JP2001237730A - Agc circuit and electronic tuner using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AGC circuit which can easily set the gain control range. SOLUTION: A resistor 59 is inserted between a connection point 45 which is the output of a pin diode 46 and a connection point 53 which is the output of a pin diode 54. Thus, the voltage at the connection point 45 and that at the connection point 53 can be controlled simultaneously by an input from an AGC terminal 49. A gain control range between an input terminal 41 and an output terminal 47 can be set easily by merely changing the value of the resistor 59, even if the values of the other resistors 44, 50, 55 and 58 and a capacitor 56 are not changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AGC circuit used for an electronic tuner and the like, and an electronic tuner using the same.

[0002]

2. Description of the Related Art An AGC circuit used in a conventional electronic tuner will be described below. As shown in FIG. 4, a conventional AGC circuit includes a capacitor 3 connected between an input terminal 1 and a connection point 2, a resistor 16 connected between the connection point 2 and the ground, A pin diode 5 connected between the connection point 4, a capacitor 7 connected between the connection point 4 and the output terminal 6, and a resistor connected in series between the connection point 4 and the AGC terminal 8 9 and a coil 17 in series, a pin diode 11 connected between the connection point 2 and the connection point 10, and a parallel connection body of a resistor 12 and a capacitor 13 connected between the connection point 10 and the ground. And a resistor 15 connected between the connection point 10 and the power terminal 14.
In, it was composed.

The cathodes of the pin diode 5 and the pin diode 11 are respectively connected to the connection point 2. The operation of the AGC circuit configured as described above will be described below.

The power supply terminal 14 is connected to a power supply of about 3 V, and the AGC terminal 8 receives an AGC voltage of 0 V to 3 V. Here, for example, AGC terminal 8
Is 3 V, the current flowing through the pin diode 5 increases. Accordingly, since the resistance of the pin diode 5 is reduced, the amount of attenuation between the input terminal 1 and the output terminal 6 is reduced.

When the voltage input to the AGC terminal 8 is low, the current flowing through the pin diode 5 decreases, and the potential at the connection point 2 decreases. As a result, the current flowing through the pin diode 11 increases. Most of the signals input to the connection point 10 flow to the connection point 10 side. At this time, since the resistance of the pin diode 5 increases, the amount of attenuation between the input terminal 1 and the output terminal 6 increases. Here, the two diodes of the pin diode 5 and the pin diode 11 are provided in order to increase the amount of attenuation.

[0006]

However, in such a conventional configuration, if the gain control range in the AGC circuit is to be changed, for example, the value of the resistor 16, the value of the resistor 9, the value of the resistor 15, and the And the value of the capacitor 13 must be changed in relation to each other, and setting the values is very troublesome.

Therefore, when it is desired to change only this gain control range in a similar set, especially in the case of a low power supply voltage, the design is very difficult.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an AGC circuit capable of easily setting a gain control range in the AGC circuit.

[0009]

In order to achieve this object, an AGC circuit according to the present invention comprises: a DC cut capacitor connected between an input terminal and a first connection point;
A first resistor connected between the connection point of
A first node connected between the first node and the second node;
A pin diode, a DC cut capacitor connected between the second connection point and the output terminal,
, An impedance connected between the AGC terminal, a second pin diode connected between the first connection point and the third connection point, and a ground between the third connection point and the ground. And a parallel connection body of a second resistor and a capacitor connected between the second connection point and the power supply terminal, and a third resistor connected between the third connection point and the power supply terminal. This is an AGC circuit in which a fourth resistor is connected to a third connection point.

This makes it possible to easily set the gain control range in the AGC circuit.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, there is provided a DC cut capacitor connected between an input terminal and a first connection point, and a DC cut capacitor connected between the first connection point and ground. A first resistor connected between the first connection point and the second connection point, and a first resistor connected between the first connection point and the second connection point.
A DC cut capacitor connected between the second connection point and the output terminal; an impedance connected between the second connection point and the AGC terminal; A second pin diode connected between the third connection point and a third connection point; a parallel connection body of a second resistor and a capacitor connected between the third connection point and the ground; A third resistor connected between the second connection point and the third connection point.
This is an AGC circuit to which the above-mentioned resistors are connected.

As described above, by inserting the fourth resistor between the second connection point and the third connection point, the voltage at the second connection point and the voltage at the third connection point are changed by the input from the AGC terminal. It is possible to control the gain control range of the AGC circuit only by changing the value of the fourth resistor without changing other first resistor, second resistor, third resistor and capacitor. Can be easily set.

According to a second aspect of the present invention, an input terminal to which a high-frequency signal is input, a high-frequency amplifier circuit connected to the input terminal, and an output of the high-frequency amplifier circuit connected to one input and the other input A mixer connected to an output of the local oscillator circuit at an input of the AGC circuit, an intermediate frequency amplifier connected between an output of the mixer and an output terminal, and a series connection of the AGC circuit according to claim 1. Is provided, and the AGC of the present invention is thus provided after the mixing circuit.
Since the circuit is inserted, it is possible to obtain an electronic tuner having a small distortion and a good NF characteristic even in a strong electric field.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram of an electronic tuner using the AGC circuit of the present invention. In FIG. 2, the electronic tuner of the present invention has a frequency of about 1.5 GHz broadcast from a satellite.
z input terminal 21 and an input terminal 2
1, an RF amplifier circuit 22 to which the output of the RF amplifier circuit 22 is connected, an RF amplifier circuit 24 to which the output of the band pass filter 23 is connected, Is connected to one input, and the other input is
5, an intermediate frequency amplifier 27 to which the output of the mixer 26 is connected, an AGC circuit 28 to which the output of the intermediate frequency amplifier 27 is connected,
A band-pass filter 29 to which the output of the AGC circuit 28 is connected, an intermediate frequency amplifying circuit 30 to which the output of the band-pass filter 29 is connected, and an output of the intermediate frequency amplifying circuit 30 which is input to one side and the other A mixing circuit 32 connected to the output of the local oscillation circuit 31 at the input of
An amplifier circuit 33 to which the output of the mixing circuit 32 is connected;
It comprises an output terminal 34 to which the output of this amplifier circuit 33 is connected.

Then, about 1.5 G from the input terminal 21
Although the signal of Hz is input, the channel is selected by the mixing circuit 26 to become the first intermediate frequency of about 100 MHz.
This intermediate frequency is about 2 MHz in the next mixing circuit 32.
Is converted to a second intermediate frequency and output from the output terminal 34.

Here, the AGC circuit 28 is about 0 to 40 dB.
However, in the present invention, the AGC circuit 28 is provided between the mixing circuit 26 and the mixing circuit 32 and is separated from the input terminal 21 so that the NF characteristic is deteriorated. Is less affected. That is, since it is not near the input terminal 21, the contribution to the NF characteristic deterioration is small. For distortion, AGC at the first intermediate frequency
, The distortion characteristics are improved without excessive input.

Here, the AGC circuit 28 will be described with reference to FIG. The AGC circuit 28 includes an input terminal 41 to which the output of the amplifier circuit 27 is connected, a DC cut capacitor 43 of about 1000 pF connected between the connection points 42, and an approximately one connected between the connection point 42 and the ground. A 470Ω resistor 44, a pin diode 46 connected between the connection point 42 and the connection point 45, and a DC cutoff connected between the connection point 45 and an output terminal 47 connected to the input of the filter 29. Of about 1000 pF and the connection point 4
5 connected to the AGC terminal 49 in series.
A series connection of a resistor 50 of Ω and a coil 51 and a connection point 42
Diode 54 connected between
And about 680 connected between the connection point 53 and the ground.
A parallel connection of a resistor 55 of Ω and a capacitor 56 of about 1000 pF, a resistor 58 of about 750 Ω connected between the connection point 53 and the power supply terminal 57, and a connection between the connection point 45 and the connection point 53 And a resistor 59. Here, the pin diodes 46 and 54 have their cathode sides connected to the connection point 42 side, respectively.

With this configuration, when the voltage of the AGC terminal 49 changes, the voltage of the connection point 45 changes. At the same time, the voltage of the connection point 53 can be changed via the resistor 59 at the same time. Therefore, by changing the value of the resistor 59, the control range of the AGC can be freely set.

FIG. 3 shows an example of the gain control range setting when this circuit is used. FIG. 3 shows how the characteristics change when the resistor 59 is not provided and when the resistor 59 is set to 10 kΩ. When the resistor 59 is not provided, the gain control range of the AGC is 40 dB as shown in a characteristic 62. However, when the value of the resistor 59 is set to 10 kΩ, a gain control amount of about 30 dB is obtained as shown in the characteristic 61.

Similarly, when the value of the resistor 59 is 1.8 kΩ, the gain control range is about 20 dB. When the value is 3.3 kΩ, the gain is about 23 dB. When the value of the resistor 59 is 15 kΩ, a gain control range of about 33 dB can be obtained. In FIG. 3, the horizontal axis represents the AGC voltage (V), and the vertical axis represents the gain control amount (dB).

[0021]

As described above, according to the present invention, since the fourth resistor is connected between the second connection point and the third connection point, by changing the fourth resistance, The gain control range in the AGC circuit can be easily set.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an AGC circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram of an electronic tuner using the AGC circuit of the present invention.

FIG. 3 is a characteristic diagram of a change in a gain control range of the AGC circuit according to the present invention.

FIG. 4 is a circuit diagram of a conventional AGC circuit.

[Explanation of symbols]

 41 Input Terminal 42 First Connection Point 43 DC Cut Capacitor 44 Resistance 45 Second Connection Point 46 Pin Diode 47 Output Terminal 48 DC Cut Capacitor 49 AGC Terminal 50 Resistance 51 Coil 53 Third Connection Point 55 Resistance 56 Capacitor 57 Power supply terminal 58 Resistor 59 Gain control range setting resistor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C025 AA25 AA27 BA18 DA04 5C026 BA20 5J100 AA03 AA09 BA10 BB05 BB09 BC06 FA02 5K061 AA08 CC52 JJ09 JJ12

Claims (2)

[Claims] A DC cut capacitor connected between an input terminal and a first connection point; a first resistor connected between the first connection point and ground; A first pin diode connected between the first connection point and the second connection point; a DC cut capacitor connected between the second connection point and an output terminal; An impedance connected between the connection point and the AGC terminal; a second pin diode connected between the first connection point and the third connection point; and an impedance connected between the third connection point and ground. A third resistor connected between the third connection point and a power supply terminal, and a second resistor and a capacitor connected in parallel between the second connection point and the power supply terminal. An AGC circuit in which a fourth resistor is connected to the third connection point. 2. An input terminal to which a high-frequency signal is input, a high-frequency amplifier circuit connected to the input terminal, and an output of the high-frequency amplifier circuit connected to one input and a local oscillation circuit connected to the other input. An electronic tuner comprising: a mixing circuit to which an output of the AGC circuit is connected; an intermediate frequency amplification circuit connected between an output of the mixing circuit and an output terminal; and a series connection of the AGC circuit according to claim 1.