JPH0119289B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable gain control circuit that can amplify or attenuate an input signal for a predetermined period of time using a control signal.

Conventionally, as a circuit for amplifying or attenuating an analog signal for a predetermined period of time using a control signal, a configuration has been adopted in which the analog signal is first extracted for a predetermined period using a timing signal and then amplified by an amplifier.

The present invention is a novel system in which the variable gain amplifier circuit is configured with a double differential amplifier circuit, and the values of the resistors that determine the gain are set equally, thereby eliminating fluctuations in gain caused by variations in the resistance values. A variable gain amplifier circuit is provided.

The present invention will be explained below with reference to the drawings. Figure 1 is a block diagram of the variable gain amplifier circuit of the present invention, and Figure 2 is a block diagram of the variable gain amplifier circuit of the present invention.
The figure shows an example of the same circuit, and Figure 3 A, B, and C are the second embodiment.
Waveform diagrams of each part in the figure, Figure 4 is the equivalent circuit of Figure 2 when the level of the control signal is low, Figure 5 is the equivalent circuit of Figure 2 when the control signal is high, Figure 6 is the polarity of the control signal. 7A, 7B, and 7 are waveform diagrams of each part in FIG. 6, FIG. 8 is an embodiment of the circuit of the present invention equipped with a function stop signal terminal, and FIG. A to D show waveforms of various parts in FIG.

In the drawing, 1 and 2 are first and second bias sources, respectively, 3 and 4 are first and second differential pairs, respectively, and 5,
6 are first and second loads, 7 and 8 are first and second switching circuits, 9 is a waveform shaping circuit, 10 is a constant current source, 11 is an input terminal, 12 is a control terminal, 1
3 indicates an output terminal.

FIG. 2 shows an example of an implementation circuit of FIG. 1, in which the bias sources 1 and 2 are transistors 14 and 15, and the differential pairs 3 and 4 are transistors 16, 17 and 18, 19, respectively. Switching circuit 7, 8
In this example, the waveform shaping circuit 9 is configured with transistors 22 and 23, and the impedance conversion stage is configured with a transistor 24.

3A shows the input signal vi applied to the input terminal 11, b shows the pulsed control signal vc applied to the control terminal 12, and c shows the output signal vo obtained from the output terminal 13.

Next, a description will be given of when the control signal is at a low level and when the control signal is at a high level.

() When the control signal is at a low level FIG. 4 shows an equivalent circuit diagram of _FIG . It is biased to a predetermined potential by the voltage dividing circuit 25 and turns on, and at this time the resistor 26
If the voltage drop at
1 is off.

The current I _O of the constant current source transistor 10 flows entirely to the transistor 20, and no current flows to the transistor 21 and the transistors 18 and 19. Therefore, in this case, a differential pair consisting only of the transistors 16 and 17 is formed, and It will operate as a dynamic amplifier, and the output signal voltage vo ₁ at that time will be determined by the values R ₈ , R ₉ of the resistors 5 and 6 and the values R ₁₀ , of the emitter resistance.
If R ₁₁ , R ₁₂ , and R ₁₃ are expressed as follows, R ₈ = R ₉ = R _C R ₁₀ = R ₁₁ = R ₁₂ = R ₁₃ = R _E , then vo ₁ = R _C /2R _E vi...(1 ) can be approximated.

However, R _E ≫re ₁ and h _FB ≒1.

(re ₁ is the emitter resistance of transistor 17 when I _E = I _O /2, and h _FB is the common base current amplification factor.) () When the control signal is at a high level Figure 5 is the equivalent of Figure 2. A circuit diagram is shown, and in Fig. 2, the peak value of the control signal vc is
2, the transistor 23 of the waveform shaping circuit ₉ is turned on, the transistor 22 is turned off, and the collector voltage of the transistor 23 is the same as that of the transistor 1.
4 and the emitter voltage of transistor 22
Since there is no voltage drop across the resistor 26, the collector voltage of is approximately equal to the emitter voltage of the transistor 14.

Therefore, a voltage approximately equal to the emitter voltage of transistor 14 is applied as a base bias to transistors 20 and 21 of the next stage switching circuit via resistors 27 and 26, respectively, so that these transistors 20 and 21 have an I _O / As shown in FIG. 5, the four transistors 16, 17 and 18, 19 operate as a differential amplifier, and the output signal voltage vo ₂ at this time is vo ₂ =R. _C / R _E vi ...... can be approximated as (2).

However, R _E ≫re ₂ , h _FB ≒1.

(re ₂ is the emitter resistance of transistor 17 when I _E = I _O /2, and h _FB is the common base current amplification factor.) Therefore, from equations (1) and (2), the control signal applied to terminal 12 is Accordingly, it becomes possible to change the output signal voltage in two stages.

Further, the DC level appearing at the output terminal 13 at this time is always V _CC -R _C I _O /2, which is constant.

Next, the voltage gain can be set arbitrarily by the emitter resistance value R _E and the collector resistance value R _C , but in particular, the four emitter resistance values R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃
If the values of the two collector resistors R ₈ and R ₉ are set equal, the gain ratio is V ₀₂ /V ₀₁ = 2...(3) V ₀₁ /V ₀₂ = 1/2... (4) becomes. Here, as is clear from equations (3) and (4), since the values of the resistances that determine the gain are equal,
Even if the resistance value varies during integration into an integrated circuit, it will all be canceled out, making it possible to accurately set the gain to 2x or 1/2.

Next, FIG. 6 shows an example of obtaining an output signal that is inverted from the control signal.The signal applied to the switching circuits 7 and 8 in FIG. 1 is inverted on the input side, and the waveforms of each signal in FIG. As shown in FIGS. 7A to 7C, the output signal voltage vo is in an inverted state with respect to the control signal VC.

In addition to the function of varying the gain, Fig. 8 shows a terminal 28 provided with an input signal vi (Fig. 9
(Figure 9B), when the function stop signal v _ST (Figure 9C) is applied to each terminal 11, 12, 28, output terminal 1
3, a signal in a stopped state is obtained as the output signal vo during the period To. This is because the switching transistors 29, 30, and 31 are turned on during the period To, the ends of the resistor 32 of the voltage divider circuit 25 are shorted, and the transistor 22 is turned off, so that the control signal
The amplification effect will stop regardless of vc.

As described above, according to the present invention, the effect of variable gain can be obtained with an extremely simple configuration, and further,
As in the above configuration, the differential pair transistors
Make the base bias the same and the load current
Since it is operated with an emitter current of I _O /2 and an emitter current of I _O /4, it is a double-balanced differential amplifier that is often used as a conventional DC type electronic volume.
Since it is possible to prevent the temperature dependence of the output voltage due to the difference in temperature characteristics at the operating point when the current division ratio of the differential pair transistor deviates from 1:1, it also provides the advantage of extremely good temperature characteristics. .

In addition, although the above embodiment was explained as an amplifier,
This operates under the assumption that R _C > R _E , and conversely R _E
> R _C , the voltage gain will be less than 1, and it can also be used as an attenuator (compressor). The present invention is most suitable for an electronic volume in an audio amplifier circuit when it is desired to amplify or compress only a burst signal in a color signal using a burst gate pulse in a color television receiver.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the variable gain amplifier circuit of the present invention, Fig. 2 is an embodiment of the same circuit, and Fig. 3 A, B,
C is a waveform diagram of each part of Fig. 2, Figs. 4 and 5 are equivalent circuit diagrams of Fig. 2, Figs. 6 and 8 are other embodiments of the same circuit, and Figs. 7 A, B, and C are 6 shows waveform diagrams of various parts in FIG. 6, and FIGS. 9A, 9B, C, and 2 show waveform diagrams of various parts in FIG. Explanation of main figure numbers, 1...first bias source, 2...second bias source, 3...first differential pair, 4...second differential pair, 5, 6...load, 7...first switching circuit,
8... Second switching circuit, 9... Waveform shaping circuit,
10...constant current source, 11...input terminal, 12...control terminal, 13...output terminal.

Claims (1)

[Claims] 1 a first transistor whose base is connected to the input terminal and whose collector is connected to the first load resistor; a second transistor whose base is connected to the bias source and whose collector is connected to the second load resistor; first and second resistors connected in series between the emitters of the first and second transistors; and a third resistor whose base is connected to the input terminal and whose collector is connected to the collector of the first transistor.
a fourth transistor whose base is connected to the bias source and whose collector is connected to the second load resistor; and third and fourth resistors connected in series between the emitters of the third and fourth transistors. and first and second switching transistors, each of which has a collector connected to a connection point between the first and second resistors and a connection point between the third and fourth resistors, and whose emitters are commonly connected. A constant current source connected to the common emitter of the second switching transistor turns on only the first switching transistor in response to a first level control signal, and turns on only the first switching transistor in response to a second level control signal. and a waveform shaping circuit that turns on a second switching transistor, and sets the values of the first and second load resistors to be equal, sets the resistance values of the first to fourth resistors to be equal, and sets the resistance values of the first to fourth resistors to be equal, and A variable gain amplifier circuit characterized in that an output signal is obtained from one end of a load resistor.