JPH0453065Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention is a device for, for example, audio equipment, television receivers, etc., in which when noise enters the input signal, the gate is turned off in order to remove the noise. The present invention relates to a gate circuit provided at a subsequent stage of a detection circuit or the like configured as described above.

[Prior Art] Fig. 1 shows a conventional gate circuit, where 1 is an input terminal, 2 is an output terminal, 3, 4, and 5 are emitter follower transistors (amplification circuits), 6 is a switching transistor, 7 is a level holding capacitor, and the input signal applied to the input terminal 1 is applied to the switching transistor 6 via the emitter follower transistor 3. When there is no noise, the input signal from transistor 6 is outputted to output terminal 2 via emitter follower transistors 4 and 5.

In the above, when noise (pulse noise) enters the input terminal 1, the switching transistor 6, which passes the input signal to the output terminal side via the transistor 3 when there is no noise,
By applying a negative pulse signal as shown in the figure, the operation of this transistor 6 is turned off so that the noise input is not outputted to the output terminal side.

[Problem to be solved by the invention] However, in such a conventional gate circuit, the DC potential level changes at the stage where the input potential moves from transistors 3, 6, 4, and 5, and the value at output terminal 2 changes from the input There is a drawback that the value deviates considerably from that of terminal 1. This is because a low-pass filter is formed by each of the transistors, resistors, and capacitors, which causes frequency fluctuations in each input signal, which causes fluctuations in the level held. Furthermore, when the switching transistor 6 is on, the _rSC time constant circuit formed by the internal resistance _rS between the emitter and collector of the switching transistor 6 and the capacitance C of the level holding capacitor 7 reduces the In the case of a signal, a delay occurs in the output signal, and furthermore, since it equivalently functions as a top-pass filter, only low frequency components pass through. These have the drawback of deteriorating frequency characteristics.

The object of the present invention is to eliminate noise in the gate circuit and to stabilize switching by making the levels and phases of the input and output signals substantially the same.

[Means for solving the problem] When the input signal applied through the impedance conversion means includes a noise component, the noise component is removed by turning off the signal using a predetermined control signal corresponding to the noise component. a switching means for
a level holding means for holding the output signal level immediately before the switching means is turned off; , is provided between one input and the output of the differential amplification means, and outputs a negative feedback signal at the level held by the level holding means to one input of the differential amplification means when the switching means is turned on. a first limiter means for adjusting the level of the output signal from the differential amplifying means during a switching operation of the switching means; and an input side of the switching means and an output side of the level holding means. a second limiter means provided between the impedance converting means and the second limiter means for adjusting the level of the output signal of the impedance converting means during the switching operation of the switching means; It is characterized by reducing noise when turning on and off.

[Function] In the gate circuit according to the present invention, when there is no noise, the switching means is on, the input signal is given to one input of the differential amplification means, and the other input is supplied with the signal from the negative feedback means. a signal is given,
The difference signal is outputted via impedance conversion means, switching means, and level holding means. If noise is present in the input signal, the switching means is turned off, and the signal at the level immediately before turning off held by the level holding means is output, and the negative feedback means is also turned off. At this time, the limiter means adjusts the level of the differential signal and stabilizes the gate action of the switching means.

[Example] An embodiment of the present invention shown in the drawings will be described below.

Figure 2 shows an embodiment of the gate circuit according to the present invention, where 1 is an input terminal, 2 is an output terminal, R ₁ to _{R 6} are resistors, 7 is a level holding capacitor, 6, 8 to 18
is a transistor. transistors 8 and 9
constitutes a differential amplifier, with input terminal 1 connected to the base of transistor 8 via resistor _R3 , and output terminal 1 connected to the base of transistor 9 via resistor _R4 .
are connected to each other. The transistors 11 and 12 and the transistors 14 and 15 each form an emitter follower amplifier circuit for impedance conversion, and are connected to a capacitor 7 at the front stage and the rear stage of the switching transistor 6 as gate switching means, respectively, and are connected to a differential amplifier (transistor 8 , 9) and the base of the other transistor 9 constituting the differential amplifier are connected via a resistor _R4 to constitute a negative feedback circuit. transistor 8,
9, the transistor 9
An active load formed by a transistor 10 is connected to the collector of the transistor 9, and an amplified output of the differential signal of each input is obtained from the collector of the transistor 9. In this case, the differential amplifier can obtain a large voltage gain, but its output impedance also becomes very high. Therefore, transistors 11 and 12 are used to convert this impedance to low impedance.
A signal is given to the switching transistor 6 through the Darlington-connected emitter follower amplifier circuit for impedance conversion. Also, the output of the differential amplifier (collector of the transistor) and the transistor 6
The collector of transistors 16, 17, 18
A limiter circuit consisting of is connected.

Switching transistor 6 without noise now
Considering the state where is on, input terminal 1
The input signal that enters the base of transistor 8 from
Since the negative feedback circuit including 4 and 15 is formed, by setting R ₃ =R ₄ , the gain of the differential amplifier becomes 1, which appears as an output signal at the output terminal 2.

This makes it possible to make the input and output DC potentials almost equal, and also to prevent the effects of the internal resistance r _S between the emitter and collector of the switching transistor 6 and the capacitance C of the level holding capacitor 7, Even if high frequencies are introduced into the signal, the delay in the output signal can be minimized.

Next, when noise enters the input signal, transistor 1 that controls switching transistor 6
When applying a positive pulse as shown in the figure to the base of 3,
The gate circuit switches to off operation. That is,
First, when the base of the transistor 13 becomes a positive potential, this transistor operates and the base and collector of the next stage switching transistor 6 become almost at the same potential, so the base bias current of this transistor 6 becomes 0. Therefore, it becomes cut-off and becomes non-conductive. At this time, since the capacitor 7 holds the DC potential immediately before cut-off, the signal of this potential is transmitted to the transistors 14 and 15.
It appears as an output signal via .

On the other hand, by cutting off the switching transistor 6, the negative feedback circuit on the input side of the transistor 9 of the differential amplifier is cut off, and the gain of the differential amplifier increases to the bare gain, and the input signal is switched off. There is a possibility that the gate effect will be lost after passing through the transistor 6. In other words, the input signal (noise) applied to transistor 8, which constitutes the differential amplifier, is greatly amplified as described above and comes out to the output side of the differential amplifier, passing through transistors 11 and 12. and is transmitted to transistor 6.

Here, the equivalent circuit of transistors 6 and 13 is:
As shown in Figure 3, if the signal potential transmitted to transistor 6 (emitter potential of transistor 12) is greater than (V _BE + base potential of transistor 14), the signal passes through transistor 6 and the gate circuit This will eliminate the gate effect. To prevent this, transistor 1
A current limiter circuit consisting of 6, 17 and 18 is used. The collector-emitter voltage V _CE of the switching transistor 6 normally becomes approximately 0V when the base current of the transistor 6 is flowing, and the transistor 6 is turned on. Therefore, the potential difference between the base of transistor 14 and the emitter of transistor 15 in the Darlington-connected emitter follower amplifier circuit including transistors 14 and 15 is equal to the potential difference between the base of transistor 16 and the emitter of transistor 17. In this state, the B _BE (base-emitter voltage)-IC (collector current) characteristics of the transistors 16 and 17 are set so that the emitter current of the transistor 17 becomes extremely small. As a result, when transistor 6 is on, transistors 16, 17 and 18 are substantially cut off. When the base current of the transistor 6 becomes 0, the emitter-collector circuit is turned off, and the level holding capacitor 7 holds the previous voltage. At this time, when the emitter voltage of the transistor 12 increases, the potential difference between the base of the transistor 16 and the emitter of the transistor 17 increases, and the emitter current of the transistor 17 flows.
It operates to lower the emitter current of transistor 12, and the collector current of transistor 17 flows into the base of transistor 18, increasing the collector current of transistor 18 and greatly lowering the base voltage of transistor 11.

In this case, since the base of the transistor 11 has a higher impedance than the emitter of the transistor 12, the limiter operation by the transistor 18 is facilitated. If the limiter operation is too strong and the emitter voltage of transistor 12 drops too much, the potential difference between the base of transistor 16 and the emitter of transistor 17 becomes small, the emitter current of transistor 17 decreases, and the emitter voltage of transistor 12 becomes appropriate. set to a certain level. Therefore, when the transistor 16 is turned off, its emitter-collector voltage becomes higher than V _BE shown in FIG. 3, and the signal is completely cut off.

Consequently, when transistor 13 is on, transistor 6 can remain cut off under any signal state. When transistor 6 is normally on, transistors 16, 17, 18
is off, so the above-mentioned limiter operation is not performed.

[Effect of the invention] As is clear from the above explanation, according to the invention,
In gate circuits that use switching means to turn off the gate operation when noise enters the input signal, the input and output DC potentials are approximately equal when on, so even if high frequencies enter the input signal, there is no delay in the output signal. Furthermore, even when the gate is off, the gate action can be stabilized by the limiter means.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing a conventional circuit and an embodiment of the present invention, respectively, and FIG. 3 is a circuit diagram showing a partial equivalent circuit of FIG. 2. 1...Input terminal, 2...Output terminal, 7...Capacitor, 3, 4, 5, 6, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18...
Transistor, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ ...Resistance.

Claims (1)

[Claims for Utility Model Registration] (1) When the input signal applied via the impedance conversion means contains a noise component, the noise component can be turned off by a predetermined control signal corresponding to the noise component. a switching means for removing the switching means; and a level holding means for holding the output signal level immediately before the switching means is turned off; the gate circuit outputs a difference component signal between two input signals, and the output is sent to the impedance conversion means. provided between the given differential amplifying means and one input and output of the differential amplifying means, and transmitting a signal at a level held by the level holding means to the differential amplifying means when the switching means is turned on. negative feedback means for outputting negative feedback to one input; first limiter means for adjusting the level of the output signal from the differential amplifier means during switching operation of the switching means; a second limiter means provided between the output side of the holding means and adjusting the level of the output signal of the impedance conversion means during the switching operation of the switching means; A gate circuit characterized in that the switching means is the same and reduces noise when the switching means is turned on and off. (2) The gate circuit according to claim 1, wherein the impedance conversion means is constituted by an emitter follower amplifier section. (3) The gate circuit according to claim 1 of the utility model registration, characterized in that the amplification degree is made approximately 1 by connecting resistors of approximately the same value to the two inputs of the differential amplifying means, respectively. .