JPH11234160A - Radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain switching of a receiving band and removal of an adjacent interference with a simple constitution by selecting one of the output signals of a first IF filter for executing the band limit of an IF signal and of a second IF filter for restricting a pass band narrower. SOLUTION: A selection circuit 19 selects an AMIF signal of a wide-band filter 17 at the time of receiving AM to allow an amplifier 20 to amplify with a first gain G1. At the time of normal receiving of FM, an FMIF signal of a band filter 18 is selected to allow the amplifier 20 to amplify with a second gain G2. In the case of occurrence of an adjacent interference at the time of receiving FM, the FMIF signal of a narrow band filter 18 is selected to allow the amplifier 20 to amplify with a third gain G3. A control circuit 24 outputs an instruction based on the output of an interference detecting circuit 23 and switching of the receiving band by a user, while a decoder 25 decodes the instruction to control the circuit 19 to select the first to third gains G1 to G3 so as to keep an amplification output level constant either a normal receiving time or in an adjacent interference time.

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 takes measures against adjacent interference.

[0002]

2. Description of the Related Art In general, in a radio receiver, an FM receiving circuit and a double-conversion AM radio receiving circuit capable of removing image interference are integrated into one chip on the same semiconductor substrate. Such a radio receiving circuit is configured as shown in FIG. In FIG. 4, at the time of FM reception, an FMRF signal is tuned and amplified by an FM-RF tuning amplifier circuit 1, and then frequency-converted into an FMIF signal having a center frequency of 10.7 MHz by a local oscillation signal in an FM mixing unit 3 of a mixing circuit 2. Is done. The FMIF signal is band-limited by the common filter 4, applied to the FM filter 7 via the buffer circuit 5 and the switching circuit 6, band-limited, and FM-detected by the FM detection circuit 8.

At the time of AM reception, the AMRF signal is
After being amplified by the RF tuning amplifier circuit 9, the frequency is converted into a first AMIF signal by the AM mixer 10. 1st AMIF
Is band-limited by a first AM filter 11 via a common filter 4, a buffer circuit 5, and a switching circuit 6, then is frequency-converted to a second IF signal by a second AM mixing circuit 12, and is further amplified by an AM detection circuit 13. It is detected. The mixing circuit 2 has double differential amplifying circuits for FM and AM, respectively. The FM and AMRF signals are applied to the respective double differential amplifying circuits, and the respective IF signals are output from a common output terminal. Since the double conversion method is adopted for the AM receiving circuit and the IF frequency of the first AMIF signal is the same as the IF frequency of the FMIF signal, the output terminal of the mixing circuit 2 can be shared. The FM and AMIF signals generated from the common output terminal are branched by the switching circuit 6 according to the reception band, and applied to the FM and AM detection circuits 8 and 13, respectively.

[0004]

In FM reception, when there is a jamming station of a strong electric field adjacent to the desired station, the radio wave of the jamming station jumps into the FM radio receiving system and the desired station is jammed by the jamming station. May occur. As a measure to prevent this, two filters of a wide band and a narrow band are prepared as IF filters for FM, and when adjacent interference occurs, the band of the FMIF signal is band-limited more narrowly to remove the interfering station. . However, when this measure is applied to the conventional radio receiver shown in FIG.
Since a filter is further provided in the receiving system, not only the number of filter circuits increases and the cost increases, but also the FMIF
There has been a problem that the circuit for switching the signal itself and the switching of the AM / FMIF signal becomes complicated. In addition, since the IF filter is generally an external circuit of the IC circuit, there is a problem that the number of external pins of the IC increases with three IF filters.

[0005]

According to the present invention, there is provided a radio receiver having two or more receiving circuits, wherein two or more IF signals are led out to an IF signal line, and a first IF filter for limiting a band of the IF signal. And a second IF filter having a pass bandwidth narrower than the pass band of the first filter to limit the band of the IF signal, and a selection circuit for selecting one of the output signals of the first and second IF filters. It is characterized by.

[0006] The present invention is characterized in that a decoder for decoding an instruction based on reception band information and information on interference with reception and controlling the selection circuit is provided. Further, an amplification circuit having a variable gain and amplifying the output signal of the selection circuit is provided, and the gain is changed so that the total gain of each reception circuit becomes a predetermined value. .

In particular, a decoder is provided which decodes an instruction based on reception band information and controls the selection circuit so as to select one of the first and second IF filters according to the reception band. In particular, the apparatus further comprises a decoder for decoding an instruction based on information on interference with reception of a predetermined band and controlling the selection circuit to select the first or second IF filter so as to remove the interference.

[0008] Further, the present invention is characterized in that a decoder is provided which decodes an instruction based on a reception band and generated interference and controls a gain of the selection circuit and the amplification circuit. According to the present invention, the two or more IF signals are band-limited by the first and second IF filters, and the output signal of the first IF filter and the output signal of the second IF filter having a band narrower than the output signal of the first IF filter. Selected. The selection of the output signals of the first and second IF filters is performed based on one or both of switching of the reception band and occurrence of interference.

[0009]

FIG. 1 is a diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 14 denotes an FM or first AM signal from a mixing circuit 2.
The primary coils from which the IF signal is derived, 15 and 16 are the first and second secondary coils corresponding to the primary coil 14, 17
Is a broadband filter having a center frequency of 10.7 MHz, for example, to which an IF signal derived to the secondary coil 15 is applied, and 18 is a broadband filter to which an IF signal derived to the secondary coil is applied. A narrow-band filter having a frequency of 10.7 MHz and a narrower bandwidth than the wide-band filter 17, a selection circuit 19 for selecting an output signal of the wide-band filter 17 or the narrow-band filter 18, and a gain 20 for adjusting the overall gain of the reception circuit Is an IF filter with the wide band and narrow band filters 17 and 18, and a filter to which the output signal of the amplifier 20 is applied,
Is a limiter amplifier that limits the amplitude level of the FM-IF signal, 23 is a disturbance detection circuit that detects adjacent disturbance,
Reference numeral 4 denotes a control circuit such as a microcomputer which outputs an IF signal selection and gain control instruction in accordance with the detection result of interference and switching of the reception band. 25 decodes the instruction and generates a selection signal SL and a gain control signal GA. I do. In FIG. 1, the same circuits as those in FIG. 2 are denoted by the same reference numerals as those in FIG.

Generally, in a radio receiver having both an AM and an FM receiving circuit, the AM receiving circuit is turned on and the FM receiving circuit is turned off at the time of AM reception, and the FM receiving circuit is turned on and the AM receiving circuit is turned off at the time of FM receiving. . Therefore, the AM RF and IF signals are not applied to the FM reception line during AM reception, and the FM RF and IF signals are not applied to the AM reception line during FM reception.

When a switching signal for switching to AM reception is applied to the control circuit 24, a command 1 is output in response thereto. When the instruction 1 is decoded by the decoder 25, a selection signal SL and a gain control signal GA are generated. In response to the selection signal SL, the selection circuit 19 is in a state opposite to that shown in the figure,
The output signal of the narrow band filter 18 is selected. here,
I from the FM and AM mixing units 3 and 10 in the mixing circuit 2
The F signal is led out to a primary coil 14 serving as a common output circuit. Further, the same IF signal is derived to the secondary coils 15 and 16, respectively, and the broadband and narrowband filters 1
Bands are limited at 7 and 18. The wideband and narrowband filters 17 and 18 each have filter characteristics as shown in FIG. The frequency of the first AMIF signal is a single 1
Since the frequency is 0.71 MHz, the frequency band of the first AMIF signal may be limited narrowly.
It is desirable that the frequency band of the first AMIF signal is narrowly limited so as not to adversely affect the amplitude of the first AMIF signal. Therefore, at the time of AM reception, a signal that has passed through the narrow-band filter 18 is selected as the first AMIF signal.

The gain of the amplifier circuit 20 is set to a first gain G1 according to the gain control signal GA. The amplifier circuit 20 includes a first gain G1, a second gain G2 larger than the first gain, and a third gain G3 larger than the second gain.
And the gain is set to one of the gains by the gain control signal GA. As is well known, AM modulation is obtained by amplitude-modulating a single-frequency carrier signal.
Cannot demodulate. Therefore, the minimum first gain G1 is selected so that the first AMIF signal is not limited. The output signal of the narrow band filter 18 is amplified by the amplifier circuit 20 with the first gain G1. After that, the second
After the band of the 1 AMIF signal is limited, the AM second mixer 12 frequency-converts the signal into a second AMIF signal.

On the other hand, when a switching signal for switching to FM reception is applied to the control circuit 24, a command 2
Is output. When the instruction 2 is decoded by the decoder 25, another selection signal SL and a gain control signal GA are generated. In response to the selection signal SL, the selection circuit 19 enters the state shown in the figure, and the output signal of the broadband filter 17 is selected. FM
Since the modulated signal is obtained by shifting the frequency of a carrier signal as is generally known, only a necessary signal is passed through the wideband filter 17 having substantially the same frequency shift range. The FMIF signal from the broadband filter 17 is
The signal is amplified by the amplifier circuit 20 with the second gain G2 set according to the gain control signal GA. Amplified FMIF
The signal is band-limited by the filter 21 and then its level is limited by a limiter amplifier.

It is assumed that an interference station Fud is generated adjacent to the desired station Fd during FM reception. This interfering station Fud is within the pass band of the wide band filter 17 and outside the pass band of the narrow band filter 18 as shown in FIG. Interference detection circuit 23
In the above, for example, by detecting the level of the FMIF signal after the selection circuit 19 and the output level of the wideband and narrowband filters 17 and 18, if adjacent interference is detected, a detection signal DET is generated. Control circuit 2
4 outputs instruction 3. The selection circuit 19 selects the output signal of the narrow band filter 18 according to the selection signal SL obtained by decoding the instruction 3. In the narrow-band filter 18, the jamming station Fud is out of the pass band, so
d is removed by the narrow band filter 18. As a result, the selected FMIF signal is a signal from which the interfering station has been removed. The gain of the amplifier circuit 20 is set to the third gain G3 by the gain control signal GA. After the FMIF signal is amplified by the third gain G3 of the amplifier circuit 20, the band is limited by the filter 21 and is limited by the limiter amplifier 20. Therefore, when the output signal of the narrow band filter 18 is selected, a part of the FMIF signal is lost, which adversely affects the FM detection signal. However, the effect of removing the adjacent interference signal is greater than that.

Here, as shown in FIG. 2A, since the attenuation of the pass band of the narrow band filter 18 is larger than that of the wide band filter, the level of the FMIF signal when adjacent interference occurs is lower than that during normal reception. Therefore, when the output signal of the narrow band filter 18 is selected, the gain of the amplifier circuit 20 is set to the third gain G3, which is larger than the second gain G2, so that the increase in the attenuation is corrected, and the FMIF signal is further reduced. Amplified to a large level. As a result, the output level of the amplifier circuit 20 does not change and the total gain of the FM receiving system does not change during normal reception or when adjacent interference occurs. However, the second and third gains G2
And G3 is the difference between the wideband and narrowband filters 17 and 18
Are set so as to be substantially equal to the difference between the attenuation amounts in the passbands.

The radio receiver shown in FIG. 1 is configured so that the same two IF signals are generated from the mixing circuit 2, and the IF signals from the mixing circuit 2 are transmitted to the wide band filter 17 and the narrow band The wide band and narrow band filters 1
It becomes possible to select those output signals in the subsequent circuits of 7 and 18. Further, the narrow band filter 18
Since the filters for reception and FM reception at the time of adjacent interference are shared, reception can be made to correspond to reception at the time of AM, normal reception of FM, and interference at the time of FM with only two filters.

FIG. 3 shows the selection circuit 19 and the amplification circuit 2 of FIG.
FIG. 26 is a diagram showing a specific circuit shared with 0, in which a transistor Q1 and a transistor Q2 are differentially connected, and resistors R1 and R2 connected in series as a load are connected;
A differential amplifier circuit having a gain G3, 27 is a differential amplifier circuit having transistors Q3 and Q4 differentially connected via a resistor R3, a resistor R1 connected as a load, and having a first gain G1, and 28 is a transistor. Q5 and Q6
Are differentially connected, a resistor R1 is connected as a load, and a differential amplifier circuit having a second gain G2. An emitter-follower transistor Q7 29 is used to output signals from the differential amplifier circuits 26 to 28. A common output stage circuit for outputting to the subsequent circuit, 30 to 32 are current sources for generating the same operating current for the differential amplifier circuits 26 to 28, and 33 is a 2-bit switch output from the decoder 25. This is a switching circuit that switches the current sources 30 to 32 according to a signal. The output signal of the narrow band filter 17 is applied to differential amplifier circuits 26 and 27, and the output signal of the wide band filter 18 is applied to a differential amplifier circuit 28.

First, at the time of AM reception, the switching signal is (0, 0).
Then, the movable terminal of the switching circuit 33 is connected to the current source 31 side, so that the differential amplifier circuit 27 operates. Therefore, the AMIF signal from the narrow band filter 18 is connected to the resistors R1 and R1.
3 is amplified by the first gain G1 determined by
Is applied to When the switching signal becomes (1, 0) during FM normal reception, the switching circuit 33 switches to the current source 32 side, and the differential amplifier circuit 28 operates. Therefore, the FMIF signal from the broadband filter 17 is amplified with the second gain determined by the resistor R1. Further, when adjacent interference occurs during FM reception, the switching signal becomes (1, 1), and the switching circuit 33 switches to the current source 30.
Works. As a result, the FMIF of the narrow band filter 18
The signal is amplified by a third gain determined by the resistors R1 and R2.

Incidentally, the gain of the differential amplifier circuit of FIG. 3 is mainly determined by the load. In the differential amplifier circuits 26 and 28, for example, assuming that the collector currents of the transistors Q1 and Q5 are respectively Ic, the output voltage of the differential amplifier circuit 26 becomes Vcc− (R1 + R2) × Ic, and the output voltage of the differential amplifier circuit 28 Is Vcc-R1 × Ic. (R
1 + R2)> R1, the output level of the differential amplifier circuit 26 is changed to the differential amplifier circuit 28 for the input signal of the same level.
Higher. The loads on the differential amplifier circuits 27 and 28 are both resistors R1. However, since the emitter resistor R3 is connected to the differential amplifier circuit 27, the transistor Q
Assuming that the voltage difference between the emitters of the transistors 3 and Q4 is ΔV, the emitter current of the transistors Q3 and Q4 is I = ΔV / R3
And is limited by the resistor R3. Therefore, for the same input signal, the collector current of transistor Q3 is smaller than that of transistor Q5, and the output level of differential amplifier circuit 28 is higher than that of differential amplifier circuit 27. From the above, the gains of the differential amplifier circuits 26 to 28 satisfy the first gain G1 <the second gain G2 <the third gain G3.

[0020]

According to the present invention, both the switching of the reception band and the countermeasure against adjacent interference can be performed with a simple configuration. In particular, in the FM and AM receiving circuits, adjacent interfering stations at the time of FM reception are removed by the IF filter for AM, so that no additional IF filter is added.
Distortion of the FM detection signal can be reduced. Since an increase in the number of circuits can be prevented, another effect that an increase in the number of external pins can be prevented is also achieved.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram for explaining the operation of FIG.

FIG. 3 is a circuit diagram showing specific circuits of a selection circuit 19 and an amplification circuit 20 of FIG.

FIG. 4 is a block diagram showing a conventional example.

[Explanation of symbols]

 17 Broadband filter 18 Narrow band filter 19 Selection circuit 20 Amplification circuit 21 Filter 22 Limiter amplifier 23 Interference detection circuit 24 Control circuit 25 Decoder

Claims (6)

[Claims] 1. A radio receiver comprising two or more receiving circuits, wherein two or more IF signals are led out to an IF signal line, wherein: a first IF filter for limiting a band of the IF signal; A radio receiver comprising: a second IF filter that is narrower than a pass band of one filter and limits a band of the IF signal; and a selection circuit that selects one of output signals of the first and second IF filters. 2. The radio receiver according to claim 1, further comprising a decoder for decoding an instruction based on reception band information and information on interference with reception, and controlling the selection circuit. 3. An amplifying circuit having a variable gain and amplifying an output signal of the selecting circuit, wherein the gain is changed so that a total gain of each receiving circuit becomes a predetermined value. The radio receiver according to claim 1, wherein: 4. A decoder for decoding an instruction based on reception band information and controlling the selection circuit so as to select one of the first and second IF filters in accordance with a reception band. The radio receiver according to 1. 5. A decoder for decoding an instruction based on information on interference with reception of a predetermined band and controlling the selection circuit to select the first or second IF filter so as to remove the interference. The radio receiver according to claim 1. 6. The radio receiver according to claim 3, further comprising a decoder that decodes an instruction based on a reception band and the generated interference, and controls a gain of the selection circuit and the amplification circuit.