JPS6313576B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a compression/expansion method for digitally modulated waves, in which the transmitting side compresses the level of the analog equivalent value of the digitally modulated wave and transmits it, and the receiving side converts the transmitted digitally modulated wave into an analogue value. By level-expanding the converted value by the amount of level compression, it is possible to transmit a digitally modulated wave with a quality that exceeds the conversion accuracy of AD converters and DA converters. Furthermore, by using a signal prediction circuit, control that indicates level compression information is possible. It is an object of the present invention to provide a compression/expansion method that can transmit digital modulated waves using a smaller number of bits than the conventional method because it does not require the transmission of digital signals.

FIG. 1 shows a block system diagram of an example of a conventional digital modulated wave compression/expansion method. In the figure, the analog signal entering input terminal 1 is passed through low-pass filter 2.
After removing unnecessary high-frequency components, the signal is supplied to the sampling and holding circuit 3, where it is sampled and held. The temporally discretized sampled signal taken out from the sampling hold circuit 3 is passed through a variable gain device 7, which will be described later.
While being applied to the AD converter 8, it is also supplied to the absolute value circuit 4, where the absolute value is taken. The output signal of this absolute value circuit 4 is supplied to a voltage comparator 6,
Here, it is compared with the reference voltage from the reference voltage setter 5, and when it exceeds the reference voltage, the gain of the variable gain unit 7 is varied.

FIG. 2 shows the input voltage versus output voltage characteristics of the variable gain device 7 in which the above gain control is performed. As can be seen from the figure, the absolute value of the input voltage increases,
When the input voltage reaches the maximum or minimum that can be transmitted by the AD converter 8, the gain is varied by the gain control signal from the voltage comparator 6, and as a result, the absolute value of the output voltage is attenuated. I am forced to do it.
As a result, the output voltage of the variable gain unit 7 is always within a predetermined voltage range (indicated by ±1 in Figure 2) determined by the number of bits of the AD converter 8, and a level compression waveform as shown in Figure 3 is generated. Become.

The output voltage of the variable gain device 7 is supplied to the AD converter 8, where it is analog-to-digital converted (specifically, quantized and encoded) into a digital modulated wave such as a pulse code modulation (PCM) signal. It is said that This digitally modulated wave is supplied to the DA converter 9 through a predetermined transmission path, where it is converted into a digital signal.
After analog conversion, the level attenuation or level enhancement in the transmission system is restored by level expansion by the variable gain unit 10, and then restored to the original analog signal by the low-pass filter 11 and sent to the output terminal 12.
It is output from

However, in the conventional digital modulated wave compression/expansion method described above, the variable gain unit 10 on the receiving side controls the gain in the opposite direction and the same amount as the gain controlled by the variable gain unit 7 on the transmitting side. Since the variable gain control signal also had to be transmitted at the same time as the transmission signal, the demand for reducing the number of transmission bits was limited.

The present invention eliminates the above drawbacks, and the fourth
Each embodiment will be described with reference to the drawings below.

FIG. 4 shows a block system diagram of a first embodiment of the digital modulated wave compression/expansion method according to the present invention.
In the figure, the same components as those in FIG. 1 are given the same numbers, and their explanations will be omitted. In Figure 4, AD
The digital modulated wave taken out from the converter 8 is
The signal is supplied to a variable gain unit 13 (which handles digital signals and is composed of a shift register or a multiplier), and its analog conversion level is varied by a control signal from a gain control unit 14, which will be described later. The signal is then transmitted and simultaneously supplied to the signal prediction circuit 15 in the gain control section 14. Now, the analog conversion level of the input digital modulated wave at time nT (T is the sampling period of the sampling and holding circuit 3) of the variable gain unit 13 is x _o , the gain of the variable gain unit 13 at that time is G ₁ , and the variable gain unit 13 Letting the analog equivalent level of the output digital modulated wave at time nT be y _o , the following equation holds true.

y _o =x _o・G ₁ (1) On the other hand, the signal prediction circuit 15 calculates the next time (n+1)
Let the analog conversion level of the digital modulation wave entering T be the input digital modulation wave y _o at the current time nT,
It is a circuit that predicts each analog conversion level of the digital modulation wave at a time at least one sample or more earlier, and the analog conversion level of the output digital modulation wave is z _o and the weighting coefficient given in the signal prediction circuit 15 is a. When _i (i=0 to N), a digital signal expressed by the following equation is output: z _o = _N 〓 ^i=q a _i ·|y _oi | (2). Equation (2) also represents the output digital signal of a kind of FIR type digital filter. Then,
The signal prediction circuit 15 described above can be composed of an FIR type digital filter. Note that in formula (2) |
y _o-1 | indicates a signal obtained by passing the digital modulated wave y _o-1 through an absolute value circuit.

As the simplest example of the signal prediction circuit 15, a ₀ =
2, a ₁ = -1, a ₂ = a ₃ =...=a _N = 0, the configuration can be made as shown in Fig. 5, and the input terminal 20
The absolute value circuit 21 converts the input digital modulated wave y _o into
After taking the absolute value at , a delay unit 23 delays the absolute value of y _o by -sampling period T using a differentiator 22.
By subtracting the absolute value of the digital modulated wave y _{o-1 from the output of - the sampled digital modulated wave y o-1} to obtain a difference signal, and adding it to the absolute value of y _o in the adder 24, the time (n+
1) A digital signal z _o with an analog conversion level predicted to enter T is used as a predicted signal to generate a digital modulation wave at the next time (n+1)T.
It is output from the output terminal 25 until y _o+1 comes in.

The output prediction signal z _o of the signal prediction circuit 15 is output from the comparator 1
7, where a variable reference level generator 16
A level comparison is made between the reference level L _o and the analog conversion value. As a result, when the digital signal z _o is at a higher level than the reference level l _o , the comparator 17 lowers the gain G ₁ of the variable gain unit 13 (specifically, the variable gain unit 13 is configured with a shift register). (if it is configured with a multiplier, shift it in the LSB direction, and if it is configured with a multiplier, reduce the coefficient), and create a new reference level by reducing the reference level of the variable reference level generator 16 by the same value. A signal is output to change to . On the other hand,
When the digital signal z _o is at a lower level than the reference level l _o , the variable gain unit 13 is selected from the comparator 17.
Increase the gain _G1 (specifically, if the variable gain unit 13 is configured with a shift register, shift in the MSB direction, and if configured with a multiplier, increase the coefficient), and A signal is output for changing the reference level of the variable reference level generator 16 to a new reference level that is higher by the same value. Note that the output of the comparator 17 is the signal prediction circuit 1.
5 is also supplied.

In this way, the gain G ₁ of the variable gain unit 13 is
Gain control (level control of analog conversion level) by the output signal of the gain control unit 14 based on the predicted signal
When the analog equivalent level change of the digitally modulated wave _{y o} obtained is large, the minimum level of quantization increases, and conversely, when the level change is small, the minimum level of quantization decreases, and finer quantization is performed. It is equivalent to the signal obtained by

The digitally modulated wave described above is received through a desired transmission path, is supplied to a variable gain unit 18 having the same configuration as the variable gain unit 13, and at the same time is supplied to a gain control unit 19. The variable gain unit 18 has the same configuration as the variable gain unit 13, and the analog conversion level of the supplied digital signal is variably controlled by the output of the gain control unit 19. Here, variable gain device 18
If the analog equivalent level of the input digital modulated wave at time nT is p _o , the analog equivalent level of the output digital modulated wave at time nT is q _o , and the gain of the variable gain unit 18 is G ₂ , the following equation is satisfied.

q _o = p _o・G ₂ (3) On the other hand, the gain control section 19 is the same as the gain control section 14 described above.
Although the configuration is similar to that of the gain control section 14, the operation is opposite to that of the gain control section 14. That is, the gain control unit 19 uses a comparator (not shown) to output the digital modulated wave p _o
When _the analog conversion level of the predicted signal obtained by In this case, the gain G ₂ of the variable gain unit 18 is lowered and the reference level is changed to a lower reference level by the same value. That is, the gain control by the gain control section 19 performs a level expansion operation complementary to the gain control by the gain control section 14, so that the relationship G ₁ ·G ₂ =1 (4) is satisfied. Also, y _o ≒ p _o (5).

The digital modulated wave (analog equivalent level q _o ) extracted from the variable gain device 18 is supplied to the DA converter 9 . Here, from equations (1), (3), (4), and (5),
Equation (6) holds true.

q _o ＝p _o・G ₂ ≒y _o・G ₂ ＝x _o・G ₁・G ₂ ＝x _o ∴q _o ≒x _o (6) Therefore, the level-compressed digital modulated wave on the transmitting side is On the receiving side, the level is expanded by the amount of level compression, and the signal is returned to the original digitally modulated wave.

According to this embodiment, the above-mentioned levels of compression and expansion are performed based on the predicted signal. For example (2)
In the equation, when a ₀ =2 and a ₁ =-1, z _o =y _o + (y _o -y _o-1 ) = y _o +dy _o /dt (7), and a predicted signal is obtained by differentiation. Similarly, by applying appropriate weighting in equation (2),
An appropriate prediction signal can be obtained depending on the nature of the input digital modulated wave. As can be seen from equation (2), such a predicted signal can be obtained from a digitally modulated wave, so there is no need to separately transmit a gain control signal to the receiving side as in the conventional method, and therefore, the signal is transmitted using fewer bits than in the conventional method. Digitally modulated waves can be compressed and expanded using a number of digits.

FIG. 6 shows a block system diagram of a second embodiment of the system of the present invention. In the figure, the same components as those in FIG. 4 are given the same numbers, and their explanations will be omitted. In this embodiment, the gain control circuit 26 for generating the variable gain control signal of the variable gain device 13 is configured using the output digital modulated wave of the AD converter 8 as an input signal,
A gain control circuit 27 that generates a control signal for varying the gain of the variable gain device 18 is configured to obtain the control signal from the output digital modulated wave of the variable gain device 18. The gain control circuits 26 and 27 have the same configuration as the gain control circuits 14 and 19, and this embodiment also has the same features as the first embodiment.

7 is a block system diagram of a third embodiment of the system of the present invention, and FIG. 8 is a block system diagram of a fourth embodiment of the system of the present invention. The third and fourth embodiments described above are different from the first and second embodiments in that the variable gainers 7 and 10 receive the sampled signal as input. Therefore, y _o in equation (1) and y _oi and zo in equation (2 ₎ represent analog modulation signal levels rather than analog conversion levels. Further, in the third embodiment, the gain control section 2
8 generates a predicted signal from the output signal of the variable gain unit 7 by the method described above, compares it with a reference level, and controls the gain of the variable gain unit 7 to be small when the predicted signal level is higher than the reference level. On the one hand, the reference level is changed to a small value, and on the other hand, when the reference level is smaller than the reference level, the gain of the variable gain unit 7 is controlled to be large, and the reference level is also changed to a large value. Further, the gain control section 29 shown in FIG. 7 has the same configuration as the gain control sections 19 and 27 and performs the same operation.

Furthermore, the fourth embodiment shown in FIG.
uses the output sampling signal of the sampling and holding circuit 3 as an input signal, and performs the same operation as the gain control section 28 to vary the gain control of the variable gain unit 7 by a control signal obtained. Part 31
performs the same operation as the gain control section 29 using the output analog signal of the variable gainer 10 as an input signal, and variably controls the gain of the variable gainer 10 using the control signal obtained, thereby compressing and expanding the digitally modulated wave. It is designed to perform actions. 3rd above
The embodiment and the fourth embodiment also have the same features as the first and second embodiments described above.

In addition, in the first and second embodiments, the analog conversion level of the digital modulation wave is level-compressed and expanded, and in the third and fourth embodiments, the analog modulation signal level of the digital modulation wave is level-compressed, and the demodulated signal is Although the level is expanded, the difference signal (m _o −m _o-1 ) is also level compressed.
The desired purpose can be achieved by elongation (however,
m _o indicates the analog conversion level of the digital modulation wave at time nT).

As described above, the digital modulated wave compression/expansion method according to the present invention includes a first variable gain device provided on the output side of an AD converter that digitally modulates an analog signal to obtain a digital modulated wave; Analog conversion of the difference signal obtained by subtracting the absolute value of the digital modulated wave at time (n-1) T from the digital modulated wave at time nT or its absolute value extracted from the output side (or input side) of the variable gainer of When the level is y _o (where T is the sampling period of the digital modulated wave) and the weighting coefficient is a _i , z _o = _N 〓 ⁱ⁼⁰ a _i・|y _oi | (however, N can be any A predicted signal with an analog conversion level z _o that satisfies the formula (natural number, a ₀ to a _N is 0 or an arbitrary number) is generated, and the reference level from the variable reference level generator and the analog conversion level of the above predicted signal are generated.
a first gain control section that causes the first variable gain unit to compress the analog equivalent level of the input digital modulated wave within a predetermined level range using control signals obtained by comparing the z o and z _o ; a second variable gain device to which the digitally modulated wave taken out from the gain control section is supplied through the transmission line and whose analog conversion level is varied according to the control signal;
The digital modulated wave extracted from the input side (or output side) of the variable gain device is operated in the opposite manner to that of the first gain control section, and the input digital modulated wave is controlled by the second variable gain control section. The second gain controller expands the analog conversion level by the level compression amount in a predetermined level range, and the circuit demodulates the output digital modulated wave of the second variable gainer into the original analog signal.
Even when a variable gain device is provided on the input side of the AD converter, the configuration is the same as above, so even if the conversion accuracy of the AD converter or DA converter is low, the input level and output level of the AD converter and DA converter are controlled. It is possible to ensure signal transmission that exceeds the performance of
Since the gain control signal of the variable gain device is obtained, there is no need to separately transmit the gain control signal as in the conventional method, and the number of transmission bits can be reduced compared to the conventional method. Furthermore, when using the same number of transmission bits as the conventional method, the amount of information that can be transmitted can be increased compared to the conventional method.
Since PCM and DPCM signals can be bit-compressed and transmitted, the number of transmission paths can be reduced.Furthermore, when the signal level is low, the minimum level of quantization is lowered and finer quantization is performed, so the signal level is low. This method also has many features such as being able to reduce quantization noise compared to conventional methods.

[Brief explanation of the drawing]

Figure 1 is a block system diagram showing an example of the conventional method, Figure 2 is a diagram showing the input/output characteristics of the variable gain unit on the transmitting side, and Figure 3 is an example of the output signal waveform of the variable gain unit on the transmitting side. 4, 6, 7 and 8 are block system diagrams showing respective embodiments of the system of the present invention, and FIG. 5 is a block system diagram showing an embodiment of the main part of the system of the present invention. It is a diagram. 1...Analog signal input terminal, 7, 10, 13,
18... Variable gain device, 8... AD converter, 9... DA converter, 12... Analog signal output terminal, 14, 2
6, 28, 30...Level compression gain control unit, 15
...signal prediction circuit, 16...variable reference level generator,
17... Comparator, 19, 27, 29, 31... Gain control section for level expansion, 25... Prediction signal output terminal.

Claims (1)

[Claims] 1. A first variable gain device provided on the output side of an AD converter that digitally modulates an analog signal to obtain a digital modulated wave; The analog conversion _level of the difference signal obtained by subtracting the absolute value of the digital modulated wave at time (n-1) T from the digital modulated wave at time nT or its absolute value extracted from (sampling period of modulated wave), and when the coefficient for weighting is a _i , z _o = _N 〓 ⁱ⁼⁰ a _i・｜y _oi | (However, N is any natural number, and a ₀ to a _N are 0 or Generate a predicted signal with an analog conversion level z _o that satisfies the formula (arbitrary number), and compare the reference level from the variable reference level generator and the analog conversion level of the above predicted signal.
a first gain control unit that causes the first variable gain unit to compress the analog equivalent level of the input digital modulated wave within a predetermined level range using control signals obtained by comparing the z o and z _o ; a second variable gain device to which the digitally modulated wave extracted from the first gain control section is supplied through the transmission line and whose analog conversion level is varied according to the control signal;
The digital modulated wave taken out from the input side (or output side) of the second variable gain device is operated in the opposite manner to that of the first gain control section to control the second variable gain device. a second gain control unit that expands the analog equivalent level of the input digital modulated wave by the level compression amount within a predetermined level range;
A digital modulated wave compression/expansion system comprising a circuit for demodulating the output digital modulated wave of the second variable gainer into an original analog signal. 2. A first variable gain device installed on the input side of an AD converter that digitally modulates an analog signal to obtain a digital modulated wave, and the time taken out from the output side (or input side) of the first variable gain device. The analog modulation signal level of the difference signal obtained by subtracting the absolute value of the digital modulation wave at time (n-1)T from the digital modulation wave at nT or its absolute value is y _o (where T is the sampling period of the digital modulation wave ), and when the coefficient for weighting is a _i , z _o = _N 〓 ⁱ⁼⁰ a _i・｜y _oi | (where, N is any natural number, and a ₀ to a _N are 0 or any number). A predicted signal having a signal level z _o that satisfies the formula is generated, and the control signal obtained by comparing the reference level from the variable reference level generator and the signal level z _o of the predicted signal is used to control the first variable A first gain control section that uses a gain unit to compress the analog modulation signal level of the input digital modulation wave within a predetermined level range, and a digital modulation wave taken out from the first gain control section is connected to a transmission path and D.A.
A second variable gain device that is supplied sequentially through the converter and whose signal level is varied according to the control signal, and an analog signal taken out from the input side (or output side) of the second variable gain device. a second gain control that performs an operation opposite to that of the first gain control unit and causes the second variable gain unit to expand the level of the input analog signal by the level compression amount in a predetermined level range; and a circuit for demodulating the output signal of the second variable gainer into an original analog signal.