D converter
The output of the A / D converter 25 is applied to a power level detector 26, respectively, and the first A / D converter 23
Is connected to the first fixed contact 271 of the switch 27, and the output of the second A / D converter 25 is connected to the second fixed contact 272 of the switch 27. The movable contact 273 of the switch 27 is connected to the transmission signal processing unit 28, and the output of the transmission signal processing unit 28
And then transmitted from the antenna. First A / D converter 23 and second A / D converter 25
Have a resolution of j bits (for example, 16 bits).

The power level detector 28 detects the output power level of the first A / D converter 23, and
And outputs control data for controlling the operation of. That is, when the output power of the first A / D converter 23 is higher than the predetermined power level, the power level detector 28 connects the first fixed contact 271 of the switch 27 to the movable contact 273, and When the output power of the A / D converter 23 becomes lower than a predetermined power level, the operation of the switch 27 is controlled by the control data such that the second fixed contact 272 of the switch 27 is connected to the movable contact 273. . Thus, when the level of the analog input signal is smaller than the predetermined level, the signal amplified and level-up by the analog amplifier 24 is A / D converted.

The power level detector 28 controls the switching operation of the switching unit 27 as described above, and instructs the transmission signal processing unit 28 that the analog input signal applied to the microphone 21 is larger than a predetermined level. Or a signal indicating whether the signal is small, in other words, the first A / D converter 2
A selection signal indicating which of the third and second A / D converters 25 has been selected is sent. In response to the selection signal, the transmission signal processing unit 28 adds a control bit corresponding to the selection signal to a digital signal output from the first A / D converter 23 or the second A / D converter 25. It works to add.

FIG. 2 shows an example of the configuration of a transmission digital signal output from the transmission signal processing section 28. The transmission digital signal includes a frame portion UW which is added for synchronizing data and is regarded as a head of data, a control bit C, and at least one data portion D1, D2,. , Parity bits P arranged between the data parts.

The control bits C inserted between the frame part UW and the head data D1 are two bits in order to improve the reliability in consideration of bit errors actually occurring on the communication path. It is desirable. Thus, for example, control bit C causes switch 27 to operate such that power level detector 26 connects movable contact 273 to first fixed contact 271 to select the output of first A / D converter 23. When the logic "1
1 ", and conversely, the power level detector 26
The movable contact 273 for selecting the output of the D converter 25
Is connected to the second fixed contact 272 by the switch 2.
7 is logic "00" when operated.

The transmission digital signal to which the control bit C is added in the transmission signal receiving section 28 and processed so as to have the signal format shown in FIG. 2 is modulated by the digital modulator 29 in accordance with a predetermined digital modulation method and transmitted. Sent from antenna.

Here, the configuration of a receiver that can be used in the communication system according to the present invention will be described with reference to FIG. The signal transmitted from the transmitter shown in FIG. 1 is received by a receiving antenna, input to a digital demodulator 31, demodulated into a received digital signal corresponding to the transmitted digital signal, and added to a received signal processing unit 32. The received signal processing unit 32 detects the control bit C in the received digital signal and controls the operation of the switch 34 (described later), and removes the frame unit UW, the control bit C, and the parity bit P. The received digital signal to D /
Add to A converter 33. As a result, the D / A converter 33 outputs an analog signal corresponding to the analog input signal applied to the microphone 21 of the transmitter in FIG. The resolution of the D / A converter 33 is the same j bits (for example, 16 bits) as those of the A / D converters 23 and 25 on the transmission side.

The switch 34 includes a movable contact 341 connected to the output of the D / A converter 33 and a first fixed contact 3
42 and a second fixed contact 343 connected to the input of the analog amplifier 35 having an amplification of -i decibels (for example, -24 dB). Therefore, the reception signal processing unit 32
Is the control bit C in the received digital signal.
Is detected as logic "11", the movable contact 341 is connected to the first fixed contact 342, and the control bit C in the received digital signal is set to logic "00".
Is detected, control data for controlling the switch 34 to connect the movable contact 341 to the second fixed contact 343 is sent to the switch 34.

Thus, depending on the control bit C sent from the transmitter, the analog signal output from the D / A converter 33 is supplied to the analog amplifier 36 directly or via the analog amplifier 35, where it is further amplified. And output from the speaker 37.

As will be understood from the above description, in the communication system according to the present invention, the power level detector 2 determines whether the level of the analog input signal applied to the microphone 21 is higher or lower than a predetermined level.
Detect at 6. When the level of the analog input signal is higher than a predetermined level, the first A / D converter 23
A digital signal including the digital signal output from the controller and the control bit C of logic "11" is transmitted to the receiving side. On the receiving side, the reception signal processing unit 32 determines that the control bit C is logic "11". Is detected, and the movable contact 341 of the switch 34 is connected to the first fixed contact 342.

On the other hand, when the power level detector 26 on the transmitting side detects that the level of the analog input signal is smaller than the predetermined level, the analog input signal is amplified by the analog amplifier 24 having an amplification factor of i decibel, and the level is increased. A / D is increased by the second A / D converter 25 after
Transmit after D-conversion. At the same time, a control bit C of logic "00" indicating that the analog signal whose level has been increased is digitized and transmitted is transmitted to the receiving side. On the receiving side, the received signal processing unit 32 detects that the control bit C included in the received digital signal is logic “00”, and the movable contact 341 of the switching unit 34
Is connected to the second fixed contact 343. This gives D
The analog signal output from the / A converter 33 is amplified by the analog amplifier 35 having an amplification factor of -i decibel, and is returned to a level corresponding to the level of the original analog input signal.

By using the transmitter and the receiver having such a configuration, for example, when an A / D converter and a D / A converter having a resolution of 16 bits are used, an A / D converter and a D / D converter having a resolution of 20 bits are used. The same effect as when the A converter is used can be obtained. Therefore, the present invention only needs to occupy the band of 16 bits + the band of control bits as compared with the wide band occupied when using a normal 20-bit converter. Very effective for use.

In the receiver shown in FIG. 3, the timing at which the switch 34 of the receiver is switched in conjunction with the switching operation of the switch 27 of the transmitter is important. On the transmission side, a digital signal obtained by digitizing an analog input signal and a control bit are output at the same timing. However, at the receiver, the D / A converter 33 outputs The timing at which the analog signal is output may be different from the timing at which the control data is output from the reception signal processing unit 32. When such a timing shift occurs, large noise due to the timing shift is generated by the D / A converter 3.
3 will be generated in the output analog signal. Further, in the receiver shown in FIG. 3, since switching is performed in the area of the analog signal, generation of switching noise is inevitable.

FIG. 4A shows that the movable contact 341 of the switch 34 is moved from the second fixed contact 343 to the first fixed contact 3.
(B) in the case of switching to the second fixed contact 343 when the movable contact 341 of the switch 34 is switched from the first fixed contact 342 to the second fixed contact 343. FIG. In (a) and (b) of FIG.
Is the timing at which control data is output from the controller, t2 is D / A
The timing at which an analog signal is output from the converter 33, and t indicates a delay time in the D / A converter 33 that causes such a timing shift. This is because when the switching unit 34 performs the switching operation according to the control data from the reception signal processing unit 32, the D / A converter 33
When a delay corresponding to the delay time t occurs, the switching operation performed by the switching unit 34 by the control data is more effective than D.
The analog signal output from the A / A converter 33 is switched by the switch 3
4 means that the delay occurs earlier by the delay time t than when it arrives. Therefore, in the case of FIG. 4A, during the period of the delay time t between the timing t1 and the timing t2, although there is an analog signal to be amplified by the analog amplifier 35, such a signal is present. Will be output without being amplified. Therefore, as shown in FIG. 4A, an output smaller than the appropriate level is instantaneously generated, resulting in noise.

Similarly to the case of FIG. 4B, during the delay time t, a signal which must not be amplified by the analog amplifier 35 is output from the D / A converter 33, but the switch 34 Operates faster by the delay time t, and is actually amplified by the analog amplifier 35, and an output larger than an appropriate level is instantaneously generated, thereby generating noise.

FIG. 5 shows a receiver in which the configuration is changed so as to eliminate the influence of the delay generated in the D / A converter 33 in the receiver of FIG. In FIG. 5,
Components that are the same as or similar to those shown in FIG. 3 have the same reference numerals. In the receiver shown in FIG. 5, the movable contact 341 of the switch 34 is connected to the output of the received signal processing unit 32, the first fixed contact 342 is connected to the input of the first D / A converter 38, The second fixed contact 343 is connected to the input of the second D / A converter 39. In this manner, the switching is performed in the digital signal area. The output of the first D / A converter 38 is output via a coupler 40 and the second D / A converter 39
Are amplified by an analog amplifier 35 and then applied to an input of an analog amplifier 36 via a coupler 40.

The received signal processing unit 32 of the receiver shown in FIG. 5 is configured to control the first A / D converter when the control bit C sent from the transmitter shown in FIG. 1 indicates that the level of the analog input signal is larger than a predetermined level. When the output of the switch 23 is selected, the operation of the switch 34 is controlled so that the movable contact 431 is connected to the first fixed contact 342. Then, the output of the first D / A converter 38 is applied to the analog amplifier 36 via the coupler 40. On the other hand, when the control bit C sent from the transmitter in FIG. 1 indicates that the level of the analog input signal is smaller than the predetermined level and the output of the second A / D converter 25 is selected, the reception signal processing is performed. The part 32 is configured to connect the movable contact 431 to the second fixed contact 343.
The operation of the switch 34 is controlled so as to be connected to the switch. Then, the output of the second D / A converter 39 is applied to the analog amplifier 36 via the analog amplifier 35 and the coupler 40.

Since the receiver of FIG. 5 is configured as described above, the problem of the timing deviation caused by the delay by the D / A converter 33 in the receiver of FIG. 3 is solved. As a result, noise does not occur. Instead, it is necessary to use two D / A converters for the receiver. However, a D / A converter for a stereo system is adopted to use the L channel and the R / A converter.
There is actually little cost penalty for using channels.

As described above, one embodiment of the communication system according to the present invention has been described, but the present invention is not limited to this embodiment. For example, the resolution of the A / D converter and the D / A converter and the amplification factor of the analog amplifier can be set to arbitrary values. Also, instead of sending out control bits indicating that the level of the analog input signal is higher or lower than the predetermined level, the control bit is set only when the level of the analog input signal becomes lower than the predetermined level. You may make it transmit. Further, the digital communication system according to the present invention is applicable not only to a wireless communication system but also to a wired communication system.

Further, in the digital communication system according to the present invention, the predetermined level at which the level of the transmitted digital signal is compared in the transmitter does not need to be one value. For example, when the transmission digital signal fluctuates near a certain level, the switching is frequently performed. In order to prevent this, the switching level can be provided with hysteresis. For example, in FIG. 1, the first level when the movable contact 273 of the switch 27 switches from the first fixed contact 271 to the second fixed contact 272, and the movable contact 273 changes from the second fixed contact 272 to the first fixed contact 272. By setting the second level at the time of switching to one fixed contact 271 to a different value, frequent switching due to a change in the transmission digital signal can be prevented.

[0037]

As is apparent from the above description, the present invention provides a low-precision A / D converter and D / D converter.
Even if an A converter is used, a sufficient dynamic range can be ensured. Therefore, it is sufficient to use a narrow frequency band. In addition, since inexpensive A / D converters and D / A converters can be used, the frequency can be greatly reduced. This has a special effect that the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an embodiment of a transmitter that can be used in a communication system according to the present invention.

FIG. 2 is a diagram illustrating a format of a transmission digital signal generated in a signal processing unit of FIG. 1;

FIG. 3 is a diagram schematically illustrating a configuration of a receiver that can be used in combination with the transmitter of FIG. 1;

FIG. 4 is a diagram for explaining the operation of the receiver shown in FIG.

FIG. 5 is a diagram schematically illustrating another configuration of a receiver that can be used in combination with the transmitter of FIG. 1;

FIG. 6 is a diagram schematically showing a configuration of a conventional communication system.

FIG. 7 shows a high precision A / D filed by the applicant of the present application.
It is a figure showing an example of composition of a converter.

[Explanation of symbols]

21: microphone, 23, 25: A / D converter, 24: analog amplifier, 26: power level detector, 27: switcher, 28: transmission signal processing unit, 29: modulator, 31: demodulator, 3
2: reception signal processing unit, 33: D / A converter,
34: switch, 35: analog amplifier,
C: control bit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J022 AA01 AB01 AC02 BA01 CC01 CF02 CF07 5K034 AA05 BB04 CC05 DD01 EE03 HH01 HH02 HH06 HH07 HH12 HH16 MM39 PP05 PP07 5K047 AA01 BB01 DD01 HH44 MM44 MM45

Claims (6)

[Claims] 1. A communication system comprising at least one transmitter and at least one receiver for receiving a digital signal transmitted from the transmitter, wherein the transmitter has an analog input signal and a predetermined level. A digital signal obtained by digitally converting the analog input signal or a digital signal obtained by digitally converting the analog input signal after analog amplification, and a control bit representing the comparison result. The receiver sends a transmission signal that includes the received digital signal converted to an analog signal or the received signal according to the control bits included in the received digital signal. The feature is to convert the digital signal to an analog signal and then output the analog amplified signal. Digital communication system according to. 2. A digital communication system comprising at least one transmitter and at least one receiver for receiving a digital signal transmitted from the transmitter, wherein the transmitter receives an analog signal. A first A / D converter for outputting a signal obtained by digitizing the analog signal; and a second A / D for outputting a digitized signal after amplifying the analog signal by a transmission analog amplifier. A converter, selecting the output of the first A / D converter when the level of the analog signal is higher than a predetermined level, and selecting the output of the first A / D converter when the level of the analog signal is lower than the predetermined level. A selector for selecting an output of the second A / D converter; and the first A / D converter or the second A / D selected by the selector. The output of the first A / D converter and the second A / D converter are added to the digital signal output from the converter.
And a transmission output unit for outputting a transmission signal in which a control bit indicating which one of the outputs of the / D conversion unit is selected is provided. The receiver converts the received digital signal into an analog signal. Convert to D
A / A conversion unit, and a reception output for outputting an analog signal output from the D / A conversion unit directly or after being amplified by a reception analog amplifier according to a control bit included in the received digital signal. And an amplification factor of the transmission analog amplifier is i decibels,
A digital communication system, wherein an amplification factor of the reception analog amplifier is -i decibels (where i> 0). 3. The selection section detects at least one of an output level of the first A / D conversion section and an output level of the second A / D conversion section, and determines that the output level is the predetermined level. The output of the second A / D conversion unit is selected by detecting that the output of the second A / D conversion unit has become smaller than the level of the second A / D conversion unit. 3. The digital communication system according to claim 2, further comprising a detector for notifying. 4. The method according to claim 1, wherein the reception output unit includes a control unit.
4. The analog signal output from the D / A converter is supplied to the reception analog amplifier when a bit indicates that the second A / D converter is selected. 5. 2. The digital communication system according to claim 1. 5. The D / A converter includes a first D / A converter and a second D / A converter, and the reception output unit determines that the control bit is the first A / D conversion. Outputting the analog signal output from the first D / A converter when the control unit indicates that the second A / D converter has been selected; 4. The digital communication system according to claim 2, wherein an analog signal output from said second D / A converter is output through said reception analog amplifier. 6. The digital communication system according to claim 1, wherein the digital communication system is a digital wireless communication system.