JPH03210826A - Am receiver - Google Patents

Abstract

PURPOSE:To attenuate a signal not having sufficiently eliminated by a band pass filter and a 1st intermediate frequency filter by providing a trap circuit having a characteristic in series resonance to a frequency being a difference between the 1st intermediate frequency and a 2nd intermediate frequency to a pre-stage of a 2nd mixer circuit. CONSTITUTION:A 1st intermediate frequency IF1 is obtained from a reception signal fs outputted from a band pass filter 3 and a 1st local oscillation signal fLOC1 at a 1st mixer circuit 6. The 1st intermediate frequency fIF1 passes through a 1st intermediate frequency filter 7 and is mixed with a 2nd local oscillation signal fLOC2=fIF1-fIF2 at a 2nd mixer circuit 9 to obtain a 2nd intermediate frequency fIF2. A trap circuit 21 is provided between a 1st intermediate frequency filter 7 and the 2nd mixer circuit 9. The trap circuit 21 has a characteristic in series resonance with a frequency being a difference between the 1st intermediate frequency and the 2nd intermediate frequency being twice the 1st intermediate frequency and a signal of (fs+2XfIF2) sufficiently attenuated is sent to the 2nd mixer circuit 9 so as not to disturb the signal of an AM broadcast station with an object reception desired frequency fs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AM receiver suitable for use as an in-vehicle radio that is installed in, for example, a car and receives AM broadcast waves.

[Conventional technology]

Fig. 3 is a block diagram showing the configuration of a conventional double conversion type AM receiver. It is a circuit.

This first local oscillation circuit 4 is controlled by a PLL (phase-locked loop) circuit II5,
The LL circuit 5 is controlled by a microcomputer 15 (hereinafter abbreviated as microcomputer).

Output frequency fLoc+ (f+r
t+fs (desired reception frequency)) and the reception frequency, that is, the output frequency f3 of the bandpass filter 3, are mixed in the first mixing circuit 6 to obtain the first intermediate frequency f IFI (9,
7Ml1g).

The first intermediate frequency is outputted to a second mixing circuit 9 through an intermediate frequency filter 7.

This second mixing circuit 9 combines the output of the intermediate frequency filter and the output frequency tLaci (-flFI) of the second local oscillation circuit 8.
-fl□) and the second intermediate frequency f1,8(4
50kHz).

The second intermediate frequency ft□ is a second intermediate frequency filter 10,
AM detection circuit 12 through the second intermediate frequency amplification circuit 11
is now entered.

The output of the AM detection circuit 12 is amplified by a low frequency amplification circuit 13 and then drives a speaker 14.

Next, the operation will be explained. For example, when receiving an AM broadcasting station with a desired reception frequency of fs, it is received by antenna 1, amplified by high frequency amplification circuit 2, inputted to bandpass filter 3, extracted reception frequency fs, and sent to first mixing circuit. Output to 6.

On the other hand, the first local oscillation circuit 4 controlled by the microcomputer 15 and the PLL circuit 5 generates fLoct−fs+f, □
A first local oscillation frequency is obtained and sent to the first mixing circuit 6.

The first mixing circuit 6 mixes the second local oscillation signal f LIICI output from the first local oscillation circuit 4 and the received signal f3 output from the bandpass filter 3, and mixes the first intermediate frequency f IF+ get.

This first intermediate frequency f, □ is combined with the first local oscillation signal fLoct=fl□-f, □, which is output from the second local oscillation circuit 8 after passing through the first intermediate frequency filter 7, and the second
By being mixed in the mixing circuit 9, the second intermediate frequency f
Get 1□.

The second intermediate frequency f1□ obtained in this way is
The signal of the target AM broadcasting station is obtained by passing through the intermediate frequency amplification circuit 11 and being detected by the AM detection circuit 12. After being amplified by the low frequency amplifier circuit 13, the speaker 14 is driven, and the signal of the target AM broadcasting station is obtained. can be heard.

[Problem to be solved by the invention]

Conventional AM receivers are configured as described above, so
In addition to the AM broadcasting station with the reception desired frequency fs of the target broadcasting station, if there is a broadcasting station with (fs + 2 9, and the signal of the AM broadcasting station of the desired receiving frequency fs of the target broadcasting station is interfered with by the signal of the broadcasting station of (fs+2

This invention was made to solve the above-mentioned problems, and even if there is a broadcasting station (fs + 2 An object of the present invention is to obtain an AM receiver that can more clearly receive fs AM broadcast stations.

[Means to solve the problem]

The AM receiver according to this invention has (f+y+ 2 Xft
A trap circuit that resonates at a frequency of oct) is provided on the preceding stage side of the second mixing circuit.

[For production]

The trap circuit in this invention interferes with the AM broadcasting station of the desired reception frequency f3 (fa+2Xf+yt
), the signal of (fs + 2 Receive signals clearly.

〔Example〕

Embodiments of the AM receiver of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment. In FIG. 1, parts that are the same as those in FIG. 3 are given the same reference numerals to avoid redundant explanation, and mainly describe the parts that are different from FIG. 3.

As is clear from comparing Figure 3 with Figure 1,
In the figure, parts indicated by numerals 1 to 15 are exactly the same as in FIG. is used.

By configuring as described above, in the double convergence run type AM receiver, when receiving an AM broadcasting station with the desired reception frequency f3 through the antenna l, in addition to this frequency f3, (fs + 2Xf + □) When a broadcasting station exists, the first mixing circuit 6 outputs ftoc+-f.
In addition to the intermediate frequency flFl obtained by s, fLo
A second intermediate frequency f1□-2XLyg obtained by ct(fs+2XfIvt) is generated, which in this embodiment is attenuated by the trap circuit 21.

This trap circuit 21 has an attenuation characteristic as shown in FIG. The 2 mixing circuit 9 has a sufficiently attenuated signal (
A signal of fs+2Xflyx) is sent.

As described above, it is possible to clearly receive the broadcasting stations fs+2X[, □ without interference. Furthermore, since a ceramic filter is used as the trap circuit 21,
It can be configured small and inexpensively.

In the above embodiment, the trap circuit 21 is inserted immediately before the second mixing circuit 9, but the first mixing circuit 6 and the first intermediate frequency filter 7 are inserted as the previous stage side.
The same effect can be obtained even if it is inserted between.

〔Effect of the invention〕

As described above, according to the present invention, even if the broadcasting station with the target reception desired frequency fs receives the signal from another broadcasting station with the frequency (fs+2Xf+□), the trap circuit is configured to attenuate this signal. Even if there is a frequency other than the target broadcast station, the target broadcast station can be clearly received without interference.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an AM receiver according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of a trap circuit in the same embodiment, and FIG. 3 is a diagram of a conventional double converter AM receiver. It is a block diagram. l...Antenna, 2...High frequency amplification circuit, 3...
Bandpass filter, 4... first local oscillation circuit, 5.
...PLL circuit, 6...first mixing circuit, 7...first
intermediate frequency filter, 8... second local oscillation circuit, 9.
...Second mixing circuit, lO...Second intermediate frequency filter, 11...Second intermediate frequency amplification circuit, 12...AM detection circuit, 13...Low frequency amplification circuit, 14...Speaker , 15...Microcomputer, 21...Trap circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] a first mixing circuit that mixes the broadcast frequency of an AM broadcasting station having a desired receiving frequency and a first local oscillation frequency to output a first intermediate frequency; a second mixing circuit that outputs two intermediate frequencies;
The output of this second mixing circuit is detected and the desired reception frequency A is detected.
A detection circuit that obtains the signal of the M broadcasting station, and a trap circuit that is provided at the front stage of the second mixing circuit and has a characteristic of series resonance at a frequency that is the difference between the first intermediate frequency and twice the second intermediate frequency. Equipped with an AM receiver.