JP2004080454A - Radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio receiver adopting a heterodyne reception system capable of realizing downsizing and cost-reduction of a reception circuit by adopting a configuration of not using a band pass filter for eliminating an image signal having conventionally been installed to the pre-stage of a mixer. <P>SOLUTION: The radio receiver is configured such that the frequency of a local oscillation signal is changed to apply heterodyne detection to both upper and lower parts of the signal to convert the received signal into an intermediate frequency band signal and both received signal levels at the upper and lower parts are confirmed, when both the received signal levels are equal to each other, the received signal is regarded as a desired wave signal, and a demodulation signal is outputted to enter a reception state. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heterodyne reception wireless receiver.
[0002]
[Prior art]
As shown in the block diagram of FIG. 4, a conventional heterodyne reception type radio receiver amplifies an input signal from an antenna 1 with a low noise amplifier 2 and then passes through a band-pass filter 3 for removing an image signal. Input to the mixer 4. The mixer 4 performs heterodyne detection based on the local oscillation signal from the local oscillator 5, converts the frequency into a signal in an intermediate frequency band, and passes through a detection circuit 7 through an intermediate frequency bandpass filter 6 including a monolithic ceramic filter (MCF). Had been entered. In addition, 8 is a CPU and 9 is a PLL circuit.
[0003]
In the conventional radio receiver of the heterodyne reception system as shown in FIG. 4, since an image signal always exists, it is necessary to provide a band-pass filter 3 for removing the image signal before the mixer 4 to suppress the image signal. there were.
[0004]
[Problems to be solved by the invention]
In a conventional radio receiver of a heterodyne reception system as shown in FIG. 4, a band-pass filter 3 for removing an image signal is required to have high selectivity as shown in FIG. It is necessary to cover a range corresponding to the reception band of the device, but if it is intended to achieve high selectivity, there is a problem that it is difficult to widen the range covered by the bandpass filter 3. Also, it is possible to set a high intermediate frequency to increase the range covered while ensuring high selection performance, but if the intermediate frequency is set high, expensive parts are used as filters used in the intermediate frequency stage. For example, it is necessary to use a monolithic ceramic filter (MCF) or the like, and there is a problem that technical difficulty increases.
[0005]
If the selectivity of the band-pass filter 3 is prioritized, it becomes difficult to cover a wide band. Conversely, if the wide band is covered, the selectivity is sacrificed, and both selectivity and coverage performance are achieved. However, even if it can be realized, there is a problem that the circuit configuration becomes complicated and the cost increases.
[0006]
The present invention has been made in view of the above-mentioned conventional problems, and it is possible to easily determine whether a received signal is a desired signal or an image signal and to remove the image signal. It is not necessary to use a bandpass filter, and an object of the present invention is to obtain a wireless reception device capable of reducing the size and cost of a reception circuit, and eliminate the need to use a bandpass filter for removing an image signal. It is an object of the present invention to provide a radio receiver that can easily design a wideband radio receiver. Furthermore, by setting the intermediate frequency to several tens of kHz, it is not necessary to use expensive components such as a monolithic ceramic filter (MCF) for the intermediate frequency band-pass filter, and the circuit can be configured by an IC. It is intended to provide a radio receiver.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the radio receiver of the present invention, in the radio receiver of the heterodyne reception system, the frequency of the local oscillation signal is changed, and heterodyne detection is performed on both the upper side and the lower side of the signal. After the frequency conversion to the signal of the intermediate frequency band, both the received signal levels on the upper side and the lower side are checked, and when the both received signal levels are the same, the demodulated signal is output assuming that the signal is the desired signal, and the receiving state is entered. It is what was constituted.
[0008]
Further, in the radio receiver of the heterodyne reception system, the frequency of the local oscillation signal is changed, the upper side of the signal is subjected to heterodyne detection, the frequency is converted to a signal in the intermediate frequency band, and the received signal level on the upper side is confirmed. Receiving signal level confirming means, and changing the frequency of the local oscillation signal, heterodyne-detecting the lower side of the signal and converting the frequency to an intermediate frequency band signal, and then confirming the received signal level on the lower side. The received signal level confirming means is compared with the two received signal levels confirmed by the first and second received signal level confirming means. If the two received signal levels are the same, the demodulated signal is output as a desired signal. If the received signal levels are different, control is performed to terminate the receiving operation and return to the standby state assuming that it is an interference wave. It is obtained by a receiving control unit.
[0009]
Furthermore, when the frequency of the local oscillation signal is changed and heterodyne detection is performed on the upper or lower side of the signal to convert the frequency to a signal in the intermediate frequency band, if there is no output of the reception signal, the reception operation is terminated and the apparatus is in standby. It may be configured to return to the state.
[0010]
Further, it is preferable that the reception signal level is confirmed by using a reception field strength (RSSI) signal to confirm the reception signal level.
It is effective to set the intermediate frequency to several tens of kHz.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described based on examples with reference to the drawings.
The same parts as those in the conventional example of FIG. 4 are denoted by the same reference numerals, and detailed description of common parts is omitted.
FIG. 1 is a block diagram showing an embodiment of a heterodyne reception type radio receiver according to the present invention.
[0012]
In FIG. 1, reference numeral 1 denotes an antenna, 2 denotes a low noise amplifier, 4 denotes a mixer, 5 denotes a local oscillator, 7 denotes a detection circuit, 8 denotes a CPU, and 9 denotes a PLL circuit. Reference numeral 10 denotes a signal line, which supplies a received signal strength (RSSI: Received Signal Strength Indicator) signal obtained from the detection circuit 7 to the CPU 8, and in the CPU 8, the level of the reception signal supplied from the detection circuit 7 (in this case, Voltage) are recorded and compared.
[0013]
In the heterodyne receiver of FIG. 1 configured as described above, the intermediate frequency is set as low as, for example, about 50 kHz. When the receiver of FIG. 1 receives a desired wave signal, as shown in FIG. 2, the local oscillator 5 outputs the "local oscillation signal fL and the desired wave signal f + intermediate frequency signal IF (when the intermediate frequency is 50 kHz, Is switched to f + 50 kHz) and a desired signal f-intermediate frequency signal IF (f-50 kHz), and heterodyne detection is performed on both the upper side and the lower side of the signal to convert the frequency into a signal in the intermediate frequency band. At this time, if the received signal is the desired signal f, the local oscillation signal fL of the local oscillator 5 is shifted upward (f + IF) or downward (f-IF) as shown in FIG. However, the image signal can be received, but cannot be received if the frequency of the local oscillator 5 changes.
[0014]
Further, if the received signal strength (RSSI) signal level in both the case where the signal is received on the upper side and the case where the signal is received on the lower side can be received at the same level, it is regarded as the correct desired signal f and the demodulated signal is output. are doing. As described above, the received signals that can be received at the same level in both the upper and lower sides are the same, so that even if the upper and lower sides are switched during reception, the received sound is not interrupted.
[0015]
On the other hand, in the radio receiver of FIG. 1, since both the upper heterodyne detection and the lower heterodyne detection are used, if the intermediate frequency is set high, the frequency range in which the local oscillator 5 operates becomes wide, and the Becomes difficult. In addition, even if the intermediate frequency is too low, it becomes difficult to suppress nearby interference waves. Therefore, in the radio receiver according to the present invention, by setting the intermediate frequency to several tens of kHz, an IC can be used without using an expensive intermediate frequency band-pass filter such as a monolithic ceramic filter (MCF) in the intermediate frequency stage. A circuit can be configured.
[0016]
Next, the actual operation will be described based on the flowchart shown in FIG. In the wireless receiver configured as shown in FIG. 1, when the operation starts from a standby state, in step S1, data is sent from the CPU 8 to the PLL circuit 9, and the local oscillation frequency fL of the local oscillator 5 is changed to the upper desired wave signal f + 50 kHz ( (When the intermediate frequency is 50 kHz). At this time, if there is no signal in step S2, the receiving operation is terminated with NO, and the process returns to the standby state. On the other hand, if there is any signal in step S2, the process proceeds to the next step S3 with YES, and assuming that the level of the received field strength (RSSI) signal is "A", the signal level "A" is changed to "A". It is recorded by the CPU 8.
[0017]
Next, in step S4, data is sent from the CPU 8 to the PLL circuit 9, and the local oscillation frequency fL of the local oscillator 5 is switched to the lower desired signal f-50kHz. The signal level at the time of reception on the lower side is confirmed based on the received field strength (RSSI) signal. If the signal level at this time is the same as the previous signal level "A", the determination in step S5 is YES that the signal is regarded as a correct desired wave signal f, a demodulated signal is output, and the reception state is entered.
[0018]
On the other hand, if the signal level at this time is not the same as the previous signal level "A", the determination in step S5 is NO, and it is determined that the signal is an image signal or other interference wave, and the process returns to the standby state.
Note that, in the above-described embodiment, the upper reception and the lower reception are configured in this order, but the same result can be obtained even if the configuration is reversed.
[0019]
【The invention's effect】
Since the present invention is configured as described above, it is possible to easily determine whether the received signal is a desired signal or an image signal, and to use a band-pass filter for removing the image signal. This makes it possible to reduce the size and cost of the receiving circuit. In addition, since it is not necessary to use a band-pass filter for removing an image signal, it is easy to design a wideband wireless receiver.
[0020]
Furthermore, by setting the intermediate frequency to several tens of kHz, a circuit configuration using an IC can be realized without using expensive components such as a monolithic ceramic filter (MCF) in the intermediate frequency stage, and the manufacturing cost can be reduced. Can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a wireless receiver according to the present invention.
FIG. 2 is an explanatory diagram illustrating a relationship between a local oscillation signal and an image signal of the wireless receiver in FIG. 1;
FIG. 3 is a flowchart illustrating the operation of the wireless receiver in FIG. 1;
FIG. 4 is a block diagram illustrating a configuration of a conventional wireless receiver.
FIG. 5 is an explanatory diagram showing a relationship between an image signal of the wireless receiver in FIG. 4 and a bandpass filter.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 antenna 2 low-noise amplifier 3 band-pass filter 4 mixer 5 local oscillator 6 intermediate-frequency band-pass filter 7 detection circuit 8 CPU
9 PLL circuit 10 signal line

Claims (5)

In a heterodyne reception type radio receiver,
After changing the frequency of the local oscillation signal, performing heterodyne detection on both the upper and lower sides of the signal and converting the frequency to a signal in the intermediate frequency band, confirm the levels of both received signals on the upper and lower sides, A radio receiver characterized in that when the levels are the same, a demodulated signal is output assuming that the signal is a desired signal, and the apparatus enters a receiving state. In a heterodyne reception type radio receiver,
First reception signal level checking means for changing the frequency of the local oscillation signal, heterodyne-detecting the upper side of the signal and converting the frequency to a signal in the intermediate frequency band, and then checking the reception signal level on the upper side;
A second received signal level checking means for changing the frequency of the local oscillation signal, heterodyne-detecting the lower side of the signal and converting the frequency to a signal in the intermediate frequency band, and then checking the received signal level on the lower side;
The two received signal levels confirmed by the first and second received signal level confirming means are compared, and if the two received signal levels are the same, a demodulated signal is output as a desired wave signal to enter a receiving state. Control, and when both reception signal levels are different, a reception control means for controlling the end of the reception operation and returning to a standby state by regarding the reception operation as an interference wave;
A wireless receiver comprising: When changing the frequency of the local oscillation signal and performing heterodyne detection on the upper or lower side of the signal and converting the frequency to a signal in the intermediate frequency band, when there is no output of the received signal, the receiving operation is terminated and the standby state is entered. The wireless receiver according to claim 1, wherein the wireless receiver is configured to return. The radio receiver according to any one of claims 1 to 3, wherein the confirmation of the reception signal level is configured to confirm the reception signal level using a reception field strength (RSSI) signal. . The radio receiver according to any one of claims 1 to 4, wherein the intermediate frequency is set to several tens of kHz.

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