JP3133170B2 - Automatic gain control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device used for a television tuner or a CATV converter.

[0002]

2. Description of the Related Art Recently, television tuners and CA
The high-frequency amplifier of the TV converter is a combination of a wideband amplifier as an RF amplifier and an automatic gain control circuit. Hereinafter, a conventional automatic gain control device will be described. FIG. 2 is a circuit diagram showing a configuration of a conventional automatic gain control device.

In FIG. 2, reference numeral 20 denotes a VHF RF amplifying transistor (hereinafter, referred to as a “VRF amplifier”);
Is a UHF RF amplification transistor (hereinafter referred to as “URF amplifier”), 9 is an AGC driving transistor, 15 is
Are transistors for anode potential setting and current amplification,
19, 21 and 30 are coupling capacitors, 5, 25 are high-pass capacitors, 3, 10 to 14, 16 to 18, 23
And 29 are resistors, 4, 8, 24 and 28 are choke coils, 6, 7, 26 and 27 are pin diodes, 2
00 is an automatic gain control unit, 30 is an automatic gain control voltage generation unit, 40 is an anode potential setting power supply, and 40 and 50 are RF
It is a signal amplifier.

The operation of the thus configured automatic gain control device will be described below. The VHF frequency band high frequency signal input from the A terminal is input to the automatic gain control unit 200 via the coupling capacitor 1. AGC
The driving transistor 9 is for power amplification, and is turned on by inputting an AGC voltage from the C terminal to the base. Thus, by conducting the pin diode 6 through the choke coil 8, a current flows to the ground through the choke coil 4 and the resistor 3. AG at C terminal
The C voltage is about 7 [V], and the cathode of the pin diode 6 has a voltage lower by two diodes.

The anode of the pin diode 7 has
The voltage from the anode potential setting / current amplifying transistor 15 is applied.
Is turned off, and the bias of the anode potential setting / current amplifying transistor 15 is set so that the pin diode 7 starts conducting gradually when the AGC voltage of the C terminal starts to decrease due to gain attenuation. The signal thus gain-controlled passes through the coupling capacitor 19 and
Input to the amplifier 20.

On the other hand, the UHF frequency band high frequency signal input from the terminal B is input to the automatic gain control section 200 via the coupling capacitor 21. The AGC driving transistor 9 is for power amplification, and has a resistor 13
Is turned on by inputting the AGC voltage via the.
Thus, by conducting the pin diode 26 through the choke coil 28, a current flows to the ground through the choke coil 24 and the resistor 23.

The anode of the pin diode 27 is connected to an anode potential setting / current amplifying transistor 15.
Is applied, the pin diode 27 is turned off at the maximum gain, and the AG of the C terminal is
When the C voltage starts to decrease, the bias of the anode potential setting and current amplifying transistor 15 is set so that the pin diode 27 starts to conduct gradually. The signal thus gain-controlled passes through the coupling capacitor 30 and UR
The signal is input to the F amplifier 31.

Note that the pin diode 7 is set to 1 when turned on.
It is necessary to pass a current of 0 [mA] or more, and a choke coil 8 is required to stop a high-frequency signal, and a resistor cannot be used. Pin diode 2
7 requires a current of 15 [mA] or more to flow when turned on, and requires a choke coil 28 to stop high-frequency signals, and cannot be replaced by a resistor.

The AGC voltage at the C terminal is about 7
At [V], the cathode of the pin diode 26 has a voltage lower by two diodes.

[0010]

However, in the conventional automatic gain control device configured as described above, even when one of the VHF frequency band high frequency signal and the UHF frequency band high frequency signal is received, the VHF / UHF automatic gain The respective control pin diodes 6, 7, 26 and 27 are operating simultaneously. As a result, there is a problem that power is increased and NF is deteriorated due to generation of heat.

An object of the present invention is to provide an automatic gain control device which suppresses the deterioration of NF by reducing power and reducing heat generation in view of the above problems.

[0012]

According to an automatic gain control device of the present invention, a cathode is connected to one end of a first coupling capacitor to which a VHF frequency band high-frequency signal is input, and a first choke coil is connected to an anode. A first pin diode having an automatic gain control voltage applied thereto, a second pin diode having a cathode connected to the other end of the first coupling capacitor, and an anode potential setting power supply connected to the anode, A second choke coil having one end connected to the other end of the capacitor, a first resistor having one end connected to the other end of the second choke coil,
A first transistor having a collector connected to the other end of the first resistor, an emitter grounded, and a first switching voltage applied to a base; a first pin diode and a first transistor;
A first RF signal amplifier connected to the connection point of the choke coil, a cathode is connected to the other end of the second coupling capacitor to which a UHF frequency band high-frequency signal is input at one end, and a third choke coil is connected to the anode. A third pin diode to which an automatic gain control voltage is applied via a second coupling capacitor, a fourth pin diode having a cathode connected to the other end of the second coupling capacitor and an anode potential setting power supply connected to the anode, and a second coupling. A fourth choke coil having one end connected to the other end of the capacitor, a second resistor having one end connected to the other end of the fourth choke coil,
A second transistor having a collector connected to the other end of the second resistor, the emitter grounded, and a second switching voltage applied to the base; a third pin diode and a third transistor.
And a second RF signal amplifier connected to the connection point of the choke coil.

[0013]

According to the structure of the present invention, at the time of selecting a signal in the VHF frequency band, the switching voltage of the VHF system and the UHF system is used.
By turning on the first transistor and turning off the second transistor, the first and second pin diodes are turned on and the third and fourth pin diodes are turned off. When a signal in the UHF frequency band is selected, the third transistor and the fourth pin diode are turned on by turning on the second transistor and turning off the first transistor in accordance with the VHF / UHF switching voltage. Then, the first and second pin diodes are turned off.

Therefore, when one of the VHF frequency band high frequency signal and the UHF frequency band high frequency signal is received,
The pin diode on the non-receiving side is in a non-operating state, and it becomes unnecessary to perform automatic gain control.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an automatic gain control device according to one embodiment of the present invention. In FIG. 1, reference numerals 2 and 22 denote switching transistors, and those having the same functions as those in FIG.

As shown in FIG. 1, the automatic gain control device comprises:
It has an automatic gain control unit 100, a first RF signal amplifying unit 50, and a second RF signal amplifying unit 60.
The UHF frequency band high frequency signal b is input from the frequency band high frequency signal a and the B terminal. The automatic gain control unit 100
A pin diode 6 having a cathode connected to the other end of the coupling capacitor 1 to which the VHF frequency band high-frequency signal a is input at one end and an automatic gain control voltage applied to the anode via a choke coil 8, and a cathode connected to the other end of the coupling capacitor And a pin diode 7 having an anode connected to an anode potential setting power supply 40, a choke coil 4 having one end connected to the other end of the coupling capacitor 1, and a resistor 3 having one end connected to the other end of the choke coil 4. The collector is connected to the other end of the resistor 3, the emitter is grounded, and the first is connected to the base.
, A switching transistor 2 for applying a VHF / UHF switching voltage, a first RF signal amplifier 50 connected to a connection point between a pin diode 6 and a choke coil 8, and a UHF frequency band high frequency at one end. A pin diode 26 having a cathode connected to the other end of the coupling capacitor 21 to which the signal b is input and an automatic gain control voltage applied to the anode through a choke coil 28, and a cathode connected to the other end of the coupling capacitor 21 and connected to the anode Pin diode 27 connected to anode potential setting power supply 40
A choke coil 24 having one end connected to the other end of the coupling capacitor 21, a resistor 23 having one end connected to the other end of the choke coil 24, a collector connected to the other end of the resistor 23, and an emitter grounded. A switching transistor for applying a second switching voltage serving as a VHF / UHF switching voltage to the base;
And the second R connected to the connection point of the choke coil 28.
And an F signal amplifying unit 60.

The operation of the thus configured automatic gain control device will be described. A description will be given of a time of selecting a signal in the VHF frequency band. The VHF frequency band high frequency signal a input from the A terminal is supplied to the automatic gain control unit 1 via the coupling capacitor 1.
00 is input. The AGC driving transistor 9 is for power amplification, and is turned on when an AGC voltage is input from the C terminal via the resistor 13. At this time, the switching transistor 2 is turned on by applying a VHF / UHF switching voltage 5 [V] to the base of the switching transistor 2. Thereby, the choke coil 8
The pin diode 6 conducts through the choke coil 4
Then, a current flows through the resistor 3 and the ground through the emitter of the switching transistor 2.

The anode of the pin diode 7 has
The voltage from the anode potential setting and current amplifying transistor 15 is applied, the pin diode 7 is turned off at the maximum gain, and the pin diode 7 starts to conduct gradually when the AGC voltage of the C terminal starts to decrease due to gain attenuation. The bias of the anode potential setting / current amplifying transistor 15 is thus set. The signal whose gain is controlled in this manner is input to the VRF amplifier 20 through the coupling capacitor 19.

On the other hand, the UHF frequency band high frequency signal b input from the B terminal is input to the automatic gain control unit 100 via the coupling capacitor 21. At this time, the switching transistor 22 is turned off by applying the VHF / UHF switching voltage 0 [V] to the base of the switching transistor 22. The AGC driving transistor 9 is for power amplification, and is connected to the A terminal via the resistor 13 from the C terminal.
It is turned on by inputting the GC voltage. As a result, the voltage of the resistor 10 is applied to the anode of the pin diode 26 via the choke coil 28, but the cathode of the pin diode 26 is open, so that the pin diode 26 does not conduct.

The anode of the pin diode 27 is provided with an anode potential setting and current amplification transistor 15.
However, since the cathode of the pin diode 27 is in an open state, it does not conduct. As described above, at the time of selecting a signal in the VHF frequency band, the switching transistor 2 is turned on by applying the VHF / UHF switching voltage 5 [V] to the base of the switching transistor 2, and the switching transistor 22 is turned on. The switching transistor 22 is turned off by applying a VHF / UHF switching voltage of 0 [V] to the base. As a result, the pin diodes 6 and 7 become conductive, and the pin diodes 26 and 27 become non-conductive.

When selecting a signal in the UHF frequency band,
The switching transistor 22 has a VHF base at its base.
The switching transistor 22 is turned on by applying the UHF system switching voltage 5 [V], and the switching transistor 2 is turned off by applying the VHF system / UHF system switching voltage 0 [V] to the base of the switching transistor 2. Let it. As a result, the pin diodes 6 and 7 are turned off, and the pin diodes 26 and 27 are turned on.

The AGC voltage at the C terminal is about 7
At [V], the cathode of the pin diode 6 has a voltage lower by two diodes. In addition, the pin diode 7 needs to flow a current of 15 mA or more when it is turned on, and the choke coil 8 is required to stop the high frequency signal.

The AGC voltage at the C terminal is about 7
At [V], the voltage of the cathode of the diode 26 becomes lower by two diodes. As described above, according to the embodiment, when selecting a signal in the VHF frequency band, the switching transistor 2 is turned ON by the VHF / UHF switching voltage,
By turning off the switching transistor 22, the pin diodes 6 and 7 are turned on and the pin diodes 26 and 27 are turned off.

When selecting a signal in the UHF frequency band,
The switching transistor 22 is turned on and the switching transistor 2 is turned off by the VHF-system / UHF-system switching voltage.
6, 27 are made conductive, and the pin diodes 6, 7 are made non-conductive. Therefore, when one of the VHF frequency band high frequency signal a and the UHF frequency band high frequency signal b is received, the pin diode on the non-receiving side is in a non-operating state, and the automatic gain control becomes unnecessary.

As a result, it is possible to obtain an automatic gain control device in which the power is reduced and the generation of heat is reduced, thereby suppressing the deterioration of the NF.

[0026]

According to the automatic gain control device of the present invention,
When selecting a signal in the VHF frequency band, the first transistor is turned on and the second transistor is turned off by the VHF / UHF switching voltage, so that the first and second pin diodes are turned on. Third and fourth
Can be made non-conductive. Also,
When selecting a signal in the UHF frequency band, the second transistor is turned on and the first transistor is turned off by the VHF-system / UHF-system switching voltage, thereby turning on the third and fourth pin diodes. First and second
Can be made non-conductive.

Therefore, when receiving one of the VHF frequency band high frequency signal and the UHF frequency band high frequency signal,
The pin diode on the non-receiving side is in a non-operating state, and it becomes unnecessary to perform automatic gain control. As a result, it is possible to realize an automatic gain control device that suppresses NF degradation by reducing power and heat generation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an automatic gain control device according to one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional automatic gain control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Coupling capacitor (1st coupling capacity) 2 Switching transistor (1st transistor) 3 Resistance (1st resistance) 4 Choke coil (2nd choke coil) 6 pin diode (1st pin diode) 7 pin Diode (second pin diode) 8 choke coil (first choke coil) 21 coupling capacitor (second coupling capacitance) 22 switching transistor (second transistor) 23 resistor (second resistor) 24 choke coil ( Fourth choke coil) 26-pin diode (third pin diode) 27-pin diode (fourth pin diode) 28 choke coil (third choke coil) 40 power supply for anode potential setting 50 first RF signal amplifier 60 second RF signal amplifier 100 automatic gain controller a VH F frequency band high frequency signal b UHF frequency band high frequency signal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Showa 48-67638 (JP, U) Japanese Utility Model Showa 52-156413 (JP, U) Japanese Utility Model Showa 2-49216 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) H04N 5/52-5/56 H03H 7/25

Claims (1)

(57) [Claims] 1. A first pin having a cathode connected to the other end of a first coupling capacitor to which a VHF frequency band high-frequency signal is input at one end, and an automatic gain control voltage applied to an anode via a first choke coil. A diode, a second pin diode having a cathode connected to the other end of the first coupling capacitor and an anode potential setting power supply connected to the anode, and a second pin diode having one end connected to the other end of the first coupling capacitance. And a first choke coil having one end connected to the other end of the second choke coil.
A first transistor having a collector connected to the other end of the first resistor, having an emitter grounded, and applying a first switching voltage to a base; the first pin diode and the first choke; A first RF signal amplifier connected to a connection point of the coil; and a second RF signal inputting the UHF frequency band at one end.
A third pin diode in which a cathode is connected to the other end of the coupling capacitor and the automatic gain control voltage is applied to the anode through a third choke coil; and a cathode is connected to the other end of the second coupling capacitor. A fourth pin diode having the anode connected to the anode potential setting power supply, a fourth choke coil having one end connected to the other end of the second coupling capacitor, and a first end connected to the other end of the fourth choke coil. The second connected
A second transistor for connecting a collector to the other end of the second resistor, grounding the emitter, and applying a second switching voltage to the base; the third pin diode and the third choke An automatic gain control device including a second RF signal amplifier connected to a connection point of the coil.