JPS6156890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in highly efficient amplitude modulation devices used, for example, in medium wave broadcasters.

As is well known, for example, in an amplitude modulation device used in a medium wave broadcasting machine, etc., a pulse width modulator, a pulse amplifier, a low-pass filter for demodulation, etc. are installed at the front stage for the purpose of high efficiency. A method has been used in which a predetermined carrier wave, which is supplied to a modulated carrier wave amplifier, is amplitude-modulated by the output signal of a filter.

That is, FIG. 1 shows an example of a conventional amplitude modulation device, and 10 is a pulse width modulator (PWM) that performs pulse width modulation on an input audio frequency signal using a higher carrier wave pulse signal. This modulator 10
The output signal of the pulse amplifier e.g. transistor 1
1. The output signal of this transistor 11 is sent to a demodulator a, for example, a chiyoke coil 1.
2. The signal is supplied to a low-pass filter consisting of a capacitor 14 and demodulated. This demodulated output signal is supplied to a modulated carrier amplifier (hereinafter abbreviated as carrier amplifier) 14. This carrier amplifier 1
4 is supplied with a carrier wave signal of a predetermined frequency from an oscillator (OSC) 15, and this carrier wave signal is amplified to a predetermined level and amplitude-modulated by the demodulated output signal. This modulated output signal is supplied to the antenna via a matching circuit (not shown) or the like. Incidentally, 16 is a flywheel diode for a damper that extracts the chiyoke energy of the chiyoke coil 12.

By the way, in the above configuration, the transistor 11
When the pulse width of the output pulse signal is narrow, unless the inductance of the chiyoke coil 12 is increased, the distortion characteristics of the low level portion of the demodulated output signal will deteriorate as shown by the solid line in FIG. 1b. For this reason, in an amplitude modulation device aiming at high efficiency, the pulse width cannot be made narrower, resulting in a decrease in efficiency, which is extremely disadvantageous.

In addition, increasing the inductance of the chiyoke coil 12 requires a larger shape of the coil 12, which makes it difficult to miniaturize the device, which is not a good idea.

This invention was made based on the above circumstances, and its purpose is to compensate for waveform distortion with a simple configuration, to achieve high efficiency, and to suppress the increase in the size of the main body of the device. The present invention aims to provide a possible amplitude modulation device.

An embodiment of the present invention will be described below with reference to the drawings. Note that the same parts as in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted.

In Fig. 2, the audio frequency signal is transmitted to the coupling inverter 2.
0. This inverter 20 reverses the phase of the input audio frequency signal, and the reverse phase output signal of this inverter 20 is supplied to an amplifier 21. This amplifier 21 is, for example, class B or class C.
The positive half wave of the negative phase output signal is amplified, and its peak portion is extracted. These inverter 20 and amplifier 21 are constructed as shown in FIG. 3a. That is, the audio frequency signal supplied from the terminal 200 is connected to the capacitor 201.
The signal is introduced into the base of the transistor 202 via the transistor 202, and is led out from the collector of the transistor 202 with its phase inverted. This negative phase signal is supplied to the base of the amplification transistor 212 via the capacitor 203 and the variable resistor 211. This transistor 212 has a variable resistor 213 for bias adjustment.
A higher bias voltage is supplied to perform class B or class C operation. The output terminal 214 provided at the collector of the amplification transistor 212 has a terminal shown in FIG.
The negative peak portion of the input audio frequency signal shown in is extracted. This extracted signal is controlled by adjusting the variable resistor 211, and when the adjustment terminal is adjusted to the ground side (downward in the drawing), the output level becomes zero, and when adjusted in the opposite direction, the output level becomes zero as shown in Figure 3. The level is increased as shown by the dotted line in b. Therefore, the output signal of the output terminal 214 is added to the output signal of the demodulator a, and this demodulated output signal becomes a signal compensated for the dotted line in FIG. 1b, as shown by the solid line in FIG. 3c. .

According to the above configuration, the phase of the audio frequency signal is reversed by the coupling inverter 20, this signal is amplified by the amplifier 21 for class B or class C amplification, and the signal is added to the demodulated output signal of the demodulator a. ing. Therefore, it is possible to easily compensate for waveform distortion that occurs when the pulse width is narrow, and as a result, it is possible to improve the efficiency of the device.
In experiments, an efficiency improvement of approximately 10% was confirmed.

Further, this configuration is simple, and since there is no need to increase the size of the chiyoke coil 12, it is possible to suppress the increase in size of the main body of the apparatus.

It should be noted that the present invention is not limited to the above-described embodiment, and for example, the output signal of the coupling inverter 20 may be passed through a half-wave rectifier circuit or a slice circuit to derive the peak signal shown in FIG. 3b. Furthermore, if the positive peak level portion of the output signal is distorted due to the operation of the pulse width modulator 10, the coupling inverter 20 shown in FIG. 2 is not necessary, and the corresponding peak level component is extracted. It is possible to compensate for the above distortion components by adding them.

It goes without saying that various other modifications can be made without departing from the gist of the invention.

As described in detail above, the present invention provides an amplitude modulation device that can compensate for waveform distortion with a simple configuration, achieve high efficiency, and suppress the increase in size of the device body. can.

[Brief explanation of the drawing]

Fig. 1a is a block diagram showing an example of a conventional amplitude modulation device, Fig. 1b is a waveform diagram shown to explain Fig. 1a, and Fig. 2 shows an embodiment of the amplitude modulation device according to the present invention. FIG. 3A is a circuit diagram showing the main part of FIG. 2, and FIGS. 3B and 3C are waveform diagrams shown for explaining the present invention. 10... Pulse width modulator, 11... Pulse amplifier, a... Demodulator, 14... Carrier wave amplifier, 20
...coupling inverter, 21...amplifier.

Claims (1)

[Claims] 1. A pulse width modulator that pulse width modulates an audio frequency signal, a pulse amplifier that amplifies the output signal of this modulator, a demodulator that demodulates the output signal of this amplifier, and an output signal of this demodulator and a predetermined carrier wave. a modulated carrier amplifier to which the signal is supplied; means for extracting a peak level component of the signal to which the audio frequency signal is supplied; and a demodulator for extracting the extracted peak level signal. 1. An amplitude modulation device comprising means for adding and synthesizing a peak level portion of an output.