JP3357790B2 - Radio receiver electric field strength detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric field intensity detecting circuit of a radio receiver for judging the electric field intensity in a strong electric field.

[0002]

2. Description of the Related Art Conventionally, a radio receiver has a search function for automatically searching for a broadcasting station, and an automatic memory function for automatically searching for a broadcasting station and presetting the searched broadcasting stations in the order of electric field strength. Provided. In the search function, the reception frequency is swept, and when there is a broadcast station having a predetermined electric field strength, a search stop is performed and the broadcast station is received. That is, the broadcasting station is found based on the electric field strength. Therefore, a radio receiver having such a function requires a means for detecting the electric field strength of a broadcasting station. FIG. 2 shows a circuit for detecting the electric field strength of the FM radio receiver.

In FIG. 2, a received RF signal is converted into an IF signal by a frequency conversion circuit 1 and amplified by multi-stage IF amplifiers 2a to 2d. The amplified IF signal is subjected to FM detection by the FM detection circuit 3. The IF stage of the FM receiver is composed of multiple stages of IF amplifiers 2a to 2d as shown in FIG. 2, so that the AM suppression effect and the capture effect are improved. The output signals of the multistage IF amplifiers 2a to 2d are level-detected by the level detection circuits 4a to 4d, respectively, and added by the addition circuit 5. Since the output signals of the IF amplifying circuits are sequentially added, an electric field strength indicating signal having good linearity from 0 dBμ to 60 dBμ can be obtained at the output terminal of the addition circuit 5 as shown in FIG. Since the output signals of the level detection circuits 4a to 4d are added to obtain the electric field strength indication signal, the dynamic range can be expanded.

[0004]

However, in the conventional example shown in FIG. 2, when the electric field strength exceeds 60 dBμ, the IF
Since the output signal of the amplifier 2d is clipped by the limiter action, even if the electric field strength changes in a range beyond that, FIG.
As shown in (a), there is a problem that the electric field strength instruction signal does not change. That is, the electric field strength cannot be determined by a strong electric field, and in particular, when a plurality of broadcasting stations are present in a strong electric field, if the auto memory function is performed, the electric field strength cannot be determined. I couldn't get it to work.

[0005]

SUMMARY OF THE INVENTION The present invention provides an antenna damping circuit for attenuating a received RF signal, an RF amplifier circuit for amplifying an output signal of the antenna damping circuit, and an RF amplifier for controlling a gain of the RF amplifier circuit. An electric field strength detection circuit in a radio receiver, comprising: an AGC circuit; and a damping signal generation circuit that generates a damping signal for controlling an antenna damping circuit according to a received electric field strength, wherein the output signal of the RF-AGC circuit is provided. And a combining circuit that combines the damping signal and obtains an electric field strength instruction signal from an output terminal thereof.

[0006] Further, the synthesis circuit is an addition circuit. Further, the synthesis circuit is a subtraction circuit. Still further, the synthesis circuit includes:
A variable current circuit whose current amount increases as the level of the damping signal increases; a transistor to which an output signal of the RF-AGC circuit is applied to a base and a resistor connected to an emitter; A current mirror circuit for reversing the current and a current mirror circuit for reversing the emitter current of the transistor are provided, and the output current of the current mirror circuit is combined.

[0007]

FIG. 1 is a view showing an embodiment of the present invention, in which 6 is an antenna, and 7 is a PIN diode 7a.
And 7b, an antenna damping circuit for attenuating the RF signal, 8 an FET constituting an RF amplifier circuit, and 10 an RF
An RF tuning circuit for tuning a signal, a local oscillation circuit 11 for generating a local oscillation signal, a mixing circuit 12 for converting the output signal of the RF tuning circuit 10 into an IF signal by the local oscillation signal, and a mixing circuit 12 R according to the output signal of
An RF-AGC circuit for generating an F-AGC signal;
A comparison circuit for generating an output signal corresponding to the difference between the output signal of the F-AGC circuit 13 and the reference value, 15 is a variable current source controlled according to the output signal of the comparison circuit 14, and 16 is a transistor from the transistors 16a to 16c A current mirror circuit for inverting the output signal of the variable current source 15;
A transistor and a resistor for converting the AGC signal into a V-I signal, 19 to 21 are current mirror circuits for inverting the current flowing through the resistor 18, 22 is a resistor to which the output difference current of the current mirror circuits 16 and 21 is supplied, and 23 is This is an output terminal from which an electric field strength instruction signal is obtained.

In FIG. 1, F received by antenna 6
The M RF signal is applied to the gate of FET 8 and
The amplified RF signal is generated from the drain 8. After the RF signal is tuned by the RF tuning circuit 10, the frequency is converted into an IF signal by the local oscillation signal in the mixing circuit 12. After the IF signal is amplified by the IF amplifier circuit 2 at the subsequent stage,
The signal is detected by the FM detection circuit 3. The output signal of the mixing circuit 12 is applied to the RF-AGC circuit 13. RF-
The AGC circuit 13 generates an RF-AGC signal by level-detecting and smoothing the output signal of the mixing circuit 12. The RF-AGC signal is applied to the gate of the FET 8, and the amplification factor of the FET 8 is changed according to the RF-AGC signal. Since the amplification rate is controlled to decrease as the output signal level of the mixing circuit 12 increases,
Harmonic generation from the mixing circuit 12 due to excessive input can be prevented.

Next, generation of an electric field intensity indicating signal when the electric field intensity is a strong electric field will be described. First, RF-AGC
As the electric field strength increases, the RF-AGC signal is generated at 60 dBμ as shown by the solid line in FIG.
Since the damping circuit 7 operates after passing μ,
B gradually changes to the electric field strength of B.
Is generated when the RF-AGC signal reaches a predetermined level Vref, as shown by the dotted line in FIG. 3B, and thereafter gradually changes to the B field intensity because the comparison circuit 14 is a differential pair. More specifically, when the electric field strength is about 60 d
Up to Bμ, there is no possibility that the input circuit will saturate the mixing circuit 12, so that the high-level RF-A as shown by the solid line in FIG.
The GC signal is generated, and the amplification factor of the FET 8 is large. When the electric field strength is 60 dBμ or more, the RF-AGC signal level decreases as shown by the solid line in FIG. In addition, as is apparent from FIG.
The C signal is also applied to the negative input terminal of the comparison circuit 14. In FIG. 3B, the electric field intensity becomes A, and the reference voltage Vre
When the voltage f becomes lower than f, an output signal is generated from the comparison circuit 14. The variable current source 15 is turned on by the output signal, and an output current is generated from the variable power supply 15. The output current is inverted by the current mirror circuit 16, and the collector current of the transistor 16b is supplied to the PIN diodes 7a and 7b. Therefore, the PIN diodes 7a and 7b turn on,
The received RF signal level is attenuated by the antenna damping circuit 7. Therefore, the input level of the RF-AGC circuit 13 decreases, and the change of the RF-AGC signal temporarily stops. Therefore, when the electric field intensity is equal to or higher than A, the RF-AGC signal gradually decreases. At the same time, the RF-AG
An output signal corresponding to the difference between the C signal and the reference voltage Vref is generated, and the output signal of the variable current source 15 gradually increases because the comparison circuit is constituted by a differential circuit. Then, when the electric field intensity becomes B in FIG.
The F signal level increases as the RF-AGC circuit 13 is further operated, and the RF-AGC signal further decreases,
The output current of the variable current source 15 increases.

The output current source of the variable current source 15 is inverted by the current mirror circuit 16 and is generated from the collector of the transistor 16c. On the other hand, the RF-AGC signal is applied to the base of the transistor 17, and the current is converted by the resistor 18. The resistor 18 receives the base-emitter voltage Vbe of the transistors 17 and 19a from the RF-AGC signal.
, And a current based on the resistance 18 and the emitter resistance of the transistor 19a flows. The current flowing through the resistor 18 is inverted by the current mirror circuits 19 to 21. Therefore, a difference current obtained by subtracting the current mirror circuit 21 from the output current of the current mirror circuit 16 is supplied to the resistor 22, and the voltage is converted. That is, as a result of subtracting the RF-AGC signal from the damping current from the variable current source 15, the output terminal 23
An electric field strength instruction signal is obtained.

Since the RF-AGC signal and the damping signal change as shown in FIG. 3B, the ratio of the current according to the damping signal is adjusted by adjusting the mirror ratio of the current mirror circuit and the value of the resistor 18. Is larger than the ratio of the RF-AGC signal, an electric field strength indication signal with good linearity can be obtained with a strong electric field of 60 dBμ to 110 dBμ as shown in FIG.

FIG. 4 is a diagram showing another embodiment of the synthesizing circuit according to the present invention. In FIG. 4, reference numeral 24 denotes a current mirror circuit for inverting the output current of the variable current source 15, and 25 denotes the output current of the current mirror circuit 19. The inverting current mirror circuit 26 is a resistor to which the added output current of the current mirror circuits 24 and 25 is supplied. In FIG. 4, the output signal of the variable current source 15 is inverted by the current mirror circuit 14, supplied to the antenna damping circuit 7, and supplied to the resistor 26. Also, RF
The current obtained by current conversion of the -AGC signal is inverted by the current mirror circuits 19 and 25 and supplied to the resistor 26.
Therefore, a current obtained by adding the output signals of the current mirror circuits 24 and 25 flows through the resistor 26. The added current is the resistance 2
6 to convert the voltage, and an electric field strength instruction signal is obtained at the output terminal 23.

Therefore, since the RF-AGC signal and the damping signal change as shown in FIG. 3 (b), the current according to the damping signal is adjusted by adjusting the mirror ratio of the current mirror circuit and the value of the resistor 18. RF-AG
If the ratio is smaller than the ratio of the C signal, 60 as shown in FIG.
An electric field strength instruction signal with good linearity can be obtained with a strong electric field of dBμ to 110 dBμ.

[0014]

As described above, according to the present invention, the RF
By combining the AGC signal and the damping current for controlling the antenna damping circuit, a signal indicating the electric field strength can be obtained with a strong electric field. Even in the strong electric field region, the electric field strength can be determined. For example, in the case of the auto memory function, even if there are a plurality of broadcasting stations having a strong electric field strength, it can be appropriately determined and the auto memory operation can be normally performed. be able to.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional example.

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

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 7 damping circuit 8 FET 10 tuning circuit 11 local oscillation circuit 12 mixing circuit 13 RF-AGC circuit 14 comparison circuit 15 variable current source 16, 19, 20, 21, 24, 25 current mirror circuit

Continuation of front page (72) Inventor Katsuo Matsumoto 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd. (JP, A) JP-A-8-56167 (JP, A) JP-A-64-62029 (JP, A) JP-A-7-336247 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ H04B 17/00 H04B 1/18

Claims (4)

(57) [Claims] An antenna damping circuit for attenuating a received RF signal; an RF amplifier circuit for amplifying an output signal of the antenna damping circuit; an RF-AGC circuit for controlling a gain of the RF amplifier circuit; And a damping signal generation circuit for generating a damping signal for controlling an antenna damping circuit in response to the electric field strength detection circuit in the radio receiver, wherein the output signal of the RF-AGC circuit and the damping signal are combined, A combining circuit for obtaining an electric field strength instruction signal from an output terminal thereof, the electric field strength detecting circuit of the radio receiver. 2. The circuit according to claim 1, wherein said combining circuit is an adding circuit. 3. The circuit according to claim 1, wherein said combining circuit is a subtraction circuit. 4. The synthesizing circuit includes a variable current circuit whose current amount increases as the level of the damping signal increases, an output signal of the RF-AGC circuit applied to a base, and a resistor connected to an emitter. And a current mirror circuit for inverting the output current of the variable current circuit, and a current mirror circuit for inverting the emitter current of the transistor, wherein the output current of the current mirror circuit is synthesized. An electric field strength detection circuit for a radio receiver according to claim 1.