JPH0897738A - Radio receiver - Google Patents

Abstract

PURPOSE: To make a distortion factor of a detection output compatible with adjacent disturbance only on the occurrence of adjacent disturbance. CONSTITUTION: An IF signal obtained by mixing a received RF signal and a local oscillation signal is given to a 1st filter 9 to be limited to a prescribed frequency band width and given to a 2nd filter 10 to be limited to a band width narrower than the frequency band width. A 1st and 2nd level detection circuits 13, 14 detect an electric field strength from output signals of the 1st and 2nd filters and a comparator circuit 15 compares the levels. When the electric field strength of the 1st level detection circuit 13 is higher, the comparator circuit, 15 generates an output signal and an output signal of the 2nd filter 10 is selected to be applied only to the detection circuit at the post-stage. Thus, only when a disturbance signal is in existence, the disturbance signal is completely eliminated and disturbance of an adjacent band is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver which prevents adverse effects due to adjacent interference.

[0002]

2. Description of the Related Art Generally, an FM radio receiver is constructed as shown in FIG. 2, a received RF signal is amplified by an RF amplification circuit (1), and a local oscillation circuit (3) oscillates in a mixing circuit (2). The signal is converted into an IF signal. IF
The signal is band-limited by the IF filter (4), amplified by the IF amplifier circuit (5), and further detected by the detection circuit (6).
Is detected by.

[0003]

By the way, in the radio receiver of FIG. 2, when a disturbing signal is generated adjacent to the desired broadcasting station, there is a problem that the disturbing signal interferes with the desired broadcasting station. Therefore, in order to remove the interference signal so that adjacent interference does not occur, an IF filter (4)
The narrower the pass band width is, the more narrow the pass band width is. However, if the pass band width is narrow, the group delay characteristic of the IF filter (4) deteriorates, and the distortion rate of the detection signal from the detection circuit (6) deteriorates. For that reason,
The pass band width of the IF filter (4) is 15 at the compromise between the removal of the interfering signal adjacent to the desired broadcasting station and the distortion of the detection signal.
It is set to 0 to 230 KHz. Therefore, it is not possible to completely remove the adjacent interfering signal with the pass band width set at the compromise point.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an RF amplifier circuit for amplifying a received RF signal, a local oscillation circuit for generating a local oscillation signal, and the reception RF signal. In a radio receiver having a mixing circuit that mixes a signal and the local oscillation signal to generate an IF signal, an IF amplification circuit that amplifies the IF signal, and a detection circuit that detects an output signal of the IF amplification circuit, The IF amplifier circuit includes a first filter that passes the IF signal in a predetermined frequency bandwidth, a second filter that passes the IF signal in a frequency bandwidth narrower than the frequency bandwidth of the first filter, and the second filter. A first detection circuit that detects the electric field strength of the output signal of the first filter, a second detection circuit that detects the electric field strength of the output signal of the second filter, and the output signals of the first and second detection circuits are compared. A comparison circuit which includes a selection circuit for selecting output signals of the first and second filter according to the output signal of the comparator circuit, and applying the IF signal selected in said detection circuit.

Further, when an interference signal is generated, an output signal is generated from the comparison circuit, and when the output signal of the comparison circuit is present, the output signal of the second filter is selected by the selection circuit and the output signal of the comparison circuit is selected. When the output signal does not exist, the output signal of the first filter is selected in the selection circuit.

[0006]

According to the present invention, the IF signal obtained by mixing the received RF signal and the local oscillation signal is limited to the predetermined frequency bandwidth in the first filter and the frequency bandwidth of the first filter in the second filter. Limited to a narrower frequency bandwidth. With respect to the output signals of the first and second filters, the electric field strengths of the respective output signals are detected by the first and second detection circuits, and the electric field strengths are compared by the comparison circuit. When a difference occurs between the electric field strengths, an output signal is generated from the comparison circuit, and the output signals of the first and second filters are switched according to the output signal.

Therefore, when the adjacent interfering signal is generated, the first
Since a difference occurs between the output signal of the second filter and the output signal of the second filter, an output signal is generated from the comparison circuit and switched to the output signal of the second filter. Therefore, the adjacent interference signal can be completely removed, and the adjacent interference can be prevented.

[0008]

FIG. 1 is a diagram showing an embodiment of the present invention,
(7) and (8) are first and second buffer circuits that pass the output IF signal of the mixer (2), (9) is a first filter that band-limits the output signal of the first buffer circuit (7),
(10) is a second filter that has a bandwidth narrower than that of the first filter and limits the output signal of the second buffer circuit (8). (11) and (12) are the first and second filters. First and second IF amplifier circuits amplifying the output signals of (9) and (10) respectively, and (13) and (14) detect the electric field strengths of the first and second IF amplifier circuits (11) and (12), respectively. First and second level detection circuits,
(15) is a comparison circuit for comparing the output signals of the first and second level detection circuits (13) and (14), and (16) and (17) are first and Third and fourth buffer circuits for passing the output signals of the second IF amplifier circuits (11) and (12), respectively (1
8) is the third or fourth buffer circuit (16) or (1
A fifth buffer circuit for passing the output signal of (7), (1
9) is a third filter for band limiting the output signal of the fifth buffer circuit (18), and (20) is a limiter amplifier circuit for amplifying the output signal of the third filter (19). Incidentally, FIG.
The same circuits as those in the conventional example are given the same reference numerals as those in the conventional example, and description thereof will be omitted.

In FIG. 1, the RF received by the antenna
The signal is amplified by the RF amplifier circuit (1) and then converted by the mixing circuit (2) by the local oscillation signal from the local oscillation circuit (3) into an IF signal having a center frequency of 10.7 MHz.
The IF signal passes through first and second buffer circuits (7) and (8), respectively, and first and second filters (9), respectively.
And (10). The output signal of the first buffer circuit (7) is, for example, 1 in the first filter (9).
The second buffer circuit (8) limits the output signal of the second buffer circuit (8) to a bandwidth of, for example, 50 MHz centered on 10.7 MHz. It That is, the bandwidths of the first and second filters (9) and (10) are as shown in (a) and (b) of FIG. 3, respectively. The passband width of the first filter (9) is generally used in a radio receiver, and the passband width of the second filter (10) is narrower than the passband width of the first filter (9). Is. The output signals of the first and second filters (9) and (10) are applied to and amplified by the first and second IF amplifier circuits (11) and (12), respectively. Then, after the output signal of the first IF amplifier circuit (11) is smoothed in the first level detection circuit (13), the level is detected, so that the electric field strength of the receiving broadcast station is detected. In the second level detection circuit (14), after the output signal of the second IF amplification circuit (12) is smoothed, the level is detected and the electric field strength is detected. The electric field strengths detected by the first and second level detection circuits (13) and (14) are compared with each other by the comparison circuit (15).
The output signal corresponding to the comparison result is applied from the comparison circuit (15) to the third and fourth buffer circuits (16) and (17). The operations of the third and fourth buffer circuits (16) and (17) are switched according to the output signal of the comparison circuit (17), and the output signals of the third and fourth buffer circuits (16) and (17) are changed. Is applied to the fifth buffer circuit (18). Fifth buffer circuit (1
The output signal of 8) is band-limited by the third filter (19), amplified by the limiter amplifier circuit (20) and amplitude-limited, and further detected by the detection circuit (6).
The third filter (19) has the same frequency characteristic as the second filter (10) and is attenuated by the second and third filters (10) and (19) when the second filter (10) is selected. The characteristics can be made steep, and when the first filter (9) is selected, the third filter (19) does not adversely affect the characteristics of the first filter (9).

Here, when the interfering signal does not exist and the receiving broadcasting station as shown in FIG. 3A exists, the IF signal from the mixing circuit (2) has the first and second filters (9) and ( Since it passes through 10), the level of the IF signal detected by the first and second level detection circuits (13) and (14), that is, the electric field strength of the receiving broadcast station is at the same level. Therefore, the first and second level detection circuits (13) and (1
Since the output signals of 4) are at the same level, the comparison circuit (1
5) no output signal is generated from the third buffer circuit (1
6) is turned on and the fourth buffer circuit (17) is turned off. Therefore, the IF signal limited to the pass band width of the first filter (9) passes through the third buffer circuit (16) and is applied to the fifth buffer circuit (18). The output signal of the fifth buffer circuit (18) is supplied to the third filter (1
9) and the limiter amplifier circuit (20) to be applied to the detection circuit (6) for detection. Since the first filter (17) has the same characteristics as a filter generally used, the detection output is the same as the detection output of a general radio receiver, and the distortion ratio of the detection output signal is good.

When a disturbing signal as shown in FIG. 3B is generated in the vicinity of the receiving broadcast station, the disturbing signal is within the pass band width of the first filter (9) and the IF depending on the receiving broadcast station.
The signal passes through the first filter (9) and is applied to the first IF amplifier circuit (11). Also, the interfering signal is outside the passband width of the second filter (10) and the interfering signal is
I cannot pass the filter (10) and I
Only the F signal originates from the second filter (10). First
In the level detection circuit (13), an IF including an interfering signal
A signal level is detected, and a second level detection circuit (14)
In, the level of the IF signal that does not include the interfering signal is detected. Therefore, the level of the IF signal detected by the first level detection circuit (13) becomes higher than the level of the IF signal detected by the second level detection circuit (14) depending on the presence or absence of the interfering signal. An output signal is generated from (15), and the third buffer circuit (1
6) is turned off and the fourth buffer circuit (17) is turned on.
Therefore, the output signal of the second IF amplifier circuit (12) passes through the fourth buffer circuit (17) and the fifth buffer circuit (18).
Is transmitted to the detection circuit (6) through the third filter (19) and the limiter amplification circuit (20) and is detected. Since the interfering signal has been removed by the second filter (10), there is no interfering signal at the time of detection, no adverse effect of the interfering signal appears on the detection output, and adjacent interference can be prevented.

Further, when ceramic filters are used as the first and second filters (9) and (10), it is possible to provide an inexpensive radio receiver which can prevent adjacent interference more than the one using a crystal oscillator.

[0013]

Therefore, according to the present invention, the level of the IF signal passing through the filters having different pass bandwidths is detected,
When there is a difference between the two levels, it is determined that there is an interfering signal in the vicinity, and the output signal of the filter that can remove the interfering signal is detected. When there is no adjacent interference, it is possible to obtain a detection output with a good distortion rate. In particular, even if the first and second level detection circuits and the comparison circuit are added, these can be integrated into an IC, so that the cost does not increase.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a characteristic diagram showing frequency characteristics according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 RF amplification circuit 2 Mixing circuit 3 Local oscillation circuit 7 1st buffer circuit 8 2nd buffer circuit 9 1st filter 10 2nd filter 11 1st IF amplification circuit 12 2nd IF amplification circuit 13 1st level detection circuit 14 2nd level detection Circuit 15 Comparison circuit 16 Third buffer circuit 17 Fourth buffer circuit 18 Fifth buffer circuit 19 Third filter

Claims (2)

[Claims] 1. An RF amplifier circuit for amplifying a received RF signal,
A local oscillation circuit for generating a local oscillation signal, and the reception RF
A mixing circuit that mixes a signal and the local oscillation signal to generate an IF signal; an IF amplification circuit that amplifies the IF signal;
In a radio receiver including a detection circuit that detects an output signal of the IF amplification circuit, the IF amplification circuit includes a first filter that passes the IF signal with a predetermined frequency bandwidth, and the IF signal A second filter for passing a frequency bandwidth narrower than the frequency bandwidth of the filter; and a first filter for detecting the electric field strength of the output signal of the first filter.
A detection circuit, and a second circuit for detecting the electric field strength of the output signal of the second filter.
A detection circuit; a comparison circuit that compares the output signals of the first and second detection circuits; and a selection circuit that selects the output signals of the first and second filters according to the output signals of the comparison circuit. IF
A radio receiver, characterized in that a signal is applied to the detection circuit. 2. When an interference signal is generated, an output signal is generated from the comparison circuit, and when the output signal of the comparison circuit is present, the output signal of the second filter is selected by the selection circuit and the output signal of the comparison circuit is selected. The radio receiver according to claim 1, wherein the output signal of the first filter is selected in the selection circuit when no output signal is present.