JP2687419B2 - Starting circuit for current source circuit - Google Patents

Description

The present invention relates to a starting circuit for a current source circuit which is driven at a low voltage.

[Summary of the Invention]

The present invention relates to a starting circuit for a current source circuit, and by setting a saturation current value of the circuit, driving at a lower voltage can be performed.

[Conventional technology]

For example, there is a current source circuit used in a monolithic IC as shown in FIG. That is, in the figure, NP
A first current mirror composed of N transistors (11) and (12) and a second current mirror composed of PNP transistors (13) and (14) are combined to connect between the first power supply Vcc and the second power supply GND. The transistor (12) is provided with an emission size that is at least twice that of the transistor (11), the transistor (12) is provided with a predetermined emission resistance (15), and the emission resistances of the transistors (13) and (14) are equal to each other. (16) and (17) are provided.

When this drives this current source circuit, Current can be drawn and this current can be drawn by connecting further transistors to the first or second current mirror.

However, in this circuit, the stable operation point of the circuit may be the state of zero current in addition to the state in which the desired current flows. Therefore, when the power is turned on, the stable point of the current of 0 is maintained, and the desired current may not be obtained.

Therefore, conventionally, as shown in the figure, for example, the first power source Vc
Connect a high resistance (100) on the order of 100 kΩ between c and the midpoint of the current mirror connection, and supply a small amount of current through this high resistance (100) when the power is turned on so that the desired current will flow. To be started.

[Problems to be solved by the invention]

However, when the above-mentioned high resistance (100) is provided: 1) High resistance (100) from the power supply Vcc during the operation of the current source circuit.
A ripple current flows in through and the stability of the current source output against ripples deteriorates.

2) Since a resistance of 100 kΩ order is usually required, the area occupied by this high resistance (100) in the IC chip becomes extremely large. It is also possible to use a tunnel resistance or a FET to reduce the area, but these semiconductor resistances have large variations in manufacturing, and as a result, variations in stability with respect to ripples become large.

There were problems such as.

On the other hand, a start-up circuit has been proposed in which the circuit is cut off after start-up by using a diode or the like.

(Gray, Meyer, “Analysis and Design of Analog Inte
grated Circuits "1977, John Wiley & Sons issue-see P.244 etc.) However, in this case, since a circuit in which a large number of diodes are connected in series is used as the starting circuit, at least the forward direction of this diode is used as the power supply Vcc. A voltage exceeding the total voltage is required, which is unsuitable for a low-voltage drive circuit.

The present application has been made in view of such points.

[Means for solving the problem]

The present invention includes a resistor (1) for supplying a current from a first power supply Vcc to a first node, and two diodes (2) (3) connected from the first node to a second power supply GND. First connection with series connection or current-voltage characteristics equivalent to it
And a resistor (4) inserted in series in one current path of a current source circuit composed of a combination of the NPN current mirror (11) (12) and the PNP current mirror (13) (14). A circuit, and a diode characteristic element (5) connected between the first node and the one current path, and a saturation current value of the first circuit is set to a saturation current value of the second circuit and the diode characteristic element. It is a starting circuit for a current source circuit, which is equal to or smaller than the current value.

[Action]

According to this, since it is not necessary to use a high resistance, there is no risk of occupying a large area in the IC chip, and stable driving can be performed at a lower voltage by setting the saturation current value of the circuit. it can.

〔Example〕

In FIG. 1, a power supply Vcc is connected to a node via a resistor (1), and this node is connected to a diode (2).
It is connected to the power supply GND through the series connection of (3). Further, the resistor (4) is inserted in one current path of the current source circuit including the transistors (11) to (14), and the diode (5) is provided between the node and the current path.

Therefore, in this circuit, the resistors (1) and (4) and the diodes (2), (3) and (5) are the starting circuits.

Immediately after the power supply voltage is applied in this circuit, the collector currents of the transistors (11) to (14) are zero.
It is. At this time, if the saturation current value of the base-emitter characteristics of the diode (5) and the transistors (11) and (12) is made equal to or larger than the saturation current value of the diodes (2) and (3), the resistance (1) The current through the diode (2) (3) and the diode (5) resistor (4) transistor (11) base-emitter junction and transistor (12) base-emitter junction and resistor (1
Divide into the circuit composed of 5).

Therefore, the collector current of each transistor begins to flow and increases, and the transistors (11)-(14) resistance (15)-
(17) Stable at the operating point of the current source circuit composed of (4). After the operating point of the circuit stabilizes, the emitter (I _E1 ) of the transistor (11) and the transistor (1)
The sum of the base current I _B2 of 2) flows.

Here, the characteristics of the voltage and current applied to the series circuit of the diodes (2) and (3) are C1, diode (5) resistor (4) transistor (11) (12) (collector is open), resistor (15) Circuit composed of (see Fig. 2)
The characteristic of the voltage and current applied to the
It looks like the figure.

Therefore, in this figure, the current of C1 rises, and
It is possible to set the operating point in the area where the C2 current does not rise. As a specific example, assuming that the resistor (4) 4.5 kΩ, the resistor (15) 360 Ω, the resistor (16) = the resistor (17), and the transistor (12) quadruple in size, and all diodes and NPN transistors have the same saturation current. , The emitter current of the transistor (11) is about 100 μA,
The potential drop of the resistor (4) is about 450 mV. As a result, the diode (5) is about 450m from the forward rising voltage.
V Low voltage is applied. At this time, the current flowing through the diode (5) is higher than that of the diode (2). And is a value that can be practically ignored.

That is, by prescribing the operating point as described above, it is possible to prevent the power supply ripple from being mixed from Vcc through the diode (5) after the start of the circuit is completed, and the stability can be extremely improved.

Thus, according to the circuit described above, since it is not necessary to use a high resistance, there is no risk of occupying a large area in the IC chip, and stable driving can be performed at a lower voltage by determining the saturation current value of the circuit. It can be carried out.

In the above circuit, the series circuit of the diodes (2) and (3) may have another configuration as long as it has equivalent current-voltage characteristics.

Further, the current mirror formed by the transistors (13) (14) and the resistors (16) (17) may have another configuration as long as it has equivalent characteristics.

Further, the diode (5) may be any other element as long as it has a diode characteristic, and in particular, in order to increase the saturation current value, an element having a larger emitter size of the transistor may be diode-connected and used.

It is also apparent that the same operation can be realized by using a complementary circuit configuration in the above circuit.

〔The invention's effect〕

According to the present invention, since it is not necessary to use high resistance, the IC
There is no risk of occupying a large area in the chip, and stable driving can be performed at a lower voltage by determining the saturation current value of the circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example of the present invention, FIGS. 2 and 3 are diagrams for explaining the same, and FIG. 4 is a diagram for explaining a conventional technique. (1) (4) (15) to (17) are resistors, (2) (3)
(5) is a diode, (11) to (14) are transistors,
Vcc and GND are power supplies.

Claims (1)

(57) [Claims] 1. A resistor for supplying a current from a first power supply to a first node and a series connection of two diodes connected from the first node to a second power supply, or a current-voltage characteristic equivalent thereto. And a second circuit in which a resistor is inserted in series in one current path of a current source circuit configured by a combination of an NPN current mirror and a PNP current mirror, the first node and the one circuit described above. A diode characteristic element connected between the current paths, the saturation current value of the first circuit being equal to or smaller than the saturation current values of the second circuit and the diode characteristic element. Starting circuit for source circuit.