JP5336444B2 - Current switching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the shutdown stably without damaging a constant current source transistor of a constant current circuit. <P>SOLUTION: A current changeover circuit has an emitter-follower circuit (an EF circuit), a constant current circuit, and a switch SW1 that turns on and off the constant current circuit. The EF circuit consists of a transistor Q1 having a base connected to a signal input terminal IN1, a collector connected to a power source VCC1, and an emitter connected to a signal output terminal OUT1. The constant current circuit consists of: a transistor Q2 having a base connected to an output of the switch SW1 and a collector connected to the emitter of the transistor Q1; a resistance RS1 having a first terminal connected to the emitter of the transistor Q2 and a second terminal connected to a power source VEE1; and a leakage current source JREAK1 having a first terminal connected to the collector of the transistor Q2 and a second terminal connected to the power source VEE1. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a current switching circuit of a semiconductor integrated circuit, and more particularly to a technique for ensuring a withstand voltage of a constant current source transistor when a circuit current is shut down.

  FIG. 11 is a block diagram showing a configuration example of a conventional laser driver circuit. Such a laser driver circuit is disclosed in Non-Patent Document 1, for example. The laser driver circuit includes an input buffer 100, a CPC (Crossing Point Control) circuit 101, a prebuffer 102, a prebuffer 103, a driver circuit 104, a bias control (BIAS Control) circuit 105, resistors RIP and RIN, Consists of. In FIG. 11, IN and INB are input terminals, OUT and OUTB are output terminals, VB1 is an output crossing control terminal, VB2 is an output crossing reference terminal, and VC1 is a modulation current control. Control) terminal, VC2 is a bias current control terminal, and VD1 and VD2 are power supply terminals.

  In the laser driver circuit shown in FIG. 11, a semiconductor laser (not shown) connected between the output terminals OUT and OUTB by outputting a modulation signal corresponding to the input signal input to the input terminals IN and INB. Drive. The bias control circuit 105 controls the bias current supplied to the semiconductor laser. In such a laser driver circuit, a constant current is consumed regardless of the laser operation, and a reduction in power consumption has been a problem.

  Therefore, as a commonly used method, a current switching circuit is provided in a constant current circuit provided in each functional block such as the input buffer 100 and the CPC circuit 101, and the current consumption of the laser driver circuit is reduced by turning off the constant current circuit during standby. There is a so-called shutdown method to turn off.

KGA4185 data sheet, OKI Semiconductor Co., Ltd., October 1, 2008, <http: // www. okisemi. com / jp / semicon / optical / driver. htm>

  However, when the current of the constant current circuit is completely cut off, or when the base voltage of the constant current source transistor is switched to a low voltage so that the constant current source transistor constituting the constant current circuit is turned off, the constant current source transistor In some cases, the constant current source transistor may be damaged due to overvoltage.

  The present invention has been made to solve the above-described problem, and does not damage the constant current source transistor of the constant current circuit at the time of shutdown for realizing low power consumption of a semiconductor integrated circuit such as a laser driver circuit. Another object of the present invention is to provide a current switching circuit capable of performing stable shutdown.

  The current switching circuit of the present invention includes an emitter follower circuit, a first constant current circuit for supplying a constant current to the emitter follower circuit, and a first constant current circuit capable of turning on / off the first constant current circuit. The emitter follower circuit includes a first transistor having a base connected to a signal input terminal, a collector connected to a first power supply, and an emitter connected to a signal output terminal. The constant current circuit includes a second transistor having a base connected to the output of the first switch, a collector connected to the emitter of the first transistor, and a first terminal connected to the emitter of the second transistor. A first resistor connected to the second power source, a first terminal connected to a collector of the second transistor, and a second terminal connected to the second transistor. A first leakage current source connected to the source or the emitter of the second transistor, and the first switch has a normal operation current mode bias voltage during normal operation according to a control signal input from the outside. Is selected and output, and in standby mode, a standby current mode bias voltage is selected and output.

  Further, according to one configuration example of the current switching circuit of the present invention, N (N is an integer of 1 or more) inserted in series between the emitter of the first transistor and the collector of the second transistor. The emitter of the first transistor is connected to the anode of the first diode and the first signal output terminal, and the Lth (L is an integer of 1 or more and 1 to N-1). The cathode of the diode is connected to the anode of the (L + 1) th diode and the output of the (L + 1) th signal output terminal, and the cathode of the Nth diode is connected to the collector of the second transistor and the (( N + 1) and the first terminal of the first leak current source.

In addition, one configuration example of the current switching circuit of the present invention further includes a single-phase input current switching logic circuit connected to a signal output terminal of the emitter follower circuit, and the single-phase input current switching logic circuit includes the emitter The output of the follower circuit is used as an input, and one power supply terminal is connected to a third power supply, and the logic circuit part or amplifier is connected to the other power supply terminal of the logic circuit part or amplifier. And a constant current source for supplying a constant current.
Further, one configuration example of the current switching circuit of the present invention further includes a differential input current switching logic circuit connected to the signal output terminals of the two emitter follower circuits, and the two emitter follower circuits have a positive phase The first emitter follower circuit for signal input and the second emitter follower circuit for reverse phase signal input are provided, and the first switch outputs the output of each of the first and second emitter follower circuits. The differential input current switching logic circuit receives the outputs of the first and second emitter follower circuits as inputs, and one power supply terminal is a third power supply. A logic circuit unit or an amplifier connected to the power source, a constant current source connected to the other power supply terminal of the logic circuit unit or the amplifier and supplying a constant current to the logic circuit unit or the amplifier; It is characterized in that Ranaru.

  In one configuration example of the current switching circuit according to the present invention, the single-phase input current switching logic circuit is a second constant current circuit that supplies a constant current to the logic circuit unit or the amplifier instead of the constant current source. And a second switch capable of turning on / off the second constant current circuit, wherein the second constant current circuit has a base connected to the output of the second switch, A third transistor having a collector connected to the other power supply terminal of the logic circuit unit or the amplifier, a first terminal connected to the emitter of the third transistor, and a second terminal connected to the fourth power supply And a second leak with the first terminal connected to the collector of the third transistor and the second terminal connected to the fourth power supply or the emitter of the third transistor. With current source The second switch selects and outputs a normal operation current mode bias voltage during normal operation and outputs a standby current mode bias voltage during standby according to a control signal input from the outside. It is characterized by this.

  In one configuration example of the current switching circuit of the present invention, the differential input current switching logic circuit is a second constant current circuit that supplies a constant current to the logic circuit unit or the amplifier instead of the constant current source. And a second switch capable of turning on / off the second constant current circuit, wherein the second constant current circuit has a base connected to the output of the second switch, A third transistor having a collector connected to the other power supply terminal of the logic circuit unit or the amplifier, a first terminal connected to the emitter of the third transistor, and a second terminal connected to the fourth power supply And a second leak with the first terminal connected to the collector of the third transistor and the second terminal connected to the fourth power supply or the emitter of the third transistor. With current source The second switch selects and outputs a normal operation current mode bias voltage during normal operation and outputs a standby current mode bias voltage during standby according to a control signal input from the outside. It is characterized by this.

In one configuration example of the current switching circuit according to the present invention, the leakage current source includes a resistor or a resistor and a capacitor connected in parallel to the resistor.
In one configuration example of the current switching circuit of the present invention, the leak current source includes a transistor having a fixed bias voltage applied to a base and a resistor having one end connected to the emitter of the transistor. It is what.

  According to the present invention, since the first leakage current source is provided in the first constant current circuit, the leakage current flowing through the first leakage current source can be reduced even when the second transistor is turned off during standby. The collector-emitter voltage of the second transistor is fixed to a certain value. Accordingly, if the breakdown voltage of the second transistor is designed to satisfy this constant value, the second transistor can be stably shut down without being damaged. In the present invention, although the power consumption itself in the standby state is slightly increased as compared with the prior art, the electrical stress applied to the second transistor, which is the constant current source transistor constituting the first constant current circuit, is slightly reduced. Since it can be reduced by addition, it is possible to prevent the second transistor from being damaged or unstable in operation at low cost.

  In the present invention, signals having different voltage levels can be generated by inserting N diodes in series between the emitter of the first transistor and the collector of the second transistor.

  In the present invention, the second constant current circuit is configured by providing the second constant current circuit in the single-phase input current switching logic circuit and providing the second leak current source in the second constant current circuit. Therefore, the third transistor, which is a constant current source transistor, can be stably shut down without being damaged.

In the present invention, the second constant current circuit is configured by providing the second constant current circuit in the differential input current switching logic circuit and providing the second leak current source in the second constant current circuit. Therefore, the third transistor, which is a constant current source transistor, can be stably shut down without being damaged.
Note that the present invention has the same effect even when an FET is used instead of the bipolar transistor.

1 is a circuit diagram showing a configuration of a current switching circuit according to a first embodiment of the present invention. It is a circuit diagram which shows the structure of the current switching circuit which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of the current switching circuit which concerns on the 3rd Embodiment of this invention. It is a circuit diagram which shows the structure of the current switching circuit which concerns on the 4th Embodiment of this invention. It is a circuit diagram which shows the structure of the current switching circuit which concerns on the 5th Embodiment of this invention. It is a circuit diagram which shows the structure of the current switching circuit based on the 6th Embodiment of this invention. It is a circuit diagram which shows the structure of the current switching circuit which concerns on the 7th Embodiment of this invention. It is a circuit diagram which shows the structure of the current switching circuit based on the 8th Embodiment of this invention. It is a circuit diagram which shows the structure of the leakage current source which concerns on the 9th Embodiment of this invention. It is a circuit diagram which shows the structure of the leakage current source which concerns on the 10th Embodiment of this invention. It is a block diagram which shows the structural example of the conventional laser driver circuit.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a current switching circuit according to a first embodiment of the present invention.
The current switching circuit of the present embodiment as a whole constitutes an emitter follower circuit (hereinafter referred to as EF circuit), the base is connected to the signal input terminal IN1, the collector is connected to the first power supply VCC1, A transistor Q1 having an emitter connected to the signal output terminal OUT1, a constant current source transistor Q2 having a collector connected to the emitter of the transistor Q1, a switch SW1 for switching a bias voltage applied to the base of the constant current source transistor Q2, and a first Is connected to the emitter of the constant current source transistor Q2, the second terminal is connected to the second power source VEE1, the first terminal is connected to the collector of the constant current source transistor Q2, and the second terminal Has a leakage current source JREAK1 connected to the second power supply VEE1.

The constant current source transistor Q2, the switch SW1, the resistor RS1, and the leak current source JREAK1 constitute a constant current circuit. Note that the leakage current source means that it functions as a current source and also functions as a leakage path through which the leakage current of the constant current circuit flows.
In the present embodiment, the magnitude of the current flowing through the transistors Q1 and Q2 can be switched by switching the switch SW1 with the control signal VCONT1.

  That is, during normal operation, the switch SW1 is made to select the normal operation current mode bias voltage VCS1 side. As a result, the normal operation current mode bias voltage VCS1 is applied to the base of the constant current source transistor Q2, so that the constant current source transistor Q2 is turned on, and a current corresponding to VCS1 flows through the transistors Q1 and Q2. At this time, the signal input to the signal input terminal IN1 is output from the signal output terminal OUT1.

  On the other hand, at the time of standby, the control signal VCONT1 causes the switch SW1 to select the standby current mode bias voltage VOFF1 side (VCS1> VOFF1). As a result, the standby current mode bias voltage VOFF1 is applied to the base of the constant current source transistor Q2, and the constant current source transistor Q2 is turned off, so that the current flowing through the transistors Q1 and Q2 is greatly reduced as compared with the normal operation. Thus, low power consumption of the EF circuit can be realized.

  In the present embodiment, the leakage current source JREAK1 is provided in the constant current circuit of the EF circuit, so that even if the constant current source transistor Q2 is turned off during standby, the constant current source for the leakage current flowing through the leakage current source JREAK1. The collector-emitter voltage of the transistor Q2 is fixed at a certain value. Therefore, if the constant current source transistor Q2 is designed so that the breakdown voltage satisfies this constant value, the constant current source transistor Q2 can be stably shut down without being damaged. In the present embodiment, although the power consumption itself in the standby state is slightly increased as compared with the prior art, the electrical stress applied to the constant current source transistor Q2 constituting the constant current circuit can be reduced by adding a few components. Therefore, it is possible to prevent the constant current source transistor Q2 from being destroyed or unstable in operation at low cost.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 2 is a circuit diagram showing a configuration of a current switching circuit according to the second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.
The current switching circuit according to the present embodiment is inserted in series between the transistors Q1 and Q2, the switch SW1, the resistor RS1, the leak current source JREAK1, the emitter of the transistor Q1, and the collector of the constant current source transistor Q2. N (N is an integer of 1 or more) diodes D1 to DN.

The emitter of the transistor Q1 is connected to the anode of the first diode D1 and the first signal output terminal OUT1. The cathode of the Lth (L is an integer equal to or greater than 1 and 1 to N−1) diode DL is connected to the anode of the (L + 1) th diode and the (L + 1) th signal output terminal output OUT (L + 1). . The cathode of the Nth diode DN is connected to the collector of the constant current source transistor Q2, the (N + 1) th signal output terminal OUT (N + 1), and the first terminal of the leak current source JREAK1.
The present embodiment is used when a voltage having a different voltage level is generated by an EF circuit in a logic circuit using a so-called series gate which is often used.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 3 is a circuit diagram showing a configuration of a current switching circuit according to the third embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.
In the current switching circuit of the present embodiment, the first terminal is connected to the collector of the constant current source transistor Q2 and the second terminal is the constant current source instead of the leak current source JREAK1 in the first embodiment. A leakage current source JREAK11 connected to the emitter of the transistor Q2 is provided. The effect of this embodiment is the same as that of the first embodiment.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 4 is a circuit diagram showing a configuration of a current switching circuit according to the fourth embodiment of the present invention. The same components as those in FIGS. 1 and 2 are denoted by the same reference numerals.
In the current switching circuit of the present embodiment, the first terminal is connected to the collector of the constant current source transistor Q2 in place of the leak current source JREAK1 in the second embodiment, and the second terminal is a constant current source. A leakage current source JREAK11 connected to the emitter of the transistor Q2 is provided. The effect of this embodiment is the same as that of the second embodiment.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. FIG. 5 is a circuit diagram showing a configuration of a current switching circuit according to the fifth embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.
The current switching circuit of the present embodiment is a circuit in which the single-phase input current switching logic circuit 1 is connected to the subsequent stage of the EF circuit. The signal input terminal ID1 of the single-phase input current switching logic circuit 1 is connected to the signal output terminal OUT1 of the EF circuit.

  The single-phase input current switching logic circuit 1 includes a transistor Q3 having a base connected to the signal input terminal ID1, a collector connected to the signal output terminal OUT2P, a reference voltage VREF1 applied to the base, and a collector connected to the signal output terminal OUT2N. The connected transistor Q4, the first terminal connected to the third power supply VCC2, the second terminal connected to the collector of the transistor Q3, and the first terminal connected to the third power supply VCC2. Connected, a load resistor RLN1 having a second terminal connected to the collector of the transistor Q4, a first terminal connected to the collectors of the transistors Q3 and Q4, and a second terminal connected to the fourth power supply VEE2. And a constant current source JL1. Transistors Q3 and Q4 and load resistors RLP1 and RLN1 constitute a logic circuit unit or an amplifier. One power supply terminal (the first terminal of the load resistors RLP1 and RLN1) of the logic circuit section or the amplifier is connected to the third power supply VCC2, and the other power supply terminal of the logic circuit section or the amplifier (the emitters of the transistors Q3 and Q4). ) Is connected to the constant current source JL1.

  The single-phase input current switching logic circuit 1 converts a single-phase signal that is input to the signal input terminal IN1 of the EF circuit and output from the signal output terminal OUT1 into a differential signal, and at the same time, logically inverts or amplifies the differential signal. The signal is output from the output terminals OUT2P and OUT2N.

  In this embodiment, the EF circuit connected to the single-phase input current switching logic circuit 1 is the same as that shown in the first embodiment. However, the EF circuit shown in the second to fourth embodiments is used. Needless to say, an EF circuit may be used.

[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be described. FIG. 6 is a circuit diagram showing a configuration of a current switching circuit according to the sixth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIG.
The current switching circuit according to the present embodiment includes a first EF circuit for positive phase signal input, a second EF circuit for negative phase signal input, a switch SW1, and a differential input current switching logic circuit 2. Have.

  The first EF circuit for positive-phase signal input includes a transistor Q1 having a base connected to the signal input terminal IN1P, a collector connected to the first power supply VCC1, and an emitter connected to the signal output terminal OUT1P. A constant current source transistor Q2 connected to the emitter of the transistor Q1, a first terminal connected to the emitter of the constant current source transistor Q2, a second terminal connected to the second power source VEE1, and a first resistor RS1; The leakage current source JREAK1 has one terminal connected to the collector of the constant current source transistor Q2 and the second terminal connected to the second power supply VEE1.

  The second EF circuit for reverse phase signal input includes a transistor Q5 having a base connected to the signal input terminal IN1N, a collector connected to the first power supply VCC1, an emitter connected to the signal output terminal OUT1N, and a collector connected to the signal output terminal OUT1N. A constant current source transistor Q6 connected to the emitter of the transistor Q5; a first terminal connected to the emitter of the constant current source transistor Q6; a second terminal connected to the second power source VEE1; The leakage current source JREAK2 has one terminal connected to the collector of the constant current source transistor Q6 and the second terminal connected to the second power supply VEE1.

  In the present embodiment, the output of the switch SW1 is connected to the bases of the constant current source transistors Q2 and Q6. The operation of the switch SW1 is as described in the first embodiment. In the normal operation, the switch SW1 selects the normal operation current mode bias voltage VCS1, thereby turning on the constant current source transistors Q2 and Q6, and the standby Sometimes, the switch SW1 selects the standby current mode bias voltage VOFF1 side, thereby turning off the constant current source transistors Q2 and Q6.

  The differential input current switching logic circuit 2 includes a transistor Q3 having a base connected to the signal input terminal ID1P, a collector connected to the signal output terminal OUT2P, a base connected to the signal input terminal IDIN, and a collector connected to the signal output terminal OUT2N. Connected to the transistor Q4, a first terminal connected to the third power supply VCC2, a second terminal connected to the collector of the transistor Q3, and a first terminal connected to the third power supply VCC2. A load resistor RLN1 having a second terminal connected to the collector of the transistor Q4, a first terminal connected to the collectors of the transistors Q3 and Q4, and a second terminal connected to the fourth power source VEE2. And a constant current source JL1.

The differential signal input terminals ID1P and IDIN of the differential input current switching logic circuit 2 are connected to the differential signal output terminals OUT1P and OUT1N of the first and second EF circuits.
The differential input current switching logic circuit 2 logically inverts the differential signals input to the differential signal input terminals IN1P and IN1N of the first and second EF circuits and output from the differential signal output terminals OUT1P and OUT1N. Amplified and output from the differential signal output terminals OUT2P and OUT2N.

  In this embodiment, by providing the leak current sources JREAK1 and JREAK2 in the constant current circuits of the first and second EF circuits, the constant current source transistors Q2 and Q6 are not damaged, and the shutdown is stably performed. be able to. Thus, in the present embodiment, the same effects as those of the first embodiment can be obtained in the EF circuit that receives differential signals.

  In the present embodiment, the first and second EF circuits connected to the differential input current switching logic circuit 2 are the same as those shown in the first embodiment. Needless to say, the EF circuit shown in the embodiment may be used.

[Seventh Embodiment]
Next, a seventh embodiment of the present invention will be described. FIG. 7 is a circuit diagram showing a configuration of a current switching circuit according to the seventh embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIGS.
In the fifth embodiment, the current switching circuit of the present embodiment is provided with a single-phase input current switching logic circuit 1a instead of the single-phase input current switching logic circuit 1.

  The single-phase input current switching logic circuit 1a is obtained by providing a constant current circuit instead of the constant current source JL1 in the single-phase input current switching logic circuit 1 of the fifth embodiment. This constant current circuit includes a constant current source transistor Q7 whose collector is connected to the emitters of the transistors Q3 and Q4, a switch SW2 for switching a bias voltage applied to the base of the constant current source transistor Q7, and a first terminal having a constant current source. The resistor RS3 is connected to the emitter of the transistor Q7, the second terminal is connected to the fourth power supply VEE2, the first terminal is connected to the collector of the constant current source transistor Q7, and the second terminal is the fourth terminal. And a leakage current source JREAK3 connected to the power supply VEE2.

The operation of the EF circuit is as described in the first embodiment. In the present embodiment, the magnitude of the current flowing through the transistors Q3, Q4, and Q7 can be switched by switching the switch SW2 with the control signal VCONT2.
That is, at the time of normal operation, the switch SW2 is made to select the normal operation current mode bias voltage VCS2 side. As a result, the normal operation current mode bias voltage VCS2 is applied to the base of the constant current source transistor Q7, so that the constant current source transistor Q7 is turned on, and a current corresponding to VCS2 flows through the transistors Q3, Q4, Q7.

  On the other hand, at the time of standby, the control signal VCONT2 causes the switch SW2 to select the standby current mode bias voltage VOFF2 side (VCS2> VOFF2). As a result, the standby current mode bias voltage VOFF2 is applied to the base of the constant current source transistor Q7, and the constant current source transistor Q7 is turned off, so that the current flowing through the transistors Q3, Q4, and Q7 is greatly reduced as compared with the normal operation. To do. Thus, low power consumption of the single-phase input current switching logic circuit 1a can be realized.

  In the present embodiment, by providing the leak current source JREAK3 in the constant current circuit of the single-phase input current switching logic circuit 1a, the constant current source transistor Q7 can be stably shut down without being damaged.

[Eighth Embodiment]
Next, an eighth embodiment of the present invention will be described. FIG. 8 is a circuit diagram showing a configuration of a current switching circuit according to the eighth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIGS.
In the sixth embodiment, the current switching circuit of this embodiment is provided with a differential input current switching logic circuit 2a instead of the differential input current switching logic circuit 2.

The differential input current switching logic circuit 2a is obtained by providing a constant current circuit in place of the constant current source JL1 in the differential input current switching logic circuit 2 of the sixth embodiment. Since this constant current circuit has the same configuration as the constant current circuit in the single-phase input current switching logic circuit 1a of the seventh embodiment, detailed description thereof is omitted. In the present embodiment, by providing the constant current circuit including the leak current source JREAK3, the power consumption of the differential input current switching logic circuit 2a can be reduced, and the constant current source transistor Q7 can be damaged. Without shutting down, stable shutdown can be performed.
In the seventh and eighth embodiments, the second terminal of the leak current source JREAK3 may be connected to the emitter of the constant current source transistor Q7.

[Ninth Embodiment]
Next, a ninth embodiment of the present invention will be described. FIGS. 9A and 9B are circuit diagrams showing the configuration of the leakage current source according to the ninth embodiment of the present invention.
This embodiment shows a specific example of the leak current sources JREAK1, JREAK2, JREAK3, and JREAK11 used in the first to eighth embodiments.

  The leak current sources JREAK1, JREAK2, JREAK3, and JREAK11 may be configured by a resistor RJ1 as shown in FIG. 9A, or a resistor RJ1 and a capacitor CJ1 are connected in parallel as shown in FIG. 9B. You may comprise by what did. In the example of FIG. 9A, one end of the resistor RJ1 is a first terminal of the leak current source, and the other end of the resistor RJ1 is a second terminal of the leak current source. In the example of FIG. 9B, one connection point between the resistor RJ1 and the capacitor CJ1 is the first terminal of the leakage current source, and the other connection point is the second terminal of the leakage current source.

  If the value of the resistor RJ1 is designed so that the current flowing through the resistor RJ1 of the leak current source is equal to or less than 1/3 of the current flowing when the constant current source transistor connected to the leak current source is on, it is sufficiently low. Power consumption can be realized. The reason why the upper limit of the current flowing through the resistor RJ1 is determined in this way (that is, the reason why the lower limit of the resistance value is determined) is that when a current exceeding 1/3 of the current flowing when the constant current source transistor is turned on flows through the resistor RJ1. This is because the effect of turning off the constant current source transistor to reduce power consumption is reduced.

  On the other hand, the upper limit of the resistor RJ1 is determined relative to the off-resistance (resistance between the emitter and the collector when the base-emitter voltage is equal to or lower than the threshold voltage) of the constant current source transistor, and is 1 than the off-resistance. Make the resistance value smaller than the digit. The reason is that if the value of the resistor RJ1 is too high, when the constant current source transistor is turned off, the electrical stress (abrupt increase in applied voltage) is not sufficiently distributed to the resistor RJ1, and the constant current source transistor This is because the voltage may be applied beyond the withstand voltage.

[Tenth embodiment]
Next, a tenth embodiment of the present invention will be described. FIGS. 10A and 10B are circuit diagrams showing the configuration of a leakage current source according to the tenth embodiment of the present invention.
The present embodiment shows another specific example of the leak current sources JREAK1, JREAK2, JREAK3, and JREAK11 used in the first to eighth embodiments.

  As shown in FIG. 10A, the leak current sources JREAK1, JREAK2, JREAK3, and JREAK11 may include a transistor QJ and a resistor RJ2 having a first terminal connected to the emitter of the transistor QJ. A fixed bias voltage is applied to the base of the transistor QJ.

  In addition, as shown in FIG. 10B, the leakage current sources JREAK1, JREAK2, JREAK3, and JREAK11 have a transistor QJ, a resistor RJ2, a first terminal connected to the collector of the transistor QJ, and a second terminal You may comprise from the capacity | capacitance CJ2 connected to the 2nd terminal of resistance RJ2. In the example of FIGS. 10A and 10B, the collector of the transistor QJ becomes the first terminal of the leak current source, and the second terminal of the resistor RJ2 becomes the second terminal of the leak current source.

In this embodiment, it is sufficient if the current flowing through the leakage current source transistor QJ is designed to be 1/3 or less of the current flowing when the constant current source transistor connected to the leakage current source is turned on. Can achieve low power consumption.
Although the first to tenth embodiments have been described using bipolar transistors, similar effects can be obtained even if FETs are used instead of bipolar transistors in each embodiment.

  The present invention can be applied to a current switching circuit of a semiconductor integrated circuit.

  DESCRIPTION OF SYMBOLS 1,1a ... Single phase input current switching logic circuit, 2, 2a ... Differential input current switching logic circuit, Q1, Q2, Q3, Q4, Q5, Q6, Q7, QJ ... Transistor, D1-DN ... Diode, RS1, RS2, RS3, RLP1, RLN1, RJ1, RJ2 ... resistor, CJ1, CJ2 ... capacitance, SW1, SW2 ... switch, JREAK1, JREAK2, JREAK3, JREAK11 ... leakage current source, JL1 ... constant current source.

Claims (8)

An emitter follower circuit;
A first constant current circuit for supplying a constant current to the emitter follower circuit;
A first switch capable of turning on / off the first constant current circuit;
The emitter follower circuit includes a first transistor having a base connected to a signal input terminal, a collector connected to a first power supply, and an emitter connected to a signal output terminal;
The first constant current circuit includes a second transistor having a base connected to the output of the first switch, a collector connected to the emitter of the first transistor, and a first terminal connected to the second transistor. A first resistor connected to the emitter of the transistor, a second terminal connected to a second power source, a first terminal connected to the collector of the second transistor, and a second terminal connected to the second power source And a first leakage current source connected to the emitter of the second transistor,
The first switch selects and outputs a normal operation current mode bias voltage during normal operation according to a control signal input from the outside, and selects and outputs a standby current mode bias voltage during standby. A current switching circuit. The current switching circuit according to claim 1,
And N (N is an integer of 1 or more) diodes inserted in series between the emitter of the first transistor and the collector of the second transistor,
The emitter of the first transistor is connected to the anode of the first diode and the first signal output terminal, and the cathode of the Lth diode (L is an integer of 1 or more and 1 to N-1) is , Connected to the anode of the (L + 1) th diode and the output of the (L + 1) th signal output terminal, the cathode of the Nth diode is the collector of the second transistor and the (N + 1) th signal A current switching circuit connected to an output terminal and a first terminal of the first leak current source. The current switching circuit according to claim 1 or 2,
Furthermore, a single-phase input current switching logic circuit connected to the signal output terminal of the emitter follower circuit,
The single-phase input current switching logic circuit has the output of the emitter follower circuit as an input, and one power supply terminal is connected to a third power supply, and the other power supply of the logic circuit section or amplifier A current switching circuit comprising a constant current source connected to a terminal and supplying a constant current to the logic circuit unit or the amplifier. The current switching circuit according to claim 1 or 2,
And a differential input current switching logic circuit connected to the signal output terminals of the two emitter follower circuits,
The two emitter follower circuits include a first emitter follower circuit for inputting a positive phase signal and a second emitter follower circuit for inputting a negative phase signal.
The first switch inputs its output to the base of the second transistor provided in each of the first and second emitter follower circuits,
The differential input current switching logic circuit has an output of the first and second emitter follower circuits as an input, and a logic circuit unit or an amplifier having one power supply terminal connected to a third power supply, and the logic circuit unit A current switching circuit comprising a constant current source connected to the other power supply terminal of the amplifier and supplying a constant current to the logic circuit unit or the amplifier. In the current switching circuit according to claim 3,
The single-phase input current switching logic circuit has a second constant current circuit for supplying a constant current to the logic circuit unit or the amplifier instead of the constant current source, and turns on / off the second constant current circuit. Having a second switch that can be turned off;
The second constant current circuit includes a third transistor having a base connected to the output of the second switch, a collector connected to the other power supply terminal of the logic circuit unit or the amplifier, and a first terminal A second resistor connected to an emitter of the third transistor, a second terminal connected to a fourth power source, a first terminal connected to a collector of the third transistor, and a second terminal; Comprises a second leakage current source connected to the fourth power source or the emitter of the third transistor,
The second switch selects and outputs a normal operation current mode bias voltage during normal operation according to a control signal input from the outside, and selects and outputs a standby current mode bias voltage during standby. A current switching circuit. The current switching circuit according to claim 4, wherein
The differential input current switching logic circuit has a second constant current circuit for supplying a constant current to the logic circuit section or the amplifier instead of the constant current source, and turns on / off the second constant current circuit. Having a second switch that can be turned off;
The second constant current circuit includes a third transistor having a base connected to the output of the second switch, a collector connected to the other power supply terminal of the logic circuit unit or the amplifier, and a first terminal A second resistor connected to an emitter of the third transistor, a second terminal connected to a fourth power source, a first terminal connected to a collector of the third transistor, and a second terminal; Comprises a second leakage current source connected to the fourth power source or the emitter of the third transistor,
The second switch selects and outputs a normal operation current mode bias voltage during normal operation according to a control signal input from the outside, and selects and outputs a standby current mode bias voltage during standby. A current switching circuit. The current switching circuit according to any one of claims 1 to 6,
The leakage current source includes a resistor or a resistor and a capacitor connected in parallel to the resistor. The current switching circuit according to any one of claims 1 to 6,
The current switching circuit according to claim 1, wherein the leakage current source comprises a transistor having a fixed bias voltage applied to a base and a resistor having one end connected to the emitter of the transistor.

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