JP4490570B2 - Wireless receiver with AGC circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such the problem of a pager of direct detection method being provided with an AGC circuit, corresponding to the reception level of reception frequency (optional wave) of its own pager in order to prevent mixed modulation of excessive reception input between the own pager and the vicinity of the radio station of the same operator, however, the AGC circuit does not operate using the optional wave and the reception sensitivity is decreased, because a mixer circuit is saturated due to excessive input. SOLUTION: A mixer output is provided with a bandpass filter of a band, ranging 50 to 100 kHz to 100 kHz so that waves from other operator as an interfering wave is extracted, and their interfering wave level is detected by an interfering wave detection circuit. According to the detected level, by controlling the level of input high frequency, the excessive input of waves from the other operator is prevent.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic gain control (AGC) circuit of a direct detection type radio receiver, for example, a radio paging terminal (hereinafter referred to as a pager).
[0002]
[Prior art]
As a conventional direct detection type pager, there is JP-A-7-135514. FIG. 2 shows an example of the configuration. In FIG. 2, the high frequency signal received from the antenna 1 is amplified by the high frequency amplifier 3 via the variable attenuator 2 which is a circuit for controlling the input amplitude of the received high frequency signal, and the output is applied to the mixer 4 and the mixer 5. ing. In this example, the input amplitude of the received high-frequency signal is determined by the attenuation factor of the variable attenuator 2 and the amplification factor of the high-frequency amplifier 3. In the mixer 4 and the mixer 5, it is mixed with the output of the local transmitter 10. The output of the local oscillator 10 has a frequency substantially equal to the center frequency of the received high-frequency signal, and the output of the local oscillator 10 applied to the mixer 4 is a phase difference of 90 degrees from the output of the local oscillator 10 applied to the mixer 5. Is given. This is because the decoder 12 cancels the beat frequency signal generated because the frequency of the local oscillator 10 does not completely match the center frequency of the received high frequency signal.
[0003]
Since the modulation method of the reception high-frequency signal of the pager is FSK (Frequency Shift Keying), the output of the mixer 4 and the mixer 5 has a frequency equal to the frequency shift amount of the FSK signal (1.6 kHz and 4.8 kHz in the FLEX method). ) Baseband signal. This baseband signal is extracted by the low-pass filter 6 and added to the decoder 12 via the amplifier 8. Further, only the baseband signal is extracted from the output of the mixer 5 by the low-pass filter 7 and is added to the decoder 12 via the amplifier 9. The decoder 12 cancels the above-described beat frequency signal (usually a four-phase detector is used), demodulates the FSK signal, and obtains received digital data. The control unit 13 determines whether the received digital data is a call of the own pager. If the received digital data is a call of the own pager, the control unit 13 drives the driver 15 to send a ringing tone from the speaker 17 or from the vibrator 18 by vibration. I do. The received digital data information is displayed on the LCD 16. The key switch 19 is a key input switch by the user from the pager. The memory 14 stores received data and a control program.
[0004]
The desired wave level detection circuit 11 and the variable attenuator 2 form an automatic gain control circuit (AGC circuit). The desired wave level detection circuit 11 receives the baseband signal from the output of the low-pass filter 6 and detects the signal level. The output of the desired signal level detecting circuit 11 is applied to the variable attenuator 2, controls the attenuation amount of a received high-frequency signal of the variable attenuator 2. That is, when the baseband signal level exceeds a certain value, the variable attenuator 2 increases the attenuation so that an excessively high frequency signal is not applied to the pager. Since the pager is moving with the user, when it comes close to the radio base station, the reception high-frequency signal level increases, an excessive input is added to the pager, and cross modulation distortion occurs in a mixer or the like. A desired wave level detection circuit 11 and an AGC circuit of the variable attenuator 2 are added for the purpose of preventing a decrease in reception sensitivity due to the cross modulation distortion.
[0005]
[Problems to be solved by the invention]
However, in the AGC circuit described above, it is possible to prevent cross modulation distortion due to an excessive signal from a radio base station of the same operator as the own pager, but the mixer circuit of an excessive input due to a radio wave received from another operator Saturation could not be prevented. FIG. 3 shows an example of the reception frequency (channel) received by the pager. A plurality of radio waves (radio channels) are usually transmitted from the radio base station of the pager at a frequency interval of 25 kHz or 50 kHz. FIG. 3 shows a case where there are four radio channels from the own pager operator and four radio channels from other operators. The frequency interval with the wireless channel of another provider is several hundred kHz to several MHz. Under such an environment, the pager receives radio waves of other channels from the same operator as well as the reception frequency (desired wave) of the own pager. In the example of FIG. 3, when the radio channel interval is 50 kHz, the desired wave frequency is +50 kHz and +100 KHz. When these radio frequencies are added to the pager, so-called IM (Inter Modulation) interference is caused. In this case, both the desired wave of the own pager and the interference wave separated by +50 kHz and +100 KHz are transmitted at the same level from the same radio base station. Therefore, the desired wave level detection circuit 11 and the AGC circuit of the variable attenuator 2 described with reference to FIG.
[0006]
On the other hand, the radio wave from the radio base station of another company other than the own pager company is a frequency separated from several hundred kHz to several MHz from the desired wave frequency of the own pager. For this reason, the baseband output from the mixer 4 with respect to the radio waves of other operators is also a signal of several hundred kHz to several MHz, and this is removed by the low-pass filter 6, so feedback to the variable attenuator 2 is not applied. Therefore, if the radio base station of another operator is located near the own pager, the radio frequency signal from the other operator becomes an excessive input even though the received signal of the own pager is not an excessive input, and the mixer There arises a problem that the circuit is saturated and the reception sensitivity is significantly deteriorated. An object of the present invention is to solve the reception sensitivity deterioration in the vicinity of a radio base station of another provider.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a direct detection radio receiver,
A circuit that controls the input amplitude of the received high-frequency signal, a mixer that mixes the received high-frequency signal and the output of the local oscillator, a low-pass filter that extracts a baseband signal from the output of the mixer, and an output of the low-pass filter A desired wave level detection circuit, a band pass filter connected to the mixer output, and an interference wave level detection circuit connected to the output of the band pass filter,
When the output of the desired wave level detection circuit exceeds a certain level, the circuit controls the input amplitude of the received high-frequency signal, and decreases the input amplitude of the received high-frequency signal as the output of the desired wave level detection circuit increases. ,
When the output of the interference wave level detection circuit exceeds a certain level, the circuit for controlling the input amplitude of the reception high-frequency signal is controlled, and the input amplitude of the reception high-frequency signal is decreased as the output of the interference wave level detection circuit increases. A wireless receiver with an AGC circuit is provided.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a block diagram of a pager with an AGC circuit according to the present invention. A high-frequency signal received from the antenna 1 is amplified by a high-frequency amplifier 3 via a variable attenuator 2 that is a circuit for controlling the input amplitude of the received high-frequency signal, and its output is applied to a mixer 4 and a mixer 5. In the mixer 4 and the mixer 5, it is mixed with the output of the local transmitter 10. The output of the local transmitter 10 has a frequency substantially equal to the center frequency of the received high-frequency signal, and the output of the local transmitter 10 applied to the mixer 4 and the output of the local transmitter 10 applied to the mixer 5 are 90 degrees in phase difference. Is given.
[0009]
The baseband signal output from the mixer 4 is extracted by a low-pass filter 6 and applied to a decoder 12 via an amplifier 8. Further, only the baseband signal is extracted from the output of the mixer 5 by the low-pass filter 7 and is added to the decoder 12 via the amplifier 9. The decoder 12 demodulates the baseband signal of the FSK signal to obtain received digital data. The control unit 13 determines whether the received digital data is a call to the own pager by comparing with the data in the memory 14, and if the call is to the own pager, drives the driver 15 and sends a ringing tone from the speaker 17. Or a call by vibration from the vibrator 18. The received digital data information is displayed on the LCD 16. The key switch 19 is a key input switch by the user from the pager.
[0010]
The desired wave level detection circuit 11 and the variable attenuator 2 form an automatic gain control circuit (AGC circuit). Desired signal level detecting circuit 11 receives the output of the low pass filter 6, the output is applied to the variable attenuator 2, controls the attenuation amount of a received high-frequency signal of the variable attenuator 2. The output of the mixer 4 through a band-pass filter 20 is added to the interference wave level detecting circuit 21, and controls the attenuation amount of a received high-frequency signal of the variable attenuator 2 at the output of the interference wave level detecting circuit 21 .
[0011]
Hereinafter, the operation of the present invention will be described in detail with the desired wave level detection circuit 11 and the interference wave level detection circuit 21 as main components. First, a case where a high frequency signal from the operator of the own pager in FIG. 3 is input will be described. In the figure, there are four channels of radio waves from the operator of the own pager. One of these channels is a desired wave to be received by the own pager. These four radio waves are added to the variable attenuator 2 via the antenna 1, amplified by the high frequency amplifier 3, and input to the mixer 4 and the mixer 5. In the mixers 4 and 5, the frequency of the center frequency of the desired wave transmitted from the local transmitter 10 is added and mixed with the input high frequency signal. As a result, a frequency-modulated baseband signal of the high-frequency signal is obtained by the mixer 4 and the mixer 5. Since the mixer 4 and the mixer 5 usually have a mixture of the baseband signal, the high-frequency signal and the output from the local transmitter 10, only the baseband signal is extracted by the low-pass filter 6 and the low-pass filter 7, and the amplifier 8 and amplifier 9 is amplified and added to the decoder 12.
[0012]
Since the local transmission frequency from the desired wave level detection circuit 11 applied to the mixer 4 and the mixer 5 is not synchronized with the input high frequency signal, the output of the mixer 4 and the mixer 5 is the input high frequency signal and the local transmission. A beat signal with a slight difference in frequency is generated. This beat signal has the same amplitude at the outputs of the mixer 4 and the mixer 5 but has a different phase, so that it can be canceled using a four-phase detector or the like. The baseband signal is detected by the decoder 12 and input to the control unit 13 as a DC digital signal for normal control as a pager.
[0013]
The above is the operation when the user is away from the radio base station of the own pager. If the pager is in the vicinity of the radio base station, the received field strength of the radio channel of the own pager operator becomes extremely large in FIG. When a plurality of radio channels are input to the mixer 4 and the mixer 5 at an extremely high level, cross modulation between each input radio channel and the local oscillation frequency occurs, and the desired wave to be received by the own pager is high in input level. In some cases, reception is not possible. However, when there is an excessive input in the desired wave of the own pager and the same frequency band, the outputs of the mixer 4 and the mixer 5 naturally increase and the output of the low-pass filter 6 also increases. When the output of the low-pass filter 6 increases, the input of the desired wave level detection circuit 11 increases, so the control voltage that is the output of the desired wave level detection circuit 11 also increases, and a large control voltage is applied to the variable attenuator 2. The variable attenuator 2 is configured to increase the amount of attenuation when a large voltage is applied, and thus attenuates the input high-frequency signal from the antenna 1. For this reason, radio waves of a plurality of channels from the own pager operator are attenuated to a level at which cross modulation does not occur in the mixer 4 and the mixer 5. That is, the output of the desired wave level detection circuit 11 and the characteristics of the AGC circuit constituted by the variable attenuator 2 may not be attenuated at the normal reception level by the pager, and the mixer 4 or the mixer 5 may cause cross modulation. When the input is excessive, the variable attenuator 2 is controlled so as to be attenuated to a level that does not cause cross modulation, thereby preventing a decrease in sensitivity due to radio waves of the own pager operator.
[0014]
Next, an operation when a strong radio wave from an operator other than the own pager operator is input to the pager will be described. As shown in FIG. 3, a radio base station of another provider usually has a frequency slightly different from the frequency of its own pager provider (difference between several hundred kHz to several MHz), and a plurality of radio signals are 25 kHz or 50 kHz steps. Is being sent out. When the own pager is in the vicinity of the radio base station of another provider, these signals are input to the pager at an excessive level, and the mixer 4 and the mixer 5 mix these signals with each other, A signal of up to several hundred kHz is generated. Although this signal is blocked by the low-pass filter 6, only the interference wave of several hundred kHz to several MHz is extracted using the band-pass filter 20, and DC detection is performed by the interference wave level detection circuit 21. The variable attenuator 2 is controlled in accordance with the detection level, the input amplitude of the high frequency signal from another operator can be reduced, and saturation in the mixer circuit can be prevented.
[0015]
In the above description, the input amplitude of the received high-frequency signal is controlled by controlling the variable attenuator 2. However, the amplification degree of the high-frequency amplifier 3 may be controlled. Further, since the input level is attenuated by the variable attenuator 2 due to the interference wave from other operators, the level of the desired wave from the own pager operator is also attenuated, and the reception sensitivity of the pager is lowered. In most of the areas used, radio waves having a level sufficiently higher than the reception sensitivity level of the pager reach, and in many cases, the desired wave can be received by the pager.
[0016]
In the above description, the pager has been described as an example of a radio receiver. However, the present invention can also be applied to a case where a base station of a plurality of providers uses a direct detection method in a radio reception circuit such as a mobile phone adjacent to the base station. Needless to say.
[0017]
【The invention's effect】
According to the present invention, it is possible to avoid intermodulation distortion due to excessive input of radio waves from the operator of the own pager and to prevent interference due to excessive input of radio waves from other operators, so that the vicinity of the radio base station of the own pager operator In any vicinity of the wireless base station of another provider, it is possible to receive a desired wave, and a paging service with higher reliability is possible.
[Brief description of the drawings]
FIG. 1 is a block diagram of a pager with an AGC circuit of the present invention.
FIG. 2 is a block diagram of a conventional pager with an AGC circuit.
FIG. 3 is an example of a frequency arrangement of jamming waves.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Antenna 2 Variable attenuator 3 High frequency amplifier 4, 5 Mixer 6, 7 Low pass filter 8, 9 Amplifier 10 Local transmitter 11 Desired wave level detection circuit 12 Decoder 13 Control unit 14 Memory 15 Driver 16 LCD
17 Speaker 18 Vibrator 19 Key switch 20 Band pass filter 21 Interference wave level detection circuit

Claims (2)

A direct detection wireless receiver,
A circuit for controlling the input amplitude of the received high-frequency signal;
A local oscillator that outputs a signal having a frequency equal to the center frequency of the desired wave to be received of the received high-frequency signal;
A mixer for mixing the output of the receiving radio-frequency signal and the local oscillator is the output of the circuit for controlling the input amplitude of the received RF signal,
A low-pass filter that extracts a baseband signal of a desired wave from the output of the mixer;
Connected to the output of the low-pass filter, and forms a circuit for controlling the input amplitude of the received high-frequency signal and an AGC circuit, and outputs a signal for controlling the received high-frequency signal attenuation amount of the circuit for controlling the input amplitude of the received high-frequency signal A desired wave level detection circuit to
A bandpass filter connected to the output of the mixer ;
An interference wave level detection circuit that is connected to the output of the bandpass filter and outputs a signal that controls the attenuation of the received high-frequency signal by an output to a circuit that controls the input amplitude of the received high-frequency signal ;
When intermodulation between the received high-frequency signal and the output of the local oscillator occurs in the mixer, a circuit for controlling the input amplitude of the received high-frequency signal is controlled according to an increase in the output of the desired wave level detection circuit, and the received high-frequency signal The input amplitude of
When a radio wave is input from a radio receiver other than its own radio receiver, an interference wave is extracted using the band-pass filter, and the input amplitude of the received high-frequency signal is controlled according to the detection level of the interference wave level detection circuit. A radio receiver with an AGC circuit, characterized by controlling a circuit and reducing an input amplitude of a received high-frequency signal. A direct detection wireless receiver,
Attenuation determined by first and second control signals input to the first and second control terminals, having an input terminal and first and second control terminals. An attenuator that controls the amplitude according to the rate,
A local oscillator that outputs a frequency equal to a center frequency of a desired wave to be received of the received high-frequency signal;
A mixer that mixes an amplitude-controlled received high-frequency signal that is an output of the variable attenuator and an output of the local oscillator;
A low-pass filter that extracts a baseband signal of a desired wave from the output of the mixer;
A desired wave level detection circuit that detects an output level of the low-pass filter and outputs the detected level to the first control terminal;
A band-pass filter that extracts an interference wave from the output of the mixer and outputs the interference wave to the second control terminal;
An interference wave level detection circuit for detecting an output interference wave level of the bandpass filter;
With
The attenuator increases an attenuation rate based on a desired detection wave level input to the first control terminal when cross modulation of the received high frequency signal and the signal of the local oscillator occurs in the mixer. The radio receiver with an AGC circuit is controlled so that the attenuation rate is increased when there is a detected interference wave level input to the second control terminal.

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