JPS5952584B2 - Digital modulated wave transmission method - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a digital modulated wave transmission system, and an object thereof is to provide a system that can transmit a digital modulated wave of quality exceeding the limited number of bits with a small number of transmission bits. .

FIG. 1 shows a block system diagram of an example of a conventional digital modulated wave transmission system.

In the figure, an analog signal entering one input terminal is supplied to a low-pass filter 2, where unnecessary high-frequency components are removed, and then supplied to a sampling and holding circuit 3, where it is sampled and held. The temporally discretized sampled signal extracted from the sampling and hold circuit 3 is applied to an AD converter 8 through a variable gain device 7, which will be described later, and is also supplied to an absolute value circuit 4, where the absolute value value is taken. The output signal of this absolute value circuit 4 is sent 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, when the absolute value of the input voltage becomes large and reaches the maximum or minimum input voltage that can be transmitted by the AD converter 8, the gain control from the voltage comparator 6 is performed. As a result of varying the gain depending on the signal, the absolute value of the output voltage is attenuated. As a result, variable gain device 7
The output voltage of the third
The waveform will be as shown in the figure. 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 via a predetermined transmission path, where it is digital-to-analog converted, and then the level attenuated or level-enhanced in the transmission system is restored by the variable gainer 10. The signal is restored to the original analog signal by the low-pass filter 11 and output from the output terminal 12. However, in the conventional digital modulated wave transmission method described above, the variable gain is controlled by the variable gain unit 10 on the receiving side in the opposite direction and by the same amount as the gain controlled by the variable gain unit 7 on the transmitting side. Since device control signals also had to be transmitted at the same time as transmission signals, the demand for reducing the number of transmission bits was limited. The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 4 shows a block system diagram of an embodiment of the digital modulated wave transmission system according to the present invention. In the figure, the same parts as in FIG. 1 are given the same numbers, and their explanations will be omitted. In FIG. 4, the sampled signal taken out from the sampling and holding circuit 3 is supplied to a signal prediction circuit indicated by a broken line 13, and is also supplied to a gain controller 24. Signal prediction circuit 1
The output signal of the sampling hold circuit 3 is first supplied to an absolute value circuit 14, where the absolute value is taken and supplied to a delay device 15 and an adder 17, respectively. The delay device 15 delays the input signal for a time equal to one sampler cycle of the sampling and holding circuit 3, and outputs the signal to the inverter 16.
The output delayed signal is supplied to the adder 17 through. The output signal of the adder 17 is subjected to gain control for appropriate weighting by a gain controller 18, and then supplied to an adder 19, where it is added to the output signal of the absolute value circuit 14. Therefore, the adder 19 combines the signal from the absolute value circuit 14 and the output signal (
(differential coefficient detection signal), thereby outputting a predicted signal. That is, if an example of the analog conversion level of the output sampling signal of the absolute value circuit 14 is shown by the solid arrow in FIG. 5, the analog conversion level at a certain time t1 and the elapsed sampling period '
The sampled signal (difference signal) indicating the difference d from the analog conversion level at time T2 is output from the adder 17 to time T2.
is output, further multiplied by a weighting coefficient α in the gain controller 18, and supplied to the adder 19, so the adder 19
The analog conversion level of the output signal is the sum of the output analog conversion level of the absolute value circuit 14 at time T2 and the analog conversion level of the difference signal αd, as shown by the broken line arrow 1 at time T3 in FIG. become.

The predicted signal indicated by the broken arrow 1 is obtained at time T2 as a signal that predicts the analog conversion level of the output obtained from the absolute value circuit 14 at time T3. Note that the solid arrow 11 indicates the actual analog conversion level of the output of the absolute value circuit 14 at time T3, which is a sampling cycle after time T2, and is a level that approximates the predicted signal. The present invention controls and transmits the input signal level of the AD converter 8 based on this predicted signal, and performs level control on the receiving side that is opposite to that on the transmitting side, thereby generating a digital modulated wave with a fixed number of bits. The transmission is performed without the need for control signal bits.

The predicted signal taken out from the adder 19 is sent to comparators 20 and 2.
1, and the level is compared with the output signal level of the upper limit level setter 22 and the lower limit level setter 23.

The level range of the difference between the upper limit level set by the upper limit level setter 22 and the lower limit level set by the lower limit level setter 23 indicates a certain level range that can be transmitted by the AD converter 8 with a small number of bits, and the predicted signal level When the predicted signal level becomes higher than the set upper limit level, this entire level range is shifted upward, and on the other hand, when the predicted signal level becomes lower than the set lower limit level, this entire level range is shifted downward. Ru. For example, as shown in FIG. 6, the set upper limit level is 111. In the state where the setting lower limit level is indicated by IV,
When the predicted value of the output analog conversion level of the absolute value circuit 14 indicated by the dashed arrow at time T3 obtained at time T2 exceeds the set upper limit level 111, the comparator 20 determines the set upper limit of the upper limit level setter 22. At the same time, a signal is output to make the level higher than the predicted value as shown by 111'', and at the same time, the lower limit level set by the lower limit level setter 23 is also set to IV''.
As shown in , it is increased by the same amount.

At the same time, the comparator 20 outputs a control signal to the gain controller 24 to reduce the gain, and attenuates the signal level supplied from the gain controller 24 to the AD converter 8 at time T3 by a predetermined level. . On the other hand, when the predicted signal level at time Tn+2 obtained at time Tn+1 becomes smaller than the previously set lower limit level as shown by the broken line arrow in FIG. At the same time that a signal is output to make the set lower limit level lower than the predicted signal level of Tn+2, as shown by I'''', the set upper limit level of the upper limit level setter 22 is also lowered by the same amount, as shown by II''. A signal is output for this purpose.

At the same time, the comparator 21 outputs a control signal to increase the gain to the gain controller 24, and increases the signal level supplied from the gain controller 24 to the AD converter 8 at time Tn+2 by a predetermined level. . In this way, the analog conversion level of the signal (sampled signal) output from the gain controller 24 and supplied to the AD converter 8 is set within a level range that can be transmitted with high quality by the AD converter 8, Control is always performed to follow the one with the largest level change.

Therefore, when a signal input with a large level change is input, the lowest level of quantization is increased, and conversely, when a level change is small, the lowest level of quantization is lowered, and finer quantization is performed. Note that FIG. 7 shows the analog converted input/output characteristics of the gain controller 24, where the solid line V shows the input/output characteristics at a certain time, the dashed line VI shows the input/output characteristics at other times, and the dynamic range P is constant. It is. The output signal of the gain controller 24 obtained as described above is converted into a digitally modulated wave (for example, a PCM signal) by the AD converter 8, and is transmitted via a transmission path, and is then transmitted to the receiving side DA shown in FIG.
The signal is supplied to a converter 9, where it is subjected to digital-to-analog conversion, and then supplied to a sampling hold circuit 25 and a gain controller 27, respectively.

The output signal of the sampling and holding circuit 25 is supplied to a signal prediction circuit 26. The signal prediction circuit 26 has the same circuit configuration as the signal prediction circuit 13, but when the predicted signal level becomes higher than the upper limit setting level, the upper limit and lower limit setting levels are increased by a predetermined amount, and at the same time, gain control is performed. Vessel 2
output a control signal to increase the gain of 7 to a predetermined gain;
On the other hand, when the predicted signal level becomes smaller than the lower limit setting level, the upper limit setting level and the lower limit setting level are respectively reduced, and at the same time, a control signal is outputted to reduce the gain of the gain controller 27 to a predetermined gain. This is different from the signal prediction circuit 13.

The output signal of the gain controller 27 obtained in this manner is passed through the low-pass filter 11, restored to the original analog signal, and outputted from the output terminal 12.

According to this embodiment, the signal prediction circuits 13 and 26 are provided, and control signals for the gain controllers 24 and 27 are obtained depending on whether the predicted signal level obtained from the sampled signal exceeds the upper limit or lower limit set level. Therefore, there is no need to transmit a special gain control signal, and the digital modulated wave can be transmitted with a smaller number of bits than before, and when the input analog signal level is small, the lowest level of quantization can be used. is lowered, finer quantization can be performed, and quantization noise is reduced.

In the above embodiment, the predicted signal is obtained from the adjacent sampled signals, but it is obtained by using the average value of the sampled signal two sampling periods and one sampling period ago, respectively, and the sampled signal at the current time. You can do it like this.

As described above, the digital modulated wave transmission method according to the present invention obtains a predicted signal from the absolute value output of the output signal of the sample-and-hold circuit and its difference signal, and controls the analog conversion level of the predicted signal to a preset upper limit using the control circuit. Only when the set level range between the level and the lower limit level is exceeded, the gain of the first gain controller to which the output signal of the sample and hold circuit is supplied is set to be small when the output signal is higher than the upper limit level, and When it is smaller than the lower limit level, it is controlled to be higher, and the upper limit level and lower limit level are changed so that the analog equivalent level of the predicted signal is within the set level range, and the first gain controller The output signal of
The gain of the second gain j controller is transmitted as a digital modulated wave by the converter, and the transmitted digital modulated wave is supplied through the DA converter by a signal prediction circuit that performs an operation opposite to that of the control circuit. Since the output signal of the second gain controller is demodulated into the original analog signal, the input signal level can be controlled even if the conversion accuracy of the AD converter or DA converter is low. In addition, there is no need to transmit a gain control signal to the receiving side, so digitally modulated waves can be transmitted with fewer bits than before, and when the input analog signal level is low. lowers the minimum level of quantization and performs finer quantization, which reduces quantization noise.
It has the advantage of being able to transmit digitally modulated waves with high quality using a limited number of bits, which is smaller than the above.

[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 is a block system diagram showing an embodiment of the method of the present invention, FIG. 5 is a diagram showing an analog conversion level for explaining the operating principle of the main part of the method of the present invention, and FIG. 6 is a diagram of the present invention. FIG. 7, which is a diagram for explaining the operation of other main parts of the inventive system, is a diagram showing an example of the input/output characteristics of the gain controller on the transmitting side of the inventive system. 1...Analog signal input terminal, 3, 25...
...Sampling hold circuit, 8...AD
Converter, 9...DA converter, 12...
Analog signal output terminal, 13, 26...signal prediction circuit, 14...absolute value circuit, 15...
・Delay device, 17, 19... Adder, 20, 21
... Comparator, 22 ... Upper limit level setter, 23 ... Lower limit level setter, 24, 27.
...Gain controller.

Claims (1)

[Claims] 1. A sample and hold circuit that samples and holds an analog signal, a first gain controller that outputs a variable output signal level of the sample and hold circuit, and an absolute value circuit that obtains an absolute value output of the output signal of the sample and hold circuit. a difference circuit which is supplied with the absolute value output signal of the absolute value circuit and outputs a difference signal corresponding to the difference between the signal at least one sampling period or more earlier and the signal at the current time; and the absolute value circuit and the difference circuit. an adder circuit that adds both output signals to output a predicted signal; and the first gain is applied only when the analog conversion level of the predicted signal exceeds a preset level range between a preset upper limit level and a lower limit level. The gain of the controller is controlled to be small when the gain is larger than the above upper limit level, and large when it is smaller than the above lower limit level, and the above upper limit level and lower limit level are set so that the analog conversion level of the above predicted signal is the above set level. a control circuit that changes the level so that the level is within a range; an AD converter that converts the output signal of the first gain controller into a digital modulated wave; and the digital modulated wave that has passed through the transmission line is supplied through the DA converter. A circuit configuration similar to the circuit configuration consisting of the second gain controller, the absolute value circuit, the difference circuit, the adder circuit, and the control circuit on the transmitting side to which the output of the DA converter is supplied is used. a signal prediction circuit that performs a gain control operation on the second gain controller that is opposite to the control operation of the gain controller; and a circuit that demodulates the output signal of the second gain controller into an original analog signal. A digital modulated wave transmission system characterized by having a structure of: