JPH01128616A - Current switch circuit - Google Patents

Abstract

PURPOSE:To attain high speed operation, to reduce a voltage loss and to simplify a circuit by constituting a transistor, which executes the switching of a base common connecting point, with an MOSFET. CONSTITUTION:An N-channel MOSFET Tr6 is connected between the base common connecting point of transistors Tr4 and Tr5 and an earth. Then, an FET Tr 6 is turned off and the transistors Tr4 and Tr5 are turned on. A constant current I1 is supplied to a load 2 and the FET Tr6 is turned on. Then, the transistors Tr4 and Tr5 are turned off and the current to be flown to the load 2 is turned off. In such a case, the FET Tr6 to be directly switched by a control pulse uses the N-channel MOSFET. Since there is no delay due to saturation in the MOSFET generally, the high speed operation can be executed. A collector potential Vc of the transistor Tr5 can be used in a wide range such as about >=0.3V and the voltage loss is small.

Description

[Detailed Description of the Invention] (Summary) The present invention relates to a current switch circuit that turns on and off current supplied to a load. The transistor that switches the base common connection point of the two transistors forming the mirror circuit is formed by a MOSFET.

[Industrial application field]

The present invention relates to a current switch circuit that turns on and off a current supplied to a load.

2. Description of the Related Art There is a current switch circuit that uses a transistor as a switching element and turns on and off the switching element using an external control signal to turn on and off a current supplied to a load. In this case, it is desirable that the switching operation be capable of high-speed operation, that the entire circuit has little voltage loss, and that the circuit configuration is simple.

[Conventional technology]

FIG. 4 shows a circuit diagram of an example of a conventional circuit. This one is E
This circuit is often used in CL (emitter-coupled logic) circuits and is capable of high-speed operation.The transistor Tr2 paired with the transistor Trl, which is applied to the reference voltage VREF as a base, is
It is turned on with a level control pulse, and constant current source 3 is connected to load 2.
A constant current 11 corresponding to the constant current ■ is applied. On the other hand, by turning off the transistor Tr2 with an L-level control pulse, the current flowing through the load 2 is turned off.

FIG. 5 shows a circuit diagram of another example of the conventional circuit. In the figure, transistor Tr3 is turned off by an L-level control pulse from control signal generator 4, transistors Tr4.
The Tr5 is turned on, and a constant current (1) corresponding to the constant current I of the constant current source 5 is caused to flow through the load 2 by the current mirror. on the other hand,
By turning on transistor Tr3 with an H-level control pulse, transistors Tr4. -'rr, 5 is turned off, and the current flowing through load 2 is turned off.

[Problem that the invention seeks to solve]

In the conventional circuit shown in FIG. 4, in order to avoid the saturation of the transistor Tr2, the collector potential ■c must be used in a range of about 1■ or more, which narrows the usable range, and furthermore, the reference voltage V REF and especially the H level control pulse v
1 requires a stabilized power supply circuit to provide a stable voltage at a low level, which has the problem of complicating the circuit.

On the other hand, in the conventional circuit shown in FIG. 5, the collector potential VC of the transistor Tr5 is about 0.3 V or more, which allows it to be used in a wider range than the circuit shown in FIG. 4, and can reduce voltage loss.
There was a problem that the transistor Tr3 became saturated and the response speed when switching from on to off became slow.

As a countermeasure against such saturation, the transistor Tr
Although it is conceivable to connect a Schottky barrier diode between the base and collector of No. 3, this method has the disadvantage of insufficient current interruption. To avoid such inconvenience, transistor Tr4. A diode must be connected between each emitter of Tr5 and ground,
This causes a problem that the circuit becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a current switch circuit that can operate at high speed, has little voltage loss, and can be easily constructed.

[Means for solving problems]

The present invention comprises a current mirror circuit using two transistors whose bases are connected in common, and a load connected to one of the two transistors by switching the base common connection point with a transistor. In the current switch circuit that switches between supplying and not supplying current, the transistor that switches the common base connection point is configured with a 1403FET.

[Effect]

For example, an L-level control signal turns off the MO3FET, turns on the two transistors, and causes a constant current to flow through the load using a current mirror. On the other hand, the 8081"ET is turned on by the H level control signal, turning off the two transistors and turning off the current flowing to the load. In this case, the common connection point of the bases of the two transistors is switched MOSFE as a transistor
Since T is used, there is generally no delay due to saturation in MOSFETs, so high-speed operation is possible compared to conventional circuits that do not use MOSFETs.

〔Example〕

FIG. 1(A) shows a circuit diagram of a first embodiment of the circuit of the present invention. As in the conventional circuit shown in FIG. 5, a constant current 1115, a transistor rr4. A current mirror circuit is configured by Tr5, and a load 2 is connected to the collector of the transistor Tr5. Transistor Tr4. N-channel HO5FE between base common connection point of Tr5 and ground
This circuit is different from the circuit shown in FIG. 5 in that the circuit T' r 6 is connected.

Turn off FETTr6 and switch transistors Tr4゜Tr5
Turn on, supply constant current ■1 to load 2, and
The basic operation is to turn on transistors Tr4 and Tr5, turn off the current flowing to load 2, and turn off the current flowing to load 2.
The circuit is similar to the one shown in the figure. However, the FET Tr6, which is directly switched by the control pulse, uses an N-channel HO3FET, and since there is generally no delay due to saturation in a MOSFET, it is possible to operate at a higher speed than the conventional circuit shown in FIG. Also, for the conventional circuit shown in FIG. 4, the collector potential VC of the transistor Tr5 is set to about 0.
．． 3■ or more, it can be used in a wide range and has low voltage loss.

FIG. 1(B) shows a circuit diagram of a second embodiment of the circuit of the present invention. This one additionally connects an N-channel HO3FET Tr7 between the bases of transistors Tr4 and Tr5, and
A FETTr8 is connected between the connection point between the TTr7 and the transistor Tr5 and the ground. FET'T
r8 is a control pulse A1, and FETTr7 is turned on and off by control pulse 8, respectively.

When FETTr7 is on (when supplying constant current I+ to load 2), the current flowing here is the same as in Figure 1 (A
) compared to the current ■ for the circuit shown in ) I/h FE
(here, hFE is the current amplification factor of the transistor Tr5). Therefore, the FETTr7 can be made smaller than the FETTr6 in the circuit shown in FIG. 1(A).

Note that the FET Tr8 functions to discharge the base charge of the transistor Tr5, and without it, the switching speed decreases. Therefore, since almost no current flows through the FET Tr8, it can be made smaller. or,
The stray capacitance that becomes a load during switching can be reduced, and as a result, the operation of the constant current source 5 is not interrupted and the voltage amplitude is reduced, so that even higher speed operation is possible.

FIG. 1(C) shows a circuit diagram of the third embodiment of the circuit of the present invention, in which the same components as in FIG. 1 <A) and <8) are given the same numbers and symbols. The explanation will be omitted. In this device, an N-channel HO3 FET Tr9 is connected between the base of the transistor Tr4 shown in FIG. 1(B) and the connection point between its collector and base. FET
Tr9 is always turned on by applying the power supply Vcc.

Since the FET Tr9 is provided, its on-resistance causes the first
Compared to the circuit shown in Figure (B), it is possible to compensate for the constant current error due to the on-resistance of the FET Tr7.

Note that the circuit shown in FIG. 1(C) uses control pulse A.

This is a circuit diagram when A is a CMOS level, but on the other hand, when control pulses A and A are TTL level, it is a FET T
It is conceivable to use a TTL H level circuit or an equivalent circuit connected to the gate of r9.

FIG. 2 shows a circuit diagram of a fourth embodiment of the circuit of the present invention. In the figure, the same components as those in FIG.

In this device, two switching portions of the circuit shown in FIG. 1(B) are provided in parallel to the load 2. In FIG. 2, FET, Tr7°Tr8. The circuits paired with the transistor Tr5 are FETs Tr7' and Tr8'.
, transistor Tr5'.

When control pulses A and B are at L level, FETTr8°Tr8
' is off, control pulse λ, when B is H level, FETT
r7. Tr7' is turned on, which causes transistors Tr5. Tr5' is turned on, and a current 1+=21, which is twice the constant current I of the constant current source 5, flows through the load 2. In this way, since the current from a plurality of current switches can be supplied from one constant current source 5, the current can be doubled while keeping the constant current error small.

FIG. 3 shows a circuit diagram of a fifth embodiment of the circuit of the present invention, and in the figure, the same components as in FIG. 2 are given the same numbers and symbols, and the explanation thereof will be omitted. This is applied to a charge pump circuit.

A charge pump circuit is a circuit that charges and discharges a smoothing capacitor using an input pulse, converts the input pulse width into a voltage, and outputs the voltage from the terminal of the capacitor.

In FIG. 3, reference numeral 5a denotes a constant current source, which supplies a constant current I as in the previous embodiment. The collectors of the transistors Tr5 and Tr5' are connected to one end of the transistor Tr10 and the smoothing capacitor C of the constant current source 5a. 6 is an output terminal. Other configurations are similar to the circuit shown in FIG.

When up, FET Tr8 is turned on by the up pulse,
FET Tr7 is turned off, and transistor Tr5 is turned off. At the same time, down pulse Niyotsu TFET
r8' is turned on, FET Tr7' is turned off, and transistor Tr5' is turned off. Transistor Tr5.
When Tr5' is turned off, a constant current flows through transistor Tr10 of constant current source 5a to charge capacitor C, and an output voltage that gradually increases is taken out from output terminal 6.

On the other hand, when neither up nor down, transistor Tr5 is turned on, transistor 5' is turned off,
Place in oven.

On the other hand, when down, FETTr8 is turned off and FETTr7 is turned on by the up pulse (opposite polarity to when up).
Transistor Tr5 is turned on. At the same time, a down pulse (opposite polarity to the up time) causes FETTr8'
is off, FET Tr7' is on, and transistor Tr
5' is turned on. Transistor Tr5. Tr5'
A constant current from a constant current source 5a flows through each of them, the capacitor C is discharged, and an output voltage that gradually decreases is taken out from the output terminal 6.

In addition, in each embodiment, an analog switch of C-HO8FET may be used instead of the N-channel NO3FET. However, when using an N-channel NO3 FET, it operates at a low potential, so for each FET, the N-channel NO3
One FET is sufficient.

Also, generally N-channel NO3FET is P-channel HO3
Since the on-resistance is lower than that of a FET, the pattern area increase due to switching is only about 1/3 of that when using a C-HO3 FET, and stray capacitance can be kept small, allowing high-speed switching.

〔Effect of the invention〕

As explained above, according to the present invention, since HO8FO is used as the transistor that switches the common connection point of the bases of the two transistors that constitute the current mirror circuit, high-speed operation is achieved compared to conventional circuits that do not use MOSFETs. In addition, compared to a conventional current switch circuit used in an ECL system in which the base of a transistor is directly switched by a control pulse, it is possible to set the collector potential of the transistor on the load side of the current mirror circuit to about 0.3 V or higher, for example. It can be used in a relatively wide range, reduces voltage loss, and can be configured with a relatively simple circuit.

[Brief explanation of the drawing]

1 to 3 are circuit diagrams of each embodiment of the present invention, and FIGS. 4 and 5 are conventional circuit diagrams. In the figure, 2 is a load, 4 is a control signal generator, 5.5a is a constant current source, 6 is an output terminal, Tr4. Tr5. Tr5' is a transistor, Tr6. T
r7. Tr7', Tr8. Tr8'. Tr9 is MOSFET. C indicates a capacitor. (A) (B) (C) Main house pIn41! #Jllll's Meki Tokai it Diagram @ 2 Diagram 3 Diagram

Claims (2)

[Claims] (1) Two transistors whose bases are connected in common (
A current mirror circuit is configured using the two transistors (Tr4, Tr5), and by switching the base common connection point with a transistor, the two transistors (Tr4, Tr5) are connected.
In a current switch circuit that switches between supplying and not supplying current to the load (2) connected to one transistor (Tr5) of Tr5), the transistor that switches the common base connection point is configured with a MOSFET (Tr6). A current switch circuit characterized by: (2) Two transistors whose bases are connected in common (
A current mirror circuit is constructed using the two transistors (Tr4, Tr5), and the above two transistors (Tr4, Tr5) are configured by switching the base common connection point with a transistor.
In a current switch circuit that switches between supplying and non-supplying current to the load (2) connected to one transistor (Tr5) of Tr5), the transistor that switches the base common connection point is connected to the first MOSFET (Tr8). and among the two transistors (Tr4, Tr5), the transistor on the constant current source (5) side (Tr
4) and the first MOSFET (Tr6), a second MOSFET (Tr8) is switched with a control signal (A) of opposite polarity to the control signal (A) for switching the first MOSFET (Tr8). A current switch circuit characterized by connecting MOSFET (Tr7). 3 Two transistors (Tr) whose bases are connected in common
4, Tr5) is used to configure a current mirror circuit,
By switching the base common connection point with a transistor, the two transistors (Tr4, Tr
5) In the current switch circuit that switches between supplying and not supplying current to the load (2) connected to one transistor (Tr5), the transistor that switches the base common connection point is connected to the first MOSFET (Tr8). and among the two transistors (Tr4, Tr5), the transistor on the constant current source (5) side (Tr
4) and the first MOSFET (Tr6), a second MOSFET (Tr8) is switched with a control signal (A) of opposite polarity to the control signal (A) for switching the first MOSFET (Tr8). A transistor (Tr4) connected to a MOSFET (Tr7) and on the constant current source (5) side
A current switch circuit characterized in that a third MOSFET (Tr9) which is always on is connected between the collector-base connection point and the base.