JP2002111522A - Radio 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

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver of a direct detection system, for example, a radio paging terminal (hereinafter referred to as a pager).
And an automatic gain control (AGC) circuit.

[0002]

2. Description of the Related 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, a high-frequency signal received from an antenna 1 passes through a variable attenuator 2 which is a circuit for controlling the input amplitude of the received high-frequency signal, is amplified by a high-frequency amplifier 3, and its output is applied to a mixer 4 and a 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 of the high-frequency amplifier 3. In the mixers 4 and 5, the output is mixed with the output of the local oscillator 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 has a phase difference of 90 degrees from the output of the local oscillator 10 applied to the mixer 5. It has. This is because the decoder 12 cancels the signal of the beat frequency generated because the frequency of the local oscillator 10 does not completely match the center frequency of the received high-frequency signal.

The modulation method of the received high-frequency signal of the pager is F
Since it is SK (Frequency Shift Keying), the output of the mixers 4 and 5 includes a baseband signal having a frequency equal to the frequency shift amount of the FSK signal (1.6 kHz and 4.8 kHz in the FLEX system). ing.
This baseband signal is extracted by the low-pass filter 6 and applied to the decoder 12 via the amplifier 8.
The output of the mixer 5 is also such that only the base signal is extracted by the low-pass filter 7 and applied to the decoder 12 via the amplifier 9. The decoder 12 cancels the above-mentioned 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 for the own pager.
The driver 15 is driven to transmit a ringing tone from the speaker 17 or to make a call from the vibrator 18 by vibration.
Further, the information of the received digital data is displayed on the LCD 16. The key switch 19 is a switch for key input by a user from a pager. The memory 14 stores received data and stores a control program.

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 wave level detection circuit 11 is applied to the variable attenuator 2, and controls the amount of attenuation of the 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 amount of attenuation to prevent an excessive high-frequency signal from being applied to the pager. Since the pager moves with the user, the level of the received high-frequency signal increases near the radio base station, an excessive input is applied to the pager, and cross-modulation distortion occurs in a mixer or the like. In order to prevent a decrease in reception sensitivity due to the cross modulation distortion, a desired wave level detection circuit 11 and an AGC circuit of the variable attenuator 2 are added.

[0005]

However, in the above-mentioned AGC circuit, it is possible to prevent cross-modulation distortion due to an excessive signal from a radio base station of the same carrier as the own pager, but it is possible to prevent cross-modulation from other carriers. It was not possible to prevent the saturation of the mixer circuit due to excessive input due to received radio waves. FIG.
2 shows an example of a reception frequency (channel) received by the pager. Usually, a plurality of radio waves (radio channels) are 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 of other operators. The frequency interval from the wireless channel of other carriers is several hundred kHz to several MHz
is seperated. Under such an environment, the pager receives radio waves of another channel from the same carrier together with the reception frequency (desired wave) of the pager. In the example of FIG. 3, if the radio channel interval is 50 kHz, the desired wave + 50 kHz
z, and a frequency of +100 KHz. When these radio frequencies are added to the pager, the so-called IM (Inter
Modulation) causes interference. In this case, the desired wave of the own pager and the interference waves separated by +50 kHz and +100 kHz are transmitted at the same level from the same radio base station. Circuit 1
1 and the AGC circuit of the variable attenuator 2 can prevent the influence of excessive input.

On the other hand, the radio wave from the radio base station of another company other than the own pager is a frequency that is several hundred kHz to several MHz away from the desired wave frequency of the own pager. For this reason, the baseband output from the mixer 4 with respect to the radio wave of the other carrier is also a signal of several hundred kHz to several MHz, which is removed by the low-pass filter 6, so that no feedback to the variable attenuator 2 is applied. Therefore, if the radio base station of another operator is located near the own pager, the radio high-frequency signal of the other operator becomes excessively input even though the received signal of the own pager is not excessively input, and the mixer is There is a problem that the circuit is saturated and the receiving sensitivity is significantly deteriorated. An object of the present invention is to solve the degradation of the reception sensitivity near the radio base station of another operator.

[0007]

SUMMARY OF THE INVENTION To achieve the above object, the present invention relates to a direct detection type radio receiver, comprising: a circuit for controlling an input amplitude of a received high-frequency signal; Mixer for mixing the output of the mixer, a low-pass filter for extracting a baseband signal from the output of the mixer, a desired wave level detection circuit connected to the output of the low-pass filter, and 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, and when the output of the desired wave level detection circuit exceeds a certain level, controls a circuit that controls the input amplitude of the received high-frequency signal, The input amplitude of the received high-frequency signal is reduced in accordance with an increase in the output of the desired wave level detection circuit, and the output of the interference wave level detection circuit is lower than a certain level. A circuit for controlling the input amplitude of the received high-frequency signal is controlled, and the input amplitude of the received high-frequency signal is reduced in accordance with an increase in the output of the interference wave level detection circuit. I do.

[0008]

Embodiments of the present invention will be described below 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 which is a circuit for controlling the input amplitude of the received high-frequency signal, and the output is applied to a mixer 4 and a mixer 5. In the mixers 4 and 5, the output is mixed with the output of the local oscillator 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 and the output of the local oscillator 10 applied to the mixer 5 have a phase difference of 90 degrees. It has.

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. The output of the mixer 5 is also such that only the baseband signal is extracted by the low-pass filter 7 and applied 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 of its own pager,
Judge by comparing with the data of
The driver 15 is driven to transmit a ringing tone from the speaker 17 or to make a call from the vibrator 18 by vibration.
Further, the information of the received digital data is displayed on the LCD 16. The key switch 19 is a switch for key input by a user from a pager.

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 includes a low-pass filter 6
Is input to the variable attenuator 2, and the variable attenuator 2 controls the amount of attenuation of the received high-frequency signal. The output of the mixer 4 is applied to an interference wave level detection circuit 21 via a band-pass filter 20, and the output of the interference wave level detection circuit 21 controls the attenuation of the received high-frequency signal signal of the variable attenuator 2. .

Hereinafter, the operation of the present invention will be described in detail mainly with respect to the desired wave level detection circuit 11 and the interference wave level detection circuit 21. First, a case where a high frequency signal is input from the operator of the own pager in FIG. 3 will be described. In the figure, there are four channels of radio waves from the operator of the own pager. One of the channels is a desired wave to be received by the pager. These four radio waves are applied 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 oscillator 10 is added and mixed with the input high-frequency signal. As a result, a baseband signal obtained by frequency-modulating the high-frequency signal is obtained by the mixers 4 and 5. Since the baseband signal, the high-frequency signal and the output from the local oscillator 10 are usually mixed in the mixers 4 and 5,
Only the baseband signal is extracted by the low-pass filters 6 and 7, amplified by the amplifiers 8 and 9, and applied to the decoder 12.

The local oscillation frequency from the desired wave level detection circuit 11 applied to the mixers 4 and 5 is not synchronized with the input high frequency signal.
At the output of the mixer 5, a beat signal having a slight difference between the input high-frequency signal and the local oscillation frequency is generated. The beat signal has the same amplitude at the output of the mixer 4 and the output of the mixer 5, but has a different phase. Therefore, the beat signal can be canceled using a four-phase detector or the like. The baseband signal is detected by the decoder 12, input to the control unit 13 as a DC digital signal, and normal control as a pager is performed.

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 wireless base station, the received electric field strength of the wireless 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, intermodulation of each input radio channel and the local oscillation frequency occurs, and the desired wave to be received by its own pager is high despite the high input level. In some cases, reception cannot be performed. However, when there is an excessive input in the desired wave of the own pager and the same frequency band, the outputs of the mixers 4 and 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 that the control voltage, which 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 attenuation when a large voltage is applied, and thus attenuates the input high-frequency signal from the antenna 1. For this reason, the radio waves of a plurality of channels from the own pager operator are attenuated to a level at which no intermodulation occurs in the mixers 4 and 5. That is, the output of the desired wave level detection circuit 11 and the AGC
If the pager does not attenuate the characteristics of the circuit at the normal reception level, and the mixer 4 or 5 has an excessive input that may cause cross-modulation, the variable attenuator 2
Is controlled to attenuate to a level that does not cause cross-modulation, whereby a decrease in sensitivity due to radio waves of the own pager operator can be prevented.

Next, the operation when a strong radio wave from a business other than the business of the own pager is input to the pager will be described. From the wireless base station of another carrier,
As shown in (1), a plurality of radio signals are transmitted at 25 kHz or 50 kHz steps at a frequency slightly different from the frequency of the own pager operator (difference of several hundred kHz to several MHz). If the own pager is in the vicinity of the radio base station of another operator, these signals are input to the pager at an excessive level, and these signals are mixed by the mixer 4 and the mixer 5 to generate tens of signals. A signal of up to several hundred kHz is generated. The signal is blocked by the hello-pass filter 6, but the signal is blocked by the band-pass filter 20.
Hz interference wave, and the interference wave level detection circuit 2
DC detection is performed at 1. The variable attenuator 2 is controlled in accordance with the detection level to reduce the input amplitude of the high-frequency signal from another carrier and prevent saturation in the mixer circuit.

In the above description, the input amplitude of the received high-frequency signal is controlled by controlling the variable attenuator 2, but the amplification of the high-frequency amplifier 3 may be controlled.
In addition, a variable attenuator 2
Since the input level is attenuated by the receiver, the level of the desired wave from the own pager operator is also attenuated, and the receiving sensitivity of the pager is reduced, but most of the area where the pager is used is received by the pager. Since a radio wave of a level sufficiently higher than the sensitivity level arrives, a desired wave can be received by a pager in many cases.

Although a pager has been described above as an example of a wireless receiver, the present invention is also applicable to a case where a base station of a plurality of operators uses a direct detection system in a wireless receiving circuit of an adjacent mobile phone or the like. Needless to say, it can be applied.

[0017]

According to the present invention, cross-modulation distortion due to excessive input of radio waves from the operator of the pager can be prevented,
Since it is possible to prevent interference due to excessive input of radio waves from other carriers, it is possible to receive a desired signal in the vicinity of the radio base station of the own pager carrier or in the vicinity of the radio base station of another carrier, A more reliable paging service becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of a pager with an AGC circuit according to 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 an interference wave.

[Explanation of symbols]

 Reference Signs List 1 antenna 2 variable attenuator 3 high-frequency amplifier 4, 5 mixer 6, 7 low-pass filter 8, 9 amplifier 10 local oscillator 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 Bandpass filter 21 Interference wave level detection circuit

Claims (1)

[Claims] 1. A radio receiver of a direct detection system, comprising: a circuit for controlling an input amplitude of a received high-frequency signal; a mixer for mixing the received high-frequency signal and an output of a local oscillator; A low-pass filter for extracting a signal, a desired wave level detection circuit connected to the output of the low-pass filter, a band-pass filter connected to the mixer output, and a detection of an interference wave level connected to the output of the band-pass filter A circuit for controlling an input amplitude of the received high-frequency signal when an output of the desired-wave level detection circuit is equal to or higher than a predetermined level; A circuit for controlling the input amplitude of the received high frequency when the output of the interference wave level detection circuit is reduced to a certain level or more when the amplitude is reduced. And decreasing the input amplitude of the received high-frequency signal as the output of the interference wave level detection circuit increases.
Radio receiver with GC circuit.