JP2008177877A - Am radio receiver, and am radio receiving program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide "an AM radio receiver and AM radio receiving program" that utilizes both advantages of an envelope detection method and a synchronous detection method. <P>SOLUTION: The AM radio receiver has a synchronous detection part 83 for performing detection by the synchronous detection method, an envelope detection part 84 for performing detection by the envelope detection method, and a switching part 88 for outputting a detection signal from the synchronous detection part 83 when the amplitude modulation rate of a received AM radio signal indicates overmodulation. The switching part 88 switches the envelope detection part 83 to the synchronous detection part 83 when it is determined that a PLL is locked, when it is determined that a receiving state is stable and even when it is determined that there is adjacent interference. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an AM radio receiver, and more particularly to an AM radio receiver that selects an optimal detection method.

In an AM radio receiver, it is known to switch from a plurality of different detection means to an optimum detection means in accordance with the reception status and the like. For example, in Patent Document 1, the optimum detection means is switched according to the received electric field strength and the lock state of the PLL (Phase Locked Loop), and in Patent Document 2, the optimum detection means is selected according to the determination result of the interference state. Various detection means can be switched.
Japanese Utility Model Publication 2-38518 JP 2001-102943 A

  By the way, the detection method of the detection means described above includes an envelope detection method, a synchronous detection method, and the like. Since the envelope detection method has a simple circuit configuration, there is a sense of stability in instantaneous operation. However, when the amplitude modulation rate exceeds 100%, distortion occurs or the adjacent interference is weak. On the other hand, in the synchronous detection method, these difficulties are suppressed, but there are problems such as a complicated circuit configuration and an unstable operation such as an inability to receive due to an unlocked state.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an AM radio receiver and an AM radio reception program that take advantage of both the envelope detection method and the synchronous detection method.

In the first aspect of the present invention, the first detection means for detecting by the synchronous detection system, the second detection means for detecting by the envelope detection system, and the amplitude modulation rate of the received AM radio signal are overmodulated. An AM radio receiver comprising: a switching unit that outputs a detection signal from the first detection unit when it is determined.
According to this configuration, when the amplitude modulation rate of the AM radio signal is overmodulated, detection by the synchronous detection method is possible.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the switching means outputs the detection signal from the first detection means when it is determined that the PLL is in the locked state. .
According to this configuration, the switching unit can perform detection by the synchronous detection method even when it is determined that the PLL is in the locked state.

According to a third aspect of the present invention, in the invention according to the first or second aspect, the switching means outputs the detection signal from the first detection means when it is determined that the reception state is a stable state. It is a feature.
According to this configuration, the switching unit can perform detection by the synchronous detection method even when it is determined that the reception state is the stable state.

According to a fourth aspect of the invention, in the invention according to any one of the first to third aspects, the switching means outputs a detection signal from the first detection means when it is determined that there is an adjacent disturbance. It is characterized by that.
According to this configuration, the switching unit can perform detection by the synchronous detection method even when it is determined that there is adjacent interference.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, when the switching means determines that the received electric field strength is a strong electric field, It is characterized by outputting a detection signal.
According to this configuration, the switching unit can perform detection by the synchronous detection method even when it is determined that the received electric field strength is a strong electric field.

According to the sixth aspect of the present invention, the computer has first detection means for detecting by the synchronous detection method, second detection means for detecting by the envelope detection method, and the amplitude modulation rate of the received AM radio signal is excessive. An AM radio reception program that functions as a switching unit that outputs a detection signal from the first detection unit when it is determined that the modulation is made.
According to this configuration, when the amplitude modulation rate of the AM radio signal is overmodulated, detection by the synchronous detection method is possible.

  According to the present invention, the advantages of both the envelope detection method and the synchronous detection method can be utilized, and a comfortable reception state can be obtained.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a functional block diagram showing a main configuration of an AM radio receiver according to an embodiment of the present invention, and FIG. 2 is a functional block diagram showing a main configuration of a DSP (Digital Signal Processor).

  As shown in FIG. 1, the AM radio receiver includes a high frequency amplifier 10, a low-pass filter 20, a mixer device 30, an intermediate frequency filter 40, a VCO (Voltage Controlled Oscillator) 50, a PLL synthesizer 60, and an intermediate frequency amplifier. 70, DSP 80 and the like.

  The DSP 80 includes an A / D conversion unit 81, a selectivity filter 82, a synchronous detection unit 83, an envelope detection unit 84, an adjacent disturbance determination unit 85, an electric field strength determination unit 86, a modulation rate determination unit 87, a switching unit 88, and the like. Is done. The PLL synthesizer 60, the adjacent interference determination unit 85, the electric field strength determination unit 86, the modulation rate determination unit 87, the switching unit 88, and the like constitute the switching means of the present invention, and the DSP 80 and the like constitute the computer of the present invention.

  Further, each functional block in the DSP 80 shown in FIG. 1 includes, as shown in FIG. ) And the like, a ROM (Read Only Memory) 80c such as a flash memory, and an I / F (interface) 80d that performs input / output with an external device are realized by a hardware configuration connected by a bus 80e.

  Therefore, the DSP core 80a reads a required program stored in the ROM 80c and performs calculations according to the program, thereby realizing each function in the DSP 80.

Hereinafter, each functional block in FIG. 1 will be described in detail.
The high frequency amplifier 10 includes an antenna 10a that receives an AM radio wave RF, and amplifies an AM radio signal. The amplifier 10 is realized by a known circuit. The amplified AM radio signal is transmitted to the low-pass filter 20. The high frequency amplifier 10 may not be provided.

  The low pass filter 20, the mixer 30 and the intermediate frequency filter 40 constitute a mixer 45, and the VCO 50 and the PLL synthesizer 60 constitute a local oscillator 65 (hereinafter referred to as PLL). The mixer 45 and the PLL 65 constitute a frequency converter 68. The frequency converter 68 converts the received AM radio signal into an intermediate frequency IF. Instead of the low pass filter 20, a band pass filter may be used. The converted intermediate frequency IF is transmitted to the intermediate frequency amplifier 70.

  The PLL synchronizes (hereinafter referred to as “lock”) by feeding back to the VCO 50 the phase difference between the output signal of the VCO 50 whose oscillation frequency is varied by voltage and the reference input signal. When there is a lock, a signal indicating that the PLL is locked is transmitted to a switching unit 88 described later.

  The intermediate frequency amplifier 70 amplifies the input intermediate frequency IF to a level where detection is possible, and suppresses an excessive intermediate frequency IF by an AGC circuit (automatic gain control circuit) or the like (not shown).

  Thus, a tuner (front end) is constituted by the above-described high-frequency amplifier 10, frequency converter 68, intermediate frequency amplifier 70, and the like.

  The DSP 80 is a device that digitally converts an analog intermediate frequency IF and performs necessary software processing. Therefore, the A / D converter 81 converts the analog intermediate frequency IF to the digital intermediate frequency IF in order to digitally process the subsequent processing.

  The selectivity filter 82 removes unnecessary components after A / D conversion. The intermediate frequency IF that has passed through the selectivity filter 82 is transmitted to either the envelope detector 81 or the synchronous detector 82. The intermediate frequency IF is used for determination by the adjacent interference determination unit 85, the electric field strength determination unit 86, and the modulation rate determination unit 87.

  The synchronous detection unit 83 is an example of the first detection means of the present invention, and performs synchronous detection on the intermediate frequency IF. The envelope detection unit 84 is an example of the second detection means of the present invention, and performs envelope detection on the intermediate frequency IF.

  The adjacent interference determination unit 85 determines whether there is adjacent interference from the output of the selectivity filter 82. The electric field strength determination unit 86 determines the strength of the electrolytic strength from the output of the selectivity filter 82. The modulation rate determination unit 87 determines whether the modulation rate is overmodulated from the output of the selectivity filter 82. The adjacent interference determination unit 85 and the electric field strength determination unit 86 can be realized by a known technique.

  The switching unit 88 is based on the signal indicating that the PLL synthesizer 60 is in the locked state, the determination result of the adjacent interference determination unit 85, the electric field strength determination unit 86, and the modulation rate determination unit 87, or the envelope detection unit 83 or the synchronous detection. It switches so that it may be connected to either of the parts 84, and outputs the detection signal of the switched side.

Here, the modulation rate determining unit 87 described above will be described in detail with reference to FIG.
FIG. 3 is a conceptual diagram of the modulation rate determination unit 87. In FIG. 3, the hardware configuration is shown to help understanding, but the processing corresponding to the functions of the following devices is realized by software.

  As shown in FIG. 3, the modulation rate determination unit 87 includes an AM signal demodulator 87a, a full-wave rectifier 87b, a modulation rate determination level comparator 87c, a peak hold detector 87d, a connection time setting level comparator 87e, a gate. 87f, a clock generator 87g, a frequency counter 87h, and the like.

  The AM signal demodulator 87a demodulates the AM radio signal by removing the carrier wave. As a result, for example, the waveform of the AM radio signal shown in (a) of FIG. 3 becomes the waveform of the baseband signal shown in (b). Subsequently, the full-wave rectifier 87b rectifies a positive signal with respect to the AM radio signal from which the carrier wave has been removed, to obtain a detection output. As a result, for example, the waveform shown in FIG. 3B is a waveform shown in FIG.

  The modulation rate determination level comparator 87c determines the amplitude modulation rate of the AM radio signal. Here, the amplitude modulation rate means the ratio of the signal wave to the carrier wave, and is represented by {(amplitude of the signal wave) / (amplitude of the carrier wave)} × 100 (%). As a result, for example, binarization is performed based on the waveform exceeding the broken line indicating 100% and the waveform below the broken line in the waveform illustrated in FIG. As a result, for example, the waveform shown in FIG. 3C becomes the waveform shown in FIG. Subsequently, the peak hold detector 87d holds the largest value or the lowest value in the input signal at a constant value. As a result, for example, the waveform shown in FIG. 3D becomes like the waveform shown in FIG.

  The duration setting level comparator 87e generates a measurement pulse from a waveform held at a constant value in order to set the duration. The AND gate circuit 87f performs an AND operation on the clock signal and the measurement pulse generated from the clock generator 87g, and transmits the operation result to the counter (frequency counter) 87h as a counting signal. The counter 87h measures the counting signal and outputs it as an overmodulation time measurement result.

  As described above, the modulation rate determination unit 87 can measure the modulation rate and the modulation time of the AM radio signal, and determines whether or not the modulation rate is overmodulated by comparing it with a predetermined threshold value or the like. can do.

Next, the operation of the above AM radio receiver will be described with reference to FIG.
FIG. 4 is a flowchart showing an example of processing in the AM radio receiver.
The AM radio receiver first receives an AM radio wave and generates an AM radio signal (step S1).

  Next, the AM radio receiver determines whether or not the PLL is locked (step S2). When the AM radio receiver determines that the PLL is in the locked state, the AM radio receiver then determines whether or not it is in a reception state that is stable for a predetermined time or longer (hereinafter referred to as a stable state) (step S3).

  That is, the AM radio receiver can generally determine that the user has finished selecting the AM radio broadcast station if the PLL is in the locked state in the process of step S2. However, as to whether or not the channel selection has been completed, it can be determined that the channel selection is in progress only after a few seconds have passed since the user started listening to the AM radio at the broadcast station. Therefore, in order to give a certain degree of certainty, in the process of step S3, it is determined whether or not a stable state is reached when a predetermined number of seconds have elapsed. The number of seconds is preferably about several milliseconds to several seconds.

  Next, the AM radio receiver determines whether there is adjacent interference (step S4). If it is determined that there is no adjacent interference, the AM radio receiver then determines whether the electric field strength is a strong electric field (step S5). Further, when the AM radio receiver determines that the electric field strength is a strong electric field, the AM radio receiver determines whether the modulation rate is overmodulation (step S6).

  That is, when the AM radio receiver determines that there is no adjacent interference in the process of step S4, and the reception input level is equal to or greater than a predetermined value (dB) and the electric field strength is a strong electric field in the process of step S5. Conventionally, detection by an envelope detection method has been performed. However, in such a case, when the reception modulation rate is overmodulation, a clipping phenomenon occurs on the negative side and distortion increases. On the other hand, in the synchronous detection method, even if the amplitude modulation rate is overmodulation, since the negative side is detected accurately, the generation of distortion is suppressed.

  Therefore, when the AM radio receiver determines that the amplitude modulation rate is overmodulation, the AM radio receiver performs detection by the synchronous detection method (step S7). Note that whether or not the amplitude modulation rate is overmodulation is determined, for example, by whether or not the time during which the modulation rate exceeds 100% continues for a predetermined time or more. The predetermined second can be arbitrarily set.

  The AM radio receiver determines that the electric field strength is a predetermined value (dB) in the process of step S5 when the PLL is not locked in the process of step S2, or is not stable in the process of step S3. If not, or if the modulation rate is not overmodulated in the process of step S6, detection by the envelope detection method is performed (step S8).

  Further, the operation result of the AM radio receiver will be described with reference to FIGS. FIG. 5 shows a waveform of an envelope and a waveform of a demodulated signal as a comparative example, and FIG. 6 shows a waveform of an AM radio signal and a demodulated signal according to the embodiment, both in the case of overmodulation (modulation rate 120%). It is a waveform.

  In the envelope waveform as a comparative example, as shown in FIG. 5, it can be seen that the envelopes a intersect each other and are overmodulated. As a result, the demodulated signal b is also distorted as surrounded by a broken line. On the other hand, also in the waveform of the envelope in the embodiment, as shown in FIG. 6, it can be seen that the envelopes a intersect each other and are overmodulated. However, in the demodulated signal b that results from this, no distortion occurs as surrounded by the broken line. As described above, when the modulation rate is overmodulation, the detection can be switched to the detection by the synchronous detection method, and comfortable reception can be performed.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. The program of the present invention can be provided not only by communication means but also stored in a recording medium such as a CD-ROM.

  As described above, according to the AM radio receiver of the present invention, the advantages of both the envelope detection method and the synchronous detection method can be utilized, and a comfortable reception state can be obtained. Probability is high.

It is a functional block diagram which shows the principal part structure of AM radio receiver. It is a functional block diagram which shows the principal part structure of DSP. It is a conceptual diagram of a modulation rate determination part. It is a flowchart which shows an example of the process in AM radio receiver. It is the waveform of the envelope which becomes a comparative example, and the waveform of a demodulation signal. It is the waveform of the envelope which concerns on embodiment, and the waveform of a demodulation signal.

Explanation of symbols

10 High Frequency Amplifier 20 Low Pass Filter 30 Mixer 40 Intermediate Frequency Filter 45 Mixer 50 VCO
60 PLL Synthesizer 65 Local Oscillator 68 Frequency Converter 70 Intermediate Frequency Amplifier 80 DSP
80a DSP core (CPU)
80b RAM
80c ROM
80d I / F
81 A / D conversion unit 82 Selective filter 83 Envelope detection unit 84 Synchronous detection unit 85 Adjacent interference determination unit 86 Electric field strength determination unit 87 Modulation rate determination unit 87a AM signal demodulator 87b Full-wave rectifier 87c Level comparison for modulation rate determination 87d Peak hold detector 87e Level setting level comparator 87f AND gate 87g Clock generator 87h Frequency counter

Claims (6)

First detection means for detecting by a synchronous detection method;
A second detection means for performing detection by an envelope detection method;
Switching means for outputting a detection signal from the first detection means when it is determined that the amplitude modulation rate of the received AM radio signal is overmodulation;
An AM radio receiver characterized by comprising:   2. The AM radio receiver according to claim 1, wherein the switching unit outputs a detection signal from the first detection unit when it is determined that the PLL is in a locked state.   3. The AM radio receiver according to claim 1, wherein the switching unit outputs a detection signal from the first detection unit when it is determined that the reception state is a stable state. 4.   4. The AM radio receiver according to claim 1, wherein the switching unit outputs a detection signal from the first detection unit when it is determined that there is adjacent interference. 5.   5. The switch according to claim 1, wherein the switching unit outputs a detection signal from the first detection unit when it is determined that the received electric field strength is a strong electric field. 6. AM radio receiver. Computer
First detection means for detecting by a synchronous detection method;
A second detection means for performing detection by an envelope detection method;
An AM radio reception program which functions as a switching means for outputting a detection signal from the first detection means when it is determined that the amplitude modulation rate of the received AM radio signal is overmodulation.

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