JP2809967B2 - Digital AM transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital A
M transmitter.

[0002]

2. Description of the Related Art For a conventional digital AM transmitter,
This will be described with reference to the circuit configuration diagram of FIG.

An input terminal 61 receives a voice signal A from the input terminal 61. The input audio signal A is applied to the A / D converter 62, and is converted into, for example, a 12-bit digital signal. In this case, the digital signal is represented by a 12-bit binary code (2 ⁰ , 2 ¹ , 2 ² ,..., 2 ¹¹ ), and the digital signal is converted into an encoder 6 in parallel for each bit.
Added to 3.

The encoder 63 has 4095 (# 1 to # 4095) output terminals corresponding to a 12-bit binary code, and among these output terminals, a predetermined signal determined by bits of a digital signal. A signal is output from the output terminal.

[0005] For example, if ^{2 0} bit of the binary code is 1 (1 in decimal), from one output terminal # 1 1 is output. Also, if the ^{2 1} bit is 1 (decimal 2), two output terminals # 2, and # 3 1 it is output. When ^{2 2} bit is 1 (4 decimal), the four output terminals # 4 to # 7 1 is output.

Therefore, when the level of the audio signal is low, 1 is output from the output terminal having the lower number, and 1 is output from the output terminal having the higher number as the level of the audio signal increases. Become.

The output terminals of the encoder 63 are connected to carrier wave switches 64 (# 1 to # 4095), respectively. Each carrier wave switch 64 is connected to a switching power amplifier 65 (# 1).
To # 4095).

When the output 1 is applied from the output terminal of the encoder 63, the carrier switch 64 is turned on.

On the other hand, reference numeral 66 denotes an input terminal of the carrier signal C. The carrier signal C inputted from the input terminal 66 is divided into 4095 equal to the number of switching power amplifiers 65 by the distributor 67, and the carrier switch 64 Is added to Then, it is applied to the switching power amplifier 65 through the carrier switch 64 in the ON state.

The carrier signal C applied to switching power amplifier 65 is amplified and applied to combiner 68. The combiner 68 includes a switching power amplifier 65 (# 1 to ##).
4095) and the primary windings (# 1 to # 40)
95) and secondary windings (# 1 to # 4095) individually coupled to each primary winding and connected in series with each other.

Therefore, among the plurality of switching power amplifiers 65, the outputs of the operating switching power amplifiers are combined by the combiner 68. The combined output becomes an AM modulated wave AM by the bandpass filter 69 and is output from the output terminal 70.

[0012]

The conventional digital AM transmitter described above is characterized by high efficiency and high performance, but has the following disadvantages.

For example, although the encoder has a plurality of output terminals, an output terminal having a large number outputs only when the level of the audio signal is large. On the other hand, an output terminal having a small number is output even when the level of the audio signal is low or high. Therefore, the output terminal with the smaller number is output more frequently.

For this reason, the switching power amplifier connected to the output terminal of the encoder having the lower number has a longer operating time than the switching power amplifier connected to the output terminal of the encoder having the higher number.

By the way, a high-power transmitter such as a medium-wave radio transmitter is usually constructed by connecting a plurality of amplifiers having the same power in parallel. Therefore, if the operation times of the power amplifiers become uneven, a particular power amplifier will fail quickly, causing a problem in the balance of reliability.

The present invention solves the above drawbacks,
It is an object of the present invention to provide a digital AM transmitter in which a switching power amplifier operates on average.

[0017]

DISCLOSURE OF THE INVENTION Digital AM of the present invention
The transmitter has a coding means for receiving a digital signal obtained by digitizing a voice signal and outputting an operation signal from a number of output terminals corresponding to all or some bits of the digital signal, and an output of the coding means. A plurality of switching power amplifiers respectively connected to the terminals and amplifying a carrier signal modulated by the audio signal; and an output terminal of the encoding means, out of the plurality of switching power amplifiers, for outputting the operation signal. And a combiner for combining the outputs of the switching power amplifiers for amplifying the carrier signal, wherein all or some of the bits of the digital signal and all or some of the bits To change the combination with the output end of the encoding means from which a signal is output
A clock generator for generating a clock signal;
A counter to which a digital signal is applied,
All or some bits of the signal and all or one
The code whose signal is output from a number corresponding to the bits of the part
The combination with the output end of the
All or a part of the bit and the bit of the counter
The combination is determined.

[0018]

According to the above arrangement, the combination of all or some bits of the digital signal obtained by digitizing the audio signal and the output terminal of the encoding means for outputting a signal from the number corresponding to the bit is: It is determined by all or some of the bits and the passage of time.

Therefore, among the plurality of switching power amplifiers respectively connected to the output terminal of the encoding means and amplifying the carrier signal modulated by the voice signal, the switching power amplifier which actually operates is the level of the input digital signal. The operation time is not uniquely determined only by each of the switching power amplifiers, and the operation time of each switching power amplifier is equalized.

As a result, the amount of heat generated by the operating switching power amplifier is reduced, and the reliability is improved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the circuit diagram of FIG.

An audio signal input terminal 11 receives an audio signal from the input terminal 11. The input audio signal is A / D
The signal is applied to a converter 12 and converted into a 12-bit digital signal. Therefore, the digital signal is represented by a 12-bit binary code (2 ⁰ , 2 ¹ , 2 ² ,..., 2 ¹¹ ). This digital signal is applied to the encoder 13 in parallel for each bit.

The encoder 13 has 4095 (# 1 to # 4095) output terminals corresponding to a 12-bit binary code, and among these output terminals, the digital signal value ,
That is, a signal is output from a predetermined number of output terminals determined by the values of all or part of the bits of the digital signal .

[0024] For example, if ^{2 0} bit of the binary code is 1 (decimal 1) from one output terminal # 1 1 is output. Also, if the ^{2 1} bit is 1 (2 in decimal) is two output terminals # 2, and # 3 1 is output.
When ^{2 2} bit is 1 (4 decimal) is
1 is output from the four output terminals # 4 to # 7.

Therefore, when the level of the audio signal is low, the lower bit becomes 1, and 1 is output from the output terminal with the smaller number. Then, as the level of the audio signal increases, the higher-order bit becomes 1, so that 1 is output from the output terminal having the larger number.

The output end of the encoder 13 is connected to the variable encoder 14. Although the operation of the variable encoder 14 will be described later, 4095 variable encoders 14 (# 1 to # 409) correspond to the output terminals of the encoder 13.
5) It has an input terminal and an output terminal. The output ends of the variable encoders 14 are respectively connected to the carrier switching units 15.
(# 1 to # 4095), and the carrier switching unit 15 similarly switches the switching power amplifiers 16 (# 1 to # 4).
095).

The carrier switch 15 is a variable encoder 1
4 is set to be ON when an output is applied.

In each of the embodiments, the carrier switching unit 15 and the switching power amplifier 16 are composed of a plurality of units. However, the expression of the carrier switching unit 15 and the switching power amplifier 16 and the like is not necessarily a generic term for these units. However, even when one or more specific ones are expressed, the description will be made with the carrier wave switch 15 or the switching power amplifier 16 being expressed.

Reference numeral 17 denotes an input terminal of the carrier signal. The carrier signal input from the input terminal 17 is divided into 4095 equal to the number of the switching power amplifiers 16 by the distributor 18, and each of them is transmitted to the carrier switch 15. Added. Then, the carrier is switched from the carrier switch 15 in the ON state to the switching power amplifier 16 and amplified. The amplified signal is applied to the synthesizer 19. The configuration and operation of the switching power amplifier 16 are described in US Pat.
80, 111, and the description is omitted.

The combiner 19 includes primary windings (# 1 to # 4095) individually connected to each switching power amplifier 16.
And secondary windings (# 1 to # 4095) individually coupled to each primary winding and connected in series.
Therefore, of the plurality of switching power amplifiers 16, the outputs of the switching power amplifiers 16 in the operating state are combined by the combiner 19. At this time, it is operating
The number of switching power amplifiers 16 depends on the digital signal
Corresponding to all or some of the values of the Accordingly
Thus, the combined output corresponds to the output of the A / D converter 12.
In response, the signal is converted into an AM modulated wave by the bandpass filter 20, and the output terminal 21
Output from

Here, the above-described encoder 13 and variable encoder 1
Operations such as 4 will be described with reference to the circuit configuration diagram of FIG.

In FIG. 2, corresponding to FIG. 1, 211 is the input terminal 11 of the audio signal, 212 is the A / D converter 12, 213 is the encoder 13, 214 is the variable encoder 14,
215 corresponds to the carrier switching unit 15 and 216 corresponds to the switching power amplifier 16, respectively.

Note that, in the embodiment of FIG.
It has been converted into a digital signal of bits, in FIG. 2, for convenience of explanation, 4 bits ^{(2 0,} 2 ^{1, 2} 2,
2 ³⁾ will be described as being converted into a digital signal.

Therefore, the A / D converter 212 has 4
The output terminals (# 1 to # 4) are connected to the encoder 213.

The encoder 213 has four input terminals (# 1 to ##).
4) and 15 output terminals (# 1 to # 15), and a buffer amplifier (B1) between each input terminal (# 1 to # 4) and each output terminal (# 1 to # 15). To B15) are connected.

[0036] For example, input # 1 corresponding to ^{2 0} bit
And one buffer amplifier B1 is, the, the input terminal # 2 corresponding to the 2 ¹ bit two buffer amplifiers B2,
B3 is, the input terminal # 3 corresponding to the ^{2 2} bit four buffer amplifiers B4 to B7, further to the input terminal # 4 corresponding to the ^{2 3} bit is connected to eight buffer amplifiers B8~15 , These buffer amplifiers have output terminals (# 1 to #
15).

The fifteen output terminals of the encoder 213 (#
1 to # 15) are connected to input terminals (# 1 to # 15) of a variable encoder 214, for example, a matrix switch SW. The matrix switch SW has the same number of output terminals (# 1 to # 15) as the input terminals. The input terminal and the output terminal of the matrix switch SW are connected through an intersection of the matrix crossing in the vertical and horizontal directions. The intersection connecting the input terminal and the output terminal is configured to move by, for example, a clock signal generated by the clock generator CL.

For example, at a certain time t = n, the intersection of the mark ○ is in a connected state, and at a time t =
In the case of n + 1, the intersection of the □ mark indicates that t
At the time of = n + 2, control is performed such that the intersection of the triangle mark is in the connected state.

Therefore, in the example shown in the figure, each time the clock signal rises, the intersections in the connected state move rightward in order.

For example, the input terminal # 1 is connected to the output terminals # 1 to # 2, # 3... In order with the passage of time, and the input terminal # 2 is connected to the output terminals # 2 to # 3,
# 4... Are sequentially connected.

The output terminals of the matrix switches SW are connected to carrier wave switches 215 (# 1 to # 15). The carrier switch 215 is turned on when an output is applied from the output terminal of the matrix switch SW.
State. Then, as described with reference to FIG. 1, while the carrier switch 215 is in the ON state, the carrier switch 215
Through (# 1 to # 15), the carrier signal C is added to the switching power amplifier 216 and amplified. The carrier signal C amplified by the switching power amplifier 216
Is then combined and converted into an AM modulated wave, as in the case of FIG.

According to the above configuration, even if the level of the audio signal is constant and the output terminal from which the signal is output from the encoder 213 is the same, the output terminal from which the signal is output from the matrix switch SW is It changes over time.

Therefore, even if there is no change in the input audio signal, the switching power amplifiers connected to the output terminal of the matrix switch SW operate uniformly, and one switching power amplifier may operate in a concentrated manner. Absent. Therefore, the balance of the reliability of each switching power amplifier is improved, and the reliability is also improved.

Here, an embodiment in which the configurations of the encoder 213 and the variable encoder 214 of FIG. 2 are realized using an EP-ROM (erasable programmable read only memory) will be described with reference to FIG. explain.

3, 311 corresponds to the audio signal input terminal 211, 312 corresponds to the A / D converter 212, EP-ROM 300 corresponds to the encoder 213 and the variable encoder 214, and 315 corresponds to FIG. Is the carrier switch 215,
Reference numerals 316 correspond to the switching power amplifiers 216, respectively. Reference numeral 301 denotes a carrier signal source, and 302 denotes a clock generator, which correspond to the carrier signal source C and the clock generator CL in FIG. 2, respectively. Reference numeral 303 denotes a 15-digit counter. In the operation of FIG. 3, a detailed description of the same parts as those of FIG. 2 will be omitted.

First, from the clock generator 302, FIG.
A series of clock signals as shown in FIG. This clock signal is applied to a decimal counter 303 and converted into a decimal signal.

The decimal counter 303 has four bit terminals (bit 0 to bit 3), from the bit 0 terminal to FIG. 4 (e), from the bit 1 terminal to FIG. 4 (c), and a signal as shown in FIG. 4 (b) is output from the bit 3 terminal. In the following description, a high level such as the output of each bit terminal of the decimal counter 303 is indicated by “1”, and a low level is indicated by “0”.

The outputs of the four bit terminals (bit 0 to bit 3) are input to the input terminal A0 of the EP-ROM 300.
To A3.

The audio signal supplied from the input terminal 311 is converted by the A / D converter 312 into, for example, a 12-bit digital signal. However, in FIG. 3, as in the case of FIG. 2, 4 bits (2 ⁰ , 2 ¹ , 2
^2, 2 ³⁾ is described as being converted into a digital signal.

Therefore, the A / D converter 312
Output terminals (# 1 to # 4).
Connected to input terminals A4 to A7 of ROM 300.

The EP-ROM 300 has, for example, 16 input terminals and 16 output terminals, respectively. In FIG. 3, eight input terminals A0 to A7 are used.
Of these, 15 output terminals D0 to D14 are used.

The EP-ROM 300 is an element that can uniquely set a combination of output terminals from which a signal is output by a combination of input terminals to which an input is actually applied. In the case of the embodiment, for example, as shown in FIG. Is set to

FIG. 5 shows a part of the combination. A0 to A7 in the horizontal direction are shown in EP-ROM 300 (FIG. 3).
Input terminals A0 to A7, and D0 to D14 are EP-
This corresponds to the output terminals D0 to D14 of the ROM 300 (FIG. 3). The vertical direction is the count value of the decimal counter 303, and the count value of the counter repeats 0 to 14 in order.

Therefore, in FIG.
The combination of the four bit terminals No. 03 and each bit of the audio signal converted into a digital signal makes the EP-ROM 3
The output terminals D0 to D14 of the 00 indicate which signals are output. Note that, among the output terminals D0 to D14, "1" indicates a state where there is an output.

When there is no output of the digitized audio signal, that is, when there is no input at the input terminals A4 to A7,
The coefficient value of the decimal counter 303, that is, the input terminals A0 to A0
Regardless of the input to A3, which output terminal D0-D
No signal is also output to 14.

Next, when there is output to the 2 ⁰ bit of the audio signal, i.e., if there is an input to the input terminal A4, to one output terminal D0 when the coefficient value in this case is 15-ary counter 303 is 0 “1” is output, and the output terminal that is output each time the coefficient value of the decimal counter 303 increases moves rightward.

[0057] Further, when there is output to the 2 ¹ bit audio signal, i.e., if there is an input to the input terminal A5, 2 pieces of output terminals example D1 when the coefficient value in this case is 15-ary counter 303 is 0, "1" is output to D2, and the output terminal that is output each time the coefficient value of the decimal counter 303 increases moves rightward in a state of two pairs.

The output terminal from which "1" is output is D1
Return to D0 from 4.

[0059] Further, when there is output to the 2 ² bit of the audio signal, i.e., if there is an input to the input terminal A6, the coefficient value in this case is 15-ary counter 303 is four output terminals example D3~ when 0 “1” is output to D6, and the output terminals that are output each time the coefficient value of the decimal counter 303 increases move rightward in a four-group state.

[0060] Finally, when there is output to the 2 ³ bit of the audio signal, i.e., if there is an input to the input terminal A7, 8 pieces of output terminals example D7 when the coefficient value in this case is 15-ary counter 303 is 0 "1" is output to .about.D14, and the output terminals which are output each time the coefficient value of the decimal counter 303 increases move in the rightward direction in a state of eight pairs. Incidentally, the digitized speech signal, if there is an output to the plurality of bits simultaneously, for example, if there is an output to the 2 ¹ bit and 2 ² bit of the audio signal, this time, the 2 ¹ bit by the above description and if there is output when the 2 ² bit is output may be considered to overlap.

For example, when the coefficient value of the decimal counter 303 is 0
If "1" is output present at the two output terminals D1, D2 of the input to the input terminal A5 (2 ¹ corresponding to a bit),
Further, "1" is output in the presence of the input to the input terminal A6 (corresponding to 2 ² bit) to the four output terminals D3～D6, "1" is output to the total of six output terminals.

The output terminals from which these "1" are output are sequentially moved to the right in the state where the six output terminals are assembled in accordance with the above-described procedure each time the coefficient value of the decimal counter 303 increases. Will do.

As described above, the signal is determined by the combination of the output of each bit (2 ⁰ , 2 ¹ , 2 ² , 2 ³ ) of the audio signal converted into the digital signal and the coefficient value of the 15-decimal counter 303. The output terminals D0 to D14 to be output are uniquely determined.

The output of the EP-ROM 300 (FIG. 3) is applied to the carrier switch 315 (# 1 to # 15) to turn on the carrier switch 315. As a result, during the period of being in the ON state as described in FIG.
5 (# 1 to # 15), the carrier signal C is added to the switching power amplifier 316 and amplified. The carrier signals amplified by the switching power amplifiers 316 (# 1 to # 15) are combined by the combiner 304, and output from the output terminal as an AM modulated wave through a bandpass filter.

According to the above configuration, even if the level of the audio signal is constant, the output terminal from which the signal is output changes with time according to the coefficient value of the decimal counter.

For this reason, even if the input audio signal does not change, the switching power amplifier that is in the operating state changes with time, and the operation does not concentrate on one switching power amplifier.

The output of each bit (2 ⁰ , 2 ¹ , 2 ² , 2 ³ ) of the audio signal converted to the digital signal and 15
FIG. 5 is an example of which output terminal D0 to D14 outputs "1" depending on the combination with the coefficient value of the binary counter, and other combinations are also possible.

Although the above description has been made for the case of 4 bits, the description can be similarly applied to the case of 12 bits.

In the above embodiment, an example is described in which all bits of the audio signal converted to a digital signal are processed. However, some bits of the audio signal converted to a digital signal, for example, 2 minutes The present invention can be applied to a case where only the processed upper bit signal or lower bit signal is processed.

[0070]

According to the present invention, a switching power amplifier operates on average, and a digital AM with improved reliability is provided.
A transmitter can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram for explaining the operation of the present invention.

FIG. 3 is a circuit configuration diagram for explaining the operation of the present invention.

FIG. 4 is a waveform diagram illustrating the operation of the present invention.

FIG. 5 is a diagram for explaining the operation of the present invention.

FIG. 6 is a circuit diagram illustrating a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Input terminal 12 ... A / D converter 13 ... Encoder 14 ... Variable encoder 15 ... Carrier wave switcher 16 ... Switching power amplifier 17 ... Input terminal 18 ... Distributor 19 ... Synthesizer 20 ... Band filter 21 ... Output terminal

Claims (1)

(57) [Claims] An encoding means for receiving a digital signal obtained by digitizing an audio signal and outputting an operation signal from a number of output terminals corresponding to all or some bits of the digital signal; A plurality of switching power amplifiers each connected to an output terminal and amplifying a carrier signal modulated by the voice signal; and among the plurality of switching power amplifiers, an output of the encoding means from which the operation signal is output. A digital AM transmitter connected to an end of the digital signal and comprising a combiner for combining the output of a switching power amplifier for amplifying a carrier signal. To change the combination with the output end of the encoding means from which the signal is output from the corresponding number
A clock generator for generating a clock signal of
A counter to which a clock signal is applied;
All or some bits of the
A signal output from a number corresponding to some bits;
The combination with the output terminal of the
Bits of all or a part of bits of the counter No.
A digital AM transmitter characterized in that the digital AM transmitter is determined in combination with the following .