JP2004104277A - Excessive input protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excessive input protection circuit in a portable telephone system which can receive even excessive (illegal) radio frequency signals incoming at an unspecified time in an unspecified radio frequency band, without deteriorating the signal quality in the radio frequency band utilized for the portable telephone system. <P>SOLUTION: The excessive input protection circuit solves the problems of the subject described above by having a branching unit for branching broadband received signal waves into a plurality of band signals for amplifying the waves with a low noise amplifier, a plurality of attenuators connected between the output of the branching unit and the input of the low noise amplifier, each having a function for controlling the attenuation normally set to 0, a plurality of detectors for detecting outputs of the branching unit, and a plurality of comparators for providing control outputs for setting and changing the attenuations of those attenuators having functions for controlling their respective attenuations to predetermined attenuations from the attenuation of 0 among the plurality of attenuators having functions for controlling the attenuations in the duration that the outputs of the detectors exceed predetermined levels. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to a device / system for transmitting a plurality of radio frequency band signal waves out of equipment such as a wireless device that provides a mobile phone service, when an unnecessary and excessive wave is input from outside, the device The present invention relates to an additional function of an amplifier for reducing an excessive input wave level in order to suppress generation of non-linear distortion in a receiving circuit of a system.
[0002]
[Prior art]
The mobile phone system, a system that provides mobile phone services, makes effective use of limited frequency resources as the number of mobile phones increases, the service content becomes more complicated, and the capacity of wireless channels increases. Has been asked.
Therefore, in this type of mobile phone system, the system technology has shifted from an analog system to a digital system, and various technologies have been introduced to the digital system.
At present, there are various radio frequency bands being used, and services are being provided that make use of the features of the radio frequency bands used by each communication carrier. Therefore, the base station device is installed at an advantageous location for service, and securing an installation location of the base station device has become an important business point for each communication carrier.
When the installation location of the base station device is limited, in the same base station device that provides a service in the service area, instead of carrying the transmission of only one of the required number of radio frequency bands, A multi-carrier transmission type base station apparatus capable of transmitting a plurality of radio frequency bands to be serviced within a service area has become mainstream.
In a multi-carrier transmission type base station apparatus, an uplink signal transmitted from various portable terminals having different services to the base station apparatus arrives and receives it. That is, a problem may occur in the broadband receiving system circuit of the base station apparatus, which causes an over-input phenomenon of the input signal.
On the other hand, the downlink signal, that is, the receiving system circuit on the mobile terminal side may have a band corresponding to a single carrier, so the multicarrier transmission type such as the receiving system circuit of the multicarrier transmission type base station apparatus has a problem. Does not wake up.
As described above, the uplink signal transmitted from the mobile terminal to the base station apparatus is allocated to the substantially same radio frequency band even when the service of the mobile phone system is different, so that the antenna radiation characteristics of the mobile terminal are generally common. Therefore, various different signals in the service of the mobile phone system are transmitted to the base station apparatus as uplink signals from the mobile terminal side.
[0003]
In order to solve the problem of the signal over-input phenomenon, the conventional over-input protection circuit uniformly limits the input level in a frequency band (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-5-29843 (page 2, paragraph 0005)
[0005]
[Problems to be solved by the invention]
In recent years, an abnormal (illegal) radio frequency signal enters a base station device at a considerably large level in a part of a radio frequency band, and a wideband low noise amplifier (LNA) used in a reception input amplifier circuit in the base station device. There is a problem that the linear operation characteristic is distorted, adversely affects the entire band of the received wideband signal required for the mobile phone system, and lowers the service required in the mobile phone system.
[0006]
In a conventional example of this type of radio frequency transmission apparatus, for example, as shown in FIG. 2, an antenna (ANT) 7 for a mobile station is provided with a duplexer (DUP) for separating a broadband reception system circuit 10 and a wideband transmission system circuit 20 from each other. 1 A low-noise amplifier (LNA) 2 is used in the broadband receiving system circuit 10, and an input level to the low-noise amplifier (LNA) 2 is limited by an attenuator (ATT) 6. The transmission amplifier 3 is used for the broadband transmission system circuit 20. A desired radio frequency band signal wave is output from the output terminal 8 of the broadband receiving system circuit 10. The transmission circuit 20 has an input terminal.
As described above, since the radio frequency transmission device used in the mobile phone system has a broadband amplifier for both transmission and reception, an abnormal (illegal) radio frequency signal can easily pass particularly in an amplifier for a wideband received signal wave. Input to the low noise amplifier (LNA) 2 in some cases. This abnormal (illegal) radio frequency signal saturates the low-noise amplifier (LNA) 2 and causes its output to have non-linear operating characteristics including non-linear distortion, distorting the required signal component and causing unnecessary harmonics. The result includes waves.
Conventionally, as an over-input protection circuit for avoiding such non-linear distortion operation characteristics due to an abnormal (illegal) radio frequency signal, a duplexer (DUP) 1 and a low-noise amplifier (LNA) 2 An attenuator (ATT) 6 having a required amount of attenuation has been inserted in advance, and the level of the received broadband signal has been simultaneously limited in all bands, thereby ensuring the linearity of the operating characteristics of the low noise amplifier (LNA) 2. In such a case, the level of the received broadband signal itself used for wireless transmission of the mobile phone system is always limited, and there is a possibility that the service of the mobile phone system used may be deteriorated.
[0007]
In such a reception amplifier circuit of a radio frequency transmission device, when an excessive and abnormal (illegal) radio frequency signal is superimposed on a broadband reception signal wave used in a mobile phone system, the superimposed frequency band is used. However, there is a problem that it is not possible to reduce and control excessive input of a wideband low noise amplifier (LNA) only when the superimposition is performed.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a mobile phone system which uses a radio frequency band used for the mobile phone system even when an excessive and abnormal (illegal) radio frequency signal arrives at an unspecified time at an unspecified time. It is an object of the present invention to provide an over-input protection circuit that can receive a signal without deteriorating the signal quality.
[0009]
[Means for Solving the Problems]
In order to achieve this object, the over-input protection circuit according to the present invention is configured to select a desired radio frequency band signal wave from a wide band received signal wave including a plurality of radio frequency band signal waves having different frequencies.
A plurality of splitters for splitting the broadband received signal wave into a plurality of band signals,
A plurality of attenuators each connected to each output of the plurality of duplexers and having a function of controlling an attenuation amount which is always set to an attenuation amount of 0,
A plurality of low-noise amplifiers respectively amplifying each output of the plurality of attenuators,
A plurality of detectors for detecting the outputs of the plurality of demultiplexers,
The attenuation of the attenuator having the function of controlling the corresponding amount of attenuation among the plurality of attenuators having the function of controlling the amount of attenuation during the period when the output of each detector exceeds a predetermined level is set to the amount of attenuation. And a plurality of comparators capable of outputting a control output for changing the attenuation from 0 to a preset attenuation so as to secure the linear operation characteristics of the plurality of low noise amplifiers.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to a wireless transmission system. Radio frequency signals transmitted and received by an antenna (ANT) 7 for mobile stations include a reception wideband signal and a transmission wideband signal. A broadband receiving circuit 11 and a wideband transmitting circuit 20 are connected to a duplexer (DUP) 1 for separating the signal. In the wideband receiving system circuit 11, when a wideband receiving signal wave required for a mobile phone system is taken as an example, a duplexer as a band division filter for dividing into two band signals A (800 MHz to 850 MHz) and B (950 MHz to 1 GHz). 4a and 4b, detectors 5a and 5b for detecting the band signals A and B, comparators 9a and 9b for comparing the outputs of the detectors 5a and 5b with a comparison voltage of a required level, and comparators 9a and 9b. An attenuator (ATT) 6a, 6b having a function of selectively controlling whether or not a required attenuation can be inserted into the level of the band signal A, B according to the output level, and a low noise amplifier (LNA) 2a or 2b as a receiving amplifier circuit. Where the circuit portion composed of the detectors 5a and 5b, the comparators 9a and 9b, and the comparison voltage generation circuit is a band passing through the duplexers 4a and 4b. Those having a function of monitoring the level of the signal A, B. The specific operation will be described in detail below.
[0011]
A transmission / reception wave in a radio frequency band (800 MHz to 1 GHz) is induced in the antenna (ANT) 7. The transmission / reception waves are separated by the duplexer (DUP) 1 and guided to the duplexers 4a and 4b on the side of the broadband reception system circuit 11 as wideband reception signal waves of 800 MHz to 1 GHz.
[0012]
Here, one branching filter 4a passes a band signal A of 800 MHz to 850 MHz out of an input frequency band of 800 MHz to 1 GHz of the branching filter 4a. For example, this band is unnecessary for the mobile phone system. If an excessively abnormal (illegal) radio frequency signal (frequency 830 MHz, high frequency level 0 dBm) is input, the output level of the detector 5a is the known detection level of the band signal A used in the mobile phone system. Is higher than the required voltage, there is a comparison voltage Vao set as the required voltage, and the output level Va of the detector 5a is compared with the comparison voltage Vao by the comparator 9a, and the output level Va of the detector 5a is compared. Indicates that the signal passed through the duplexer 4a is determined to be at an excessive level, and a required comparison determination output is set as a control output Vac. It appears at the output of a. The control output Vac is changed to a preset attenuation of 30 dB by controlling an attenuator (ATT) 6a having a function of controlling the attenuation connected to the output of the duplexer 4a. The output side of the attenuator (ATT) 6a is connected to the input of the low noise amplifier (LNA) 2a, so that the input of the low noise amplifier (LNA) 2a has a level of 0 dBm-30 dB = -30 dBm. ), And the linear operation characteristics of the low noise amplifier (LNA) 2a are secured.
[0013]
The other splitter 4b passes a band signal B of 950 MHz to 1 GHz out of the input frequency band 800 MHz to 1 GHz of the splitter 4b, and transmits a radio frequency signal (for example, frequency When 980 MHz and a high frequency level of -30 dBm are input, the output level of the detector 5b includes a comparison voltage Vbo set as a required voltage by a known detection level of a frequency band signal used in the mobile phone system. The output level Vb of the detector 5b is compared with the comparison voltage Vbo in the comparator 9b, and the output level Vb of the detector 5b is determined to be the desired signal level by determining that the signal passing through the splitter 4b is the desired wave level. Appear at the output of the comparator 9b as a control output. The control output Vbc is always set to 0 without the setting change of the attenuator (ATT) 6b having the function of controlling the attenuation connected to the output of the duplexer 4b. The output side of the attenuator (ATT) 6b is connected to the input of the low noise amplifier (LNA) 2b, so that the input of the low noise amplifier (LNA) 2b receives a level of -30 dBm-0 dB = -30 dBm, The linear operation characteristics of the amplifier (LNA) 2b are ensured.
[0014]
The band signal A (830 MHz of unnecessary wave, -30 dBm) which is level-limited by the attenuator (ATT) 6a and the band signal B (980 MHz, -30 dBm of desired wave) which is not level-limited by the attenuator (ATT) 6b. Each is amplified by low noise amplifiers (LNAs) 2a and 2b having a gain (G) of 10 dB, and the signals of the band signals A and B obtain an output of -20 dBm and are combined to ensure operation as a wide band linear amplification characteristic. The required signal component is output to the output terminal of the broadband receiving system circuit 11 without distortion.
[0015]
The above operation is performed such that even if an unnecessary wave, which is an excessive and abnormal (illegal) radio frequency signal, enters in an unspecified band and unspecified time, the desired wave of the mobile phone system can be used. The noise amplifier (LNA) 2a or 2b is a wide-band linear amplifier having a wide dynamic range. As long as the level diagram is designed to ensure the operation as the amplification characteristic, the desired desired signal, which is a required normal signal, can be passed to the circuits subsequent to the output terminal 8.
The level limitation of the broadband radio frequency required for the mobile phone system, that is, the level of the desired wave itself is avoided or limited only when necessary in practice.
Therefore, it is possible to suppress the unnecessary excessive input signal level of the mobile phone system and selectively receive the signal without deteriorating the signal quality of the received broadband signal used in the mobile phone system.
[0016]
In the above embodiment, the demultiplexing number is 2, but it is also possible to use a plurality of demultiplexing numbers of 3 or more as the number of bands that can be divided into band signals required for the wireless transmission system. That is, in the mobile telephone system having the multi-carrier transmission type base station apparatus, it is possible to determine an appropriate number of demultiplexing for a previously assigned frequency band.
[0017]
【The invention's effect】
As described in detail above, according to the present invention, a selective over-input protection circuit for limiting the level of an abnormal (illegal) radio frequency signal is realized, and the linear operation characteristic of a low noise amplifier (LNA) is improved. Can be secured. That is, according to the present invention, since the level limitation of the wideband radio frequency itself required for the mobile phone system is inevitably limited to only when necessary, it is necessary to limit unnecessary services in the necessary band. Without this, the reliability of the transmission quality can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a circuit configuration example of over-input protection according to the present invention.
FIG. 2 is a block diagram showing a circuit configuration example of a conventional over-input protection.
1 Duplexer (DUP)
2a, 2b Low noise amplifier (LNA)
3 Transmission amplifiers 4a, 4b Demultiplexers 5a, 5b Detectors 6a, 6b Attenuator (ATT)
7 Antenna (ANT)
8 Output terminals 9a, 9b Comparator A, B Band signal Va, Vb Detector output Vao, Vbo Comparison voltage Vac, Vbc Control output

Claims (1)

In order to select a desired radio frequency band signal wave from a wide band received signal wave including a plurality of radio frequency band signal waves having different frequencies,
A plurality of splitters for splitting the broadband received signal wave into a plurality of band signals,
A plurality of attenuators each connected to each output of the plurality of duplexers and having a function of controlling an attenuation amount which is always set to an attenuation amount of 0,
A plurality of low-noise amplifiers respectively amplifying each output of the plurality of attenuators,
A plurality of detectors for detecting the outputs of the plurality of demultiplexers,
The attenuation of the attenuator having the function of controlling the corresponding amount of attenuation among the plurality of attenuators having the function of controlling the amount of attenuation during the period when the output of each detector exceeds a predetermined level is set to the amount of attenuation. An over-input protection circuit comprising: a plurality of comparators capable of outputting a control output for changing a setting to a preset attenuation amount so as to secure linear operation characteristics of the plurality of low noise amplifiers from 0. .

Images