JP2001223599A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver with very excellent user-friendliness that can reduce the effect of a disturbing wave on reception sensitivity without the need for external provision of an attenuator. SOLUTION: An attenuator provided to a post-stage of an amplifier attenuates modulation distortion generated from a disturbing wave because of nonlinearity of an input output characteristic of the amplifier. Since the attenuation of the intermodulation distortion by the attenuator is higher than the attenuation of a received signal, a ratio (C/N) of a level of the received signal to the intermodulation distortion is increased. Thus, the effect of a disturbing wave or an undesired wave can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for reducing the influence of interference waves on reception sensitivity.

[0002]

2. Description of the Related Art In a conventional receiver, since a band-pass filter and an amplifier exist in a stage preceding a frequency converter, reception sensitivity is affected by an interference wave in a reception frequency band. For example, since input / output characteristics of an amplifier and a frequency converter are non-linear, when a received signal is input, intermodulation distortion occurs due to an interfering wave, and the intermodulation distortion may deteriorate reception sensitivity.

Next, an example of intermodulation distortion generated by input / output characteristics of an amplifier and a frequency converter will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of the relationship between the frequency of a received signal and the frequency of an interfering wave when third-order modulation distortion occurs. When receiving the reception signal 11 of the reception frequency f1, the interference wave 12 in the frequency band of the reception signal 11,
13 (interference waves of frequencies f2 and f3) are also received. Then, the reception frequency f1, the frequency f2 of the interfering waves 12 and 13,
When f3 has the relationship shown in Expressions (1) and (2) (the relationship shown in FIG. 2), third-order intermodulation distortion 14 of frequency f1 occurs. f2 = f1 + a (1) f3 = f2 + a = f1 + 2a (2) f1: reception frequency (Hz) f3: interference wave frequency (Hz) f2: interference wave frequency (Hz) a: interference wave Difference between frequency f1 and reception frequency (Hz)

[0004]

In the above-mentioned prior art,
When the interfering wave is received together with the received signal, the relationship between the frequency of the received signal and the frequency of the interfering wave is determined by the above equation (1) because the input / output characteristics of the amplifier and the frequency converter are nonlinear.
When the relationship shown in (2) is satisfied, intermodulation distortion (third-order intermodulation distortion) may occur. There is a problem that it is necessary to provide an attenuator outside the radio to remove the intermodulation distortion.

An object of the present invention is to provide an extremely convenient receiver capable of reducing the influence of an interfering wave on reception sensitivity by removing intermodulation distortion without providing an external attenuator. It is in.

[0006]

According to the present invention, in order to achieve the above object, the level change of the intermodulation distortion is larger than the level change of the received signal (for example, the level change of the third-order intermodulation distortion is equal to the reception level). By providing an attenuator after the amplifier, the intermodulation distortion is greatly attenuated by the attenuator and the attenuation of the received signal is minimized. . As a result, the ratio between the level of the received signal and the intermodulation distortion (C /
Since N) increases, it is possible to reduce the influence of the interference wave on the reception sensitivity.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a receiver according to an embodiment of the present invention will be described. First, the operation of the receiver according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the receiver of this embodiment. 1 is an antenna input terminal, 2
Is a bandpass filter, 3 is an amplifier, 4 is a bandpass filter, 5 is an amplifier, 6 is an attenuator, 7 is a local signal, 8 is a frequency converter, 9 is an intermediate frequency section, and 10 is a demodulation section. It is. The reception signal and the interference wave received at the antenna input terminal 1 pass through the band-pass filter 2, the amplifier 3, the band-pass filter 4, and the amplifier 5, and are input to the attenuator 6. The attenuator 6 greatly attenuates third-order intermodulation distortion (this third-order intermodulation distortion will be described later in detail) caused by the input / output characteristics of the amplifiers 3 and 5 due to non-linearity. At the same time, the attenuation of the received signal is minimized, and the ratio (C / N) between the level of the received signal and the intermodulation distortion is increased.
The output signal from the attenuator 6 (the reception signal from which the intermodulation distortion has been removed) and the local oscillation signal 7 are mixed by the frequency converter 8, so that the frequency of the reception signal is converted to the intermediate frequency. Then, the received signal is output by being demodulated by the demodulation unit 10.

Next, third-order intermodulation distortion generated from an interfering wave will be described with reference to FIGS. FIG.
FIG. 7 is a diagram illustrating a relationship between the frequency of a received signal and the frequency of an interfering wave when the next intermodulation distortion occurs. FIG. 3 is a diagram illustrating the relationship between the frequency of the band-pass filter 2 and the amount of attenuation. Due to the characteristics of the band-pass filter 2 shown in FIG. 3, the reception frequency f1 = 365 (MHz) and the bandwidth BW = 15
The received signal 11 of (MHz) is output to the amplifier 3. Due to the input / output characteristics of the amplifier 3, when the relationship between the reception frequency f1 and the frequencies f2 and f3 of the interfering waves 12 and 13 is the relationship shown in Expressions (3) and (4) (the relationship shown in FIG. 2),
Third-order intermodulation distortion of the frequency f1 occurs. f2 = f1 + a (3) f3 = f2 + a = f1 + 2a (4) f1: reception frequency (for example, f1 = 365 (MH)
z)) f2: frequency of the interfering wave (for example, f2 = 365.01)
25 (MHz)) f3: frequency of the interfering wave (for example, f3 = 365.02)
5 (MHz)) a: Difference between frequency f2 of interference wave and reception frequency (for example,
a = 12.5 (KHz))

The band-pass filter 4 is a band-pass filter 2
Since the input / output characteristics of the amplifier 5 are nonlinear, the reception frequency f1 and the interference wave 1
The relationship between the frequencies f2 and f3 of the frequencies 2 and 13 is expressed by the above equation (3),
In the case of the relationship shown in (4), similarly, third-order intermodulation distortion of the frequency f1 occurs.

The third-order intermodulation distortion generated by the amplifiers 3 and 5 is attenuated by the attenuator 6. The amount of attenuation is three times the amount of attenuation of the received signal. (When the level of the received signal changes by 1 dB, the level of the intermodulation distortion changes by 3 dB.)
As a result, the ratio between the level of the received signal and the intermodulation distortion (C
/ N) is increased, so that the influence of the interference wave on the reception sensitivity can be reduced.

In this embodiment, a case has been described in which the third-order intermodulation distortion (third-order intermodulation distortion having the same frequency as the reception frequency) caused by receiving the interfering wave is attenuated. However, the present invention is not limited to this. Absent. Obviously, even when an intermodulation distortion other than the third-order intermodulation distortion (for example, the fifth-order intermodulation distortion) occurs, it can be similarly attenuated.

[0012]

According to the present invention, the intermodulation distortion generated from an interfering wave or an unnecessary wave can be greatly attenuated by the attenuator in the receiver, so that the level of the received signal and the intermodulation can be reduced. The ratio (C / N) to the distortion is increased, and the receiving sensitivity is improved. Therefore, it is possible to reduce the influence of the interference wave on the receiving sensitivity without providing an attenuator outside the receiver, and thus it is possible to provide a receiver with extremely high convenience.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a receiver according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a reception frequency and a frequency of an interference wave when third-order modulation distortion occurs.

FIG. 3 is a diagram showing the relationship between the frequency and the attenuation of the band-pass filter used in the receiver of the present embodiment.

[Explanation of symbols]

1: antenna input terminal 2: band-pass filter 3: amplifier 4: band-pass filter 5: amplifier 6: attenuator 7: local oscillator signal 8: frequency converter 9: intermediate frequency section 10: demodulation section 11: Received signal 12: Interference wave 13: Interference wave 14: Third-order intermodulation distortion

Claims (2)

[Claims] 1. A receiver comprising: a receiving section; and an amplifier for amplifying an output signal of the receiving section, comprising: an attenuator at a stage subsequent to the amplifier; and intermodulation distortion generated when two interfering waves are received. Attenuated by the attenuator to reduce the influence of the interfering wave on reception sensitivity. 2. The receiver according to claim 1, wherein the intermodulation distortion includes third-order intermodulation distortion, and the difference between the frequency of the first interference wave and the reception frequency, and the frequency of the second interference wave and the second A receiver configured to attenuate the third-order intermodulation distortion generated when the difference between the frequency of the first interfering wave and the frequency of the one interfering wave is equal to each other by the attenuator.