JPS6236402B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output switching circuit using a constant current circuit which is often used in transistor circuits, especially integrated circuits. The present invention relates to a circuit that controls the amount of output current or switches output current.

A constant current circuit forms a current with a correlation, such as a current equal to a predetermined current value or a current proportional to a predetermined current value, and supplies it as a current source. It has been used since. 1A to 1C are circuit connection diagrams showing three examples of typical conventional constant current circuits, in which 1 is an input terminal, 2 is an output terminal, and 3 is a current supply terminal.
In Figure 1a, the input current _I1 supplied to the input terminal 1 becomes the current flowing through the diode 4 and the base current of the transistor 5, and the collector current in the transistor 5 corresponds to the forward potential drop of the diode 4. flows and provides an output current I ₂ to output terminal 2. In Figure 1b, the diode 4 in Figure 1a is replaced with a transistor 6 whose collector and base are coupled.If the characteristics of the transistors 5 and 6 are the same, a current approximately proportional to the emitter current density will flow. The current flows through each transistor. Therefore, in an integrated circuit, input current I 1 and output current I ₂ can be adjusted by appropriately selecting the shapes of transistors 5 and ₆ , that is, the emitter area ratio.
relationship can be set. FIG. 1c shows a constant current circuit using a lateral PNP transistor 7 having a multi-collector structure, and it is known that in this case, the current ratio is determined by the ratio of the collector-emitter facing areas of the respective collectors. In FIG. 1b, a resistor is inserted between the emitter of each transistor 5 and transistor 6 and the current supply terminal 3 to stabilize the operation.
Also, NPN transistors with reversed polarity are used in exactly the same way.

As explained above, in constant current circuits used in conventional integrated circuits, the output current is approximately a fixed value depending on the design of the constant current circuit.
There is no means to freely control it from the outside.

SUMMARY OF THE INVENTION An object of the present invention is to provide an output switching circuit whose output current can be controlled externally and which is suitable for integration into an integrated circuit.

Hereinafter, the present invention will be explained in detail by way of examples with reference to the drawings.

FIG. 2 is a block diagram of a current circuit used in the present invention, where 11 is a first constant current circuit, and 12 is a second constant current circuit.
These constant current circuits each consist of a constant current circuit as shown in FIG. A second constant current circuit 13 supplies a current I ₁₃ to the input terminal 16 of the second constant current circuit 12.
A current source 14 is connected to the input terminal 18 of the first constant current circuit 11 and the output terminal 17 of the second constant current circuit 12 and supplies a current I ₁₄ .
Reference numeral 5 denotes a load circuit or a next-stage circuit block connected to the output terminal 19 of the first constant current circuit 11 and through which the output current _I15 flows.

Since the input terminal 18 of the first constant current circuit 11 is coupled to the output terminal 17 of the second constant current circuit 12 and then connected to the first current source 14, the current
I ₁₄ is the current I ₁₁ flowing to input terminal 18 and output terminal 1
7 and the current _I12 , and the following equation holds true.

I ₁₄ = I ₁₁ + I ₁₂ , that is, I ₁₁ = I ₁₄ - I ₁₂ (1) As an example, the first current source 14 is used as an input circuit, and the current I ₁₄ is converted into the current I ₁₅ via the first constant current circuit 11. Assuming a circuit _system that transmits _{the current} to
-I ₁₂ ), the current I ₁₅ to the output circuit ₁₅ can be controlled by changing the current I ₁₃ flowing through the second current source 13 that determines the current I 12 . This is the first power source 1 which becomes the input circuit.
4 without affecting the operation of output circuit 15.
This means that the amount of current transmitted to the first constant current circuit 11 and the second constant current circuit 12 can be freely controlled from the outside,
If the relationship with the current source 13 is set appropriately, the current
The control gain and/or control range based on the current I ₁₃ of I ₁₅ can be selected. Also, the second current source 1
3 as an input circuit, the current I _{14 of the first current source 14}
The same thing can be said when controlling the output current _I15 by changing . It is also possible to add a third constant current circuit and a third current source to the block diagram in Figure 2, and it can be configured by connecting at least two or more constant current circuits in series. can.

FIG. 3 is a circuit connection diagram showing an embodiment of the present invention, in which the output signal from the signal generation circuit 20 is transferred to the output terminal 22 by the switching operation of the switching circuit 21.
A constant current circuit is applied to the signal switching circuit that takes out the signal. The signal generating circuit 20 may be one that generates an AC signal such as a pulse or a square wave, or one that generates a signal given as a DC voltage, and is directly connected to the collector of the NPN transistor 23. The emitter of the transistor 23 is grounded via the resistor 24 and simultaneously connected to the output terminal 2.
2, and its base is coupled to one collector of a double collector PNP transistor 25 corresponding to the first constant current circuit. The emitter of the transistor 25 is connected to the power supply terminal 26, and the base is coupled to the other collector to serve as an input terminal of the first constant current circuit and connected to the collector of the transistor 27. The emitter of the transistor 27 is grounded via a resistor 28, and the transistor 27 is driven by a switching circuit 21 connected to its base to cause a current _I27 to flow through its collector, thereby operating as a first current source. Therefore, when the transistor 27 is biased by the switching circuit 21 and a current I ₂₇ flows, a corresponding current I ₂₅ flows into the base of the transistor 23, forcing the transistor 23 into the saturation region and causing conduction between collector and emitter. In this state, the output signal from the signal generation circuit 20 is taken out to the output terminal 22. Further, when the switching circuit 21 cuts off the transistor 27, the transistors 25 and 23 are also cut off, and no signal appears at the output terminal 22. 29 is a double collector PNP transistor corresponding to the second constant current circuit, one collector is connected to the base of the transistor 25 corresponding to the first constant current circuit, and the other collector is connected to the base to form the transistor. Connected to 30 collectors. The emitter of the transistor 30 is grounded via the resistor 31, and the base is connected to the input terminal 32.
A DC voltage is applied externally to control the current. The collector of the transistor 30 receives a current I ₃₀ determined by the DC voltage applied to the input terminal 32.
flows, this becomes the input current of the transistor 29, and the corresponding output current _I29 is the input current of the transistor 29.
It flows out from one collector of 9.

Therefore, currents I ₂₅ and I ₂₇ flow through transistor 2.
3 is conductive, if a voltage is applied to the input terminal 32 to cause a current I ₂₉ to flow, the current I ₂₅
changes almost proportionally to changes in the current I ₃₀ , so when forcing the transistor 23 into a cutoff state with the input voltage applied to the input terminal 32, it is necessary to give a time constant to the change in the input voltage. This allows the response speed to be adjusted, and can also have the effect of suppressing shock noise during switching. This has the effect of greatly reducing the adverse effects of shock noise that can be heard as shock, especially when this circuit is related to an audio signal system and the final stage is connected to a speaker.

In addition to the embodiments described above, the present invention can be applied to various electronic circuits. In particular, when applied to integrated circuits, integrated circuit technology that is advantageous due to the symmetry of elements can be applied, so signal control by current transmission, etc. It becomes possible to design highly accurate and rational circuits that have signal processing functions such as switching.

[Brief explanation of the drawing]

Figures 1 a to c are circuit connection diagrams showing three examples of typical conventional constant current circuits, Figure 2 is a block diagram of a current circuit used in the present invention, and Figure 3 is a concrete implementation of the present invention. FIG. 3 is a circuit connection diagram showing an example. 1, 16, 18: input terminal of constant current circuit, 2,
17, 19: Output terminal of constant current circuit, 3, 26:
Power supply terminal, 4: diode, 5, 6, 23,
30: NPN transistor, 7, 25, 29: double collector PNP transistor, 11: first constant current circuit, 12: second constant current circuit, 13: second
current source, 14: first current source, 15: load or next stage circuit block, 20: signal generation circuit, 21:
Switching circuit, 22: Output terminal, 32: Input terminal, 24, 28, 31: Resistor, I ₁ , I ₂ , I ₁₃ ,
I ₁₄ , I ₁₅ , I ₂₇ , I ₂₉ , I ₃₀ : Current.

Claims (1)

[Claims] 1. A first and second current circuit each outputting an output current proportional to the input current, a first current source supplying current to the input terminal of the first current circuit, and an output of the first current circuit. a second current source that supplies current to a connection between the terminal and the input terminal of the second current circuit, a signal generation source, a signal output terminal, and between the output terminal of the signal generation source and the signal output terminal a transistor whose base is connected to an output terminal of the second current circuit, the second current source generating a first control signal current that makes the transistor conductive or non-conductive; The first current source generates a second control signal current to force the transistor into a non-conducting state even though the second control signal current has information to make the transistor into a conducting state. An output switching circuit characterized by: