JPH07142934A - Waveform distortion compensation method and method and circuit for amplitude modulation using it - Google Patents

Abstract

PURPOSE:To prevent the phase difference of digital stage output and analog stage output, which occurs by a D/A conversion processing and the like, and to prevent/reduce waveform distortion in output. CONSTITUTION:A waveform distortion compensation circuit 26 is arranged before a D/A converter 16. A phase shifter 28 constituting the waveform distortion compensating circuit 26 shifts LSB-side eight bits among the 12-bit outputs of an A/D converter 10 in accordance with a shift clock supplied from a frequency multiplication circuit 30. The frequency multiplication circuit 30 generates the shift clock by multiplying a carrier by two, for example. Since delay occurring in the D/A converter 16 can be compensated by a phase shift processing by the phase shifter 28, the phase difference between digital stage output and analog stage output can be prevented. Thus, waveform distortion does not occur in broadcasting device output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplitude modulation method and circuit used in a medium-wave radio broadcaster and the like, and more particularly to a waveform distortion compensation method in this method and circuit.

[0002]

2. Description of the Related Art As a medium-wave radio broadcaster, a hybrid type system as disclosed in, for example, Japanese Patent Laid-Open No. 5-63458 has been developed and proposed. In Figure 2,
An amplitude modulation circuit having a configuration similar to the system proposed in this publication is shown.

The circuit shown in this figure has an A / D converter 10 for quantizing a voice input as an input signal into 12 bits. The quantization in the A / D converter 10 is performed in synchronization with the carrier wave generated by the carrier wave oscillator 12. The 12-bit signal output from the A / D converter 10 is supplied to the subsequent decoder 14 and D / A converter 16. Of the 12 bits, the most significant bit (MSB) side 4 bits are supplied to the decoder 14, and the least significant bit (LSB) side 8 are supplied to the D / A converter 16.
Is a bit.

This circuit includes a digital type power amplifier 18 and an analog type power amplifier 20 as amplifiers for amplifying a carrier wave generated by the carrier wave oscillator 12. The digital power amplifier 18 is an amplifier in charge of a relatively large amplitude component of the amplitude modulation wave to be generated, and is turned on / off by a control signal output from the decoder 14.
Controlled off. That is, the decoder 14 converts the MSB side 4 bits supplied from the A / D converter 10 into 16 control signals, and supplies this signal to each of the 16 digital power amplifiers 18. Therefore, the 16 digital power amplifiers 18 are turned on / off by the signal output from the decoder 14 and by the 4 bits on the MSB side of the 12 bits output from the A / D converter 10.
Will be turned off. The digital power amplifier 18, which is turned on in response to the control signal, amplifies the carrier wave output from the carrier wave oscillator 12 and supplies the amplified carrier wave to the power adder 22 in the subsequent stage as a digital stage output.

On the other hand, the analog power amplifier 20 has a D /
This is an amplifier whose gain is controlled by the signal supplied from the A converter 16. That is, the D / A converter 16 is A
Of the 12-bit output of the / D converter 10, 8 bits on the LSB side are converted into an analog signal, and this is supplied to the analog power amplifier 20 as a gain control signal. The amplification gain of the analog power amplifier 20 is controlled by the output of the D / A converter 16. As a result, from the analog power amplifier 20, the carrier wave amplified according to the value of 8 bits on the LSB side of the 12-bit output of the A / D converter 10,
It is output as the tonal amplitude component of the amplitude modulated wave to be generated (analog stage output).

The power adder 22 electrically adds the digital stage output from the digital power amplifier 18 and the analog stage output from the analog power amplifier 20. The high-power amplitude-modulated wave obtained as a result of addition is filtered and filtered by the BPF 24 and then output as a broadcaster.
It is supplied to a transmitting antenna (not shown).

In this way, a so-called hybrid type circuit in which the large amplitude component of the amplitude modulated wave is generated by the digital power amplifier 18 and the small amplitude component is generated by the analog power amplifier 20 is, for example, all amplitude components are digital power amplifiers. Compared with the system configuration generated by the amplifier, it has the advantages that the number of power amplifiers can be reduced and the quantization noise can be reduced.

[0008]

However, in such a configuration, a non-negligible phase difference may occur between the digital stage output and the analog stage output. For example, D / used to control an analog power amplifier
The delay generated in the A converter causes such a phase difference. Such a phase difference becomes an obstacle in obtaining a good composite waveform (amplitude modulated wave).

The present invention has been made to solve the above problems, and an object of the present invention is to improve the waveform of an amplitude modulation wave in a hybrid system, for example.

[0010]

In order to achieve such an object, the waveform distortion compensating method according to the present invention applies predetermined processing to each component constituting an input signal, and each processed component In the signal processing method for generating an output signal by synthesizing, the phase difference between the components caused by the processing is compensated before the processing, thereby reducing the waveform distortion generated in the output signal due to the phase difference. And

In the amplitude modulation method according to the present invention, the input signal is quantized into a plurality of bits, and a relatively large amplitude component based on the first bit group on the MSB side of the quantized input signal is generated on the LSB side. In the amplitude modulation method in which a relatively small amplitude component is generated on the basis of the second bit group of, and the amplitude-modulated wave is generated by synthesizing the amplitude components, the phase difference from the other is generated at the time of synthesis. It is characterized in that the phase distortion of the first or second bit group is shifted so as not to occur so that the waveform distortion caused in the amplitude modulated wave due to the phase difference between the respective components is reduced.

In the amplitude modulation method according to the present invention, further, a relatively large amplitude component is generated by turning on / off a plurality of digital type power amplifiers for amplifying a carrier wave of a predetermined frequency based on the first bit group. Then, the second bit group is converted into an analog signal, and the relatively small amplitude component is generated by controlling the gain of the analog type power amplifier that amplifies the carrier wave based on the obtained analog signal. And

An amplitude modulation circuit according to the present invention has an A / D conversion means for quantizing an input signal into a plurality of bits, and a relatively large amplitude based on the MSB side first bit group of the quantized input signal. A large amplitude component generating means for generating a component,
A small amplitude component generating means for generating a relatively small amplitude component based on the second bit group on the LSB side of the quantized input signal; and a power adding means for synthesizing the generated amplitude components, In an amplitude modulation circuit that generates an amplitude modulation wave while sharing the large amplitude component and the small amplitude component by the large amplitude component generation means and the small amplitude component generation means, respectively,
Phase shift means for shifting the phase of the first or second bit group is provided so as not to generate a phase difference with each other at the time of synthesis, and waveform distortion generated in the amplitude modulated wave due to the phase difference between the respective components is reduced. Is characterized by.

In the amplitude modulation circuit according to the present invention, further, the large amplitude component generating means decodes the first bit group and converts it into a plurality of digital power amplifier control signals, and digital power amplifier control. A plurality of digital type power amplifiers that turn on / off based on a signal, and amplify a carrier wave of a predetermined frequency when turned on, and the small amplitude component generation means converts the second bit group into an analog signal D
It is characterized in that it has an A / A conversion means and an analog type power amplifier for amplifying the carrier wave with a gain according to the obtained analog signal.

Further, in the amplitude modulation circuit according to the present invention, the phase shift means generates a shift clock by multiplying the carrier wave, and the phase of the first or second bit group is used as the shift clock. And a phase shifter that shifts in synchronization with each other.

[0016]

In the signal processing method according to the present invention, prior to the predetermined processing being applied to the respective components forming the input signal, the phase difference between the respective components which may be caused by this processing is compensated. Therefore, the output signal obtained by combining the processed components does not have the waveform distortion due to the phase difference caused by the process. As a result, in the signal processing method according to the present invention, the waveform distortion caused by the phase difference is prevented or reduced.

In the amplitude modulation method and circuit according to the present invention, first, the input signal is quantized into a plurality of bits, and a relatively large amplitude component based on the first bit group on the MSB side on the LSB side is quantized. A relatively small amplitude component is generated based on the second bit group. At that time, the phase shift process is executed for the first or second bit group. This phase shift is executed so that a phase difference between the amplitude components does not occur when the generated amplitude components are combined. Therefore, in the amplitude modulation method and circuit according to the present invention, the phase difference generated in the process of generating each amplitude component is compensated by the phase shift process preceding it, and the waveform distortion does not occur in the amplitude modulated wave related to the output. .

In the amplitude modulation method and circuit according to the present invention, the above-described generation processing of each amplitude component is executed by the control of the power amplifier. That is, the relatively large amplitude component described above is generated by a plurality of digital power amplifiers that are on / off controlled based on the first bit group, and the relatively small amplitude component described above is obtained from the second bit group. It is obtained by an analog power amplifier whose gain is controlled by an analog signal to be obtained. Therefore, in the amplitude modulation method and circuit according to the present invention, in addition to the above-described actions, actions such as reduction of the number of power amplifiers and reduction of quantization noise occur. Further, in particular, the phase difference due to the delay of the D / A conversion means for converting the second bit group into an analog signal is compensated.

In the amplitude modulation circuit according to the present invention, the phase shift of the first or second bit group in the above-mentioned amplitude modulation method is executed by the phase shift means. This phase shift means can be simply configured by a frequency multiplication circuit and a phase shifter.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. It should be noted that the same components as those of the conventional example shown in FIG.

FIG. 1 shows the configuration of an amplitude modulation circuit according to an embodiment of the present invention. The circuit shown in this figure has a configuration in which a waveform distortion compensation circuit 26 is further added to the circuit of the conventional example shown in FIG. The waveform distortion compensating circuit 26 is provided between the A / D converter 10 and the D / A converter 16, and includes the phase shifter 28 and the frequency multiplying circuit 3.
It consists of zero.

The phase shifter 28 is a 1 of the A / D converter 10.
Of the 2-bit output, 8 bits on the LSB side are shifted in synchronization with the shift clock supplied from the frequency multiplication circuit 30, and the 8 bits on the LSB side that have been shifted are shifted by the D / A converter 16.
Output to. The frequency multiplication circuit 30 includes a carrier wave oscillator 12
The output of is multiplied to generate the shift clock. For example, when the frequency multiplier circuit 30 is configured as a doubler circuit, the minimum phase shift amount in the phase shifter 28 is 0.5 wavelength. Further, when the phase shifter 28 is configured as an 8-stage phase shifter, the phase adjustment range by the phase shifter 28 is 0.5 wavelength × 8 stages = 4 wavelengths.

Therefore, according to this embodiment, the delay generated in the D / A converter 16, for example, is caused by the waveform distortion compensation circuit 26,
In particular, it is compensated by the phase shifter 28. As a result, the digital stage output from the digital power amplifier 18
It is possible to prevent a phase difference between the analog power amplifier 20 and the analog stage output. That is, by appropriately adjusting the phase shifter 28 and the frequency multiplication circuit 30, the waveform distortion in the output of the power adder 22 can be preferably prevented. In addition, this adjustment has good stability, and once adjusted, there is almost no need to readjust it. As described above, according to this embodiment, the waveform distortion that appears in the output of the power adder 22 due to the delay of the D / A converter 16 or the like can be precisely removed by a relatively simple adjustment process.

The present invention does not need to limit the number of bits of the phase shifter 28 or the multiplication ratio of the frequency multiplication circuit 30.

[0025]

As described above, according to the waveform distortion compensating method according to the present invention, the phase difference between the respective components which may occur due to the processing is processed before the respective components constituting the input signal are processed. Is compensated, it is possible to prevent or reduce the waveform distortion caused in the output signal by the phase difference.

Further, according to the amplitude modulation method and the circuit of the present invention, when the large amplitude component and the small amplitude component are combined, a phase difference between the first and second bit groups does not occur. Since the phase is shifted, it is possible to prevent or reduce the waveform distortion of the amplitude modulation wave caused by the phase difference between the components.

According to the amplitude modulation method and circuit of the present invention, since the large amplitude component is generated by the digital power amplifier and the small amplitude component is generated by the analog power amplifier, the number of power amplifiers can be reduced. Effects such as reduction of quantization noise can be obtained.

According to the amplitude modulation circuit of the present invention, the phase shifter can be realized with a simple circuit configuration using a frequency multiplication circuit or a phase shift circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an amplitude modulation circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an amplitude modulation circuit according to a conventional example.

[Explanation of symbols]

 10 A / D converter 12 Carrier wave oscillator 14 Decoder 16 D / A converter 18 Digital power amplifier 20 Analog power amplifier 22 Power adder 24 BPF 26 Waveform distortion compensation circuit 28 Phase shifter 30 Frequency multiplier circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sakuhisa Iwaiwa 2-2-1 Jinnan, Shibuya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Center (72) Inventor Nakasho 2-2-1, Jinnan, Shibuya-ku, Tokyo No. 1 within Japan Broadcasting Corporation Broadcasting Center

Claims (6)

[Claims] 1. By subjecting each component constituting an input signal to a predetermined process and synthesizing each processed component,
In a signal processing method for generating an output signal, a waveform distortion compensating method characterized by reducing a waveform distortion generated in an output signal by this phase difference by compensating for a phase difference between respective components caused by the processing prior to the processing. . 2. An input signal is quantized into a plurality of bits, and a relatively large amplitude component is generated based on a first bit group on the most significant bit side of the quantized input signal and a second bit on the least significant bit side. In an amplitude modulation method in which a relatively small amplitude component is generated based on a group, and the generated amplitude components are combined to generate an amplitude-modulated wave, the An amplitude modulation method characterized in that the phase distortion of an amplitude modulated wave due to a phase difference between respective components is reduced by shifting the phase of the first or second bit group. 3. The amplitude modulation method according to claim 2, wherein a plurality of digital power amplifiers for amplifying a carrier wave of a predetermined frequency are turned on / off based on the first bit group, whereby the relatively large amplitude component is generated. Generating a second bit group into an analog signal and controlling the gain of an analog power amplifier that amplifies the carrier wave based on the obtained analog signal to generate the relatively small amplitude component. Characteristic amplitude modulation method. 4. A / A for quantizing an input signal into a plurality of bits
D conversion means, large amplitude component generation means for generating a relatively large amplitude component based on the first bit group on the most significant bit side of the quantized input signal, and the least significant of the quantized input signal A small amplitude component generating means for generating a relatively small amplitude component based on the second bit group on the bit side, and a power adding means for synthesizing the generated amplitude components,
In the amplitude modulation circuit that generates the amplitude-modulated wave while the large-amplitude component and the small-amplitude component are respectively shared by the large-amplitude component generation means and the small-amplitude component generation means, the An amplitude modulation circuit comprising phase shift means for shifting the phase of the first or second bit group, and reducing the waveform distortion generated in the amplitude modulation wave due to the phase difference between the components. 5. The amplitude modulation circuit according to claim 4, wherein the large amplitude component generation means decodes the first bit group and converts it into a plurality of digital power amplifier control signals, and a digital power amplifier. A plurality of digital type power amplifiers which are turned on / off based on a control signal and which amplifies a carrier wave of a predetermined frequency when turned on, and the small amplitude component generating means converts the second bit group into an analog signal D / An amplitude modulation circuit comprising: A conversion means; and an analog power amplifier that amplifies the carrier wave with a gain according to the obtained analog signal. 6. The amplitude modulation circuit according to claim 5, wherein the phase shift means generates a shift clock by multiplying the carrier wave, and the phase of the first or second bit group is set to the shift clock. And a phase shifter that shifts in synchronization with the amplitude modulation circuit.