JPS6113405B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is for changing the gain of an amplifier in response to changes in input signal voltage in automatic gain control (hereinafter referred to as AGC) circuits used in television receivers and the like. This invention relates to a device that generates an AGC voltage, and in particular provides an AGC voltage generator that is stable against fluctuations in power supply voltage, temperature changes, etc.

Generally, when the input signal to an amplifier exceeds the operating range of the amplifier, the output signal becomes saturated and waveform distortion occurs.

In order to prevent such excessive input and saturation conditions, AGC circuits are widely used to control the gain of the amplifier according to the input signal level so that the output is always constant.

As shown in Figure 1, the AGC circuit of a television receiver receives an input high-frequency signal e _i
is amplified and detected by the tuner 1, the video intermediate frequency amplification section 2, and the video detection/video amplification section 3 so that the detected output signal level e _p always has a constant amplitude.
That is, when the detected output e _p deviates from a predetermined amplitude, the AGC voltage detection circuit 4 and the AGC amplifier 5 generate control voltages V ₁ and V ₂ according to the magnitude of e _p , and this voltage is used to control the tuner 1 and the video signal. It controls the gain of the intermediate frequency amplification section 2 and acts so that e _p is always constant.

Recently, as television receivers and the like have become smaller and lighter, their use outdoors has increased, and there is a desire to realize circuits that operate stably even under battery operation and harsh operating environments. However, in television receivers that are powered by batteries, it is necessary to configure the circuit so that the current consumption is as low as possible and the operating voltage is as low as possible. It is also necessary to lower the operating lower limit voltage as much as possible so that normal image reception can be achieved even if the voltage decreases. In addition, from the aspect of circuit miniaturization, it is necessary to reduce the use of capacitors as much as possible and create a circuit system suitable for IC implementation.

The present invention satisfies these requirements, and allows AGC operation to always be stable against voltage fluctuations due to battery consumption and temperature changes, as well as an AGC voltage that is particularly suitable for integrating circuits into ICs. A generator is provided. Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 2 is a wiring diagram showing one embodiment of the present invention. In the figure, 6 is a first voltage detection amplification section;
7 is a second voltage detection amplification section that generates the AGC voltage V ₁ for the tuner, and 8 is a video intermediate frequency amplification section.
A voltage amplifier circuit 9 generates the AGC voltage _V2 , and 9 is a reference voltage source that always generates a stable output voltage against fluctuations in power supply voltage, temperature changes, and the like.

The base of the transistor 10 is normally biased with a voltage _E1 , and when the input signal e _p (=detected output in Figure 1) is superimposed, its emitter voltage V _e becomes V _e = E ₁ + e _p . This emitter voltage V _e
is divided by resistors 24 and 26, and the midpoint potential V _B2 is inputted to the base of transistor 11, and similarly voltage V _B3 is applied to the base of transistor 13 by resistors 28 and 29. At V _B2 〓V _B2 , the transistor 11 becomes conductive. That is, the resistor 24,
The magnitude of the signal input e _p that can make the transistor 11 conductive is determined by the division ratio of 26 (=base voltage V _B2 of the transistor 11).

By setting the gains of the transistors 11 and 14 high, when the amplitude of the input signal e _p exceeds a predetermined level, the collector voltage V _c of the transistor 14 is suddenly increased, as shown in characteristic A in FIG. can be raised to Note that since the input signal e _p is usually an alternating current component,
It is important to compensate for high-frequency components with the capacitor 25 and to connect a capacitor 32 in parallel with the collector resistor 31 of the transistor 14 to convert the signal transmitted to the next stage into a DC signal.

Thereby, when the amplitude of the input signal e _p exceeds a predetermined level, a DC output signal V _c corresponding to the magnitude of the input signal e _p is obtained at the collector of the transistor 14.

Next, this DC output signal V _c is inputted via the resistor 33 to the transistor 15 that constitutes the emitter follower transistor circuit, and the emitter output is input to one base of the differential amplifier constituted by the transistors 16 and 17. input. A predetermined bias voltage is applied to the other base from a bias circuit composed of resistors 36, 37, 38 and a transistor 19. That is, the voltage between the base and emitter of the transistor is V _BE , and the power supply voltage of the power supply line 45 is V _cc
Then, the base voltage V _B4 of the transistor 16 is V _B4 = V _c + V _BE , and the base voltage V _B5 of the transistor 17 is V _B5 = V _cc [resistance 38/(resistance 3
7+resistor 38)] +V _BE , and the transistor 16 becomes conductive at V _B4 〓V _B5 . Here, by setting the gains of transistors 16 and 20 sufficiently high and biasing the emitter of transistor 21 to a constant level with resistors 41 and 42, the emitter voltage of transistor 21 is
As shown in characteristic A in Fig. 4, V ₁ has a voltage value determined by resistors 41 and 42 in the region of V _B4 < V _B5 , and V
It rises at the V _c level (V _B4 = V _c + V _BE ) where _B4 = V _B5 .

Note that the transistors 16, 17, 19, 20,
The second voltage detection and amplification section 7 whose main components are transistors 10, 11, 13, and 14 has almost the same circuit configuration as the first voltage detection and amplification section 6 whose main components are transistors 10, 11, 13, and 14. The voltage amplification section having a gain is compensated for temperature changes by using a diode 12 for the transistor 14, a diode 18 for the transistor 20, and a transistor 15 for the transistor 19. Operates stably against temperature changes.

Further, the voltage amplification circuit 8 including the transistors 22 and 23 is driven by a common input voltage (=emitter output voltage of the transistor 15) with the second voltage detection amplification section 7, and its output voltage V ₂ is as shown in FIG. As shown in characteristic B of , it decreases as V _c increases. Here, transistor 22 is also transistor 1
5, the embodiment of the present invention shown in FIG. 2 operates stably with respect to temperature changes. In particular, if the circuit is configured as shown in FIG. 2, transistors 15 and 19 and transistor 2
Since it is necessary to stabilize only the power source 2, there is an advantage that the reference voltage source 9 also requires low power.

Next, the operation and effect of the embodiment of the present invention shown in FIG. 2 will be explained in detail by giving specific numerical values. In the embodiment shown in FIG. 2, resistor 24 = 18KΩ, resistor 26 = 220KΩ, resistor 27 = 1KΩ, resistor 28 = 4K
Ω, resistance 29 = 6.5KΩ, resistance 30 = 100Ω, resistance 31 = 10KΩ, resistance 33 = 1KΩ, resistance 34 = 3K
Ω (=resistance 36), resistance 35=500Ω, resistance 37=
33KΩ, resistance 38=3KΩ, resistance 39=100Ω, resistance 40=10KΩ, resistance 41=16KΩ, resistance 42=
Set to 10KΩ, resistor 43 = 3KΩ (=resistance 44), capacitor 25 = 470PF, capacitor 32 = 3.3μF, power supply voltage V _cc = 6.0V, reference power supply =
In the case of 1.8 volts, the first voltage detection amplifier section 6
As shown in the characteristics of FIG. 3, rises at e _p =800 mV _pp , and the voltage gain is approximately 40 dB. Further, the output of the second voltage detection amplification section 7, that is, the voltage V ₁ of the output terminal 46 is 2.3 at V _c =0.38 volts.
When V _c >0.38 volts, the voltage rises as shown in characteristic A in FIG. 3, and the voltage gain is approximately 40 dB. In addition, the voltage amplification circuit 8
The voltage V ₂ at the output terminal 47 was approximately 1.0 volts when V _c =0 volts, and approximately 0.7 volts when V _c =0.38 volts.

When an AGC voltage generator having such characteristics is used as the AGC voltage detection circuit 4 and AGC amplifier section 5 of a television receiver shown in Fig. 1, the input/output characteristics are shown in Fig. 5. An extremely stable output e _p was obtained with respect to changes in e _i .
Moreover, the embodiment of the present invention shown in FIG.
It has been confirmed that operation is extremely stable even with temperature changes of +60℃, and in addition, power supply voltage fluctuations of +20%
(V _cc = 7.2 volts) and -20% (V _cc = 4.8 volts), it was confirmed that it operated stably.

As described above, the present invention provides a circuit system that includes the first voltage detection amplification section 6, the second voltage detection amplification section 7, and the voltage amplification circuit 8, and performs temperature compensation for each component. By driving the transistors 15, 19, and 22 with a reference voltage source, an AGC voltage generator that operates stably against fluctuations in power supply voltage, temperature changes, etc. was realized. In addition, all circuits can be directly connected, making it effective for IC implementation. In the above-described embodiments of the present invention, an example has been described in which the present invention is applied to a television receiver, but it goes without saying that the present invention can be similarly effectively implemented in other receivers, amplifiers, etc.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the AGC system of a television receiver, Fig. 2 is a wiring diagram showing an embodiment of the present invention, Figs. 3 and 4 are diagrams showing characteristic examples of the embodiment, FIG. 5 is an input/output characteristic diagram when the second embodiment is adopted in the AGC system of FIG. 1. 6... First voltage detection amplification section, 7... Second voltage detection amplification section, 8... Voltage amplification circuit, 9... Reference voltage source, 10, 11, 13, 14, 15, 16,
17, 19, 20, 21, 22, 23...transistor, 24, 26, 28, 29, 31, 33,
37, 38, 41, 42...Resistor, 32...Capacitor.

Claims (1)

[Claims] 1. A first voltage detection amplifier that operates when the peak value of the input signal voltage exceeds a predetermined level, and an emitter follower transistor circuit whose base receives the output voltage of the first voltage detection amplifier. , a second voltage detection amplifier section that operates when the emitter voltage of the emitter follower transistor circuit exceeds a predetermined level and generates an output voltage corresponding to the emitter voltage; A voltage amplification circuit driven by a voltage is provided, and when the peak value of the input signal voltage to the first voltage detection amplification section increases, the output voltage of the second voltage detection amplification section increases, and the voltage amplification circuit is configured such that the output voltage of
The first voltage detection amplification section includes a first emitter follower transistor to which the input signal voltage is inputted to the base, and divides the emitter voltage of the first emitter follower transistor by a resistor, and divides the emitter voltage of the first emitter follower transistor at the dividing point. a second transistor having a base coupled to the transistor and a series load of a resistor and a diode to the collector;
A differential amplifier is formed with the second transistor.
a third transistor whose base bias voltage is set so as to make the second transistor conductive when the base voltage of the transistor reaches a predetermined level; and a common-emitter amplifier whose base is connected to the collector of the second transistor. and a capacitor connected in parallel with the collector load resistance of the fourth transistor, and the second voltage detection amplification section includes A fifth transistor having an output voltage inputted to its base and having a series load of a resistor and a diode on its collector forms a differential amplifier, and the base voltage of the fifth transistor reaches a predetermined level. a sixth transistor whose base bias voltage is set so as to make the fifth transistor conductive when the voltage is reached; a seventh emitter follower transistor which applies a predetermined bias voltage to the base of the sixth transistor; an eighth transistor forming a common emitter amplifier whose base is connected to the collector of the fifth transistor; and a ninth emitter follower transistor whose base is connected to the collector of the eighth transistor. An automatic gain control voltage generator characterized by: