JP3143393B2 - AM radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AM radio receiver which prevents signal suppression during asynchronous reception.

[0002]

2. Description of the Related Art Conventionally, there has been known an AM radio receiver having a reception mode for receiving an RF signal in a wide band and a reception mode for receiving an RF signal in a narrow band as shown in FIG. In such an AM radio receiver, the RF at the time of automatic tuning is set.
Tracking errors were eliminated by receiving signals over a wide band.

In FIG. 2, during normal reception, a received RF signal is received by an RF amplifier circuit (1) and then tuned by an RF tuning circuit (2). The output signal of the RF tuning circuit (2) is applied to the first mixing circuit (4) via the selection circuit (3). In the first mixing circuit (4), the output signal of the selection circuit (3) and the local oscillation signal of the local oscillation circuit (5) are mixed to generate, for example, a first IF signal of 10.7 MHz. The first IF signal is limited to a predetermined band by the first IF filter (6), and a desired station and a station near the desired station are generated at an output terminal of the first IF filter (6). An output signal of the first IF filter (6) is mixed with an output signal of a fixed frequency of the oscillation circuit (8) in a second mixing circuit (7), and a second IF signal of, for example, 450 KHz is generated from the second mixing circuit (7). . The second IF signal is limited to a predetermined band by a second IF filter (9), and only a desired station is generated at an output terminal of the second IF filter (9). The output signal of the second IF filter (9) is amplified by an IF
AM detection is performed by the detection circuit (11).

When a signal indicating the start of automatic channel selection is applied to the control circuit (12) during automatic channel selection, the control circuit (12) switches the selection circuit (3) and the local oscillation circuit (5).
Is applied with a control signal. The selection circuit (3) selects an output signal of the non-tuning circuit (13) according to the control signal. Since the non-tuning circuit (13) passes the RF signal as it is, a tracking error in which the tuning frequency of the RF stage deviates from the reception frequency is prevented. In this state,
The reception frequency is changed by changing the local oscillation frequency, and each time the reception frequency is changed, the IF amplification circuit (1
The output signal of 0) is applied to an electric field strength detection circuit (14), and the electric field strength of the receiving station is detected. An output signal of the electric field strength detection circuit (14) is supplied to a comparison circuit (1) serving as a station detection circuit.
5) and compared with a reference value. If the electric field strength is equal to or lower than the reference value, the comparison circuit (15) does not generate a station detection signal, and the automatic tuning is continued. When the electric field strength is equal to or higher than the reference value, the station detection signal is applied from the comparison circuit (15) to the control circuit (12). The automatic tuning operation is stopped by the control signal of the control circuit (12), and the broadcast station is received. At the same time, the selection circuit (3) selects the output signal of the tuning circuit (2).

[0005]

The conventional AM
The receiver detects the level of the first IF signal and controls the gain of the RF amplifier circuit (1) according to the detection result in order to prevent the second mixing circuit (7) from being saturated by the large input first IF signal. RFAG for suppressing first IF signal
It has a C circuit (16). However, during the automatic channel selection operation, if a disturbing station having a stronger electric field than the desired station is adjacent to the desired station, a signal corresponding to the desired station and the disturbing station for non-tuned reception is output from the first filter (6). Since the RFAGC operates in response to a large input signal, the IFAGC operates to keep the electric field strength of the interfering station at a predetermined level. Accordingly, the first IF signal level of the desired station is also lowered, and further,
The output signal level of the IF amplifier circuit (10) decreases. Therefore, there is a problem that a desired station having an electric field strength equal to or higher than the reference level is not detected by the comparing circuit (15) by the adjacent interfering station, and the desired station is erroneously passed during automatic channel selection.

[0006] In addition to the automatic tuning, when another broadcast station is selected, the frequency of 1/2 of that broadcast station is set to A, for example.
When detecting an electric field intensity of 1/2 frequency in the M band, signal suppression occurred due to adjacent interference, and accurate electric field intensity detection was not possible.

[0007]

SUMMARY OF THE INVENTION The present invention provides an RF amplifier circuit for amplifying a received RF signal, a tuning circuit for tuning an output signal of the RF amplifier circuit, and a tuning circuit for tuning an output signal of the RF amplifier circuit. A non-tuning circuit to be passed, a selection circuit for selecting one of the tuning circuit or the output signal of the non-tuning circuit, a frequency conversion circuit for converting the output signal of the selection circuit into an IF signal, An AM radio receiver comprising: a control signal generation circuit for generating a first control signal for selecting an output signal of a tuning circuit; an RFAGC loop for controlling a gain of the RF amplification circuit according to a level of the IF signal; , The RFAG according to a second control signal generated from the control signal generation circuit.
And a sensitivity adjusting circuit for adjusting the sensitivity of the C loop.

An RF amplifier circuit for amplifying a received RF signal; a tuning circuit for tuning an output signal of the RF amplifier circuit; a non-tuning circuit for passing an output signal of the RF amplifier circuit without tuning; A selection circuit that selects one of an output signal of the tuning circuit or the non-tuning circuit, a frequency conversion circuit that frequency-converts the output signal of the selection circuit into an IF signal, and the selection circuit selects an output signal of the non-tuning circuit A level control circuit for controlling the level of said IF signal in accordance with a second control signal generated from said control signal generation circuit, comprising: a control signal generation circuit for generating a first control signal for generating said first control signal; An RFAGC circuit that controls a gain of the RF amplifier circuit according to an output signal of the level control circuit.

[0009]

FIG. 1 is a diagram showing an embodiment of the present invention. (17) is an amplifier serving as a level control circuit for controlling an output signal level of a first IF filter (10);
(18) RF signal according to the output signal of the amplifier (17)
An RFAGC circuit for controlling the gain of the amplifier circuit (1);
A control circuit (19) controls the selection circuit (3) and the local oscillation circuit (5) to automatically select a channel based on a search signal and controls the gain of the amplifier (17). FIG.
2, the same circuits as those in the conventional example of FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, the operation at the time of normal reception is the same as that of the conventional example of FIG. However, the gain of the amplifier (17) is equal to the second gain of the control circuit (19).
It is set large by the control signal. After the output signal of the first IF filter (6) is amplified by the amplifier (17),
Applied to the FAGC circuit (18). The RFAGC circuit (18) detects the output signal level by level-detecting the output signal of the amplifier (17) and generates an output signal for controlling the gain of the RF amplifier circuit (1) according to the output level. I do. When the output signal level of the amplifier (17) is low, the gain of the RF amplifier circuit (1) becomes large, and when the output signal level of the amplifier (17) is high, the gain of the RF amplifier circuit (1) becomes small. The gain of the RF amplifier circuit (1) is set according to the output signal level of the amplifier (17). Since the gain of the RF amplifier circuit (1) is controlled by the output signal level of the first IF filter (6), the first
The output signal level of the IF filter (6) does not exceed a predetermined level, and the second mixing circuit (7) and the AM detection circuit (1)
The saturation of 1) is prevented.

When a search signal is applied to the control circuit (19), the radio receiver shown in FIG. 1 enters an automatic channel selection state. The amplifier (1) is controlled by a second control signal of the control circuit (19).
The gain of 7) becomes small. In addition, the selection circuit (3) causes the non-tuning circuit (1)
The output signal of 3) is selected, and the frequency characteristic of the input signal of the first mixing circuit (4) becomes wide. Further, the sweep of the local oscillation circuit (5) is started by the third control signal. First,
When the local oscillation circuit (5) generates the first local oscillation signal, the electric field intensity of the first broadcast station is detected by the electric field intensity detection circuit (14) according to the output signal of the IF amplification circuit (10). Then, the output signal of the electric field strength detection circuit (14) is compared with a reference value in a comparison circuit (15). If the output signal level of the electric field strength detection circuit (14) is smaller than the reference value,
No output signal is generated from the comparison circuit (15). For that reason,
Local oscillation circuit (5) according to a control signal of control circuit (19)
Generates the next second local oscillation signal, and detects whether or not the electric field strength is equal to or higher than the reference value as in the case of the first local oscillation signal generation.
On the other hand, when the first local oscillation signal is generated, when the output signal level of the electric field strength detection circuit (14) is equal to or higher than the reference value, the comparison circuit (15) generates a local detection signal, and the control circuit (12)
The sweeping of the local oscillation circuit (5) is stopped by the third control signal, the local oscillation signal of the local oscillation circuit (5) is changed to the first local oscillation signal, and the selection circuit (3) is switched to the tuning circuit (2). Select the output signal. Also, the gain of the amplifier (17) is returned to a large value, and the radio receiver operates in the normal reception mode. In this way, the radio receiver continues to automatically select a station until a broadcast station having a predetermined electric field strength or more is detected.

During automatic channel selection, the gain of the amplifier (17) is reduced by the second control signal.
The output signal level of 7) is lower for the same input level than the output signal level of the amplifier (17) during normal reception. Therefore, the gain of the RF amplifier circuit (1) is set to be larger than that during normal reception. Therefore, the first IF signal is not suppressed as compared with the normal reception. Therefore, it is possible to reliably detect the desired station without excessively suppressing the output signal of the IF amplifier circuit (10) by RFAGC. In particular, when adjacent interference occurs, signal suppression can be reduced even if signal suppression occurs due to a large-level adjacent station.

FIG. 1 shows a double conversion type AM.
Although this is an example of a radio receiver, the technology according to the present invention may be applied to a single conversion system.

[0014]

FIG. 3 is a circuit diagram showing a specific circuit example of the amplifier (7). (20) is a transistor to which an input signal which is an output signal of the first IF filter (6) is applied to a base, (21) ) Is a transistor constituting a differential amplifier together with the transistor (20), and (22) is a transistor (20)
And a resistor connected between the emitters of (21), (23)
And (24) are first and second load resistors of the differential amplifier, and (25) is a switch connected to the second load resistor (24) and controlled according to a control signal of a control circuit (19). is there.

In FIG . 3 , an input signal generated from a first IF filter (6) is applied to a base of a transistor (20) and is amplified by a differential amplifier composed of transistors (20) and (21). The amplified signal is transmitted from the collector of the transistor (20) to the subsequent IFAGC circuit (18) via the output terminal OUT. In the differential amplifier, the gain is determined by the resistance (22) and the transistor (2).
0) and (21), and the first and second load resistors (23) and (24). At the time of automatic channel selection, for example, the control signal of the control circuit (19) is "H".
Switch (25) is turned on and the first
And the second load resistors (23) and (24) are connected in parallel. Therefore, the gain G1 of the differential amplifier is equal to the resistance (22)
Is defined as RE, and transistors (20) and (2)
Let the emitter resistance of 1) be re, and let the resistance values of the first and second load resistors (20) and (21) be RL1 and R1, respectively.
Assuming L2,

[0016]

(Equation 1)

## EQU1 ## Here, the resistance values of the first and second load resistors (23) and (24) are equal, and RL1 = RL
Assuming that 2, the gain G1 ′ is

[0018]

(Equation 2)

## EQU1 ## At the time of normal reception, the control circuit (1
The switch (25) is turned off because the control signal of (9) becomes "L" level. Therefore, the second load resistance (24)
Are not connected in parallel to the first load resistor (23). At this time, the gain G2 of the differential amplifier is

[0020]

(Equation 3)

The gain becomes larger than the gain of the differential amplifier at the time of automatic channel selection. FIG. 4 shows the state of the output signal of the control circuit (19). The control circuit (19), as shown in FIG.
When the search start signal is applied, the selection circuit (3) selects the first signal for selecting the output signal of the non-tuning circuit (13).
The control signal and the second for reducing the gain of the amplifier (17)
A control signal and a third control signal for causing the local oscillation circuit (5) to perform a search operation are generated. When the station detection signal is applied during automatic channel selection, the first control signal is a signal for the selection circuit (3) to select the output signal of the tuning circuit (2), and the second control signal is an amplifier ( 17) is a signal for increasing the gain, and the third control signal is a signal for causing the local oscillation circuit (5) to stop the search. Control circuit (1
9) can be achieved by a comparatively simple configuration so that such a control signal is generated, and a specific circuit example of the control circuit (19) is omitted.

[0022]

As described above, according to the present invention, at the time of automatic channel selection, the sensitivity of the RFAGC loop is lowered, and the desired station is not unnecessarily suppressed by an adjacent interfering station having a strong electric field due to non-tuned reception. The desired station can be reliably detected, and erroneous passage of the desired station during automatic channel selection can be prevented. In addition, the effect of adjacent interference can be reduced by lowering the sensitivity of the RFAGC loop when performing non-tuned reception as well as during automatic channel selection.

Further, since the amplifier whose gain can be changed is used in the level control circuit, the circuit configuration can be simplified, which is suitable for IC.

[Brief description of the 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 diagram showing a specific circuit example of an amplifier (17).

FIG. 4 is a waveform chart for explaining the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 RF amplification circuit 2 tuning circuit 3 selection circuit 4 first mixing circuit 5 local oscillation circuit 6 first IF filter 7 second mixing circuit 8 oscillator 9 second IF filter 10 IF amplification circuit 11 AM detection circuit 13 non-tuning circuit 14 electric field strength detection Circuit 15 Comparison circuit 17 Amplifier 18 RFAGC circuit 19 Control circuit

Claims (2)

(57) [Claims] An RF amplifier for amplifying a received RF signal; a tuning circuit for tuning an output signal of the RF amplification circuit; a non-tuning circuit for passing an output signal of the RF amplification circuit without tuning; A selection circuit for selecting one of the output signals of the circuit or the non-tuned circuit, and a local oscillation signal.
A local oscillation circuit to live, the output signal of the selection circuit
A frequency conversion circuit for converting a frequency into an IF signal by a local oscillation signal, and the RF amplifier according to a level of the IF signal;
An RF AGC loop for controlling a gain of a circuit , wherein a first control signal for controlling a selection operation of the selection circuit, RF
A second control signal for adjusting the sensitivity of the AGC loop;
A third control signal for controlling the oscillation frequency of the oscillation circuit is generated.
Control station and performs station detection based on the IF signal level
And a station detection circuit, wherein the control circuit generates a third control signal based on the search signal.
To cause the local frequency to be swept,
The output signal of the non-tuned circuit is selected according to the control signal.
Increase the sensitivity of the RFAGC loop and detect stations during search
Stopping the local frequency sweep based on the output of the circuit
In both cases, the output of the tuning circuit is selected, and the sense of the RFAGC is detected.
A radio receiver characterized by reducing the degree . 2. An RF amplifier for amplifying a received RF signal, a tuning circuit for tuning an output signal of the RF amplification circuit, a non-tuning circuit for passing an output signal of the RF amplification circuit without tuning, and the tuning. A selection circuit for selecting one of the output signals of the circuit or the non-tuned circuit, and a local oscillation signal.
A local oscillation circuit to live, the output signal of the selection circuit
A frequency conversion circuit for converting a frequency into an IF signal by a local oscillation signal, and the RF amplifier according to a level of the IF signal;
An RFAGC circuit for controlling the gain of the circuit.
In the M radio receiver, the gain can be switched and the level of the IF signal can be changed
A level control circuit for supplying the RFAGC circuit with
A first control signal for controlling a selection operation of the selection circuit,
A second control signal for adjusting the gain of the control circuit;
Generates a third control signal for controlling the oscillation frequency of the local oscillation circuit
Control circuit and station detection based on IF signal level
Performing a third control signal based on a search signal.
Signal and sweeps the local oscillation frequency.
And an output signal of the non-tuned circuit in response to the second control signal.
Signal, and reduce the gain of the level control circuit.
Based on the output of the station detection circuit during the search.
Stop sweep and select the output of the tuning circuit
To increase the gain of the level control circuit.
And a radio receiver.