JP2005217772A - Broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein the noise generated by a switching power source causes a false detection of the auto-tuning in a broadcast receiver. <P>SOLUTION: The broadcast receiver comprises: a means for receiving broadcasts, a switching power source for feeding broadcast receiver sections with power; a means for detecting the frequency of a broadcast received by the receiving means; a means for changing the switching frequency of the switching power source; and a means for controlling the switching frequency changing means to change the switching frequency at shorter time intervals than the time length of a received signal which is an object to detect the receiving frequency at detecting the frequency of the broadcast received by the frequency detecting means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a broadcast receiving apparatus that receives a radio broadcast or the like.

When receiving a broadcast such as a radio broadcast, there is a broadcast receiving apparatus having a function called auto-tuning that automatically detects a receivable broadcast by sequentially changing a reception frequency from a low frequency to a high frequency. Broadcasts received by auto-tuning are determined by the broadcast receiving device when the voltage level of the received broadcast is equal to or higher than a predetermined voltage level. The auto-tuning operation is stopped when a broadcast having a predetermined voltage level or higher is detected, and the broadcast of the frequency is received. When the auto-tuning start operation is performed again, the broadcast receiving apparatus sequentially changes from the frequency to a higher frequency and performs an operation of detecting the next receivable broadcast.

When receiving a broadcast such as a radio broadcast, a broadcast receiving apparatus converts a radio frequency (Radio Frequency, hereinafter referred to as RF) signal received by an antenna into an intermediate frequency (hereinafter referred to as IF) signal. And detect. For example, in radio broadcasting in Japan, IF = 450 kHz is used for AM (Amplitude Modulation) broadcasting, and IF = 10.7 MHz is used for FM (Frequency Modulation) broadcasting. Also, when performing auto tuning, in order to prevent the influence of external noise, after detecting that the voltage level of the received broadcast is equal to or higher than a predetermined voltage level, the IF is detected, and the detected IF When the difference from the IF reference value (for example, 450 kHz for AM broadcast and 10.7 MHz for FM broadcast) is within a predetermined error range, the frequency of the RF signal is the frequency at which the broadcast is received. There was also a broadcast receiving device that discriminates as

In a broadcast receiving apparatus having a switching power supply for supplying power for operating the broadcast receiving apparatus, when detecting a receivable broadcast by performing auto tuning, noise generated by the switching operation of the switching power supply can be received. In some cases, the detection is affected, and it is erroneously detected that the broadcast has a predetermined voltage level or higher despite the frequency at which the broadcast is not present. That is, although the antenna and the detection / demodulation circuit receive the noise having the fundamental wave component or the harmonic wave component of the switching operation frequency of the switching power supply (hereinafter referred to as the switching frequency), the frequency is not broadcast. In some cases, the auto tuning operation was stopped and noise was output. Even a broadcast receiving apparatus having a function of detecting the IF after detecting the received signal voltage level to determine the frequency for receiving the broadcast is erroneously detected if the switching frequency and the IF match.

In order to prevent such erroneous detection of auto-tuning, there has been a broadcast receiving apparatus that includes a switching power supply capable of selecting a plurality of switching frequencies and has means for switching to a switching frequency that does not affect the detection of receivable broadcasts. (See Patent Document 1).

JP 2000-165205 A

The broadcast receiving apparatus described in Patent Document 1 needs to perform control to determine and switch switching frequencies that do not affect detection of receivable broadcasts. Since the switching frequency of the switching power supply changes due to fluctuations in power supply voltage, load current, temperature, etc., even if a switching frequency that does not affect the detection of receivable broadcasts is selected, the switching frequency changes. There was a risk of affecting the detection of receivable broadcasts.

The object of the present invention is to perform switching without discriminating the switching frequency that does not affect the detection of receivable broadcasts, even if there is a change in the switching frequency due to fluctuations in power supply voltage, load current, temperature, etc. An object of the present invention is to provide a broadcast receiving apparatus that can prevent erroneous detection of auto-tuning due to the influence of power supply noise.

The broadcast receiving apparatus according to claim 1 of the present invention is a receiving means for receiving a broadcast, a switching power supply for supplying power to each part of the broadcast receiving apparatus, and a frequency detecting means for detecting the frequency of the broadcast received by the receiving means. Switching frequency changing means for changing the switching frequency of the switching power supply, and when detecting the frequency of the broadcast received by the frequency detecting means, at a time interval shorter than the time length of the received signal to be detected as one reception frequency And a control means for controlling the switching frequency changing means to change the switching frequency.

According to the broadcast receiving apparatus of the present invention, it is possible to prevent the operation of stopping the auto tuning by the fundamental wave or the harmonic of the switching frequency of the switching power supply after the auto tuning operation is started and before the auto tuning operation is finished.

FIG. 1 is a block diagram showing a configuration of an embodiment of a broadcast receiving apparatus of the present invention. The antenna 1 receives the broadcast and inputs it to the detection / demodulation circuit 2 as a radio frequency (hereinafter referred to as RF) signal. The detection / demodulation circuit 2 converts the RF signal into an intermediate frequency (hereinafter referred to as IF) signal, detects and demodulates it, and inputs the audio signal to the muting circuit 3. The reception frequency of the detection / demodulation circuit 2 is controlled by the microcomputer 6. The muting circuit 3 normally inputs the audio signal to the amplifier 4 as it is. The muting circuit 3 attenuates the audio signal or stops outputting the audio signal under the control of the microcomputer 6. The amplifier 4 amplifies the audio signal and inputs it to the speaker 5. The speaker 5 converts the audio signal into sound and outputs it.

The microcomputer 6 controls the detection / demodulation circuit 2, the muting circuit 3, the switching power supply 8, and the load resistance switching circuit 9. The input switch 7 performs an operation input for starting auto tuning. The switching power supply 8 supplies power to each part of the broadcast receiving apparatus. The load resistance switching circuit 9 is connected to the switching power supply 8 and switches the load resistance value of the switching power supply 8 under the control of the microcomputer 6. The switching frequency is changed by switching the load resistance value of the switching power supply 8. For example, when the switching frequency is 200 kHz and the load resistance value is 280Ω, the switching frequency is changed to 180 kHz by changing the load resistance value to 175Ω.

FIG. 2 is a flowchart showing an auto-tuning operation of an embodiment of the broadcast receiving apparatus of the present invention. When there is an operation input of the input switch 7 for starting auto tuning, the microcomputer 6 starts auto tuning operation (S1). The microcomputer 6 controls the muting circuit 3 to attenuate or stop the output of the audio signal output from the detection / demodulation circuit 2 (S2), and suppress the output of noise during auto-tuning. The microcomputer 6 controls the load resistance switching circuit 9 to switch the load resistance, and starts the process of changing the switching frequency of the switching power supply 8 (S3).

The microcomputer 6 controls the detection / demodulation circuit 2 to change the reception frequency at every broadcast frequency interval (S4). For example, in radio broadcasting in Japan, the frequency interval of broadcasting is 9 kHz for AM broadcasting and 100 kHz for FM broadcasting. When the voltage level of the broadcast received by the detection / demodulation circuit 2 is stored in a memory (not shown) in the microcomputer 6 and is equal to or higher than a predetermined voltage level (YES in S5), the detection / demodulation circuit 2 detects IF ( S6). If the detected IF is within a predetermined error range stored in the memory in the microcomputer 6 (YES in S7), the microcomputer 6 sets the received broadcast frequency as a receivable frequency in the microcomputer 6. (S8), the switching frequency is returned to a predetermined value (S9), muting of the muting circuit 3 is canceled (S10), and an audio signal is output from the speaker 5.

Note that the switching frequency changing process in S3 is performed so that the amount of one change is equal to or greater than a predetermined error stored in the memory in the microcomputer 6. For example, when a radio AM broadcast is received here, the predetermined error is set to 1 kHz with respect to IF = 450 kHz, and the amount of one change of the switching frequency is set to 1 kHz or more. The switching frequency changing process in S3 is performed at a time interval shorter than the time length used to determine whether or not the broadcast frequency received by the microcomputer 6 is a receivable frequency. Here, the time length used to determine whether or not the broadcast frequency received by the microcomputer 6 is a receivable frequency is the IF detection time, for example, 64 msec. By performing the switching frequency change processing in S3 in less than 64 msec, even if the reception frequency matches the switching frequency, the switching frequency is changed until the IF detection time of 64 msec elapses. Broadcast misdetection can be avoided.

In S5, when the voltage level of the broadcast received by the detection / demodulation circuit 2 is lower than a predetermined voltage level stored in the memory in the microcomputer 6 (NO in S5), or in S7, the detected IF is When it is outside the range of the predetermined error stored in the memory in the microcomputer 6 (NO in S7), the microcomputer 6 sets the reception frequency as a frequency without broadcasting, returns to S4, and receives the next reception frequency. The process after S4 is performed.

When the auto-tuning operation is continued (NO in S11), the process returns to the muting process of S2, and the processes after S2 are performed. When the auto-tuning of the broadcast reception frequency range is completed or when there is an operation input for terminating auto-tuning from the input switch 7, the auto-tuning operation is terminated (YES in S11).

In this embodiment, the switching frequency is changed by switching the load resistance value of the switching power supply, but when there is a circuit that does not need to be operated during the auto-tuning operation in the broadcast receiving apparatus, the switching power supply to the circuit is The switching frequency can be changed by switching between connection and disconnection of the power supply.

It is a block diagram which shows the structure of one Example of the broadcast receiver of this invention. It is a flowchart which shows the auto-tuning operation | movement of one Example of the broadcast receiver of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Detection / demodulation circuit 3 Muting circuit 4 Amplifier 5 Speaker 6 Microcomputer 7 Input switch 8 Switching power supply 9 Load resistance switching circuit

Claims (1)

Receiving means for receiving broadcast, switching power supply for supplying power to each part of the broadcast receiving device, frequency detecting means for detecting the frequency of the broadcast received by the receiving means, and switching frequency change for changing the switching frequency of the switching power supply And a control for causing the switching frequency changing means to change the switching frequency at a time interval shorter than the time length of the reception signal to be detected as one reception frequency when detecting the frequency of the broadcast received by the frequency detecting means. A broadcast receiving apparatus comprising a control means.

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