JP3104738B2 - Carrier PWM type amplitude modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier-wave PWM type amplitude modulator used for broadcasting in a medium wave band, a short wave band or the like.

[0002]

2. Description of the Related Art Conventionally, as a device having the same mechanism as that of this type of device, there is a power amplifier for obtaining good linearity as disclosed in, for example, JP-A-2-234503.

FIG . 3 shows a configuration of such a power amplifier.
FIG. The audio signal Va from the signal source 11 is input to the output system selection circuit 12. The output system selection circuit 12 compares the voltage level of the input signal with the reference level, and switches the first system when the input level is equal to or higher than the reference level.
When the level is lower than the reference level, the second system is selected and operated.

Next, the operation of the conventional power amplifier shown in FIG. 3 will be described. When the first system is selected, the audio signal is power-amplified by a PWM power amplifier including a PWM circuit 13, a pulse amplifier 14, and a low-pass filter 15. On the other hand, when the second system is selected, the audio signal is delayed for a predetermined time by the delay circuit 17 and is linearly amplified by the linear power amplifier circuit 18. The power amplification output of each system is made unidirectional by the diodes 16 and 19, respectively, added by the addition unit 20, and output via the output terminal 21.

[0005]

In this conventional power amplifier , since the device is divided into two systems, not only the circuit is complicated and the redundancy is large, but also the output can be made unidirectional. There was a problem that it became necessary.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a carrier PWM type amplitude modulation device which has a simple circuit configuration and can maintain the linearity of an output voltage even when an input signal is at a low level.

[0007]

According to the present invention, a carrier wave generator for generating a carrier wave siny and a first waveform sin (y-sin-1Vin) are provided in a carrier wave PWM type amplitude modulator having an input signal Vin. ), A means for generating a second waveform sin (y + sin-1Vin), a transformer for inputting a first waveform at one end of the primary terminal and a second waveform at the other end, is connected to the transformer secondary terminals, carrier PWM type amplitude modulator, characterized in that it comprises a low pass filter for outputting the output signal of the carrier wave PWM type amplitude modulation device is obtained.

Further, according to the present invention, the above-mentioned carrier PW
In the M -type amplitude modulation apparatus, the means for generating the first and second waveforms includes the third waveform siny · cos (sin ^−1).
Vin), and a fourth waveform -cosy · V
in, an adding circuit for adding the third and fourth waveforms to generate a first waveform, and a fourth
A waveform subtraction carrier PWM type amplitude modulator, characterized in that it comprises a subtraction circuit for generating a second waveform is obtained.

[0009]

Since two waveforms having different phases are generated and the waveforms are amplified, it is not necessary to use a pulse whose width required at a low level is close to zero. Therefore, errors due to rising and falling of the waveform in the modulation device can be reduced, and good linearity in pulse width versus output voltage characteristics can be obtained.

[0010]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the structure of the signal source.
The audio signal Vin from 1 is input to the SIN- ¹ circuit 32 and the multiplication circuit 37. The output is calculated with the signal of the carrier generator 33, and the adder circuit 38 and the subtractor circuit 39 output waveforms having the same frequency but different phases. These are separately D-class amplified by the first amplifier circuit 40 and the second amplifier circuit 41, and only the portions having different phases are obtained by the transformer 42. The output of only the necessary fundamental frequency component is obtained by the low-pass filter 43.

Next, the operation of the circuit of FIG. 1 will be described with reference to FIG. In FIG. 2, (A) is an RF
Voltage, (B) is Vin voltage, (C) is V1 voltage, (D)
Shows waveforms of the V2 voltage, (E) shows the V3 voltage, and (F) shows the Vout voltage waveform.

The audio signal Vin from the signal source is input to the COS circuit 34 through the SIN- ¹ circuit 32, and outputs the following equation (1).

[0014]

(Equation 1) When the output waveform of the carrier generator 33 is expressed by the following equation (2),
The input of the multiplication circuit 37 is the following equation (3).
The output of 8 is the following equation (4). Similarly, the subtraction circuit 39
Is also given by the following equation (5).

[0015]

(Equation 2)

[0016]

(Equation 3)

[0017]

(Equation 4)

[0018]

(Equation 5) With these waveforms, a first amplifier circuit 40 and a second amplifier circuit 41 perform class D amplification. Only when a potential difference exists at both ends of the primary terminal of the transformer 42, an output pulse is generated on the secondary side, and the width of the pulse is expressed by the phase difference between the equations (4) and (5). It is an expression.

[0019]

(Equation 6) Here, returning to the principle of the carrier PWM type amplitude modulator, assuming that the pulse period is 2π, the pulse height is π, and the pulse width is 2α, the pulse is a periodic function having the phase angle θ as a variable. Therefore, the following equation 7 is obtained by Fourier series expansion, but the following equations 8 and 9 are obtained. Fundamental wave component contained in this pulse (cos when n = 1)
When only the term relating to θ) is extracted, the following equation 1 is obtained from Expression (7).
0, the amplitude of which is a function of the pulse width α. Therefore, by changing the pulse width, the amplitude of the carrier changes, and amplitude modulation can be performed.

[0020]

(Equation 7)

[0021]

(Equation 8)

[0022]

(Equation 9)

[0023]

(Equation 10) Therefore, by obtaining the fundamental wave component included in the pulse by the low-pass filter 43 based on the above principle, it is possible to obtain an amplitude-modulated wave by the audio signal Vin.

[0024]

As described above, the carrier PWM type amplitude modulator according to the present invention does not require a pulse width close to 0 for each circuit even when the level of the input signal is low. This has the effect of improving the linearity of the voltage characteristics.

Therefore, it is possible to provide a carrier PWM type amplitude modulator which can maintain the linearity of the output voltage even when the input signal is at a low level with a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a carrier PWM type amplitude modulation device according to an embodiment of the present invention.

FIG. 2 is a time chart showing an operation of the carrier PWM type amplitude modulation device according to one embodiment of the present invention, where (A) is an RF signal;
Voltage, (B) is Vin voltage, (C) is V1 voltage, (D)
Shows waveforms of the V2 voltage, (E) shows the V3 voltage, and (F) shows the Vout voltage waveform.

FIG. 3 is a block diagram showing a circuit configuration for improving linearity in a conventional power amplifier .

[Explanation of symbols]

31 signal source 32 sin ^-1 circuit 33 carrier generator 34 cos circuit 35 multiplication circuit 36 integration circuit 37 multiplication circuit 38 addition circuit 39 subtraction circuit 40 first amplification circuit 41 second amplification circuit 42 transformer 43 low-pass filter Vin audio signal Vout transmission output

Claims (2)

(57) [Claims] 1. A carrier PWM type amplitude modulator for the input signal Vin, and the carrier wave generator for generating a carrier SiNy, means for generating a first waveform ^{sin (y-sin -1 Vin)} , a second Means for generating a waveform sin (y + sin ^-1 Vin) of the first side, and the first waveform at one end of a primary terminal and the second waveform at the other end.
And a transformer connected to the secondary terminal of the transformer, and the carrier wave PW
Carrier PWM type amplitude modulator, characterized in that it comprises a low pass filter for outputting the output signal of the M-type amplitude modulator. 2. The carrier PWM type amplitude modulation apparatus according to claim 1, wherein said means for generating said first and second waveforms includes means for generating a third waveform siny · cos (sin ⁻¹ Vin). Means for generating a fourth waveform -cosy · Vin; an adding circuit for adding the third and fourth waveforms to generate the first waveform; and a fourth waveform from the third waveform. carrier PWM type amplitude modulator, characterized in that it comprises a subtraction circuit for generating the by subtracting the second waveform.