JP4363416B2 - Amplitude modulation circuit - Google Patents

Description

  The present invention relates to an amplitude modulation circuit, and more particularly to an amplitude modulation circuit used for a radio transmitter such as a medium wave band and a short wave band.

  FIG. 4 is a diagram showing a configuration of a conventional amplitude modulation circuit. In FIG. 4, an adder circuit 51 receives an input analog audio signal S1 and an output setting bias voltage Vb, performs addition processing, and outputs the result. The output setting bias voltage Vb is a bias voltage for setting an output signal level at the time of non-modulation where the analog audio signal S1 is not input. The A / D conversion circuit 3 converts the analog signal from the adder circuit 51 into a binary multi-bit digital signal.

The modulation encoder 4 outputs a control signal for on / off control of the equal output voltage amplifiers 7-1 to 7-n and the binary voltage amplifiers 8-1 to 8-m in accordance with the digital signal from the A / D conversion circuit 3. . The binary voltage amplifiers 8-1 to 8 -m are, as shown in FIG. 5 to be described later, binary such as 1/2, 1/4... 1/2 ^m of the output voltage of the equal output voltage amplifier. This is a power amplifier that outputs an output amplitude and complements the gap of the stepped output of the equal output voltage amplifier.

  A carrier signal S4 is input to the equal output voltage amplifiers 7-1 to 7-n and the binary voltage amplifiers 8-1 to 8-m through the high-frequency oscillator 5 and the distributor 6. The outputs of these amplifiers are combined by an output transformer 9 and output through a filter 10. The first power supply 11 is a power supply for the equal output voltage amplifiers 7-1 to 7-n, and the second power supply 12 is a power supply for the binary voltage amplifiers 8-1 to 8-m.

  FIG. 5 is a diagram showing the voltage sharing of each amplifier according to the amplitude of the audio signal when six equal output voltage amplifiers 7-1 to 7-6 are used, and the equal output is obtained when there is no modulation (0%). The voltage amplifiers 7-1 to 7-3 operate, and all the equal output voltage amplifiers 7-1 to 7-6 operate at the positive peak time (+ 100%) of 100% modulation, and conversely at the negative peak time. On (−100%), the modulation encoder 4 performs on / off control so that the operation of all the power amplifiers is turned off.

  When the analog audio signal S1 is not present, the characteristics may be deteriorated by setting the output setting bias voltage Vb. The reason is that the amplitude modulation circuit faithfully operates the equal output voltage amplifier 7 and the binary voltage amplifier 8 in accordance with the minute noise mixed in the analog audio signal S1. When the operation of the power amplifier is turned on / off, the output signal of the equal output voltage amplifier 7 and the output signal of the binary voltage amplifier 8 cannot coincide with each other on the time axis, and noise is generated in the output. And the characteristics deteriorate.

  In particular, as shown in FIG. 5, when the output of the binary voltage amplifier 8-1 having a large output, such as the equal output voltage amplifier 7 or 1/2, is turned on and off, for example, when the setting is close to the point a or the point b, the characteristics are deteriorated. . At point a in FIG. 5, the operations of the equal output voltage amplifiers 7-1 to 7-3 and the binary voltage amplifier 8-1 are turned on, and the operations of the other amplifiers are turned off. In such a combination, when the output signal level at the time of non-modulation decreases due to minute noise mixed in the analog audio signal S1, the operation of the binary voltage amplifier 8-1 having a large output is turned off, and instead, the binary voltage amplifier 8- 2 and 8-3 are turned on. By repeating this, the characteristics deteriorate. Further, at point b in FIG. 5, the operations of the equal output voltage amplifiers 7-1 to 7-3 are turned on, the operations of the other amplifiers are turned off, and the combination of the amplifiers whose operations are turned on is If the output signal level at the time of non-modulation decreases due to minute noise mixed in the analog audio signal S1, the operation of the equal output voltage amplifier 7-3 is turned off, and the operation of the binary voltage amplifiers 8-1 to 8-3 instead. Turns on. By repeating this, the characteristics deteriorate.

Japanese Patent Laid-Open No. 09-284053

  In order to reduce the occurrence of such noise, Patent Document 1 proposes an improvement method using an analog power amplifier. However, in this method, a complex peripheral circuit using an inefficient analog type power amplifier is required, and a conventional amplitude modulation circuit composed of an equal output voltage amplifier and a binary voltage amplifier is modified by the modification. There is a problem that it is very difficult to use this solution. Therefore, conventionally, a method in which a human detects the output of the filter 10 and periodically confirms characteristics when no analog audio signal S1 is present to set and adjust the output setting bias voltage Vb is generally performed.

  An object of the present invention is to provide an amplitude modulation circuit capable of automatically correcting characteristics when no analog audio signal is present.

An amplitude modulation circuit according to the present invention includes an arithmetic means for adding a predetermined bias voltage to an input analog audio signal and outputting the signal, an A / D conversion means for converting an output signal of the arithmetic means into a digital signal, and the digital signal. An amplitude modulation circuit including a plurality of power amplification units that are controlled on and off in response to amplify the carrier wave and a combination unit that combines and outputs the amplified outputs of the power amplification units, and when the analog audio signal is not signaled, wherein based on digital signals, look including a control means for combining the power amplifying means whose operation is turned on in response to said digital signal to variably control the output signal level of said operational means when a predetermined combination, the control The means has signal generation means for outputting a correction signal, and the calculation means further adds the correction signal to variably control the output signal level. It is characterized in.

  As described above, according to the present invention, the arithmetic means for adding a predetermined bias voltage to the input analog audio signal and outputting it, the A / D conversion means for converting the output signal of the arithmetic means into a digital signal, and the digital signal In an amplitude modulation circuit including a plurality of power amplifying means that are controlled on and off to amplify a carrier wave and a combining means that combines and outputs the amplified outputs of these power amplifying means, a digital signal that is an output of the A / D conversion means is used as a basis. In addition, the output signal level of the arithmetic means when there is no analog audio signal is variably controlled, that is, the bias voltage is corrected when there is no analog audio signal. It is possible to suppress the operation of the power amplifying means with a combination that has a high possibility of deteriorating, thus reducing noise when no analog audio signal is present. Characteristics of No. noise ratio (S / N) can be improved.

  According to the present invention, by adopting the configuration and operation as described below, it is possible to automatically correct the characteristics when there is no analog audio signal.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an amplitude modulation circuit according to an embodiment of the present invention, and shows the configuration of an amplitude modulation transmitter including this circuit. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the description of the same parts as those in FIG. 4 is omitted.

  In FIG. 1, an input analog audio signal S <b> 1 is input to a no-signal detection circuit 1 and an arithmetic circuit 2. The no-signal detection circuit 1 has a function of monitoring the voltage level of the analog audio signal S1 and detecting that there is no signal. When it is detected that there is no signal, the no-signal detection signal S3 is sent to the arithmetic circuit 2. send.

  When the no-signal detection circuit 1 detects that there is no signal, the arithmetic circuit 2 monitors the output Da of the A / D conversion circuit 3 and thereby sets the audio signal S1 set by the output setting bias voltage Vb. Check that the combination of the output voltage amplifier 7 and the binary voltage amplifier 8 that are turned on when no signal is turned on is a combination that deteriorates the characteristics, and adjust if the combination is a combination that deteriorates the characteristics. It has a function. The output of the arithmetic circuit 2 is input to the A / D conversion circuit 3 and converted into a binary multi-bit digital signal Da.

  FIG. 2 is a diagram showing a configuration of the arithmetic circuit 2 of FIG. In FIG. 2, an arithmetic circuit 2 includes a one-shot circuit 21, an inverter 22, a flip-flop 23, AND circuits 24 and 26, a ROM (Read Only Memory) 25, and a signal generation circuit 27 that outputs a correction signal. And switches 28 and 30, and an adder circuit 29 that receives the analog audio signal S1, the output setting bias voltage Vb, and the correction signal, adds them, and outputs them.

  Next, the operation of the amplitude modulation circuit according to the embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a timing chart showing the operation of the arithmetic circuit 2 of FIG.

  Normally, when the amplitude modulation transmitter is activated, the analog audio signal S1 is often not input for a while. FIG. 3 shows an operation example in which correction is performed using the time.

  The rising edge of the transmitter activation instruction S2 is changed to a single pulse by the one-shot circuit 21, and the flip-flop 23 is set. The switch 30 is turned on by the transmitter activation command S2. When the flip-flop 23 is set and the no-signal detection signal S3 is input, the switch 28 is turned off by the output of the AND circuit 24 to prevent external noise from entering the A / D conversion circuit 3.

  When the analog audio signal S1 is input while the switch 28 is off, the flip-flop 23 is immediately reset by a signal obtained by inverting the no-signal detection signal S3 and fine adjustment is stopped.

  The ROM 25 outputs a signal S6 corresponding to the digital signal Da that is the output of the A / D conversion circuit 3. This signal S6 indicates whether or not fine adjustment is necessary. The modulation encoder 4 turns on and off the operations of the equal output voltage amplifier 7 and the binary voltage amplifier 8 according to the digital signal Da. Therefore, if the combination of the equal output voltage amplifier 7 and the binary voltage amplifier 8 whose operation is turned on is known, the digital signal Da in that case can be obtained conversely. Therefore, data is written in the ROM 25 so as to output the signal S6 when the digital signal Da calculated backward from a predetermined combination that deteriorates the characteristics as described above with reference to FIG. 5 is input.

  When the analog sound signal S1 is not present, the signal generation circuit 27 generates a slight level analog correction signal and gradually changes the level while the ROM 25 outputs the signal S6. Therefore, the addition circuit 29 adds the output setting bias voltage Vb and the correction signal from the signal generation circuit 27 and outputs the addition signal to the A / D conversion circuit 3, and its output level gradually changes. As a result, when the combination of the equal output voltage amplifier 7 and the binary voltage amplifier 8 whose operation is turned on is other than the predetermined combination, that is, when the signal S6 of the ROM 25 is lost, the signal generation circuit 27 The output voltage is maintained and the adjustment is finished.

  When the no-signal state ends and the input of the analog audio signal S1 continues, no signal is returned again, and when the ROM 25 outputs the signal S6, the signal generation circuit 27 gradually increases the output level that has been maintained until then. The correction signal is output while changing to. As shown in FIG. 3, the signal generation circuit 27 gradually decreases the output level while the ROM 25 outputs the signal S6, and then gradually increases it, but gradually increases it. Only or may be decreased gradually.

  As described above, in the embodiment of the present invention, if the desired output setting bias voltage Vb is coarsely adjusted, fine adjustment is automatically performed thereafter. Therefore, humans periodically change the characteristics over time when there is no analog audio signal S1. There is no need to check and adjust automatically.

  Further, when set by a human in the past, there may be a marginal setting with respect to minute noise, but in the embodiment of the present invention, the characteristic is based on the digital signal output Da of the A / D conversion circuit 3. Since an optimum value is automatically set while avoiding a setting that is highly likely to deteriorate, a margin for minute noise mixed in the analog audio signal S1 is automatically secured.

  Further, in order to implement the solution of Patent Document 1, it is necessary to make a significant design change of the existing amplitude modulation transmitter. However, the embodiment of the present invention is a part of the amplitude modulation circuit of the amplitude modulation transmitter. It is possible to implement by changing only, and it is not necessary to make a significant design change.

It is a figure which shows the structure of the amplitude modulation circuit by the Example of this invention. It is a figure which shows the structure of the arithmetic circuit of FIG. 3 is a timing chart showing the operation of the arithmetic circuit in FIG. 2. It is a figure which shows the structure of the conventional amplitude modulation circuit. It is a figure which shows the voltage sharing of each amplifier according to the amplitude of the audio | voice signal at the time of using six equal output voltage amplifiers.

Explanation of symbols

1 No-signal detection circuit
2 Arithmetic circuit
3 A / D conversion circuit
4 Encoder for modulation
5 High frequency oscillator
6 Distributor 7-1 to 7-n Equal output voltage amplifier 8-1 to 8-m Binary voltage amplifier
9 Output transformer
10 Filter
11 First power supply
12 Second power supply
21 One-shot circuit
22 Inverter
23 Flip flop 24, 26 AND circuit
25 ROM
27 Signal generation circuit 28, 30 switch
29 Adder circuit

Claims (2)

Calculation means for adding a predetermined bias voltage to the input analog audio signal and outputting it, A / D conversion means for converting the output signal of the calculation means into a digital signal, and amplifying the carrier wave controlled on and off according to the digital signal An amplitude modulation circuit including a plurality of power amplifying means and a combining means for combining and outputting the amplified outputs of the power amplifying means,
When the analog audio signal is not present, the output signal level of the arithmetic means is variably controlled based on the digital signal when the combination of the power amplifying means whose operation is turned on according to the digital signal is a predetermined combination. control means for viewing including,
The amplitude modulation circuit , wherein the control means includes signal generation means for outputting a correction signal, and the calculation means further adds the correction signal to variably control the output signal level . The control means maintains the signal level of the correction signal output from the signal generating means when the combination of the power amplifying means whose operation is turned on according to the digital signal is other than the predetermined combination. 2. The amplitude modulation circuit according to claim 1, wherein the addition of the correction signal in the arithmetic means is continued .

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