JPH04367105A - Radio receiver - Google Patents

Abstract

PURPOSE:To equalize sensitivity characteristic of all over the reception band width. CONSTITUTION:A coupling circuit 6 composed of a pair of variable capacity diodes 6a and 6b where the capacity changes relatively by the channel selection voltage is connected between an antenna tuning circuit 4 and a high frequency amplification element 7 amplifying the tuning output. The antenna tuning output is coupled with the high frequency amplification element with a low coupling degree when the channel selection voltage is high and with a high coupling degree when the channel selection voltage is low.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver with uniform sensitivity characteristics over the entire reception bandwidth.

0002

[Prior Art] Conventionally, over the entire receiving frequency band,
In order to equalize the load, power gain, noise figure, and band characteristics, a variable coupling capacitor that is variable in conjunction with the variable tuning capacitor is connected between the variable tuning capacitor and the high-frequency amplification element. A receiver input circuit is known, for example, from Japanese Utility Model Application Publication No. 51-160006.

0003

[Problems to be Solved by the Invention] However, according to the above-mentioned conventional configuration, since the coupling variable capacitor connected to the tuning variable capacitor is simply connected to the signal path,
The degree of coupling obtained between the tuning circuit and the next-stage amplification element is large and the rate of change is small, resulting in a decrease in selectivity, and
It was not possible to obtain uniform sensitivity characteristics over the entire receiving bandwidth.

Therefore, the present application increases the rate of change in the degree of coupling between the tuned circuit and the amplifying element, thereby increasing the sensitivity at higher reception frequencies and the sensitivity at lower reception frequencies without reducing the selectivity. The characteristics are as follows:
A pair of variable capacitance elements whose capacitance changes relatively depending on the tuning voltage are provided in the front stage or the rear stage of at least one tuning circuit, and have a small coupling capacitance when the tuning voltage is high;
This is because a coupling circuit with a large coupling capacitance is connected when the channel selection voltage is low.

[0005]

[Operation] Therefore, the signal input to the antenna input terminal is
For example, in the subsequent stage of the antenna tuning circuit, the tuning output is input to a high frequency amplification circuit that amplifies the tuning output according to the degree of coupling determined by the coupling circuit. In the above, the pair of variable capacitance diodes forming the coupling circuit is such that when the capacitance of one of the variable capacitance diodes changes in the direction of increasing due to the channel selection voltage, the capacitance of the other variable capacitance diode changes in the direction of decreasing. In other words, since it changes in a seesaw-like manner, the rate of change in the degree of coupling in the coupling circuit is large. Therefore, when the tuning frequency is low and the resonant impedance and resonant voltage are also low, the antenna tuning circuit changes with an extremely high degree of coupling. The tuning signal is input to the high frequency amplification element, and the tuning frequency is high,
When the resonant impedance and resonant voltage are also high, the tuning signal of the antenna tuning circuit is input to the high frequency amplification element with an extremely low degree of coupling.

[0006]

[Embodiment] An embodiment of the present application will be described below in detail based on the drawings.A band-pass type antenna tuning circuit 4 is connected to the antenna input terminal 1 and includes a tuning coil 2 and a pair of tuning variable capacitance diodes 3a and 3b. and an attenuation circuit 5 consisting of a pair of pin diodes are connected between the antenna tuning circuit 4 and the first gate g1 of a high frequency amplifying element 7 consisting of a MOSFET that amplifies the tuned output.
A coupling circuit 6 consisting of a pair of variable capacitance diodes 6a and 6b whose capacitance changes relatively depending on the channel selection voltage VT is connected. In this coupling circuit 6, the anode of one variable capacitance diode 6a is connected to the antenna tuning circuit 4, the cathode thereof is connected to the anode of the other variable capacitance diode 6b, and a tuning voltage VT is applied to the other. A power supply bias voltage Vcc is applied to the cathode of the variable capacitance diode 6b, and the variable capacitance diode 6b described above
The first gate g1 of the high frequency amplification element 7 is connected to the series connection point of a and 6b via a coupling capacitor C1, and the output of the drain d is connected to a π-type high frequency tuning circuit 8 via a coupling capacitor C2. It is connected to.

[0007] An impedance conversion element 9 consisting of an FET is connected to the subsequent stage of the high frequency tuning circuit 8, and a second π-type high frequency tuning circuit 10 is connected to the source thereof via a coupling capacitor C3. Further, the output of the high frequency tuning circuit 10 is transmitted through a coupling capacitor C4 to a frequency conversion circuit 11, an intermediate frequency amplification circuit 12 and a gain control signal circuit 1.
The FM front end IC (for example LA1175 manufactured by Sanyo Electric) 14 is connected to the fifth terminal which is the input terminal of the frequency conversion circuit 11, and the eighth and ninth terminals which are the output terminals of the frequency conversion circuit 11 are connected to the intermediate frequency It is connected to the primary coil of the transformer T, and its secondary coil is connected to the 12th terminal, which is the input terminal of the intermediate frequency amplification circuit 12, through a series circuit of the resistor R1 and the filter F. The 15th terminal, which is the output terminal, is connected to the detection stage through the intermediate frequency transformer T, and the secondary side of the intermediate frequency transformer T is connected to the 10th terminal, which is the input terminal of the gain signal control circuit 13, through a series circuit of a resistor R2 and a capacitor C5. A sixth terminal is connected to the attenuation circuit 5 and outputs a drive signal to the attenuation circuit 5 via the circuit 13, and a thirteenth terminal which is an AGC signal output terminal of the gain control circuit 13 is connected to the first MOSFET. The second gate g2 of L0/DX is connected to the terminal 15 of L0/DX.
is connected.

[0008] Thus, the input signal input to the antenna input terminal 1 is selected by the antenna tuning circuit 4 and then sent to the coupling circuit 6 consisting of a pair of variable capacitance diodes 6a and 6b.
It is input to the first gate g1 of MOSFET 7 according to the coupling degree determined by. In the coupling circuit 6, the tuning voltage V
When the capacitance of one variable capacitance diode 6a increases due to T, the capacitance of the other variable capacitance diode 6b relatively decreases. That is, a pair of variable capacitance diodes 6
The capacitances of a and 6b vary in a see-saw manner depending on the channel selection voltage VT.

Now, when one variable capacitance diode 6a constituting the coupling circuit 6 changes from 50P to 5P depending on the channel selection voltage VT, the other variable capacitance diode 6b changes from 5P to 50P.
Assuming that it is variable relative to P, the degree of coupling is the combined capacitance 55P of the pair of variable capacitance diodes 6a and 6b and the capacitance of one variable capacitance diode 6a connected to the first gate g1 of the high frequency amplification element 7. Therefore, when the tuning frequency is low, the coupling degree is 50/55, whereas when the tuning frequency is high, the coupling degree is 50/55.
It becomes 5/5, and the rate of change is about 10 times.

That is, when the tuning frequency is low and the resonant impedance and resonance voltage are also low, the tuning signal of the antenna tuning circuit 4 is input to the high frequency amplification element 7 with an extremely high degree of coupling, and the tuning frequency is high. When the resonant impedance and resonant voltage are also high, the tuning signal of the antenna tuning circuit 4 is input to the high frequency amplification element 7 with an extremely low degree of coupling, so that the output voltage can be kept constant with respect to the tuning frequency.

After the signal input to the first gate g1 of the MOSFET is amplified in this manner, it is selected again in the π-type high frequency tuning circuit 8 via the coupling capacitor C2, and is connected to an impedance conversion element whose drain is connected to ground. Input to gate g of 9. In the above, the input signal is π
It resonates at high impedance in the high-frequency tuning circuit 8 of the type, and therefore, the output of the circuit 8 is input to the gate g of the impedance conversion element 9, which is set to high impedance, so that high selectivity can be maintained. At the same time, the sensitivity difference can also be corrected due to the large change in the coupling degree caused by the coupling circuit 6, and the coupling degree of the coupling circuit can also be set small so as not to reduce the selectivity.

The signal inputted to the impedance conversion element 9 is converted to a low output impedance, and inputted from the source S to the subsequent π-type high frequency tuning circuit 10 via the coupling capacitor C3, and then further selected. It is input from the fifth terminal to the frequency conversion circuit 11 of the FM front end IC 14 via the coupling capacitor C4, and after being converted into an intermediate frequency signal, it is output from the eighth and ninth terminals, respectively, and the output is sent to the intermediate frequency transformer. The signal is input to the intermediate frequency amplification circuit 12 from the 12th terminal through a series circuit of T, the resistor R1, and the ceramic filter F, where it is amplified, and the amplified output is output from the 15th terminal to the detection stage. Further, a part of the wideband intermediate frequency signal that has passed through the intermediate frequency transformer T is inputted from the tenth terminal to the gain control circuit 13 via a series circuit of resistor R2 and capacitor C5, and from the circuit 13 is input to the gain control circuit 13 through the series circuit of resistor R2 and capacitor C5. An AGC voltage for driving the diode and an AGC voltage for controlling the high frequency amplification element 7 are generated, and these AGC voltages are
The C voltage is output from the 6th terminal and the 13th terminal, respectively,
The attenuation circuit 5 attenuates the signal according to the electric field strength of the antenna input signal, and the high frequency amplification element 7 controls the amplification factor according to the electric field strength.

The above-mentioned embodiment shows the case where the coupling circuit 6 is connected at the downstream stage of the antenna tuning circuit 4, that is, between the antenna tuning circuit 4 and the first gate g1 of the high frequency amplification element 7 that amplifies its tuning output. However, the coupling circuit 6 is
When connected via a coupling capacitor before the antenna tuning circuit 4, that is, between the antenna tuning circuit 4 and the antenna input terminal 1, or between the drain d of the high frequency amplification element 7 and the π-type high frequency tuning circuit 8. A similar result can be achieved even when connecting via a coupling capacitor between the π-type high frequency tuning circuit 10 and the fifth terminal of the FM front end IC 14. .

[0014]

As described above, according to the present invention, the degree of coupling in the coupling circuit can be changed greatly depending on the channel selection voltage, so that the sensitivity characteristics can be made uniform over the entire receiving bandwidth, and There is flexibility in setting the capacitance of the coupling circuit, especially when the tuning circuit is a π-type tuning circuit.
It has the advantage of improving selectivity.

[Brief explanation of drawings]

[Figure 1] Circuit diagram

[Explanation of symbols]

1 Antenna input terminal 4 Antenna tuning circuit 6 Coupling circuit 6a, 6b Variable capacitance diode 7 High frequency amplification element 8,10 π type high frequency tuning circuit 9 Impedance conversion element

Claims (2)

[Claims] Claim 1: A pair of variable capacitance elements, the capacitance of which changes relatively depending on the tuning voltage, are provided before or after at least one tuning circuit, and have a small coupling capacitance when the tuning voltage is high; A radio receiver characterized in that a coupling circuit having a large coupling capacity when the station voltage is low is connected. 2. The radio receiver according to claim 1, wherein the high frequency tuning circuit comprises a π type tuning circuit.