JPH1022943A - Radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect electric field intensity of not less than 120 dBμ. SOLUTION: The output signal of an RF-AGC circuit 7 is added with that of a differential amplifier circuit 9 by an adding circuit 11. When the receiving electric field intensity of more than 100 dBμ is detected according to the output level of the circuit 11, the output of a forcedly driving circuit 10 in an RF-AGC loop is fixed to obtain the attenuation quantity of 100 dB in a receiving line. Then, when the output signal of an electric field intensity detection circuit 6 is higher than a prescribed level, the gain of an RF amplifier circuit 1 is reduced as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver capable of detecting an electric field strength higher than a strong electric field.

[0002]

2. Description of the Related Art Conventionally, a radio receiver has an auto-tracking function for preventing a tracking error and an auto-memory function. In the auto-tracking function, after searching, each electric field strength is detected while changing the RF tuning frequency, and then the largest one is detected from the detected electric field strengths, and the RF tuning frequency is set to a frequency at which the maximum electric field strength can be obtained. Setting to prevent tracking errors. In addition, the auto memory function automatically searches for a broadcast station,
The found broadcasting stations are preset in order of decreasing electric field strength. For this reason, a radio receiver having such a function requires a means for detecting the electric field strength of a broadcasting station. FIG. 2 is a circuit diagram showing a radio receiver provided with a circuit capable of detecting an electric field intensity up to a medium / strong electric field.

In FIG. 2, a received RF signal is amplified by an RF amplifier circuit 1 and then mixed with a local oscillation signal from a local oscillation circuit 2 by a mixing circuit 3 to be converted into an IF signal. The IF signal is amplified by an IF amplifier 4 and then FM detected by an FM detector 5. The output signal of the IF amplifier circuit 4 is peak-detected by the electric field strength detection circuit 6 and then smoothed, so that the electric field strength detection circuit 6
From 0 to 60 dBμ. Further, the output signal of the mixing circuit 3 is peak-detected by the RF-AGC circuit 7 and then smoothed.
An F-AGC signal is generated. The RF-AGC signal is R
The gain is applied to the F amplifier circuit 1 and the gain of the RF amplifier circuit 1 is controlled. With such an RF-AGC loop, RF
When the signal level increases, the gain of the RF amplifier circuit 1 decreases, so that saturation of the mixing circuit 3 can be prevented in a medium electric field. By the RF-AGC operation, the electric field strength instruction signal changes linearly between 0 and 60 dBμ as shown by the solid line in FIG.
The received electric field intensity can be detected well up to Bμ.

The radio receiver shown in FIG. 2 is provided with a damping circuit 8 for attenuating a received RF signal. The RF-AGC signal is applied to a positive input terminal of the differential amplifier circuit 9 and a reference voltage V applied to a negative input terminal thereof.
An output signal is generated from the differential amplifier circuit 9 according to the difference between the ref and the RF-AGC signal. Then, the damping circuit 8 operates according to the output signal of the differential amplifier circuit 9, and the attenuation amount becomes 40 dB. Therefore, the received RF signal is attenuated by the damping circuit 8, and the electric field strength indication signal is
As shown by the dotted line in (a), the characteristic of the solid line is shifted by 40 dBμ, and the received electric field strength can be detected well in the range of 40 to 100 dBμ. Also, the reference voltage Vre
f denotes a damping circuit 8 when the received electric field intensity is around 60 dBμ.
Is set to operate, so that the mixing circuit 3 can be prevented from being operated by the strong electric field due to the operation of the damping circuit 8.

Further, in FIG. 2, it is possible to obtain a further 20 dB of attenuation by lowering the conversion gain of the mixing circuit 3 and to obtain a good linearity of the electric field strength indicating signal up to about 60 to 120 dBμ. .

[0006]

SUMMARY OF THE INVENTION However, 120
It is not possible to obtain the linearity of the electric field strength indication signal at an electric field strength of dBμ or more (hereinafter, referred to as an ultra-strong electric field),
There is a problem that a difference in electric field strength cannot be determined in an ultra-strong electric field. Therefore, when the auto-tracking function was operated near the broadcasting base station, the maximum electric field intensity could not be determined in an extremely strong electric field, and the auto-tracking could not be performed. Also, in an area where there are a plurality of broadcasting stations close to the listener, for example, when using the auto memory function, since a plurality of broadcasting stations having an extremely strong electric field strength are received, the electric field strength cannot be determined, and the auto memory function cannot be determined. The function could not be performed.

[0007]

SUMMARY OF THE INVENTION The present invention provides a damping circuit for attenuating a received RF signal, a local oscillation circuit for generating a local oscillation signal, an output signal of the RF amplification circuit, and an output signal of the local oscillation circuit. , A first electric field intensity detection circuit for detecting a received electric field intensity according to the IF signal, and an RF-AGC loop for automatically controlling the level of the RF signal. A second electric field intensity detecting circuit for detecting an electric field intensity of a medium / strong electric field, and a judging means for judging whether or not the received electric field intensity is in a first range based on an output signal of the second electric field intensity detecting circuit. And forced driving means for forcibly driving the RF-AGC loop so as to greatly reduce the RF signal level when the received electric field intensity is in the first range. Characterized in that to obtain an instruction signal instructing the electric field strength.

[0008] Further, in the forced driving state of the RF-AGC loop, detecting means for detecting whether or not the received electric field strength is larger than a predetermined value, and the detecting means detects that the received electric field strength is larger than the predetermined value. A first control unit for maintaining a state of forced driving of the RF-AGC loop. Further, the first determining means is configured to control the first
Determining whether the received electric field intensity is in a second range lower than the range, and, when the received electric field strength is in the second range, operating the damping circuit and reducing a conversion gain of the mixing circuit; It is characterized by.

Further, when the detecting means detects that the received electric field strength is smaller than a predetermined value, the RF-A
It is characterized by comprising a third control means for canceling the forced drive of the GC loop, operating the damping circuit and lowering the conversion gain of the mixing circuit. Still further, the second electric field strength detection circuit receives an input of a signal in the RF-AGC loop and a reference signal, and outputs an output signal corresponding to a difference between the two inputs;
It is characterized by comprising an adding circuit for adding the signal in the loop and the output signal of the amplifier.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention. In FIG.
A forced drive circuit for forcibly lowering the gain of the F amplifier circuit 1, an adder circuit 11 for adding the RF-AGC signal and an output signal of the differential amplifier 9, and a digital converter 12 for converting the output signal of the adder circuit 11 into a digital signal. 1 A / D conversion circuit 13 is a second A / D for digitally converting the output signal of electric field strength detection circuit 6
The conversion circuit 14 is a microcomputer that controls the mixing circuit 3, the damping circuit 8, and the forced drive circuit 10 according to the output signals of the first and second A / D conversion circuits 12 and 13. In FIG. 1, the same circuits as those in the conventional example of FIG. 2 are denoted by the same reference numerals.

In FIG. 1, the detecting operation of the super strong electric field is shown in FIG.
This will be described with reference to the flowchart of FIG. One broadcasting station
, The output signal of the RF-AGC circuit 7 is applied to the adder circuit 11 and to the differential amplifier circuit 9. The differential amplifier circuit 9 is RF-A
An output signal corresponding to the difference between the output signal of the GC circuit 7 and the reference voltage Vref is generated, and the output signal is applied to the addition circuit 11. In the addition circuit 11, the RF-AGC circuit 7
And the output signal of the differential amplifier circuit 9 are added.
The characteristics of the output signal of the RF-AGC circuit 7 with respect to the electric field intensity are as shown in FIG. 5A because the received RF signal is attenuated by the damping circuit 8 during the RF-AGC. That is, the RF-AGC signal has an electric field strength of 6
At 0 dBμ, the RF-AGC signal becomes Vr
When ef is reached, the damping circuit 8 operates, so that about 100
It becomes substantially flat up to dBμ, and at 100 dBμ or more, the RF signal level further increases and the RF-AGC signal changes. Further, the characteristic of the output signal of the differential amplifier circuit 9 with respect to the electric field strength is as shown in FIG. That is, when the electric field strength reaches 60 dBμ, a damping signal is generated,
Above dBμ, the RF-AGC signal becomes substantially flat but the differential amplification of the differential amplifier circuit 9 increases the damping signal. In addition, since the ratio of the output signal of the differential amplifier circuit 9 is set to be larger than the ratio of the output signal of the RF-AGC circuit 7 at the time of addition in the adder circuit 1, the characteristics of the output signal of the adder circuit 11 are shown in FIG. 60 to 110 dBμ as in 5 (c)
, The characteristics can be improved, and detection can be performed up to a reception electric field strength of 110 dBμ. The output signal of the addition circuit 11 is digitally converted by the first A / D conversion circuit 12,
It is applied to the microcomputer 14. The microcomputer 14 initially detects the received electric field strength based on the output data of the first A / D conversion circuit 12 (S1).

In the microcomputer 14, the electric field strength detected according to the output signal of the adder circuit 11 is 1
In the first range of 100 to 110 dBμ or 60 to 100 dBμ.
It is determined whether it is in the second range of dBμ or in the third range of 60 dBμ or less (S2). When the electric field strength detected according to the output signal of the adder circuit 11 is within the first range, the microcomputer 14 applies a switching signal to the forced driving circuit 10 and the RF-AGC generated from the forced driving circuit 10 by the switching signal. The signal is at a fixed level. Therefore, the gain of the RF amplifier circuit 1 is fixed to a small value,
An attenuation of dB is obtained. Therefore, the electric field strength detection circuit 6
FIG. 3 shows the characteristics of the electric field strength indicating signal with respect to the electric field strength.
As indicated by the dotted line in (b), the characteristics are shifted from the characteristics of the solid line in (b) to the strong electric field side (S3).

The output signal of the electric field strength detection circuit 6 having the characteristic shown by the dotted line in FIG.
The digital signal is then applied to the microcomputer 14. The microcomputer 14 detects the received electric field strength based on the output data of the second A / D conversion circuit 13 (S4). Thereafter, the microcomputer 14 detects whether or not the output data of the second A / D conversion circuit 13 is larger than the predetermined data. The predetermined data is set as shown by a dashed line in FIG. 3B, and is a level indicating whether or not the electric field strength can be detected even when the gain of the RF amplifier circuit 1 is in the original state. Since the RF-AGC loop is forcibly driven, if the output data of the second A / D conversion circuit 13 is smaller than the predetermined data, the detection processing cannot be performed well. FIG.
(B) As is clear from this detection, it is detected whether or not the received electric field strength is substantially larger than 120 dBμ (S5).

When the output data of the second A / D conversion circuit 13 is larger than the predetermined data, the microcomputer 14 directly applies the switching signal to the forced drive circuit 10, and sets the output signal of the forced drive circuit 10 to a fixed level, and
The gain of the amplifier circuit 10 becomes small. As shown in FIG. 3, the characteristic of the solid line is shifted to the dotted line by the forced driving of the AGC loop.
An electric field strength instruction signal with good linearity is obtained as shown by the dotted line in FIG. 3B in the region of the super strong electric field of 60 dBμ (S6).

In S5, when the output data of the second A / D conversion circuit 13 is smaller than the predetermined data, it is determined that the received electric field strength is substantially lower than 120 dBμ.
Therefore, the microcomputer 14 first stops generating the switching signal, the forced drive circuit 10 operates as a buffer circuit, and the RF-AGC loop returns to the normal AGC operation state. Therefore, the electric field strength instruction signal from the electric field strength detection circuit 6 becomes as shown by the solid line in FIG. 3 (b) (S7). Thereafter, the microcomputer 14 applies the first and second control signals to the mixing circuit 3 and the damping circuit 8, respectively. Since the conversion gain of the mixing circuit 3 decreases according to the first control signal, an attenuation of 20 dB is obtained. Further, since the damping circuit 8 is turned on in response to the second control signal, 4
An attenuation of 0 dB is obtained. Thus, the mixing circuit 3 and the damping circuit 8 can provide a total attenuation of 60 dB. Since the output characteristic of the electric field strength detection circuit 6 becomes a one-dot chain line in which the solid line characteristic is shifted to the strong electric field side as shown in FIG.
An electric field intensity indicating signal with good linearity in the middle / strong electric field region of Bμ is obtained as shown by the two-dot chain line in FIG. 3B (S8).

In S2, when it is determined that the received electric field strength detected by the output signal of the adding circuit 11 is in the second range of 60 to 120 dBμ, the microcomputer 14 generates first and second control signals. Similarly to S8, the conversion gain of the mixing circuit 3 is reduced and the damping circuit 8 is turned on, so that a total attenuation of 60 dB is obtained. Therefore, an electric field intensity instruction signal having good linearity in the medium / strong electric field region of 60 to 120 dBμ is obtained at the output terminal of the electric field intensity detection circuit 6 as shown by the two-dot chain line in FIG. 3B (S9).

In S2, the received electric field strength is 60
When it is determined that the value is in the third range of dBμ or less, the microcomputer 14 does not generate any switching signal, first and second control signals. Therefore, the gain of the compulsory driving circuit 10 is large, the conversion gain of the mixing circuit 3 is the same as in the normal case, and the damping circuit 8 is off. Therefore, an electric field intensity instruction signal having good linearity in the range of a weak electric field of 0 to 60 dBμ is obtained at the output terminal of the electric field intensity detection circuit 6 as shown by the solid line in FIG.

[0018]

As described above, according to the present invention, when the received electric field strength is within the first range, the RF of the radio receiver is reduced.
-By forcibly stopping the AGC loop and forcibly reducing the RF signal, it is possible to obtain a good electric field strength instruction signal in the super-strong electric field region. For this reason, when auto-tracking is performed under the broadcast base station, the difference in electric field strength can be determined by an ultra-strong electric field, so that the tuning frequency of the RF signal can be adjusted to the frequency at which the maximum electric field strength is obtained. In addition, for example, when an auto memory function is performed in a region where a plurality of broadcasting stations having an extremely strong electric field exist, a difference in the electric field intensity of the broadcasting stations can be detected, and the auto memory can be performed reliably.

Further, the detected electric field strengths are first to third.
By determining the range, the electric field strength instruction signal suitable for the received electric field can be obtained, so that the electric field strength instruction signal having a wide dynamic range according to the received electric field strength can be obtained.
Further, since the electric field strength is detected by the addition signal of the RF-AGC signal and the output signal of the differential amplifier circuit corresponding to the RF-AGC signal, the initial detection from the medium electric field to the strong electric field can be performed without affecting the reception signal line. Can be.

[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 characteristic diagram showing a relationship between an electric field strength and an instruction signal thereof.

FIG. 4 is a flowchart for explaining the operation of the present invention.

FIG. 5 is a characteristic diagram illustrating a relationship between an electric field intensity and an output level of each circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Variable gain amplifier circuit 11 Addition circuit 12 1st A / D conversion circuit 13 2nd A / D conversion circuit 14 Microcomputer

Claims (5)

[Claims] A damping circuit for attenuating a received RF signal; a local oscillation circuit for generating a local oscillation signal;
A mixing circuit that mixes the output signal of the amplifier circuit and the output signal of the local oscillation circuit to generate an IF signal; a first electric field intensity detection circuit that detects a received electric field intensity according to the IF signal;
In a radio receiver having an RF-AGC loop for automatically controlling the level of an F signal, a second electric field intensity detection circuit for detecting an electric field intensity of a medium / strong electric field, based on an output signal of the second electric field intensity detection circuit Means for determining whether the received electric field strength is in the first range, and forcibly driving the RF-AGC loop so as to greatly reduce the RF signal level when the received electric field strength is in the first range. A radio receiver comprising: a forced driving unit; and obtaining an instruction signal for instructing a first electric field intensity detection circuit to indicate an electric field intensity higher than a strong electric field. 2. In a state where the RF-AGC loop is forcibly driven,
Detecting means for detecting whether or not the received electric field strength is larger than a predetermined value; and a first means for maintaining a state of forced driving of the RF-AGC loop when the detected electric field strength is detected to be larger than the predetermined value. The radio receiver according to claim 1, further comprising control means. 3. The method according to claim 1, wherein the first determining means determines whether the received electric field intensity is in a second range lower than the first range. 2. The radio receiver according to claim 1, further comprising second control means for reducing a conversion gain of the mixing circuit. 4. When the detecting means detects that the received electric field intensity is smaller than a predetermined value, the forced driving of the RF-AGC loop is released, the damping circuit is operated, and the conversion gain of the mixing circuit is reduced. The radio receiver according to claim 1, further comprising a third control unit. 5. An amplifier for inputting a signal in the RF-AGC loop and a reference signal, and an output for outputting a signal corresponding to a difference between the two inputs, the second electric field strength detection circuit comprising: 2. The radio receiver according to claim 1, further comprising an adding circuit for adding a signal in a loop and an output signal of the amplifier.