JP2000341146A - Amplitude modulation transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct stable amplitude modulation. SOLUTION: An amplitude modulation transmitter uses a noise interrupter 13 to eliminate uncertain digital noise accompanying A/D conversion from a digital voice signal as a result of A/D conversion by an A/D converter 12. Furthermore, similarly an output adjustment device is connected to the post- stage of the A/D converter 12 to adjust an output, so s to obtain output power in response to a desired conversion cure and a power compensation section is connected to compensate the output with respect to fluctuations in a power supply voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplitude modulation transmitting apparatus capable of performing stable amplitude modulation by digital signal processing.

[0002]

2. Description of the Related Art Amplitude modulation transmitters include an amplitude modulation transmitter which directly generates amplitude modulation power by digital signal processing.
It is often used for 602 KHz medium wave radio broadcasters and the like.

In an amplitude modulation transmitting apparatus used in such a medium-wave radio broadcaster, first, an analog audio signal is input through a low-pass filter and converted into a digital audio signal.
/ D (analog-digital) conversion, a plurality of power amplifiers are switched according to the weight of the output by the digital audio signal, the amplitude of the carrier is controlled by the digital audio signal for each power amplifier, and the output from each power amplifier is controlled. After combining the carrier waves, removing the harmonic components, and finally outputting the combined amplitude-modulated wave.

In order to adjust the output power and the modulation degree of the amplitude modulated wave to appropriate levels, adjustment is necessary. In the conventional device, the DC bias of the analog signal before the A / D converter is adjusted. At the same time, it is necessary to change the input analog signal level in order to properly set the modulation degree.

[0005]

However, the conventional amplitude modulation transmitting apparatus has the following disadvantages.

First, when the signal level of the input analog audio signal changes between two digital values, one bit of the digital value is not determined, and this appears as digital noise. The appearance probability of the digital noise becomes higher when minute noise is superimposed on the analog audio signal.

When noise is generated on the output side of the low-pass filter, the noise includes frequency components equal to or higher than the voice frequency. Therefore, each power amplifier is controlled by high-frequency noise. For this reason, each power amplifier is forced to operate in a region where the transient response is poor. In such a state, for example, the output of the A / D converter is 7FF in hexadecimal.
At the transition point from to, the effect of noise appears on all 12 bits. Here, a large number of power amplifiers are switched in a region where the transient response is poor. For this reason, the influence of the original noise and the influence of the transient response are added, and the signal-to-noise ratio is reduced.

[0008] Second, the adjustment of the output and the adjustment of the modulation factor are separate. Therefore, every time the output power is adjusted, the degree of modulation must be adjusted. That is, in a method of adding a DC voltage to an input of an A / D converter or a reference voltage input as means for adjusting output power, for example, the A / D converter has 12 bits and the A / D converter When the input voltage of the A / D converter is 5 V, the output digital value of the A / D converter is 4095 at the maximum, and the output digital value of the A / D converter corresponding to the output power at the time of non-modulation of 100 W is 1850. In this case, the digital value of the output 101 W is (√101 / √100) × 1850 = 1850, and the A / D converter input conversion voltage per 1 W near 100 W is 5/4095 × (1859-1850) = about 11 mV, which is a very small voltage. For this reason, D
It is necessary to make the C bias stable so that the voltage does not change with temperature, and to minimize fluctuations due to external factors. In addition, since the change curve of the output power uniquely depends on the generation of the DC bias voltage, there is a problem that the degree of freedom in setting the change curve is small.

Further, since the DC bias operates independently of the amplitude voltage of the audio signal, there is a disadvantage that changing the DC bias voltage changes the degree of modulation of the amplitude modulation wave at the output. For example, FIG. 2 is an explanatory diagram showing a modulation waveform when 100% amplitude modulation is performed at the time of 100 W output, and FIG. 3 is an explanatory diagram showing a waveform of the amplitude modulation wave when the DC bias is adjusted so that the output becomes 50 W. FIG. At this time, if the DC bias is adjusted to change the output power, the degree of modulation changes, and the example of FIG. 3 indicates that overmodulation has occurred. Therefore, D
In the output power adjustment by adjusting the C bias, there is a problem that the input level of the audio signal must be adjusted in order to keep the modulation degree constant each time.

Third, as described above, as a means for absorbing output power fluctuations due to power supply voltage fluctuations, in the method of adding or subtracting power supply voltage fluctuations to the input of an A / D converter or a reference voltage input, Since the fluctuation of the voltage is independent of the amplitude voltage of the audio signal, there is a problem that the modulation degree of the amplitude modulation wave at the output changes. For example, FIG. 4 shows a modulation waveform of 100% amplitude modulation at the time of a steady power supply voltage, and FIG. 5 shows a 100% amplitude modulation waveform when the power supply voltage is increased by + 10% and output power compensation is not performed. Since the voltage component of the waveform of FIG. 5 is increased by 10% as compared with FIG. 4,
Since the output power is proportional to the square of the voltage, it increases by 21%. FIG. 6 shows a modulation waveform when the output power is compensated in the state of FIG. 5 by the conventional method, and shows that the modulation degree changes and an overmodulation state occurs.

When the voltage supplied to the plurality of power amplifiers is supplied from, for example, a 200V unstable power supply and a 15V stabilized power supply, the fluctuation of the input power supply affects only 200V of the unstable power supply. Therefore, in the conventional system, the fluctuation of the power supply voltage and the amplitude modulation output do not have a perfect proportional relationship, and a modulation waveform distortion occurs.

FIG. 7 is an explanatory diagram showing this. As shown in FIG. 7, when the voltage of the unstable power supply fluctuates, the output amplitude modulated wave is distorted. Therefore, in order to perform stable amplitude modulation so as to obtain a predetermined modulation degree and output power, it is necessary to eliminate these disadvantages.

[0013]

The present invention employs the following structure in order to solve the above problems. <Structure 1> The amplitude modulation transmitting apparatus according to claim 1
An A / D converter for digitizing a voice signal, a plurality of power amplifiers for amplifying a carrier wave to a predetermined output, and a synthesizing means for synthesizing the output of the power amplifier are provided. An amplitude modulation transmitting apparatus for obtaining the amplitude modulation power in the composite output by switching the number or output of the power amplifier, wherein an uncertain noise accompanying the A / D conversion is obtained from the digital data output from the A / D converter. A noise removing means for removing noise is provided.

<Structure 2> In the amplitude modulation transmitting apparatus according to the second aspect of the present invention, the noise eliminator digitally determines the magnitude of the difference between the current data and the previous data of the digital data output from the A / D converter. A change amount calculating means for calculating as the change amount of the data, the change amount calculated by the change amount calculating means is compared with a predetermined value, and when the change amount exceeds the predetermined value, it is determined that the signal component has changed, Determining means for determining that the noise is a noise when the amount of change is equal to or less than a predetermined value; outputting the current data when the determining means determines a change in the signal component; and outputting the current data when the determining means determines a noise. And output selection means for replacing the current data with the output data.

<Structure 3> An amplitude modulation transmitting apparatus according to a third aspect of the invention combines an A / D converter for digitizing an audio signal, a plurality of power amplifiers for amplifying a carrier into a predetermined output, and the power amplifier output. And a synthesizing means for performing A /
In an amplitude modulation transmitting apparatus for obtaining the amplitude modulation power in the composite output by switching the number or the output of the power amplifier according to the output digital data of the D converter, an average value of the amplitude modulation power by inputting the digital data Output setting means for setting the output setting means and data conversion means for converting the output digital data of the A / D converter in accordance with the digital data of the output setting means. The relationship between the average values of the power is set by an arbitrary output setting curve.

<Structure 4> An amplitude modulation transmitting apparatus according to a fourth aspect of the invention combines an A / D converter for digitizing an audio signal, a plurality of power amplifiers for amplifying a carrier into a predetermined output, and the power amplifier output. And a power supply for supplying a predetermined voltage to the plurality of power amplifiers.
In an amplitude modulation transmitting apparatus for obtaining the amplitude modulation power on the composite output by switching the number or the output of the power amplifier according to the output digital data of the D converter, the amplitude modulation wave is modulated irrespective of the fluctuation of the power supply voltage. Power compensation means for compensating the output power so as to keep the temperature and the average power constant.

<Structure 5> In the amplitude modulation transmitting apparatus according to a fifth aspect of the present invention, the power compensating means includes a second A / D converter for digitizing a voltage of the power supply, and a second A / D converter.
A fluctuation amount calculating means for calculating a fluctuation amount of the power supply voltage with respect to the rated voltage based on the power supply voltage data digitized by the D converter; and a fluctuation amount of the power supply voltage calculated by the fluctuation amount calculating means. And data conversion means for converting data digitized by the first A / D converter into a relationship to obtain an amplitude-modulated wave having a predetermined average output power and a predetermined modulation factor. .

<Structure 6> In the amplitude modulation transmitter according to the invention of claim 6, the power supply is constituted by a plurality of power supplies having different voltages, and the second A / D converter, the variation calculating means and The data conversion means is provided for each power supply.

<Structure 7> In the amplitude modulation transmitter according to the invention of claim 7, the power supply is constituted by a plurality of power supplies in which a stabilized power supply and an unstable power supply are mixed, and the second A / D is provided. A converter, a variation calculation means and a data conversion means are provided for each unstable power supply.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below using specific examples. <Specific example 1> In specific example 1, in the amplitude modulation transmitting apparatus,
This is to remove digital noise associated with A / D conversion of an analog audio signal.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the amplitude modulation transmitting apparatus according to the present invention. As shown in FIG. 1, from an input terminal IN to an output terminal OUT, a low-pass filter (hereinafter referred to as “LPF”) 11, an A / D
The converter 12, the noise breaker 13, the switch 14, the power amplifier 15, the synthesizer 16, and the band-pass filter (hereinafter referred to as "B
PF ") 17 are connected.

Such an amplitude modulation transmitting apparatus is used for a medium-wave radio broadcaster or the like, and in the following specific example, the case will be described. However, the present invention is not limited to these specific examples.

Hereinafter, each configuration will be described. The power amplifying unit 15 processes the carrier by a digital signal processing method to generate amplitude modulated power. n (n ≧
1) Each of the power amplifiers 15-1 to 15-n is separately controlled in accordance with a signal from a switch, is excited by a carrier signal, and performs high-efficiency power amplification. Each power amplifier output is output to the next-stage combiner 1 according to the respective weight.
6 to be added in series.

In the amplitude modulation transmitting apparatus, for example, 20
0V, 100V, 15V, etc.
Power supplies (not shown) of different voltages are provided according to the output levels of -1 to 15-n, and this power supply voltage is applied to each of the power amplifiers 15-1 to 15-n according to the output level. .

The LPF 11 is a filter that cuts over the audio frequency of the analog audio signal and passes only the audio frequency band signal. A / D converter 12, noise breaker 1
The sampling signal synchronized with the carrier is input to 3 and the switch 14.

The A / D converter 12 samples the analog audio signal at the cycle of the sampling signal and converts it into a digital audio signal. The noise breaker 13 is a noise removing means for removing uncertain digital noise from the digital audio signal A / D converted by the A / D converter 12, and its configuration will be described later.

The switch 14 generates a switch control signal for the power amplifiers 15-1 to 15-n based on the digital value output from the noise breaker 13 at the cycle of the sampling signal.

The combiner 16 includes power amplifiers 15-1 to 15-1.
This is a synthesizing means for weighting and synthesizing the power from each of the power amplifiers, which has been highly-efficiently amplified by 5-n, to obtain amplitude modulated power as a synthesized output. The BPF 17 removes harmonic components from the amplitude-modulated wave added and synthesized by the synthesizer 16 and outputs an amplitude-modulated wave to be finally transmitted.

Next, the configuration of the noise breaker 13 will be described. FIG. 8 is a block diagram showing a configuration of the noise breaker 13. As shown in FIG. D-type flip-flops (hereinafter, referred to as “DFF”) 21 and 22 are sequentially connected to the A / D converter 12. The DFFs 21 and 22 receive the sampling signal and latch the digital audio signal, and output the latched digital audio signal when the next sampling signal is input. The digital audio signals output from the DFFs 21 and 22 become current data and previous data, respectively.

The subtractor 23 comprises a DFF 21 and a DFF 22
The present data and the previous data of the digital audio signal output from are input and the difference is calculated. Absolute value calculator 24
Is connected to the subtractor 23, and calculates the absolute value of the difference between the current data and the previous data calculated by the subtractor 23 as the amount of change in the digital audio signal. The subtractor 23 and the absolute value calculator 24 correspond to a change amount calculator.

The comparator 25 has a predetermined value and absolute value calculator 2
The absolute value of the difference between the current data and the previous data calculated in step 4 is input, and the absolute value of the difference (the amount of change in the digital audio signal) of the digital audio signal is compared with a predetermined value to compare the absolute value of the digital audio signal. Whether the change is a change in the signal component, A
This is a determination means for determining whether the noise is uncertain digital noise accompanying the / D conversion. The predetermined value is a value set in advance by estimating the peak value of the digital noise so that the digital noise can be determined. The comparator 25 determines that the change of the digital audio signal exceeds a predetermined value, determines that the signal component has changed, and outputs data “0” (low level). Otherwise, the comparator 25 determines that the digital noise is digital noise. Data "1" (high level) is output.

The inverter 26 inverts the sampling signal and outputs the inverted signal.
Of the sampling signal based on the comparison result of
This is a gate for controlling the input to the FF 22.

The selector 28 is an output selection means for selecting and outputting the digital audio signal output from the DFF 21 or the DFF 22 according to the comparison result of the comparator 25. When the comparison result is "0", the output value of the DFF 21 is selected. That is, when the current data of the digital audio signal is "1", the DFF 22
, Ie, the previous data of the digital audio signal is selectively output.

<Operation> The LPF 11 cuts off the audio frequency or higher of the analog audio signal input from the input terminal IN, and the analog audio signal in the audio frequency band is input to the A / D converter 12. The analog audio signal is sampled by the A / D converter 12 every time the sampling signal is input to the A / D converter 12, converted into a digital audio signal, and input to the noise breaker 13.

Note that A / D conversion is performed in consideration of data skipping.
The frequency of the sampling signal input to the converter 12, the noise breaker 13, and the switch 14 is set sufficiently higher than the analog audio signal.

An audio signal used in a general medium-wave radio broadcaster is defined as 50 Hz to 7.5 kHz, and a carrier band is 531 kHz to 1602 kHz.

For example, at a low frequency of about 50 Hz, data skipping occurs by an amount corresponding to a peak value of digital noise predicted by a “peak” or “valley” of a modulation having a gentle change. If the frequency of the audio signal is set sufficiently higher than that of the audio signal, the lower the frequency of the audio signal, the larger the number of samplings in one cycle, and the smaller the influence of the modulation distortion due to the data jump.

On the other hand, if the frequency of the audio signal increases, the number of samplings in one cycle decreases, and the "peak" of the modulation increases.
Alternatively, since the amount of change in the data in the “valley” increases, no data jump occurs.

In the noise breaker 13, each time a sampling signal is input, the digital audio signal sampled by the A / D converter 12 is latched by the DFF 21. The digital audio signal latched by the DFF 21 is then output from the AND gate 27 to “1”.
Is latched by the DFF 22 when is output.

The digital audio signals output from the DFF 21 and the DFF 22 are input to a subtractor 23, where the difference between the present data and the previous data of the digital audio signal is calculated.
Further, the absolute value is calculated by the absolute value calculator 24,
As a result, the amount of change in the digital audio signal is detected.

The amount of change in the digital audio signal is compared with a predetermined value by the comparator 25, and it is determined whether the change in the digital audio signal is a signal component change or digital noise. As described above, the predetermined value is set in advance in anticipation of the peak value of the digital noise, and as a result of the comparison by the comparator 25, when the change amount of the digital audio signal exceeds the predetermined value, the change of the signal component And the comparator 25 outputs “0”. At this time, the current data of the digital audio signal output from the DFF 21 is selected by the selector 28 and output.

Next, when the analog audio signal is at the level of switching the digital value to be A / D converted,
One bit of the A / D converted digital value becomes uncertain, and this one bit appears as digital noise. When the change in the digital audio signal is caused by digital noise, the amount of change in the digital audio signal does not exceed a predetermined value.

When the change amount of the digital audio signal does not exceed the predetermined value, "1" is output from the comparator 25,
The selector 28 is switched to the DFF 22 side. Then, the previous data of the digital audio signal latched by the DFF 22 is selected by the selector 28 and output.

When "0" is output from the comparator 25, even if the output of the inverter 26 becomes "1", AND
Since the output of the gate 27 becomes “0”, the data output from the DFF 21 is not latched by the DFF 22. That is, the digital noise is not latched by the DFF 22, and only the signal component is latched by the DFF 22. Accordingly, while “0” is output from the comparator 25, only the signal component is continuously output from the DFF 22 as data preceding the digital audio signal.

The digital audio signal output from the noise circuit breaker 13 is input to the switch 14, and a switching control signal is generated at a sampling period based on the digital audio signal. The output carrier power of the power amplifiers 15-1 to 15-n is switched. The output of the power amplifier selected in accordance with the digital audio data is supplied with a carrier power having an amplitude corresponding to the data, and the outputs of all the switched power amplifiers are synthesized and added by the synthesizer 16 to be synthesized. Amplitude modulated power is obtained as output. Further BP
The harmonic component is cut by F17 and the output terminal OUT
Output a final amplitude modulated wave.

<Effect of Specific Example 1> As described above, according to Specific Example 1, when the change in the A / D converted digital value is small, it is determined that the digital noise is uncertain due to the A / D conversion. Then, the output is cut off and the previous data of the digital audio signal is output, so that digital noise can be effectively removed.

When this amplitude modulation transmitting apparatus is used in a medium-wave radio broadcaster, it is possible to prevent the signal-to-noise ratio in the apparatus from deteriorating. Further, when the noise is determined to be digital noise by the noise breaker 13, the data latched by the DFF 22 is not updated. Can be output.

<Example 2> In Example 2, an A / D-converted digital audio signal is converted in accordance with a preset output power line of an amplitude-modulated wave.

FIG. 9 is a block diagram showing the configuration of the second embodiment. In the specific example 2, the output adjuster 31 is connected between the A / D converter and the switching unit. The same elements as those in the specific example 1 are denoted by the same reference numerals, and description thereof will be omitted.

The output adjuster 31 is an output adjusting means for converting a digital audio signal in accordance with a preset output power line of an amplitude modulated wave. Then, for example, a digital output rotary switch is connected to the output adjuster 31, and the output power set value is input as a digital value to the output adjuster 31 from the rotary switch.

FIG. 10 is a diagram showing the configuration of the output adjuster 31. As shown in FIG. 10, the output adjuster 31 is constituted by a ROM (Read Only Memory) 32 storing a conversion table for adjusting the output according to the power.

The input to the ROM 32 is divided into an upper address and a lower address, the output power set value from the rotary switch is input as the upper address of the ROM 32, and the digital audio signal from the A / D converter 12 is input to the lower address. Enter as

FIG. 11 is an explanatory diagram showing an example of the conversion table stored in the ROM 32. In the figure, the upper column shows the output power set value input from the rotary switch,
The right column shows the digital audio signal input from the A / D converter 12, and the numerical value in the conversion table shows the converted digital audio signal. In the specific example 2, the digital audio signal is described as 12-bit offset binary data, and the output power setting value is set as 5-bit binary data.

<Operation> The analog audio signal is converted by the A / D converter 12 into a 12-bit digital audio signal.
It is input to M32 as a lower address. The output power set value is input from the rotary switch to the ROM 32 as 5-bit binary data as an upper address. The output of the digital audio signal is adjusted based on the conversion table shown in FIG.

Since the digital audio signal is 12 bits,
As shown in FIG. 11, the lower address has 4096 steps. Therefore, the median value “204” of the digital audio signal
7 is an input value at the time of no signal, and the digital audio signal changes in the range from the digital value "0" to "4095" around the central value "2047".

Since the output power set value is 5 bits,
There are 32 steps from 0 to 31. The conversion table of the ROM 32 is set such that the output power set value at the time of, for example, 100 W output is “31”, and the converted digital value is proportional to the output power set value.

When the output power is set to 100 W based on this conversion table, the output power set value “31” is input to the output adjuster 31 from outside by turning the rotary switch.

When the output power set value "31" is input, the median value "2047" of the digital audio signal is "1".
850 ", the maximum value at the time of 100% amplitude modulation is" 3700 ", and the minimum value is" 0 ", so that the digital audio signal has an amplitude ranging from" 0 "to" 3700 ". Become.

Similarly, when the output power set value at 100 W output is set to "31" and the output power set value is set to "10", the median value "2047" of the digital audio signal is converted to "1000", The maximum value at the time of 100% amplitude modulation is “2000”, and the minimum value is “0”.

Here, the output power is 2 of this digital value.
Since it is proportional to the power, the converted digital value is “100”.
The output power W at the time of “0” is W = (1000/1850) ² × 100 ≒ 29 (W).

As described above, the conversion of the median value of the digital audio signal means the determination of the output power at the time of non-modulation, which is the same as adding the bias voltage to the input of the A / D converter in the prior art. Further, since the conversion table is set so that the digital value to be converted is proportional to the output power set value, the modulation degree does not change even if the output power is changed.

The digital audio signal whose output has been adjusted in this way is input from the output adjuster 31 to the switch 14 and converted into a control signal by the switch 14 as in the first embodiment. A carrier power corresponding to the control signal is output by amplification, weighted serial addition is performed by the combiner 16, and a harmonic component is cut by the BPF 17, and a final amplitude modulated wave is output from the output terminal OUT.

<Effect of Specific Example 2> As described above, according to Specific Example 2, the A / D-converted digital audio signal is converted based on the output power set value, and the output is adjusted. It can be adjusted to a desired output power.

Further, it is possible to eliminate a change in the modulation factor due to the adjustment. For this reason, especially when such an amplitude modulation transmitting apparatus is used in a medium-wave radio broadcaster, adjustment can be simplified, and the output can be stabilized against temperature, external factors, and the like.

Since the output power set value is inputted by using a digital output rotary switch,
A desired output power set value can be easily set by remote control.

Also, no matter what output power set value is set,
Since the conversion table is set so that the conversion value is proportional to the digital audio signal, the output power can be changed without changing the modulation factor.

Note that the output power set value can be set according to a desired curve. FIG. 12 is an explanatory diagram illustrating a setting example of the output power set value. When the output power set value is set by 5 bits as shown in FIG. 12, the output power set value is set in a numerical range from “0” to “31” according to this conversion curve.

<Embodiment 3> In Embodiment 3, the output level of a digital audio signal is adjusted according to a predetermined power supply voltage.

FIG. 13 is a block diagram showing the configuration of the third embodiment. In the specific example 3, as shown in FIG. 13, a power compensator 41 as a power compensator is interposed between the A / D converter 12 and the switch 14, and a power supply voltage is input to the power compensator 41.

FIG. 14 is a block diagram showing a configuration of the power compensator 41. The A / D converter 42 receives the power supply voltage of the power amplification unit 15 and converts the power supply voltage into a digital value. The A / D converters 12 and 42 correspond to a first A / D converter and a second A / D converter, respectively.

The arithmetic unit 43 is a variation calculating means for calculating the variation of the power supply voltage based on the power supply voltage A / D converted by the A / D converter 42. The ROM 44 has A /
Data conversion means for inputting a digital audio signal as a lower address from the D converter 42, inputting a variation in power supply voltage as an upper address from the A / D converter 42, and outputting a control signal for compensating output power. It is.

FIG. 15 is an explanatory diagram showing an example of the conversion table stored in the ROM 44. In the figure, the upper column shows the digital value of the fluctuation amount of the power supply voltage, the left column shows the digital audio signal input from the A / D converter 12, and the numerical value in the conversion table shows the digital audio signal after conversion. . In the specific example 3, the digital audio signal is described as 12-bit offset binary data as in the specific example 2. The details of the conversion will be described later. The same elements as those in the specific example 1 are denoted by the same reference numerals, and description thereof will be omitted.

<Operation> The power supply voltage of the power amplification unit 15 is A /
The A / D conversion is performed by the D converter 42, and the amount of fluctuation with respect to the rated voltage is calculated by the calculator 43 based on the digitized power supply voltage.

In the specific example 3, the power supply voltage is 200 V ± 20
V (10%), and the variation of the power supply voltage is converted to 7-bit binary data. That is, when the power supply voltage is 200V ± 20V, the maximum fluctuation amount is ± 20V, when the power supply voltage is 180V, the fluctuation amount is “0”, and when the power supply voltage is 220V, the fluctuation amount is “20V”. 127 ". That is, the actual fluctuation amount of the power supply voltage is represented by a digital value within the range of 0 to 127.

The output power Vstep per one step of the digital value of the variation of the power supply voltage is as follows: Vstep = 40V / 127 = about 0.315V because the maximum variation of the power supply voltage is 40V. The output power is compensated in steps.

Further, the power Wstep per step near 100 W at a power supply voltage of 200 V is as follows: Wstep = 100 × (200.315 / 200) ² −100 = 0.315 (W)

When the power supply voltage is at the rated voltage of 200 V, the fluctuation amount of the power supply voltage is "63". At this time, the median value “2047” of the digital audio signal is the data “B204”.
7 when the power supply voltage is 180 V. The fluctuation amount of the power supply voltage is “0.” At this time, the data “A2047” is converted to the median value “2047” of the digital audio signal. And the power supply voltage is 220V,
The fluctuation amount of the power supply voltage is “127”, and the median value “2047” of the digital audio signal is converted into data “C2047”.

The data thus converted is output from the power compensator 41 to the switch 14, and the switch 14 switches the power amplifiers 15-1 to 15-n based on the data.

For example, when the data is "B2047", the power amplifiers 15-1 to 15- are set so that the power supply voltage is 200 V, the modulation degree does not change, and the output power at the time of 100% modulation is 100 W. n is switched.

Similarly, when the data is "A2047", the power amplifiers 15-1 to 15-n at the subsequent stage which can obtain an output of 100 W by this data "A2047".
, And a modulated wave having a constant modulation factor and output power can be obtained even when the power supply voltage is 180 V.

Similarly, when the data is "C2047", when the power supply voltage is 220 V, each of the power amplifiers 15-1 to 15-n so that an amplitude-modulated wave can be obtained while keeping the modulation degree and the output power constant. Is switched.

Then, as in the first embodiment, the power amplifying unit 15 outputs a carrier power corresponding to the control signal by high-efficiency amplification, and performs weighted serial addition by the combiner 16.
After the harmonic component is cut by the BPF 17, the final amplitude modulated wave is output from the output terminal OUT.

<Effect of Specific Example 3> As described above, according to Specific Example 3, the output of the amplitude modulation wave is compensated based on the fluctuation amount of the power supply voltage. Also, the output power can be kept constant without changing the modulation factor, and the performance of the medium-wave radio broadcaster is improved, especially when this device is used as the medium-wave radio broadcaster.

In the third embodiment, a case has been described in which power compensation is performed for a power supply voltage of 200 V. However, in an amplitude modulation transmitting apparatus, a plurality of power supply voltages are mixed as described above. Such power compensation may be performed for each power supply voltage.

For example, when power supplies of 15 V, 100 V, and 200 V are mixed, a power compensation unit is provided for the power supply voltages of 15 V, 100 V, and 200 V. Of these, the 15V power supply is a stabilized power supply,
When the power supply of 00V is an unstable power supply, 100V, 2V
Such power compensation can be performed for a power supply voltage of 00V.

With this configuration, even when the voltage of the unstable power supply fluctuates, compensation can be made so as not to impair the modulation linearity, and even if each power supply voltage fluctuates independently. , The degree of modulation and the output power can be kept constant, so that waveform distortion due to such voltage fluctuation of the power supply can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a specific example 1 of an amplitude modulation transmission device according to the present invention.

FIG. 2 is an explanatory diagram showing a modulation waveform at the time of conventional 100 W / 100% modulation.

FIG. 3 is an explanatory diagram showing a modulation waveform at the time of conventional 50 W / 100% modulation.

FIG. 4 is an explanatory diagram showing a modulation waveform at the time of 100% modulation at a steady power supply voltage.

FIG. 5 shows a conventional power supply voltage when the power supply voltage is increased by 10%.
FIG. 9 is an explanatory diagram showing a modulation waveform at the time of% modulation.

FIG. 6 is 100% when output power compensation is performed by a conventional method when the power supply voltage rises by 10% from the steady voltage.
FIG. 4 is an explanatory diagram showing a waveform of a modulated wave at the time of amplitude modulation.

FIG. 7 is an explanatory diagram for describing output of an amplitude-modulated wave when a power supply voltage fluctuates when unstable power supplies are mixed.

FIG. 8 is a block diagram illustrating a configuration of a noise breaker according to a first specific example.

FIG. 9 is a block diagram illustrating a configuration of a specific example 2 of the amplitude modulation transmission device according to the present invention.

FIG. 10 is a block diagram illustrating a configuration of an output adjuster according to a specific example 2.

FIG. 11 is an explanatory diagram illustrating an example of a conversion table stored in a ROM according to the second embodiment.

FIG. 12 is an explanatory diagram for describing a setting example of an output power set value in a specific example 2.

FIG. 13 is a block diagram illustrating a configuration of a specific example 3 of the amplitude modulation transmission device according to the present invention.

FIG. 14 is a block diagram illustrating a configuration of a power compensating unit according to a third specific example.

FIG. 15 is an explanatory diagram illustrating an example of a conversion table stored in a ROM according to the third embodiment.

[Explanation of symbols]

 12, 42 A / D converter 13 noise breaker 15 power amplifier 23 subtractor 24 absolute value calculator 25 comparator 28 selector 31 output adjuster 32, 44 ROM 41 power compensator 43 calculator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K060 BB08 CC04 DD03 EE02 FF02 FF06 HH06 HH11 HH31 HH33 HH39 KK01 KK03 LL01 LL11

Claims (7)

[Claims] An analog signal for digitizing an audio signal.
A digital converter (hereinafter referred to as an A / D converter), a plurality of power amplifiers for amplifying a carrier to a predetermined output, and a synthesizing means for synthesizing the output of the power amplifier; In response, the number or the number of the power amplifiers or the output is switched to obtain an amplitude-modulated power in the composite output.
An amplitude modulation transmission device comprising a noise removing means for removing uncertain noise due to conversion. 2. The change amount calculating means for calculating the magnitude of the difference between the current data and the previous data of the output digital data of the A / D converter as the change amount of the digital data; The change amount calculated by the amount calculation means is compared with a predetermined value, and when the change amount exceeds the predetermined value, it is determined that the signal component has changed, and when the change amount is equal to or less than the predetermined value, it is determined that the signal component is noise. And output selection means for outputting the current data when the determination means determines a change in the signal component, and replacing the current data with the previous data when the determination means determines that the change is noise. The amplitude modulation transmission device according to claim 1, wherein the transmission is performed. 3. An A / D converter for digitizing an audio signal, a plurality of power amplifiers for amplifying a carrier to a predetermined output, and a synthesizing means for synthesizing the output of the power amplifier.
An amplitude modulation transmission apparatus for switching the number or output of said power amplifiers in accordance with output digital data of a / D converter to obtain amplitude modulation power in said composite output. Output setting means for setting a value; and A / D corresponding to digital data of the output setting means.
Data conversion means for converting output digital data of the D converter, wherein the relationship between the set value of the output setting means and the average value of the amplitude modulation power is set by an arbitrary output setting curve. Transmission device. 4. An A / D converter for digitizing an audio signal, a plurality of power amplifiers for amplifying a carrier to a predetermined output, a synthesizing means for synthesizing the output of the power amplifier, and applying a predetermined voltage to the plurality of power amplifiers. And a power supply for supplying power.
An amplitude modulation transmitting apparatus that obtains amplitude modulation power on the composite output by switching the number or output of the power amplifiers according to the output digital data of the / D converter. An amplitude modulation transmission device comprising: power compensation means for compensating output power so as to keep a modulation degree and an average power constant. 5. The power compensating means includes: a second A / D converter for digitizing a voltage of the power supply; and a power supply voltage data digitized by the second A / D converter. A variation calculating means for calculating a variation of the power supply voltage with respect to the rated voltage; and a digitalization by the first A / D converter based on the variation of the power supply voltage calculated by the variation calculating means. Data conversion means for converting the data into a relationship to obtain an amplitude modulated wave having a predetermined average output power and a predetermined modulation degree,
The amplitude modulation transmitting apparatus according to claim 4, further comprising: 6. The power supply is configured by a plurality of power supplies having different voltages, and is configured to include the second A / D converter, the variation calculation means, and the data conversion means for each power supply. The amplitude modulation transmission device according to claim 5, wherein: 7. The power supply is constituted by a plurality of power supplies in which a stabilized power supply and an unstable power supply are mixed, and the second A / D converter, the variation calculation means and the data conversion means are provided with an unstable power supply. The amplitude modulation transmission device according to claim 5, wherein the amplitude modulation transmission device is configured to be provided for each power supply.