JPS632364B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an antenna reception input circuit for a receiver.

BACKGROUND ART An AGC (automatic gain control) circuit is indispensable in the tuner circuit of a receiver.
Figure 1 shows a circuit diagram of a tuner with an AGC circuit. An RF (high frequency) received signal from the antenna element 1 is introduced via a capacitor C ₁ to a level control circuit 2 consisting of diodes D ₁ and D ₂ which are variable impedance elements. The impedance of each impedance element D ₁ and D ₂ of this level control circuit 2 is controlled by the AGC voltage V _A to control the antenna reception signal level. Note that capacitor _C2 is a bypass capacitor.

The output of this level control circuit 2 is the capacitor C ₃
RF that has a hum noise blocking coil _L1 that lowers the commercial power frequency to the reference potential point and an active element FET (field effect transistor) _Q1 .
It is input to the buffer amplifier 3. This RF buffer amplifier 3 itself receives the received signal from the antenna element 1 in a non-tuned manner, and the load of this amplifier 3 includes a parallel circuit consisting of a tuning transformer T, a variable capacitance element VD, a trimmer capacitor _C4 , and a resistor _R1. A tuning circuit 4 is connected to selectively derive frequencies within the desired reception band. The capacitance value of the variable capacitance element VD is controlled by applying a tuning voltage V _T via a resistor R ₂ . Note that capacitor _C5 is for bypass.

The selectively derived RF tuning output is amplified by the RF amplifier 5 and then sent to the frequency converter 6.
It becomes an IF (intermediate frequency) signal and is guided to the IF amplifier and detector 7. The output of this detector 7 becomes the tuner output. Then, a voltage V′ _A corresponding to the IF signal or detection signal level is generated in the circuit 7, and this is applied to the AGC of the IF amplifier and further the RF amplifier 5.
Used as voltage. In addition, the voltage V′ _A is impedance-converted by the AGC buffer circuit 8,
It is output as the control voltage V _A of the level control circuit 2 mentioned above.

In such a configuration, the signal level that has passed through the filters provided in the RF stage and the IF stage is detected.
Since it generates AGC voltages V _A and V′ _A ,
The relationship between AGC voltage and frequency exhibits an extremely narrow band characteristic as shown in FIG. Therefore, although the AGC effect is effective against received desired waves, it does not work at all against interference waves other than the desired waves. Therefore, when receiving a desired wave of a medium electric field in a strong electric field, or at night when the electric field is relatively strong, there is a drawback that interference phenomena due to IM (intermodulation) interference waves etc. become noticeable. this is,
A delay is applied to the AGC of the RF input stage to prevent S/N deterioration, and this is also caused by the fact that the AGC of the RF input stage is not applied due to the desired wave in a medium electric field.

Furthermore, since the AGC loop is duplicated, there is also the disadvantage that the entire circuit inevitably becomes unstable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an antenna reception input circuit that can eliminate interference caused by IM interference waves and the like.

An antenna receiving input circuit according to the present invention includes an active element that receives an RF signal from an antenna element in an asynchronous manner, a load circuit provided as an output load of the active element, and an output signal obtained by the load circuit. a control voltage generating means that generates a control voltage according to the level of this output signal; and a control voltage generating means that receives the control voltage from the control voltage generating means and sets the level of the RF signal at the connection point between the antenna element and the active element to the control voltage. control to attenuate according to
RF input control means, the load circuit is constituted by a series connection circuit of a resistor and a frequency selection circuit, and the output signal derived from the active element side end of the resistor in the series connection circuit is applied to the control voltage. It is characterized in that it is applied to the generating means and has a broadband AGC function.

Example The present invention will be explained below using the drawings.

FIG. 3 is a circuit diagram of one embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same symbols.
To show only the parts that are different from Fig. 1, there is a resistor connected in series with the primary coil of the tuning transformer T of the parallel tuning circuit 4, which is the drain load of FETQ ₁ of the RF buffer amplifier 3, that is, the output load of the buffer amplifier 3.
Insert R ₃ and resistor R ₃ in this series connected circuit
The signal derived from the end of the FETQ ₁ side is inputted to the control voltage generating means, that is, the wideband AGC processing circuit 9, and the AGC voltage V _A is generated. This voltage V _A causes variable impedance elements D ₁ , D ₂
The impedance of the antenna is controlled to control the antenna input signal level.

As this wideband AGC processing circuit 9, for example,
A circuit configuration for RF amplification, detection, and smoothing may be used. Since the other circuit configurations are the same as those shown in FIG. 1, their explanations will be omitted.

In this configuration, since the resistor R ₃ is inserted between the drain of FETQ ₁ and the tuning transformer T, the selection characteristic showing the relationship between the frequency and V _A seen from the drain becomes as shown in Figure 4. . In other words, for the selection characteristic when the resistance R ₃ is zero (same as that in Figure 2), by increasing the value of the resistance R ₃ , the frequency waves on both the upper and lower sides of the selection frequency ₀ are changed. On the other hand, the approximately flat characteristic gradually increases. Therefore, it becomes possible to perform a wideband AGC operation having arbitrary frequency characteristics, and interference due to IM interference waves and the like is significantly reduced.

Here, since the output impedance of FETQ ₁ is extremely high compared to the primary winding of the tuning transformer T, the selection characteristics for the received signal can maintain sharp characteristics without being affected by the resistor R ₃ , and the loss can also be reduced. Almost never occurs. Furthermore, depending on the AGC voltage V _A
Since it controls the RF input signal level and is not an AGC method that changes the operating point of FETQ ₁ ,
This will prevent the generation of distortion due to operating point fluctuations of active elements, as well as IM interference and cross-modulation interference due to this distortion. Furthermore, since the AGC loop does not form a double loop, the entire circuit becomes stable.

Effects of the Invention As described above, the load circuit provided as an output load of an active element is configured by a series connection circuit of a resistor and a frequency selection circuit, and the active element side end of the resistor in this series connection circuit More AGC
Since the signal used for this purpose is derived, the wideband AGC function can operate stably, thereby eliminating interference in strong electric fields, and the wideband AGC characteristics can be freely set while considering sensitivity suppression. There are advantages that can be achieved. In particular, this invention
Although it is suitable for use in an on-vehicle tuner for the MW (medium wave) or LW (long wave) frequency band, it is not particularly limited. Furthermore, it goes without saying that the circuit example described above can be modified in various ways.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional tuner, Figure 2 is a diagram showing the AGC characteristics of Figure 1, Figure 3 is a circuit diagram of a tuner using a circuit according to an embodiment of the present invention, and Figure 4 is a diagram showing the AGC characteristics of Figure 1. 3 is a diagram showing the AGC characteristics of FIG. 3. FIG. Explanation of symbols of main parts, 1...Antenna, 2...
...Input level control circuit, 3...RF input circuit, 4
... Tuning circuit, 9... Wideband AGC processing circuit.

Claims (1)

[Claims] 1. An active element that receives an RF signal from an antenna element in an asynchronous manner, a load circuit provided as an output load of the active element, and an output signal obtained by the load circuit as an input. control voltage generating means for generating a control voltage according to the level of the output signal; and receiving the control voltage from the control voltage generating means, adjusting the level of the RF signal at the connection point between the antenna element and the active element to the control voltage. RF input control means for controlling the attenuation according to the frequency selection circuit, wherein the load circuit is constituted by a series connection circuit of a resistor and a frequency selection circuit, and An output signal derived from the active element side end of the control voltage generating means is applied to the control voltage generating means, and the control voltage is applied to the control voltage generating means with a wide band characteristic centered on a selection frequency ₀ determined by the frequency selection circuit.
An antenna reception input circuit characterized in that the antenna reception input circuit is supplied to an RF input control means. 2. The RF input control means has one end connected to a connection point between the antenna element and the active element,
2. The antenna reception input circuit according to claim 1, further comprising a voltage-dependent variable impedance element whose other end is connected to a reference potential point.