JPH05102868A - Fm receiver - Google Patents

Abstract

PURPOSE:To remove an interference wave component interfered in an intermediate frequency signal. CONSTITUTION:Intermediate frequency signals S12 and S22 of reception parts 1 and 2 set local oscillation frequencies so as to invert upper and lower side band wave arrangements each other. FM demodulation circuits 17 and 27 respectively demodulate the intermediate frequency signals S12 and S22 and output base band signals b11 and B12 inverting phases each other. An inverter 4 inverts the phase of the base band signal B11. A synthesizing part 5 cancels the interference wave component interfered from the outside to the intermediate frequency signal by synthesizing the phase-inverted base band signals B12 and B21 and synthesizes the base band signals. On the other hand, the synthesizing part 5 extracts the interference wave component interfered in the intermediate frequency signals by synthesizing the base band signals B11 and B12 inverting the phase each other. A local oscillation control part 7 controls the oscillation frequency of a local oscillation circuit 15 at the reception part 1 so that the frequency difference of the extracted interference wave component can be 0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver for microwave radio communication, and more particularly to an FM receiver having two systems for converting a received signal into an intermediate frequency signal and demodulating it. The present invention relates to an FM receiver that synthesizes demodulated outputs.

[0002]

2. Description of the Related Art Generally, in order to improve the S / N of a demodulated output signal and to improve the reliability of the line, it is common to combine the demodulated outputs (baseband signals) from the receivers of the two systems. ing.

As shown in FIG. 3, a conventional FM receiving apparatus of this type has a branching unit 3 for branching a received signal into two, receiving units 8 and 9 having the same configuration, and a base demodulated by the receiving units 8 and 9. And a synthesizing section 5 for synthesizing band signals.

Here, the receivers 8 and 9 receive the received signal as a first signal.
Mixers 81 and 91 for converting to intermediate frequency signals, local oscillation circuits 82 and 92 for transmitting first local oscillation signals, bandpass filters 83 and 93 for removing unnecessary signal components, and second intermediate frequencies for the first intermediate frequency signals. Mixers 84, 9 for converting into frequency signals
4 and a local oscillation circuit 85 for transmitting a second local oscillation signal,
95 and bandpass filters 86 and 9 for removing unnecessary signal components
6 and FM demodulation circuits 87 and 97 for demodulating the second intermediate frequency signal and outputting a baseband signal.

[0005]

In the conventional FM receiving apparatus described above, the S / N for thermal noise and the like can be improved by combining the demodulated output signals from the two-system receiving sections, but an external intermediate frequency is used. The interference wave that has entered the band cannot be removed by synthesis. Therefore, the interference wave component mixes with the baseband signal and is output as noise, which causes a problem of S / N deterioration.

An object of the present invention is to provide an FM receiver capable of reducing the interference wave mixed in the intermediate frequency signal and improving the S / N.

[0007]

An FM receiver according to the present invention includes first and second receivers for mixing a received signal and a local oscillation signal, converting the mixed signal into an intermediate frequency signal, and demodulating a baseband signal. In the FM receiver having the first receiving unit, the first receiving unit includes means for generating an intermediate frequency signal in which upper and lower sidebands of the intermediate frequency signal are arranged opposite to the received signal; And a means for demodulating one baseband signal; the second receiving unit is the same as the means for generating an intermediate frequency signal in which the arrangement of the upper and lower sidebands of the intermediate frequency signal is the same as that of the received signal. Means for demodulating a second baseband signal from the arranged intermediate frequency signal; and means for inverting the phase of the first baseband signal, and the baseband signal output by the phase inverting means and the First Constructed and means for outputting a baseband signal component and a base band signal by canceling the interference wave component mixed from outside to the intermediate frequency signal by combining. Furthermore, means for extracting the interference wave component by synthesizing baseband signals having mutually opposite phases output from the demodulation means of the first and second receivers,
A means for detecting the frequency difference between the interference wave components extracted by the extracting means, and controlling the frequency of the local oscillation signal in at least one of the first and second receiving sections so that the frequency difference becomes zero. It is configured to include.

[0008]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. A branch unit 3 that branches the received signal into two, receivers 1 and 2 that demodulate the received signal and output baseband signals B11 and B21, respectively, and a baseband signal B1.
An inverter 4 for inverting the phase of 1; a combiner 5 for combining the baseband signal B12 output by the inverter 4 and the baseband signal B21 output by the receiver 2; and a baseband signal B11 and a baseband signal B21. It includes a synthesizing unit 6 for synthesizing and a local oscillation control unit 7 for detecting an interference wave and controlling the local oscillation frequency of the receiving unit 1.

The receiving units 1 and 2 also include mixers 11 and 21 for converting the received signals into first intermediate frequency signals S11 and S21.
And the local oscillation circuits 12 and 2 for transmitting the first local oscillation signal.
2 and bandpass filters 13 and 23 for removing unnecessary signal components
And the first intermediate frequency signal to the second intermediate frequency signals S12, S2
The mixers 14 and 24 for converting to 2, the local oscillator circuits 15 and 25 for transmitting the second local oscillation signal, the bandpass filters 16 and 26 for removing unnecessary signal components, and the second intermediate frequency signal S.
12, S22 are demodulated to obtain baseband signals B11, B2
The FM demodulation circuits 17 and 27 that output 1 are included.

Next, the operation will be described for the case where the center frequencies of the second intermediate frequency signals S12 and S22 are f1 and f2 and the interference wave U of the frequency fu intrudes into the second intermediate frequency band from the outside.

FIGS. 2A and 2B show examples of the spectral distributions of the second intermediate frequency signals S12 and S22, respectively, when the interference wave of the frequency fu is mixed. here,
The spectral distributions of the second intermediate frequency signals S12 and S22 are
The upper sideband and the lower sideband are arranged opposite to each other with respect to the center frequencies f1 and f2, and the hatching indicates the same information. Therefore, for example, the second local oscillation frequency of the receiving unit is set higher than the first intermediate frequency on one receiving unit side and lower than the first intermediate frequency on the other receiving unit side. ..

By the way, as described above, the second intermediate frequency signals S12 and S in which the upper sideband and the lower sideband are arranged in reverse to each other.
By demodulating the signal 22, the baseband signals B11 and B21 having mutually opposite phases are obtained. Therefore, the baseband signal components are canceled by combining the baseband signals B11 and B21 by the combining unit 6,
As shown in FIG. 2C, the interference wave components U1 and U2 having frequencies (fu-f1) and (fu-f2) can be extracted.

The local oscillator controller 7 detects the frequency difference between the interference wave components U1 and U2, and controls the local oscillation frequency of the local oscillator circuit 15 of the receiver 1 so that the frequency difference becomes zero.

Further, as shown in FIG. 2D, the spectrum distribution of the output signal of the synthesizing unit 5 is obtained by inverting the phase of the baseband signal B11 by the inverter 4 and synthesizing it with the baseband signal B21. The band signal components are combined. On the other hand, the interference wave components U1 and U2 are in a state where their phases are mutually inverted. Here, the local control unit 7
By controlling the frequency difference between the interference wave components U1 and U2 to be 0, it is possible to reliably cancel the interference wave components U1 and U2 even if the local oscillation frequency of the receiving unit changes.
The S / N is greatly improved.

[0016]

As described above, according to the present invention, 2
Demodulation is performed so that the upper and lower sidebands of the intermediate frequency signals of the receiving section of the system are opposite to each other, the baseband signals of opposite phases are generated, and the phase of one of the baseband signals is inverted and combined. By doing so, it is possible to cancel the interference wave component mixed in the intermediate frequency signal from the outside and synthesize the baseband signal component.
/ N can be greatly improved. In addition, the interference wave component is extracted by synthesizing the baseband signals having opposite phases,
By controlling the frequency of the local oscillation signal of the receiving unit so that the frequency difference between the interference wave components becomes zero, the interference wave component can be reliably canceled regardless of the fluctuation of the local oscillation frequency of the receiving unit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a spectrum distribution of a signal of each part for explaining the operation of the present embodiment, (a) and (b).
Shows the spectral distribution of the second intermediate frequency signals S12 and S22, (c) shows the spectral distribution of the output signal of the combining unit 6, and (d) shows the spectral distribution of the output signal of the combining unit 5, respectively.

FIG. 3 is a block diagram showing an example of a conventional FM receiver.

[Explanation of symbols]

 1, 2 Reception section 4 Inverter 5, 6 Synthesis section 7 Local oscillation control section 11, 21 Mixer 12, 22, 15, 25 Local oscillation circuit 17, 27 FM demodulation circuit B11, B12, B21 Baseband signal S11, S21, S12 , S22 Intermediate frequency signal U Interference wave

Claims (2)

[Claims] 1. An FM receiving apparatus having first and second receiving sections for respectively mixing a received signal and a local oscillation signal, converting the mixed signal to an intermediate frequency signal and demodulating a baseband signal, wherein the first receiving section is provided. Has means for generating an intermediate frequency signal in which the arrangement of the upper and lower sidebands of the intermediate frequency signal is opposite to that of the received signal, and means for demodulating the first baseband signal from the intermediate frequency signal in the opposite arrangement. The second receiving unit includes means for generating an intermediate frequency signal in which the upper and lower sidebands of the intermediate frequency signal have the same arrangement as the received signal, and the second baseband signal from the intermediate signal having the same arrangement. And means for inverting the phase of the first baseband signal, and combining the baseband signal output by the phase inverting means with the second baseband signal. Yo And a means for canceling out an interference wave component mixed into the intermediate frequency signal from the outside and outputting a baseband signal component. 2. The FM receiver according to claim 1, wherein
Means for extracting the interference wave component by synthesizing baseband signals having mutually opposite phases output from the demodulation means of the first and second receivers, and the frequency of the interference wave component extracted by the extraction means. An FM receiving apparatus, comprising means for detecting a difference and controlling the frequency of the local oscillation signal of at least one of the first and second receiving sections so that the frequency difference becomes zero.