JPH0130330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor circuit, and particularly to a transistor circuit including a switch circuit that operates according to the output of a switching circuit, and relates to prevention of malfunction of the switch circuit.

A conventional example will be explained using FIG. Transistors 1 and 2 are connected between a common emitter connection point and a reference ground 3. It is driven by a constant current source 4 and constitutes a comparator 5. The collector of the transistor 1 is connected to the power supply 101, and the base of the transistor 1 is the second input 13 of the comparator, and this input is connected to a constant voltage circuit 8 consisting of a diode 6 and a constant voltage element 7, and a constant current source. 9. Connect the constant voltage circuit 8 of the second reference voltage source 12 composed of the capacitor 10 and the switch 11, and the connection point between the capacitor 10 and the constant current source 9. On the other hand, the collector of transistor 2 is the output terminal 14 of comparator 5, and this output terminal 1
4, a current inversion circuit (current mirror circuit) 16 configured by shorting the base of the multi-collector transistor 15 and the first collector of the multi-collector is connected between the power supply 101 and the multi-collector transistor 15. 15 is used as an output terminal 17 of a current inversion circuit 16, and the base of a transistor 18 is connected to this output terminal 17. The emitter of the transistor 18 is connected to the ground line 3, and the collector is connected to a load circuit 19 which is operated by turning on and off the transistor 18 (switch circuit). The base of the transistor 2 is connected to the first input 20 of the comparator 5.
, the resistor 21 of the first reference voltage source 23 is created by dividing the power supply 101 and the ground 3 by the resistors 21 and 22.
22 dividing points 23 are connected. Since the voltage V1 of the first reference voltage source 23 is provided by dividing the power supply 101 by resistance, the reference voltage V1 is instantaneously generated when the power supply 101 is turned on. That is, it is earlier than the rise of the second reference voltage source 12. The steady-state value of the voltage V2 of the external second reference voltage source 12 is determined by passing a constant current through the constant voltage circuit 8 from the constant current source 9.
Since the capacitor 10 is not charged when the switch 11 is OFF, the constant current of the constant current source 9 is used to charge the capacitor 10, and the voltage of V2 is
Following the voltage curve shown in figure a, the V2 voltage is
The value determined by the constant voltage circuit 8 becomes a steady value.
By selecting the steady-state value of V2 to be higher than the voltage V1 of the first reference voltage 23, the transistor 2 of the comparator 5 turns on and generates a current in the second collector of the current inverting circuit 15, and this current This turns on the transistor 18. Next, when V2≧V1, the comparator 5 is inverted and the output terminal 17 of the current inversion circuit 16 is
No current is generated and the transistor 18 is turned off. However, when these functions are manufactured on an integrated circuit, there is a drawback that the transistor 18 malfunctions if there is a collector current I1eak of the transistor 15 constituting the current inversion circuit 16. FIG. 2b shows a temporal change in the base current of the transistor 18.

Such a transistor circuit can be used, for example, in a muting circuit of an amplifier. That is,
The muting operation is controlled by the operation of transistor 18.

The present invention aims to improve the above-mentioned drawbacks and prevent malfunctions of the switch circuit due to leakage current of the comparator output.

The present invention provides a comparator including first and second transistors whose emitters are commonly connected, a first reference voltage source that applies a first reference voltage to one transistor of the comparator, and a constant current a second reference voltage source that has a source and a constant voltage element and applies a second reference voltage whose voltage level changes continuously and whose voltage level is approximately constant in a steady state to the other transistor of the comparator; and is turned on/off by the output of a first current inversion circuit interposed between the output terminal of the one transistor of the comparator and the power supply.
In the transistor circuit including a switching transistor whose off-state is controlled, a second current inversion circuit is connected in series with the constant current source and the constant voltage element of the second reference voltage source, and the second current inversion circuit is connected in series with the constant current source and the constant voltage element of the second reference voltage source. The present invention is characterized in that a third transistor that operates in response to the output of the circuit is connected to the base of the switching transistor.

Next, the present invention will be described in detail with reference to Examples and drawings.

FIG. 3 is a circuit connection diagram showing one embodiment of the present invention, in which the same components as in FIG. 1 are given the same numbers, and only the different points will be explained. The constant voltage circuit 8 is composed of a constant voltage diode 7 and transistors 24 and 25. The bases and emitters of the transistors 24 and 25 are connected in common, and the collector of the transistor 24 and the anode side of the constant voltage diode 7 are connected to this common connection point. It is connected. transistor 24,
25 common emitters are connected to the second input 13 of the comparator 5.
It is connected to the. The voltage V ₁ of the constant voltage circuit 8 is
It is expressed as the sum of the voltage Vz of the constant voltage element 7 and the emitter-base voltage VBE of the transistor 24, as shown in equation (1).

V ₁ = Vz + VBE ...(1) The temperature coefficient of VBE of a transistor manufactured in a general integrated circuit is -2 mV/℃, and if a Sienar diode is used as a constant voltage element, the temperature coefficient of the Sienar diode voltage is is +2mV/
℃, and the temperature coefficient of V ₁ voltage is approximately 0 mV/
A second reference voltage having excellent temperature characteristics in degrees Celsius can be constructed. The collector of transistor 25 is connected to the base of transistor 26, and the emitter of transistor 26 is connected to reference ground 3. The collector of the transistor 26 is connected to the output terminal 17 of the current inversion circuit 16 and the base connection point of the transistor 18 which is a switch circuit, and the transistor 26 constitutes a current absorption circuit 27.

The voltage V ₁ of the first reference power supply 23 is the power supply voltage 10
1 is divided by resistors 21 and 22 and supplied, so the rise is fast and is represented by the V ₁ curve in FIG. 4a.
On the other hand, the voltage V ₂ of the second reference voltage source 12 is given by equation (2) and is represented by the V ₂ curve in FIG. 4a.

V ₂ =I·t/C (2) where I is the constant current of the constant current source 9, C is the capacitance of the capacitor, and t is the time. The time t ₁ until V ₂ becomes V ₁ is the inversion time of the comparator 5, as will be explained next, and can be set to any value since it is determined by the capacitance and constant current of the capacitor. In FIG. 4a, during V ₁ >V ₂ (t ₁ >t > 0), current flows out from the output terminal 17 of the current inverting circuit 16 and drives the transistor 18 as in the conventional example. Here, if the current value Io of the differential constant current source 4 constituting the comparator 5 is, then the current inverting circuit 16 when V ₁ > V ₂
The current IOUT flowing out from the output terminal 17 of is IOUT≒Io (3). When V ₁ ≦ V ₂ , the output of the comparator 5 is inverted, and the output current of the comparator 5 begins to decrease, and the inversion current of the current inversion circuit 16 also decreases, so that the transistor 18
Turn off. When V ₂ reaches the steady voltage value determined by the constant voltage circuit 8, the current of the constant current source 9 switches from charging the capacitor 10 to almost flowing to the constant voltage circuit 8. If the constant current value of the constant current source 9 is _I1 , the transistors 24 and 25 constitute a current mirror circuit, so the emitter area ratio of the transistors 24 and 25 is 1:n, which is 24,
25 collector currents are divided. Therefore, the collector current Ic of the collector of the transistor 25, which is the output of the current mirror circuit (current inversion circuit), is (4)
It is expressed by the formula.

IC=n/1+nIo...(4) The collector current of the transistor 25 seems to be able to absorb the leakage current I1eak generated by the current inversion circuit 16(5)
By setting an IC that satisfies the conditions of the formula, even if the comparator circuit 5 is inverted under the condition of V ₁ ≦ V ₂ , the leakage current I1eak will be reduced.
This can prevent malfunctions in which the transistor 18 turns on.

IC≧I1eak …(5) In Fig. 4 a and b, V ₁ , V ₂ , transistor 18
The time chart of the base-emitter voltage, VBE (18) and base current IB (18) is shown.

After the switching operation of transistor 18 is completed between time t ₁ and time _{t 2} in FIG. 4, from t ₂ onwards, transistor 1
8 is completely turned off.

FIG. 5 is a circuit connection diagram showing another embodiment of the present invention, in which a constant voltage circuit 8 is constructed by connecting in series a constant voltage element 7 and a transistor 28 connected in a diode manner. The transistor 28 and the transistor 26 constitute a current inversion circuit, and the number of constituent elements can be saved.

As described above, according to the present invention, the leakage current of the comparator output can be completely absorbed, so that the load circuit 19 can be prevented from being driven erroneously.
Further, according to the present invention, since the output of the transistor 25 of the current inverting circuit connected in series with the constant current source 9 and the constant voltage element 7 is used to control the on/off of the transistor 26 for leak absorption, Due to the constant voltage characteristics of the voltage element, the second reference voltage source 12
When the output of the first current reversing circuit 16 reaches a substantially constant voltage level in a steady state, the leakage absorbing transistor 26 acts to absorb the leakage current of the first current inverting circuit 16. Therefore, even if the leakage absorption transistor 26 is provided at this position, the switching speed of the switch transistor 18 will not be reduced, so malfunctions due to leakage can be prevented while maintaining high-speed switching characteristics. This has an excellent effect. Moreover, since the second reference voltage source 12 includes a constant current source 9 and a constant voltage element 7 and has good temperature characteristics, there is an advantage that leak absorption is not influenced by temperature changes.

[Brief explanation of drawings]

Fig. 1 is a circuit connection diagram showing a conventional example, Fig. 2 a and b are explanatory diagrams for explaining the conventional example, Fig. a is a time chart of the voltage, Fig. b is a time chart of the base current of the transistor 18, 3 is a circuit connection diagram showing an embodiment of the present invention, and FIGS. 4a and 4b are explanatory diagrams for explaining the present invention. Figure a is a time chart of voltage, and Figure b is a diagram of base current of transistor 18. The time chart and FIG. 5 are circuit connection diagrams showing another embodiment of the present invention. 1, 2, 15, 18, 24, 25, 26, 28
...Transistor, 21, 22...Resistor, 3...
Reference ground, 101... Power supply, 4, 9... Constant current source, 5... Comparator, 6... Diode, 7... Constant voltage element, 8... Constant voltage circuit, 10... Capacitor, 11... Switch, 12...Second reference voltage source, 13, 20, 14, 17...Terminal, 16...
Current inversion circuit, 19...load circuit, 23...first
Reference voltage source, 27... current absorption circuit.

Claims (1)

[Claims] 1 A comparator including first and second transistors whose emitters are commonly connected, a first reference voltage source that applies a first reference voltage to one transistor of the comparator, a constant current source, and a constant current source. a second reference voltage source having a voltage element and applying a second reference voltage whose voltage level changes continuously and whose voltage level is approximately constant in a steady state to the other transistor of the comparator; a first transistor interposed between the output terminal of the one transistor of the comparator and a power supply;
and a switch transistor whose on/off is controlled by the output of a current inversion circuit, wherein a second current inversion circuit is connected in series with the constant current source and the constant voltage element of the second reference voltage source. A transistor circuit, characterized in that a third transistor responsive to the output of the second current inverting circuit is connected to the base of the switching transistor.