JPH09186618A - Radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To configurate a radio receiver where a mixing circuit is adopted as one and AM and FM receiving circuits are added. SOLUTION: One of the output signals of an AM-RF amplifier circuit 1 or an FM-RF amplifier circuit 10 is selected by a first switch and impressed on the mixing circuit 17. An RF signal is frequency-changed into an IF signal by a local oscillation signal, amplified by an amplifier circuit 19 and impressed on an emitter follower circuit 20. The output signal of the emitter follower circuit 20 is impressed on an AM filter 4 or an FM filter 13 in accordance with reception with the second switch 21. Since the gain of the amplifier circuit 19 is changed-over in accordance with AM reception or FM reception, the total gain of the AM and FM receiving circuits is set to a gain value where S/N is made to be favorable.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an AM receiving circuit and an F
And a M receiver circuit.

[0002]

2. Description of the Related Art Conventionally, in a radio receiver including an AM receiving circuit and an FM receiving circuit, an AM receiving system and an FM receiving system are used.
The receiving systems are arranged separately. That is, the radio receiver is configured as shown in FIG.
The M-RF signal is amplified by the AM-RF amplifying circuit (1), and is AM local oscillator circuit (3) by the first AM mixing circuit (2).
The frequency is converted to the first AM-IF signal by the AM local oscillation signal from. The first AM-IF signal is limited to a predetermined frequency band by the AM filter (4),
After being amplified by the amplifier circuit (5), the second AM mixing circuit (6) outputs the second AM-I by the output signal of the oscillation circuit (7).
The frequency is converted to an F signal. The second AM-IF signal is the second
After being amplified by the AM-IF amplifier circuit (8), AM detection is performed by the AM detection circuit (9). Further, the received FM-RF signal is amplified by the FM-RF amplifier circuit (10), and frequency-converted into an FM-IF signal by the local oscillation signal from the FM local oscillation circuit (12) in the FM mixing circuit (11). FM-
The IF signal is limited to a predetermined frequency band by the FM filter (13), amplified by the FM-IF amplification circuit (14), and then FM-detected by the FM detection circuit (15).

[0003]

However, in the circuit of FIG. 2, since the AM receiving circuit and the FM receiving circuit are separate systems, a mixing circuit for converting an RF signal into an IF signal is provided in each receiving circuit. Two mixing circuits were needed as they were required. In particular, when the circuit of FIG. 2 is integrated, since the mixing circuit includes a coil, there is a problem that the number of external elements and the number of external pins for the coil increase.

[0004]

According to the present invention, in a radio receiver including an AM radio receiving circuit and an FM radio receiving circuit, an AM-RF signal or an FM-RF signal is converted into an IF signal according to a local oscillation signal. A frequency conversion circuit for frequency conversion, an amplifier circuit having a variable gain for amplifying an output signal of the frequency conversion circuit, an emitter follower circuit to which the output signal of the amplifier circuit is applied, and an output signal of the emitter follower circuit To limit the frequency to the first frequency band
An F filter, an AM-IF filter for limiting the output signal of the emitter follower circuit to a second frequency band, and an AM
And a switching signal generating circuit for generating a switching signal for switching the gain of the amplifier circuit according to a signal indicating reception or FM reception.

Further, the AM radio receiving circuit is provided with the AM
-First frequency conversion of RF signal into first AM-IF signal
A frequency conversion circuit and a second AM for the first AM-IF signal.
A double conversion type reception circuit including a second frequency conversion circuit for frequency-converting to an IF signal. Further, the amplifier circuit is incorporated in the FM-IF filter and the AM-IF filter.

[0006]

FIG. 1 is a diagram showing an embodiment of the present invention, in which (16) is one of the output signals of the AM-RF amplifier circuit (1) or the FM-RF amplifier circuit (10). Switch for selecting the output signal of (1), (17) a mixing circuit for converting the output signal of the first switch (16) into an IF signal, (18) a local oscillation circuit for generating a local oscillation signal, (19) ) Is an amplifier circuit for amplifying the output signal of the mixing circuit (17) with a variable gain, and (20) is an amplifier circuit (1
An emitter follower circuit to which the output signal of 9) is applied,
(21) is a second switch for branching the output signal of the emitter follower circuit (20), and (22) is first and second switches.
A switching signal generation circuit for generating an output signal for switching the switches (16) and (21) and for varying the gain. The same circuits as those in the conventional example of FIG. 2 are denoted by the same reference numerals as those in the conventional example, and the description thereof is omitted.

In FIG. 1, when a signal indicating AM reception is applied, a switching signal generating circuit (22) generates a switch switching signal and a gain switching signal, and the first and second switches (in accordance with the switch switching signal). 16) and (21) are in the opposite states to those shown, and the gain of the amplifier circuit (19) is 1. In this state, the received AM-RF signal is AM-
The first switch (16) is amplified by the RF amplifier circuit (1).
Is applied to the mixing circuit (17) via. Mixing circuit (1
In 7), the local oscillation signal from the local oscillation circuit (18) is frequency-converted into a first AM-IF signal having a frequency of 10.7 MHz. The first AM-IF signal is transmitted to the amplifier circuit (1
In 9), it is amplified with a gain of 1 and applied to the emitter follower circuit (20). Emitter follower circuit (2
0) output signal is sent to the AM via the second switch (21).
It is applied to the filter (4) and is limited to the frequency band as shown by the solid line in FIG. The output signal of the AM filter (4) is amplified by the first AM-IF amplifier circuit (5) and then converted into a second AM-IF signal of 450 KHz by the output signal of the oscillation circuit (7) in the second AM mixing circuit (6). Frequency converted. The second AM-IF signal is amplified by the second AM-IF amplifier circuit (8) and then detected by the AM detection circuit (9).

When a signal indicating FM reception is applied, the switching signal generating circuit (22) does not generate the switch switching signal and the gain switching signal, so that the first and second switches (16) and ( 21) becomes the illustrated state, and the gain of the amplifier circuit (19) becomes G. In this state, the received FM-RF signal is amplified by the FM-RF amplifier circuit (10) and is mixed via the first switch (16) with the mixing circuit (17).
Is applied to In the mixing circuit (17), the center frequency is 1 due to the local oscillation signal from the local oscillation circuit (18).
The frequency is converted into a 0.7 MHz FM-IF signal. The output signal of the mixing circuit (17) is amplified by the gain G in the amplification circuit (19), and the emitter follower circuit (20).
Is applied to The output signal of the emitter follower circuit (20) is applied to the FM filter (13) via the second switch (21) and is limited to the frequency band as shown by the dotted line in FIG. The output signal of the FM filter (13) is
After being amplified by the FM-IF amplification circuit (14), it is FM-detected by the FM detection circuit (15).

In the AM conversion circuit, the RF signal in the AM band of the double conversion system is transferred to the first AM of 10.7 MHz.
-The up-conversion method of frequency-converting to an IF signal is used, and the FM receiving circuit frequency-converts an RF signal in the FM band into an FM-IF signal having a center frequency of 10.7 MHz. Therefore, the change of the local oscillation signal of the local oscillation circuit (18) is between several MHz and several tens of MHz, and if the local oscillation circuit that can change in such a frequency range is used, one local oscillation circuit can be provided. As a result, there can be only one mixing circuit. Further, even if the local oscillation circuit (18) is composed of an AM local oscillation circuit and an FM local oscillation circuit and switches the output signals of the respective local oscillation circuits according to AM reception and FM reception, the mixing circuit is Can be one.

By the way, the total gain is different between the AM receiving circuit and the FM receiving circuit. What is total gain?
It is a total gain obtained by adding the gains from the RF amplification stage to the IF amplification stage of the radio receiver. As the total gain changes, the S / N (signal-to-noise ratio) in a weak electric field changes, and the input signal level and the noise level change depending on whether the total gain is large or small as shown in FIG. In other words, in FIG. 3B, assuming that the case where the input signal and the noise change as shown by the solid line is the total gain that is an appropriate value, the input signal and the noise level change like the dotted line when the total gain becomes large, When the total gain becomes small, it changes like the one-dot chain line. Depending on the AM reception and FM reception, the S / N is optimized and the total gain for improving the audibility is different. Since the gain of the amplifier circuit (19) is switched according to the reception of AM or FM, the total gain becomes a value suitable for each reception. Therefore, even if only one mixing circuit (17) is provided, S
It is possible to provide a radio receiver having a good / N. In FIG. 1, the gain of the amplifier circuit (19) is increased at the time of FM reception, but the gain of the amplifier circuit (19) is increased at the time of AM reception depending on the receiving situation according to the destination of the radio receiver set, for example. You may.

Generally, when either AM reception or FM reception is selected, the selected reception system is turned on and the non-selected reception system is turned off. In this case, even if a signal to be supplied to the other receiving system is applied to one receiving system, no adverse effect occurs, so the first and second switches (1
6) and (21) can be removed. FIG. 4 is another example of the amplifier circuit (19) and the AM and FM filters (4) and (13). However, this is an example configured by removing the first and second switches (16) and (21). In FIG. 4, the output signal of the mixing circuit (17) is limited to a predetermined frequency band by the first filter (23) and then amplified by the amplification circuit (19) to form the emitter follower circuit (20). It is applied to the base of (20 '). The output signal of the emitter follower circuit (20) generated from the emitter of the transistor (20 ') is applied to the second and third filters (24) and (25),
The second filter (24) limits the frequency band as shown by the solid line in FIG. 3A, and the third filter (25) limits the frequency band as shown by the dotted line in FIG. After that, the output signal of the second filter (24) is transmitted to the IF amplification stage of AM and the output signal of the third filter (25) is transmitted to the IF amplification stage of FM. Further, a gain switching signal is generated from the switching signal generating circuit (22) in response to AM and FM reception, and the gain of the amplifier circuit (19) is switched. In addition, the amplifier circuit (1
9) and the input resistances of the second and third filters (24) and (25) are set to the same value in order to improve matching.

For example, if a configuration such as a ceramic filter in which filtering elements are connected in series for the purpose of improving the filtering characteristic is used as shown in FIG. 4, the first stage filter such as the first filter (23) is used. Can be shared by the AM and FM receiving circuits, and the number of filtering elements can be reduced.

[0013]

As described above, according to the present invention, the AM
The receiving circuit is a double conversion type receiving circuit,
Since the frequency-converted IF signal is applied to the amplifier circuit whose gain is switched according to AM reception or FM reception, one mixing circuit can be used, and the AM reception and F reception can be performed.
It is possible to provide a radio receiver that enables good reception of S / N for both M reception. Further, when integrated into an IC, the number of coils in the mixing circuit can be reduced and the number of external elements can be reduced.

In addition, the amplifier circuit is an IF for AM and FM.
Since it is built in the filter, it is possible to reduce the number of filtering elements, and particularly to reduce the number of external elements when integrated into an IC.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a conventional example.

FIG. 3 is a characteristic diagram for explaining the present invention.

FIG. 4 is a block diagram showing a main part of the present invention.

[Explanation of symbols]

 1 AM-RF amplification circuit 4 AM filter 5 1st AM-IF amplification circuit 6 2nd AM mixing circuit 7 Oscillation circuit 8 2nd AM-IF amplification circuit 9 AM detection circuit 10 FM-RF amplification circuit 13 FM filter 14 FM-RF amplification circuit 15 FM detection circuit 16 First switch 17 Mixing circuit 18 Local oscillation circuit 19 Amplifying circuit 20 Emitter follower circuit 21 Second switch 22 Switching signal generating circuit

Claims (3)

[Claims] 1. A radio receiver including an AM radio receiving circuit and an FM radio receiving circuit, and a frequency conversion circuit for frequency-converting an AM-RF signal or an FM-RF signal into an IF signal according to a local oscillation signal. An amplifier circuit having a variable gain for amplifying an output signal of the frequency conversion circuit, an emitter follower circuit to which the output signal of the amplifier circuit is applied, and an output signal of the emitter follower circuit limited to a first frequency band FM-IF filter, an AM-IF filter that limits the output signal of the emitter follower circuit to a second frequency band, and a switching signal that switches the gain of the amplifier circuit according to a signal indicating AM reception or FM reception. And a switching signal generating circuit for generating the signal. 2. The AM radio receiving circuit is the AM-RF.
A first frequency conversion circuit for frequency converting the signal into a first AM-IF signal; and a second AM-IF signal for converting the first AM-IF signal.
2. The radio receiver according to claim 1, wherein the radio receiver is a double conversion type reception circuit including a second frequency conversion circuit that frequency-converts a signal. 3. The radio receiver according to claim 1, wherein the amplifier circuit is built in the FM-IF filter and the AM-IF filter.