JP2002359656A - Digital modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital modulator that uses a digital circuit to optimally manage a maximum modulation factor. SOLUTION: The digital modulator is provided with: an analog/digital converter means 11 that converts a signal to be modulated into a digital signal; a compression processing means 12 that applies compression processing to the converted digital signal; a level adjustment means 13 that adjusts the level of the digital signal subjected to the compression processing so that the modulation factor of an output signal of the digital modulation means is a desired maximum modulation factor when the amplitude of the output signal from the compression processing means is a maximum amplitude specified in the compression processing; and a digital modulation means 14 that applies modulation processing to a digital carrier signal by the digital signal whose level is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator using a digital circuit.

[0002]

2. Description of the Related Art In an AM modulator or an FM modulator, it is necessary to appropriately manage a maximum modulation degree in order to prevent overmodulation or to prevent an occupied band from becoming wider than necessary. For example, for an AM modulator, the maximum modulation depth is 100
%, And the FM modulator needs to manage the maximum frequency deviation (deviation) so as to fall within a standard range. In order to appropriately manage such a maximum modulation degree, the amplitude of the modulated signal may be managed. Therefore, conventionally, in an AM modulator or an FM modulator, clipping processing is performed so as to limit the maximum amplitude of a modulated signal to a specific level, and a harmonic component generated thereby is removed by a low-pass filter. Have been done. In some cases, a method of limiting the maximum amplitude of the modulated signal to a specific level by AGC processing is used.

[0003]

However, since the harmonic distortion generated by the above-described clip processing extends to a considerably high frequency, when the clip processing is constituted by a digital circuit, the higher-order distortion generated by the clip processing is high. Harmonics appear as aliasing distortion. Therefore, if processing is not performed at an extremely high sampling frequency with respect to the frequency of the input signal, aliasing will appear near the input frequency. Such aliasing present near the input frequency cannot be dealt with by a low-pass filter for removing harmonic distortion. In addition, in the AGC process, the gain is adjusted at the peak level portion of the sound, so that the average modulation degree tends to be lower than that in the clip process.

Accordingly, an object of the present invention is to provide a digital modulator capable of optimally managing the maximum modulation using a digital circuit.

[0005]

In order to solve such a problem, it is conceivable to apply a compression processing device used for increasing the average power of a modulated signal in an SSB transmitter. An example of such a compression processing apparatus is disclosed in Japanese Patent Application Laid-Open No. 2000-165253. In this compression processing device, the processing is performed so as not to exceed the specified maximum amplitude. Therefore, by applying this method to the processing of the modulated signal, the maximum amplitude of the modulated signal is specified in the compression processing device. It can be limited to the maximum amplitude. However, the maximum amplitude specified in the compression processing device is fixed to 1 in advance. Therefore, when the maximum amplitude to be limited differs depending on the type of modulation and the characteristics of the modulation processing for each modulator, processing corresponding to these is required. Therefore, in the digital modulation apparatus according to claim 1 of the present invention, A / D conversion means for converting a modulated signal into a digital signal, compression processing means for performing compression processing on the converted digital signal, and compression processing means When the amplitude of the output signal is the maximum amplitude specified in the compression processing, the digital signal subjected to the compression processing is processed so that the modulation degree of the output signal of the digital modulation means described later becomes a desired maximum modulation degree. Means is provided that includes modulation degree adjusting means for adjusting the level of the signal and digital modulation means for performing a modulation process on the digital carrier signal with the digital signal whose level has been adjusted.

According to a second aspect of the present invention, the compression processing means accumulates the absolute value of the previous digital input data including the latest input digital input data while constantly updating the absolute value by a preset number of samples. Accumulating means, detecting means for detecting the maximum value among the absolute values of the accumulated digital input data, and inputting the latest digital input data or digital input data that is a predetermined number of samples earlier by the maximum value. And a calculating means for dividing and outputting.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A modulation device according to the present invention will be described below in detail with reference to the drawings showing an embodiment.

FIG. 1 is a block diagram of a modulation device according to the present invention. In FIG. 1, reference numeral 10 denotes a modulator, 11 denotes an A / D converter for converting an input modulated signal into a digital signal, 12
Reference numeral denotes compression processing means for performing a compression process on the modulated signal converted into a digital signal by the compression processing device having the configuration shown in FIG. Reference numeral 13 denotes modulation degree adjusting means for adjusting the level of the output signal of the compression processing means 12, which includes an amplifier or an attenuator. In the modulation degree adjusting means 13, the amplification rate or the attenuation rate is set in advance so that the output of the digital modulation means 14 at the subsequent stage has the desired maximum modulation degree when the output signal of the compression processing means 12 has the maximum amplitude. Have been. Therefore, the amplification rate or the attenuation rate is determined according to the maximum amplitude specified by the compression processing means, the desired maximum modulation degree, and the characteristics of the digital modulation means 14. The digital modulator 14 is an AM modulator or an FM modulator, and outputs a digitally modulated signal.

Next, details of the compression processing means will be described with reference to FIG. In FIG. 2, reference numeral 21 denotes an absolute value output means for obtaining an absolute value of each sample of the digital input data input from the A / D conversion means 11, and reference numeral 22 denotes a digital input data output from the absolute value output means 21. Shift buffer means for storing the absolute values for the number of samples set by the size setting means 24 in advance. In the shift buffer means 22, when the latest data is input as shown in FIG. 3, the oldest data stored up to that point is erased, so that a preset sample is set in order from new data. It is constantly updated and stored for a few minutes. Each time 23, the latest data is input to the shift buffer means 22,
As shown in FIG. 3, it is a detecting means for detecting the maximum value of the data stored in the shift buffer means 22. 2
Numeral 5 is a comparing means for comparing the maximum value detected by the detecting means with the reference value preset by the reference value setting means 26 and outputting the larger one. Numeral 27 divides the latest digital input data input from the A / D converter 11 or the digital input data earlier by a predetermined number of samples by the value output from the comparator 25 (multiplication by the reciprocal may be performed). This is an arithmetic means for outputting the result. According to the above configuration example, the modulated signal input from the input terminal is A
The signal is converted into a digital signal by the / D conversion means 11 and output to the compression processing means 12. Here, the digital signal output to the compression processing means 12 is normalized in the range of -1 to +1. In the compression processing means 12, when the latest digital input data is input from the A / D conversion means 11, the absolute value data is output from the absolute value output means 21,
The data is input to the shift buffer means 22. Where A / D
The digital input data input from the conversion means 11 is-
Digital data normalized to the range of 1 to +1;
The shift buffer means 22 has its absolute value of 0 to +1
The digital data of the range is stored.

In the shift buffer means 22, the stored data is updated, and the previous data including the latest data is stored for a preset number of samples in the new order. The detecting means 23 detects a peak of a predetermined section in the input signal by detecting the updated maximum value of the data stored in the shift buffer means 22. The detected maximum value is compared with the reference value by the comparing means 25, and the larger value is calculated by the calculating means 27.
Is output as the divisor in. The calculating means 27 calculates A /
By dividing the latest digital input data input from the D conversion means 11 or digital input data which is a predetermined number of samples earlier by the value output from the comparison means 25, the peak of a predetermined section in the input signal is saturated. The most recent digital input data is amplified and output at an amplification factor of 1, which is the maximum level that is not used.
That is, in the compression processing means 12, the maximum amplitude is defined as 1. Furthermore, A /
When the next digital input data is input from the D conversion means 11, the same processing as described above is repeated. The modulation degree adjusting means 13 adjusts the signal level by amplifying or attenuating the digital signal output from the compression processing means 12 and outputs the signal to the digital modulation means 14. Here, the amplification rate or the attenuation rate is a value such that when the amplitude of the output signal of the compression processing means 12 becomes the maximum amplitude of 1, the modulation degree of the output signal of the digital modulation means 14 becomes a desired maximum modulation degree. Is set in advance. That is, for example, when the digital modulator 14 has a characteristic of outputting a signal having a desired maximum modulation degree when a signal having an amplitude h is input, the amplification factor or the attenuation factor is set as h. As a result, the maximum modulation factor can be optimally managed using the existing compression processing means 12 without the necessity of changing the design. The digital modulator 14 performs a predetermined modulation process on a separately generated digital carrier signal based on the digital signal output from the modulation degree adjuster 13, and outputs the resultant signal. As a result, a digital modulation signal in which the maximum modulation degree is optimally managed is obtained from the output terminal.

Next, an embodiment in which the digital modulator of the present invention is realized by software will be described with reference to FIGS.
A description will be given based on the flowchart of FIG. FIG. 4 shows a DSP (Diode) used for signal processing of AM modulation or FM modulation.
3 is a flowchart illustrating an overall process of a digital signal processor. FIG. 5 is a flowchart showing details of the compression processing in FIG. In FIG. 4, in step S1, a low-frequency signal to be modulated, which is digitized by the A / D conversion means 11, is input. In step S2, the input digital signal is
The compression processing shown in is performed. In step S3, when the compression-processed output signal has the maximum amplitude, amplification or attenuation is performed at a preset amplification rate or attenuation rate so that the output of the later-described digital modulation means 14 has a desired maximum modulation degree. Damping is performed. And
In step S4, a digital signal subjected to AM or FM modulation is output from the DSP. Note that this DS
All digital values input to P are normalized in the range of -1 to +1 and processing is performed in this range even in the DSP.

The details of the compression processing in step S2 are as shown in FIG. In FIG. 5, NEW_DATA indicates a variable indicating the latest digital input data converted into a digital signal, N indicates a buffer size of a preset shift buffer, and PEAK
_BUFF [J] indicates a variable indicating the J-th accumulated data of the shift buffer, and the size of the shift buffer is N
And the range of J is from 0 to N−1. ABS_IN is NEW
_DATA indicates a variable representing an absolute value, PEAK indicates a variable for obtaining a maximum value, SET_VALUE indicates a reference value (> 0) for defining a preset maximum amplification factor, and MAX
(X, Y) indicates a function representing an operation for obtaining the larger of the variables X and Y. COMP_OUT indicates a variable representing an output value of the compression process.

In step S11, the absolute value of the latest digital input data (NEW_DATA) is
Substitute S_IN for the 0th data (PE
AK_BUFF [0]) is substituted for PEAK, and the absolute value of the latest digital input data is obtained in ABS_IN and the initial value of PEAK is set. In step S12, the shift buffer
Compare the (J + 1) th data (PEAK_BUFF [J + 1]) with PEAK and substitute the larger value into PEAK. 1]) is assigned to the J-th (PEAK_BUFF [J]) from J = 0 to J = (N-2)
Repeat until As a result, except for the latest digital input data, the maximum value of the data stored in the shift buffer is obtained in PEAK, and the data stored in the shift buffer is shifted to the 0th, respectively. The oldest data (PEAK_BUFF [0]) is discarded as shown in FIG.

In step S13, the absolute value (ABS_IN) of the latest digital input data is stored in (N-1) of the shift buffer.
) -Th (PEAK_BUFF [N-1]) to complete the shift of the shift buffer.
By substituting the larger value into PEAK, the maximum value of the data stored in the shifted shift buffer is obtained in PEAK. Then, PEAK and the reference value (S
ET_VALUE) and substituting the larger value into PEAK to obtain a divisor for signal amplification in PEAK. In step S14, the result obtained by dividing the latest digital input data (NEW_DATA) by PEAK is substituted for COMP_OUT representing the output value of the compression processing, and the data is processed in the next step (the modulation degree adjusting means 13 in FIG. It is used in step S4) in FIG. Or later,
The above processing is repeated each time the latest digital input data is input, so that the input signal is subjected to compression processing.

Note that, in this case as well, step S1
4, the latest digital input data (NEW_DATA)
Although it is configured to divide by the divisor obtained finally and output, a variable (PEAK_BUFF [J]
In addition to the above, a similar variable that stores NEW_DATA as it is may be added, and the object to be divided in step S14 may be the data at the predetermined position of the added variable. Thereby, the digital input data corresponding to any position in the section for detecting the maximum value can be set as a calculation target at that time. Also, the setting constant N
And SET_VALUE can be set in advance according to preference.

[0016]

According to the digital modulator of the first aspect of the present invention, since the maximum amplitude is managed by the compression processing without performing the limiter processing, it is possible to suppress the generation of harmonic distortion which is difficult to remove. it can. Further, when the compression processing is realized by DSP software, the processing method is simple and the number of steps is small, so that the load on the DSP is light. Further, since the existing compression processing means used for the SSB transmitter can be used, the design is easy and the reliability is sufficient.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital modulation device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a compression processing unit used in the digital modulation device.

FIG. 3 is an explanatory diagram of a shift buffer used in the compression processing means.

FIG. 4 is a flowchart when the digital modulation device is realized by software of a DSP.

FIG. 5 is a flowchart in a case where compression processing in the digital modulation device is realized by software.

[Explanation of symbols]

 Reference Signs List 10 digital modulation device, 11 A / D conversion means, 12 compression processing means, 13 modulation degree adjustment means, 14 digital modulation means, 21 absolute value output means, 22 shift buffer means, 23 detection means, 24 size setting means, 25 comparison Means, 26 reference value setting means 27 calculating means,

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J002 BB02 BB09 DD01 FF10 FF14 5K004 AA03 AA04 DD05 EE08

Claims (2)

[Claims] An A / A converter for converting a modulated signal into a digital signal.
D conversion means, compression processing means for performing compression processing on the converted digital signal, and when the amplitude of the output signal of the compression processing means is the maximum amplitude specified in the compression processing, the output signal of the digital modulation means described later And a modulation degree adjusting means for adjusting the level of the digital signal subjected to the compression processing so that the modulation degree becomes a desired maximum modulation degree, and modulating the digital carrier signal with the level-adjusted digital signal. A digital modulation device, comprising: 2. A storage means for storing the absolute value of the previous digital input data including the latest input digital input data while constantly updating the absolute value of the digital input data by a preset number of samples; Detecting means for detecting the maximum value of the absolute values of the input digital input data, and an operation of dividing the input latest digital input data or digital input data a predetermined number of samples earlier by the maximum value and outputting the result. 2. The digital modulation apparatus according to claim 1, further comprising: