JP3120909B2 - Automatic gain control 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 automatic gain control circuit for a double super tuner used in CATV converters and television receivers.

[0002]

2. Description of the Related Art In recent years, an automatic gain control circuit of a double super tuner often uses a pin diode. Hereinafter, a conventional automatic gain control circuit of a double super tuner will be described. FIG. 2 is a circuit diagram showing a configuration of an automatic gain control circuit and an RF amplifier used in a conventional double super tuner.

In FIG. 2, reference numeral 64 denotes a signal input terminal;
Is the voltage V when receiving the VHF channel. _vTerminal with 6
6 is the voltage V when receiving the UHF channel._uTerminal
102 is a terminal to which AGC voltage is applied, 71 is an input for VHF
Filter, 72 is an input filter for UHF, and 75 and 76 are
Pin used for automatic gain control (AGC) circuit for VHF
Diodes, 83 and 84 are used for AGC circuit for UHF
Pin diodes, 114 and 115 are UHF, VHF
Pin diode used for common AGC circuit, 118
Is a mixer circuit, 119 is a local oscillation circuit, 73, 74, 7
8, 81, 88, 93, 104, 108, 112, 12
1,125 and 126 are capacitors, 67,70,7
9,82,85,86,90,91,92,96,9
8,99,100,105,107,110,113 and
And 117 are resistors, 77, 80, 87, 95, 101,
103, 111 and 116 are coils, 89 and 97 are coils
The transistors 68, 69, 106 and 109 are switches.
Diode, 94 and 120 are RF amplifiers, 150 is output
Force terminal, V_cIs the power supply voltage.

The operation of the conventional automatic gain control circuit configured as described above will be described. When a signal of the VHF channel is received by this circuit, a received signal 64a input from the signal input terminal 64 is turned on when the VHF channel is received, a switch diode 68, a VHF channel input filter 71, a pin diode 75, and an RF amplifier. 1
20, the signal passes through the switch diode 109 and the pin diode 114 which are turned on when receiving the VHF channel, and is input to the mixer circuit 118 (hereinafter, referred to as “signal path C”).

When a UHF channel signal is received, a reception signal 64a input from a signal input terminal 64 is received.
Is a switch diode 69 which is turned on when receiving a UHF channel, an input filter 72 for UHF, a pin diode 84, an RF amplifier 94, which is turned on when receiving a UHF channel.
Switch diode 106 and pin diode 1
14, and is input to the mixer circuit 118 (hereinafter, referred to as “signal path D”).

A portion surrounded by a symbol B controls the AGC voltage, and a portion surrounded by a symbol A is a constant voltage source.
The operating point of C is determined. The constant voltage source A applies a voltage to the anodes of the pin diodes 76 and 83 via the resistors 85 and 86. The AGC voltage applied to the terminal 102 changes the resistance component of the pin diode, changes the signal level, and the AGC operates (the pin diodes 75 and 84 are turned on, the pin diodes 76 and
83 is off (off)), and AGC is not operating (pin diodes 75 and 84 are off)
In both cases (the pin diodes 76 and 83 are ON), the pin diodes 76 and 83 make the impedance of the pin diodes 75, 76, 83 and 84 on the cathode side approximately constant.

[0007]

However, in the conventional automatic gain control circuit as described above, both the VHF pin diode 75 and the UHF pin diode 84 remain operating during reception of the VHF channel. The local oscillation signal from the local oscillation circuit 119 is V
In addition to the HF signal path C, the OFF switching diodes 69 and 106 have a very small capacitance, so that the local oscillation signal returning to the signal input terminal 64 through the UHF signal path D has a higher signal level. In addition, the same can be said for the local oscillation signal at the time of receiving the UHF channel because the local oscillation signal passes through the signal path C in addition to the signal path D. As a result, when jointly receiving signals from antennas, there is a problem in that the possibility of giving interference signals to other CATV converters and television receivers increases.

[0008] In view of the above problems, an object of the present invention is to provide
An object of the present invention is to provide an automatic gain control circuit that reduces the level of a local oscillation signal leaking from an input side (input terminal) and does not adversely affect other CATV converters or television receivers during joint reception.

[0009]

According to a first aspect of the present invention, there is provided an automatic gain control circuit having a VHF pin diode.
An automatic gain control unit for VHF for controlling the gain of the VHF channel signal by changing the voltage applied to the anode side of the pin diode for F; an RF amplifier for VHF for amplifying the output signal of the automatic gain control unit for VHF; A UHF automatic gain control unit having a pin diode for controlling the gain of a UHF channel signal by changing the voltage applied to the anode side of the UHF pin diode; and a UHF for amplifying an output signal of the UHF automatic gain control unit. VHF RF amplifier and UHF having a common pin diode
A common gain control unit for inputting an output signal of the RF amplifier for use and controlling the gain by changing the voltage applied to the anode side of the common pin diode.
The HF pin diode is turned off, and the VHF pin diode is turned off when receiving a UHF channel.

An automatic gain control circuit according to a second aspect of the present invention is the automatic gain control circuit according to the first aspect, wherein the cathode of the first pin diode is connected to the cathode of the VHF pin diode. Connected to the anode side of the first transistor via a first resistor,
Connecting the collector of the first transistor to a voltage source,
The cathode of the second pin diode is connected to the cathode of the pin diode for F, the emitter of the second transistor is connected to the anode side of the second pin diode via the second resistor, and the collector of the second transistor is connected. Is connected to the voltage source, the cathode of the first switch diode is connected to the emitter of the first transistor, the cathode of the second switch diode is connected to the emitter of the second transistor, and the first switch diode is connected. And an anode of the second switch diode is connected to a constant voltage source, the first transistor is turned on when receiving a UHF channel, and the second transistor is turned on when receiving a VHF channel. circuit.

[0011]

According to the structure of the present invention, the UHF pin diode used in the UHF automatic gain control unit is turned off when receiving a VHF channel, and the VHF pin used in the VHF automatic gain control unit when receiving a UHF channel. By turning off the diode, the level at which the local oscillation signal returning from the output side leaks to the input terminal can be reduced.

[0012]

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a circuit diagram showing a configuration of an automatic gain control circuit according to one embodiment of the present invention. In FIG. 1, 1 is a signal input terminal, and 2 is a voltage V _v when receiving a VHF channel.
, The terminal 7 receives the voltage V _u when receiving the UHF channel.
, A terminal to which the AGC voltage is applied, 8 an input filter for VHF, 9 an input filter for UHF, 1
Reference numerals 2 and 13 denote pin diodes used in an AGC circuit for VHF (automatic gain control unit for VHF), and reference numerals 14 and 15 denote UHF.
Diode used in the AGC circuit (automatic gain control unit for UHF), 32 is a VHF RF amplifier, and 37 is U
RF amplifiers for HF, 51 and 52 are pin diodes used in an AGC circuit (shared automatic gain control unit) shared by VHF and UHF, 54 is a mixer circuit, 55 is a local oscillator circuit, 10, 11, 28, 31, 40 , 44,46,4
8, 60, 63, 123 and 124 are capacitors,
3, 6, 16, 17, 21, 23, 24, 25, 27,
34, 35, 36, 42, 43, 49, 50, 56, 5
7, 59 and 62 are resistors, 29, 30, 38, 39,
47, 53, 58 and 61 are coils, 20, 22, 2
6 and 33 are transistors, 4, 5, 18, 19, 4
1 and 45 are switch diodes, 151 is an output terminal, and A is a constant voltage source. The pin diode for VHF according to claims 1 and 2 is a pin diode 12, a UHF
The pin diode for use is the pin diode 15, the common pin diode is the pin diode 52, the first pin diode is the pin diode 13, the first resistor is the resistor 16, the first transistor is the transistor 20, and the second pin diode is the pin diode. 14, the second resistor corresponds to the resistor 17, the second transistor corresponds to the transistor 26, the first switch diode corresponds to the switch diode 18, and the second switch diode corresponds to the switch diode 19.

The operation of the thus configured automatic gain control circuit will be described. When receiving the VHF channel, the received signal 1a input from the signal input terminal 1 is turned on when receiving the VHF channel. The switch diode 4, the VHF input filter 8, the pin diode 12, the VHF RF amplifier 32, and the switch that is turned on when receiving the VHF. The signal passes through the diode 41 (the switch diode 45 is OFF at this time) and the pin diode 52 and is input to the mixer circuit 54 (hereinafter, this signal path is referred to as “signal path E”). At this time, the transistor 26 is turned on and a voltage is applied to the emitter so that the anode voltage of the pin diode 14 is always higher than the anode voltage of the pin diode 15. As a result, the pin diode 14
N, the pin diode 15 is turned off.

Similarly, during reception of the UHF channel, the reception signal 1a input from the signal input terminal 1 includes the switch diode 5, UH
Input filter 9 for F, pin diode 15, R for UHF
F amplifier 37, switch diode 45 which is turned on when receiving UHF channel (at this time, switch diode 4
1 is OFF. ) And the pin diode 52 and input to the mixer circuit 54 (hereinafter, this signal path is referred to as “signal path F”). At this time, the transistor 20 is turned on so that the anode voltage of the pin diode 13 is always higher than the anode voltage of the pin diode 12.
Then, a voltage is applied to the emitter. As a result, the pin diode 13 turns on and the pin diode 12 turns off.

Here, when the transistors 20 and 26 are turned on, the pin diode 51 shared by VHF and UHF is used.
Is not always higher than the voltage applied to the pin diode 52.
19 are placed between the emitter of transistor 22 and the emitters of transistors 20 and 26, respectively. Thus, according to this embodiment, when receiving a VHF channel,
By turning on the transistor 26, the pin diode 14 is turned on and the pin diode 15 is turned off. As a result, the automatic gain control for the UHF signal becomes inactive. Therefore, although the switch diodes 5 and 45 in the OFF state have a very small capacitance, the signal path F
The local oscillation signal leaking to the signal input terminal 1 through the signal can be reduced.

Similarly, when the UHF channel is received, the pin diode 13 is turned on and the pin diode 12 is turned off by turning on the transistor 20. As a result, the automatic gain control for the VHF signal becomes inactive. Therefore, although the switch diodes 4 and 41 in the OFF state have a small capacitance, the local oscillation signal leaking to the signal input terminal 1 through the signal path E can be reduced.

[0017] Therefore, even when signals from the antenna are received jointly, it is possible to suppress interference signals from being given to other CATV converters and television receivers. Further, the voltage source used for switching between the VHF input filter 8 and the UHF input filter 9 is used to turn on and off the above-mentioned VHF and UHF pin diodes 13 and 14, so that the VHF signal transmitted from the microcomputer terminal is used. , UHF switching voltage sources can be eliminated.

[0018]

As described above, according to the automatic gain control circuit of the present invention, the UHF pin diode used in the UHF automatic gain control section is turned off when receiving the VHF channel, and the VHF automatic gain is used when receiving the UHF channel. By turning off the VHF pin diode used in the control unit, the level at which the local oscillation signal returned from the output side leaks to the input terminal can be reduced. for that reason,
Even when signals from the antennas are jointly received, it is possible to suppress giving an interference signal to other CATV converters and the television receiver.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a configuration of a conventional automatic gain control circuit of a double super tuner.

[Explanation of symbols]

 Reference Signs List 1 signal input terminal 12 (for VHF) pin diode 13 (first) pin diode 14 (second) pin diode 15 (for UHF) pin diode 16 (first) resistor 17 (second) resistor 18 ( (First) switch diode 19 (second) switch diode 20 (first) transistor 26 (second) transistor 32 RF amplifier for VHF 37 RF amplifier for UHF 52 (shared) pin diode A constant voltage source

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/52-5/56 H03H 7/25

Claims (2)

(57) [Claims] 1. A semiconductor device having a pin diode for VHF.
An automatic gain control unit for VHF for controlling the gain of the VHF channel signal by changing the voltage applied to the anode side of the pin diode for HF; and a VH for amplifying the output signal of the automatic gain control unit for VHF.
An RF amplifier for F, a pin diode for UHF, an automatic gain control unit for UHF for controlling the gain of the UHF channel signal by changing the voltage applied to the anode side of the pin diode for UHF, and an automatic gain for UHF. UH to amplify the output signal of the control unit
A common gain having an RF amplifier for F and a common pin diode, receiving the output signals of the RF amplifier for VHF and the RF amplifier for UHF, and controlling the gain by changing the voltage applied to the anode side of the common pin diode An automatic gain control circuit comprising a control unit, wherein the UHF pin diode is turned off when receiving a VHF channel, and the VHF pin diode is turned off when receiving a UHF channel. 2. The automatic gain control circuit according to claim 1, wherein a cathode of the first pin diode is connected to a cathode of the VHF pin diode, and a first resistor is connected to an anode of the first pin diode. The collector of the first transistor is connected to a voltage source, the cathode of a UHF pin diode is connected to the cathode of a second pin diode, and the second pin The anode side of the diode is connected to the emitter of a second transistor via a second resistor, the collector of the second transistor is connected to a voltage source, and the emitter of the first transistor is connected to the emitter of a first switch diode. A cathode side is connected, and a cathode side of a second switch diode is connected to an emitter of the second transistor, and the first switch is connected to an emitter of the second switch diode. And the anodes of the first diode and the second switch diode are connected to a constant voltage source, the first transistor is turned on when receiving a UHF channel, and the second transistor is turned on when receiving a VHF channel. Automatic gain control circuit.