JP3028486U - Medium wave broadcasting device - Google Patents

Abstract

(57) [Abstract] (Corrected) [PROBLEMS] To reduce the number of pulse width modulation circuits, power amplifiers, and output combining circuits in a digital medium-wave broadcasting device. SOLUTION: An A / D converter 1 for converting a sound signal applied to an input terminal 21 into a digital signal, a memory circuit 2 for correcting linearity, and an oscillator 3 for generating a carrier wave.
A harmonic generation circuit 4a, 4b, a circuit 5a, 5b for changing the pulse width in 4 steps according to 2 bits of the digital signal, and a pulse width in 4 steps for 3 bits of the digital signal. Circuit 5c, 5d for changing the voltage, driver circuits 6a, 6b, 6c, 6d, power amplifier 7a,
7b and 7c and circuits 8a, 8b and 8c for synthesizing outputs
8d and the band pass filter 9 are provided, and the amplitude modulation is realized by digitizing the audio signal, pulse-width modulating it, and amplifying the power. The number of power amplifiers is reduced by making the output of the power amplifier large and corresponding to 2 bits, and the one of the small output corresponding to 3 bits or more.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 This invention is an amplitude modulation by converting an audio signal into a digital signal by an A / D converter that performs sampling at a frequency equal to the frequency of a carrier wave, controlling the pulse width of the carrier wave according to the digital signal, and amplifying by a power amplifier. It is related to the medium-wave broadcasting device that performs.

[0002]

[Prior art]

 FIG. 2 is a block diagram of a conventional medium-wave broadcasting device described in, for example, IEICE Technical Bulletin EMCJ95-66, where 1 is an A / D converter for converting audio into a digital signal, and 2 is a straight line. Memory circuit for correcting the noise, 3 is an oscillator that generates a carrier wave, 4 is a harmonic generation circuit of the oscillator, 5a, 5b, 5c, 5d, and 5e are in four stages according to 2 bits of the digital signal. Pulse width changing circuits, 6a, 6b, 6c, 6d, and 6e are driver circuits, 7a, 7b, 7c, and 7d are power amplifiers, and 8a, 8b, 8c, 8d, and 8e are power amplifier outputs. A circuit to synthesize, 9 is a band pass filter, 21 is an input terminal of an audio signal, 22 is an output terminal of the memory circuit 2, 23 is an output terminal of the oscillator 3, 24 is an output terminal of the harmonic generation circuit, and 25 is a high frequency signal. Output terminal. Next, the operation will be described. The analog signal voice signal applied to the input terminal 21 is converted into a 10-bit digital signal by the A / D converter 1, and the linearity is corrected by the memory circuit 2. Sent. On the other hand, from the carrier wave oscillated by the oscillator 3 and the output of the harmonic generation circuit 3 thereof, pulses are generated in the phase shifter and selector circuits 5a, 5b, 5c, 5d, and 5e in accordance with 2 bits of the digital audio signal. Converted to a signal of varying width, amplified in drivers 6a, 6b, 6c, 6d, and 6e and power amplifiers 7a, 7b, 7c, and 7d, and combined in synthesis circuits 7a, 7b, 7c, 7d, and 7e. They are combined and taken out from the high frequency output terminal 25. FIG. 3 shows the relationship between the signal at the output terminal 24 of the carrier wave harmonic generation circuit and the output terminals ΦA and ΦB of the phase shifter and the selector.

[0003]

[Problems to be solved by the device]

 In the conventional digital medium-wave broadcasting device, a 10-bit digitized audio signal is handled in 2-bit units, so that five sets of pulse width conversion circuits, power amplifiers, and output synthesis circuits are required. This is because even if the pulse width of a high power power amplifier is reduced, the power does not decrease proportionally and linear amplitude modulation cannot be performed. The present invention has been made to solve the above-mentioned problems, and a pulse width modulation circuit is provided by making the equivalent of a small and medium output power amplifier capable of modulating a narrow pulse width 3 bits. There is an advantage that the number of power amplifiers and output combining circuits can be reduced to four.

[0004]

[Means for Solving the Problems]

 The invention according to claim 1 reduces the number of power amplifiers by supporting the pulse width modulation circuit of the medium-wave broadcasting device for 2-bit for high power and 3-bit or more for small and medium power. . The invention of claim 2 is characterized in that a voice signal is input as a digital signal and a digital filter is added.

[0005]

[Action]

 According to the device of the first aspect, a medium-wave broadcasting device can be realized with four sets of power amplifiers for a 10-bit digitized audio signal. According to the invention of claim 2, all circuits can be digitized.

[0006]

【Example】

 An embodiment of this invention will be described below with reference to the drawings. In FIG. 1, 1 is an A / D converter for converting a sound into a digital signal, 2 is a memory circuit for correcting linearity, 3 is an oscillator for generating a carrier wave, 4a and 4b are harmonic generation circuits for the oscillator, 5 a and 5b are circuits for changing the pulse width in four steps according to 2 bits of the digital signal, and 5c and 5d are circuits for changing the pulse width in four steps according to 3 bits of the digital signal, 6a. , 6b, 6c, and 6d are driver circuits, 7a, 7b, and 7c are power amplifiers, 8a, 8b, 8c, and 8d are circuits that combine the output of the power amplifier, 9 is a bandpass filter, and 21 is audio. Input terminal of signal, 22 is output terminal of memory circuit 2, 23 is output terminal of oscillator 3, 24a and 24b are output terminals of harmonic generation circuit, and 25 is output terminal of high frequency signal A. The analog audio signal applied to the input terminal 21 is converted into a 10-bit digital signal by the A / D converter 1 and linearity correction is performed by the memory circuit 2 and then output from the output terminal 22 to the next stage. Sent. On the other hand, from the carrier wave oscillated by the oscillator 3 and the output of the harmonic generation circuit 3a thereof, the oscillator 3 oscillates in the phase shifter and selector circuits 5a and 5b according to 2 bits of the digital audio signal. The carrier wave and the output of the harmonic generation circuit 3b are converted into signals whose pulse widths change in the phase shifter and selector circuits 5c and 5d according to 3 bits of the digital voice signal, and the drivers 6a and 6b are converted. , 6c, and 6d, and power amplifiers 7a, 7b, and 7c are amplified, combined in combining circuits 7a, 7b, 7c, and 7d, and taken out from high-frequency output terminal 25. FIG. 2 shows a case where a digital signal is connected to the audio signal input terminal 31, the frame sync signal is reproduced by the frame sync extraction circuit 10, and smoothing is performed in the digital filter 11 at the same cycle as the carrier frequency. The linearity can be corrected by making the digital filter 11 function or by preparing a memory circuit as in FIG.

In the above description, the case of having the pulse width control circuits corresponding to 2 bits and 3 bits was described, but the combination of the pulse width control circuits corresponding to 2 bits, 3 bits, and 3 or more bits. It is also possible to further reduce the number of amplifiers by preparing.

[0010]

[Effect of device]

 According to the first aspect of the present invention, a medium-wave broadcasting device can be realized by preparing a four-stage power amplifier for a voice signal converted into a 10-bit digital signal. According to the invention of claim 2, the input of the audio signal can be replaced with the digital signal.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing another embodiment of the medium-wave broadcasting device of the present invention.

FIG. 3 is a block diagram of a conventional medium-wave broadcasting device.

FIG. 4 is an operation explanatory diagram of a pulse width control circuit of a conventional medium wave broadcasting device.

[Explanation of symbols]

 1 A / D converter 2 Memory circuit 3 Oscillator 4 Harmonic generation circuit 5a, 5b, 5c, Phase shifter and selector 5d, 5e Same as above 6a, 6b, 6c, Drives 6d, 6e Same as above 7a, 7b, 7c, Power amplifier 7d Same as above 8a, 8b, 8c, power combiner circuits 8d, 8e Same as above 9 Band pass filter 21 Antenna 22 Audio signal input terminal 23 Memory circuit output terminal 24a, 24b Harmonic generation circuit output terminal 25 High frequency signal output terminal 31 Digital audio signal input terminal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Zhang Huang Dong, 1-1-3 Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo Miyoshi Electronics Co., Ltd.

Claims (2)

[Scope of utility model registration request] 1. An A / D converter for sampling an audio signal at the same cycle as the frequency of the carrier wave, and controlling the pulse width of the carrier wave in four steps corresponding to 2 bits of the audio signal digitized by the converter. Power amplifier which performs amplitude modulation by controlling the pulse width of carrier wave in 8 steps or more corresponding to 3 bits or more of digital audio signal A medium-wave broadcasting apparatus having a small-output power amplifier, a means for synthesizing the large-output power amplifier, and the output of the medium-output or small-output power amplifier. 2. In place of the A / D converter, there is provided means for extracting a frame synchronization signal from a digital audio input, and means such as a digital filter for smoothing in accordance with a sampling frequency substantially equal to a carrier wave. Medium wave broadcasting device according to claim 1 of the utility model registration claim