JPH0441847B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is applicable to digital-to-analog converters, light emitting diode constant current drive circuits, etc.
This invention relates to a current mirror circuit for a switch that is controlled by a digital input.

[Technical background of the invention]

When using this type of current mirror circuit for switches in a digital-to-analog converter, transistors are connected in series to multiple constant current sources with binary weighting, and each transistor is controlled by the switch according to the digital input. By doing so, it is possible to obtain an analog output corresponding to the magnitude of the digital input. In addition, the current mirror circuit for the switch is replaced with a light emitting diode (LED).
When used in a drive circuit, the conventional structure was as shown in FIG. 5 or 6. That is, in FIG. 5, a PNP transistor 1 whose base and collector are connected between the V _CC power supply and the ground terminal,
Constant current circuit 2 is connected in series, and multiple PNP type transistors are connected to the base of transistor 1.
The bases of Q ₁ -Q _o are connected, and the emitters of these transistors Q ₁ -Q _o are connected to the V _CC power supply. And the above transistors Q ₁ ~ _{Q o}
NPN transistors Q11 to Qo1, which form the input side of the current mirror circuit, are connected between each collector and the ground terminal, and NPN transistors _Q11 to _Qo1 , which form the output side of the current mirror circuit, are connected between each collector and the ground terminal.
The respective collectors of Q ₁₂ to _{Q o2} serve as LED drive current output terminals 3 ₁ to 3 _o . Further, in parallel with the input side transistors Q ₁₁ to Q _o1 of the current mirror circuit, each base is connected to a digital signal input terminal 4.
NPN type transistors Q ₁₃ to Q _o3 for switch control are connected to terminals ₁ to 4 _o .

On the other hand, in FIG. 6, a constant current circuit 5 and an NPN transistor 6 whose collectors and bases are connected to each other are connected in series between the V _CC power supply and the ground terminal.
The bases of NPN transistors Q ₂₁ -Q _2o are connected, and the emitters of these transistors Q ₂₁ -Q _2o are grounded. The above transistor Q ₂₁ ~
NPN transistors Q ₃₁ -Q _3o are connected between the collectors of Q _2o and the V _CC power supply, and the bases of the transistors Q ₃₁ -Q _3o are commonly connected and a constant voltage V _B is applied thereto. Further, the collectors of the transistors Q ₂₁ -Q _2o are connected to NPN type transistors Q ₄₁ -Q _4o for switch control, the bases of which are connected to the digital signal input terminals 4 _{1 -4o} .
The emitters of the transistors Q ₄₁ to _{Q 4o} are connected to each other, and the collectors of the transistors Q 41 to Q 4o serve as LED drive current output terminals 3 ₁ to 3 _o .

[Problems with background technology]

In the current mirror circuit for a switch shown in Figure 5, the input side transistor of the current mirror circuit is
Current flows through one of Q ₁₁ to _{Q o1} and the switch control transistors Q ₁₃ to Q _o3 connected in parallel to these, and even when the drive output is off, current flows through the input side transistors Q ₁₃ to Q _o3 . flows, resulting in large current consumption and the problem of using a large number of elements.

On the other hand _, in the _switch current mirror circuit shown in _{FIG .} Even when the drive output is off, current flows through the transistors Q ₃₁ to Q _3o , resulting in large current consumption. Moreover, since two transistors are connected in series between the LED drive current output terminals 3 ₁ to 3 _o and the ground terminal, a voltage drop equivalent to two transistors' collector-emitter voltage V _CE occurs. , it is difficult to perform a driving operation when the voltage of the load power source is low, and it is difficult to reduce the voltage of the load power source.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
The present invention provides a current mirror circuit for a switch that consumes less current when the switch output is off, uses fewer elements, and can lower the voltage of the load power supply.

[Summary of the invention]

That is, in the current mirror circuit for a switch of the present invention, a MOS transistor is inserted in series in the base circuit of each of a plurality of bipolar transistors for current drive (switch output).
This device is characterized in that the MOS type transistor is switch-controlled in accordance with digital input.

As a result, when the switch output is off, both the MOS transistor and the bipolar transistor are off, reducing current consumption. Furthermore, since the number of elements used is small, costs can be reduced. Furthermore, only one bipolar transistor is connected to the drive load, making it possible to lower the voltage of the load power supply.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

The current mirror circuit for switches shown in Figure 1 is, for example, a bipolar MOS (insulated gate type)
It is integrated into an integrated circuit using an integrated circuit process, and bipolar transistors and MOS transistors are mixed on the same semiconductor substrate. That is, a constant current circuit 11 is connected between the power supply terminal and the ground terminal.
NPN transistors 12 are connected in series, and a P channel enhancement type (E type) MOS transistor 13 is connected between the collector and base of the transistor 12, and its gate is grounded, and these form a current supply circuit. ing. The collector of the NPN transistor 12 has its gate connected to a digital signal input terminal 4 ₁ to 4 _o.
The respective sources of a plurality of P-channel E-type MOS transistors Q ₅₁ to _{Q 5o} for switch control are connected to. And the above transistor Q ₅₁ ~
The bases of NPN transistors Q ₆₁ to _{Q 6o} for drive current output are connected to each drain of Q _5o .
The emitters of the transistors Q ₆₁ to Q _6o are grounded, and the collectors thereof serve as drive current output terminals 3 ₁ to 3 _o .

In the above current mirror circuit for a switch, the base current is supplied to the constant current NPN transistor 12 through the MOS transistor 13 in the on state, and this NPN transistor 1
A constant current is flowing through 2. The MOS transistors Q ₅₁ to _{Q 5o} for switch control and the NPN transistors Q ₆₁ to _{Q 6o} for switch output are controlled on and off according to the digital input, and when the switch output is off, the above Since no current flows through the transistor, current consumption is reduced. In addition, the number of elements used is smaller than that of the conventional example, which enables cost reduction and is suitable for integrated circuit implementation. In addition, only one NPN transistor is inserted between each of the drive output terminals ₃₁ to _3o and the ground terminal, which facilitates drive operation at low voltages of the load power supply. Lower voltage is possible.

The current mirror circuit for a switch shown in FIG. 2 shows another embodiment, and, compared to the circuit described above with reference to FIG. 1, (1) suppresses fluctuations in the constant current flowing through the constant current transistor 12 Therefore, an NPN transistor 1 is connected in series with the MOS transistor 13 between the collector and base of this transistor 12.
(2) An N-channel E-type MOS transistor 1 is inserted between the base and emitter of the transistor 14 and the collector of the transistor 14 is connected to the power supply terminal.
5 is connected, and the respective gates of two complementary MOS transistors 13 and 15 connected to the base of the constant current transistor 12 are commonly connected and connected to the control input terminal 16, (3 ) N-channel E-type MOS transistors Q ₇₁ to Q _7o are connected between the bases of the switch output NPN transistors Q ₆₁ to _{Q 6o} and the ground terminal, and these MOS transistors Q ₇₁
~Q _7o and P channel E type MOS transistor _Q51 ~
It differs from Q _5o in that each corresponding gate is connected to each other.

As a result, a "1" level (power supply potential) is applied to the control input terminal 16, and the MOS transistor 1
When transistor 5 is turned on, constant current transistor 1
2 can be turned off. If a “0” level (ground potential) is applied to the control input terminal 16 to turn on the MOS transistor 13,
The constant current transistor 12 can be turned on, and the switch output can be turned on and off in accordance with the digital input, similar to the circuit shown in FIG. In this case, for example, the leakage current when the switch output transistor Q ₆₁ is in the off state is caused by the leakage current flowing through the N-channel transistor Q ₇₁ connected between its base and the ground terminal (when the "1" level of the digital input is applied to the gate). The base current is supplied through the P-channel transistor _Q51 , which turns on the next time the digital input becomes "0". ₆₁ is turned on at high speed. Also, when the digital input becomes “1”, the P channel MOS transistor Q ₅₁
When the switch output transistor Q ₆₁ is turned off, the digital input "1" turns on the N-channel MOS transistor Q ₇₁ and discharges the accumulated charge at the base of the switch output transistor Q ₆₁ . , the switch output transistor _Q61 can also be turned off at high speed.

Note that the present invention is not limited to the above embodiments, and the NPN type transistor in the circuits of FIGS. 1 and 2 may be replaced with a PNP type transistor, the P channel transistor replaced with an N channel transistor,
It is also possible to implement modifications as shown in FIGS. 3 and 4 by replacing each channel transistor with a P channel transistor and replacing the power supply potential relationship. In FIG. 3, the same parts as in FIG. 1 are designated by the same reference numerals, and corresponding parts are represented by the same numbers and a ''.
Similarly, in FIG. 4, parts that are the same as those in FIG.

〔Effect of the invention〕

As described above, according to the current mirror circuit for a switch of the present invention, a MOS transistor is inserted in series in the base circuit of each of a plurality of bipolar transistors for current driving, and
By controlling the MOS transistors by digital input, no current flows through the transistors when the switch output is off, reducing current consumption. Furthermore, since the number of elements used is small, costs can be reduced, and since there is only one transistor between the drive current output terminal and the ground terminal, it is possible to lower the voltage of the load power supply.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the current mirror circuit for a switch according to the present invention, FIGS. 2 to 4 are circuit diagrams showing other embodiments, and FIGS. FIG. 2 is a circuit diagram showing a current mirror circuit for a switch. Q ₅₁ ~ _{Q 5o} , Q ₅₁ ′ ~ _{Q 5o} ′...MOS type transistor, Q ₆₁ ~ _{Q 6o} , Q ₆₁ ′ ~ _{Q 6o} ′... Bipolar type transistor.

Claims (1)

[Claims] 1. A current supply circuit that outputs a constant current, each of whose sources are connected in common and connected to the current output terminal of the current supply circuit, and whose gate is connected to a digital signal input terminal and turned on. , multiple MOS transistors that are controlled off, and these
A plurality of bipolar transistors are provided, each of which has its base connected to its drain, its emitter connected to a predetermined potential terminal, and its collector connected to a drive current output terminal. A current mirror circuit for a switch, characterized in that the current of each of the drive current output terminals of the plurality of bipolar transistors corresponds to the current of the current supply circuit according to a control signal from a digital signal input terminal. 2. The current mirror circuit for a switch according to claim 1, wherein the MOS transistor and the bipolar transistor are integrated on the same semiconductor substrate.