JPH0614497Y2 - Multi constant current source circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a multi-current operating circuit that is connected to a plurality of current operating circuits and is selectively selected to supply a current to each of the current operating circuits. The present invention relates to a constant current source circuit.

[Outline of device]

In the multi-constant current source circuit of the present invention, N sets of transistor pairs serving as current sources for the currents I ₀ and nI ₀ are provided corresponding to N control inputs, and N pairs serving as current sources for the current nI ₀ are provided.
The emitters of these transistors are commonly connected to a resistor R to form a first transistor group, and the N transistors serving as a current source of the current I ₀ have their emitters commonly connected to the resistor nR and their collectors also commonly connected. To form a second transistor group, and one transistor pair is selected from N pairs according to the control input.
It is designed to be a constant current source circuit for two current operating circuits. Then, the current I ₀ . The ratio of nI ₀ is determined by the resistances R and nR.

As a result, it is possible to improve the output accuracy of the currents I ₀ and nI ₀ , and lower the operation lower limit voltage and offset voltage of the current output terminal.

[Conventional technology]

 First, a conventional technique will be described with reference to the drawings.

FIG. 5 shows that the two amplifiers A ₁ and A ₂ which are applying negative feedback to the resistors R ₁₀ and R ₁₁ and R ₁₂ and R ₁₃ are switched by the switch S, and two input signals V _in 1 and V _in 2 are used. FIG. 6A shows an example of a switch-equipped amplifier that selectively outputs the output of FIG. 6 as an output voltage V _0. For example, when the switch-equipped amplifier is realized in an IC circuit, a configuration as shown in FIG. A means for switching the constant current source of the differential pair which is the input stage is generally used.

In FIG. 6 (a), 30A is the first amplifier A ₁
The input differential pair composed of the transistors Q ₃₅ and Q ₃₆ constituting the same and the second input differential pair 30B composed of the transistors Q ₃₇ and Q ₃₈ also constituting the second amplifier A ₂ are surrounded by a chain line. 31 is the first and second differential pair 30
A switching current source circuit for supplying a current to A and 30B is shown, and includes a current source 32 of 2I ₀ , a current source 33 of I ₀ , and a switch unit 34.

The current source 33 supplies the current I ₀ of the transistors Q ₃₉ and Q ₄₀ forming the current mirror circuit,
Transistor Q ₄₁ represents an output transistor for applying feedback.

The switching current source circuit 31 described above is realized by the circuit shown in FIG. 6 (b).

That is, the current 2 is generated by the transistor Q ₃₁ and the resistor R.
A current source 32 for I ₀ is constructed and also a transistor Q ₃₂
And the resistor 2R form a current source 33 for the current I ₀ , and the current source 32 operates in response to the control input voltages V _C1 and V _C2 , and one of the transistors Q ₃₃ or Q ₃₄ operates to cause the above-mentioned first source. Will be connected to one of the differential pair 30A or the second differential pair 30B.

By the way, in the circuit of FIG. 6 (b), the transistor Q
_{Since 33} (Q ₃₄ ) and Q ₃₁ are connected in series, if the operating voltage V _CC is low, there is a problem that the input differential pair connected to this switching power supply does not operate sufficiently.

Therefore, as shown in FIG. 7, a method of switching the current source itself can be considered.

In this circuit, 50A and 50B are the first and second differential pairs,
51 surrounded by the one-dot chain line corresponds to the constant current source circuit, 52,
Reference numeral 53 denotes a current source for the currents 2I _r and I _r .

In this circuit, when the transistors Q ₆₃ and Q ₆₄ are switched according to the control input voltages V _C1 and V _C2 , the transistors Q ₅₁ and Q ₅₄ or the transistors Q ₅₂ and Q ₅₄ are switched.
_When either one of ₅₅ is turned on, the current source 52
The current 2I _r is transmitted as a current 2I ₀ to one of the first differential pair 50A or the second differential pair 50B by the current mirror effect, and the current I ₀ is transmitted to the current source 53. Current I _r can be supplied by a current mirror circuit.

[Problems to be solved by the invention]

Thus, as the switchable constant current source circuit, the one shown in FIG. 6 and the one shown in FIG. 7 can be considered. In the circuit shown in FIG.
_Since the ratio of ₀ and 2I ₀ is determined, the accuracy of this current ratio is kept relatively good, but the lower limit of the control input voltage range is set because the bias voltages of the transistors Q ₃₁ and Q ₃₂ are required independently. Due to the limitation, it is difficult to lower the operation lower limit voltage of the current output terminal, and it is not suitable for use in low-voltage equipment.

On the other hand, in the circuit shown in FIG. 7, it is possible to cope with a relatively low power supply voltage, but since the reference currents 2I _r and I _r are transmitted by the current mirror and become 2I ₀ and I ₀ ,
2I from 2I _{r 0,} and an error occurs during the conversion to _{I 0} from _{I r,} deteriorates the accuracy of the current ratio of 2I ₀ and _{I 0,} which is not preferable leading to an increase in the output offset voltage.

[Means for solving problems]

The present invention has been made in consideration of the above problems.
A pair of transistors serving as current sources for the currents I ₀ and nI ₀ corresponding to the respective control inputs (current actuating circuits) are switchably provided, and N transistors of the first transistor group serving as current sources for the current nI ₀ are provided. The emitters of the transistors are connected in common to the resistor R, and the emitters of N transistors of the second transistor group serving as the current source of I ₀ are connected to the resistor nR.
Is commonly connected to.

[Action]

With this arrangement, the ratio of the currents I ₀ , nI ₀ is determined by the resistors R, nR when one control input is supplied in order to activate one current operating circuit. Also, depending on the control input voltage,
It is possible to supply a bias voltage for a pair of transistors serving as a current source.

〔Example〕

FIG. 1 (a) shows an embodiment of a circuit using the present invention, which corresponds to two current operating circuits.

In the figure, the portion surrounded by the one-dot chain line corresponds to the multi-constant current source circuit of the present invention, which corresponds to two control input voltages (V _C1 , V _C2 ).

That is, the transistors Q ₁ and Q ₃ become a transistor pair corresponding to V _C2 , and the transistors Q ₃ and Q ₄ become a transistor pair corresponding to V _C1 , and when each control input voltage is supplied, a current 2I ₀ , And act as current sources for I ₀ .

Further, the transistors Q ₁ and Q _{2 serving as} the current source of the current 2I ₀ have the emitters commonly connected to the resistor R to form a first transistor group, and the transistors Q ₃ and Q serving as the current source of the current I _{0. In 4,} the collectors are commonly connected and the emitters are commonly connected to the resistor 2R, forming a second transistor group. The collector of the second transistor group is connected to the current mirror circuit composed of the transistors Q ₁₄ and Q ₁₅ , and the current I ₀ is transmitted.

2A, 2B shows the current operation circuit such as a differential amplifier, respectively consist transistors Q _10, Q ₁₁ and Q _12, Q _13.

Transistor Q ₁₆ represents an output transistor for applying feedback.

The PN junction areas of the emitters of the transistors Q ₁ and Q ₂ are doubled so that they have junction voltages (V _BE ) with the transistors Q ₃ and Q ₄ , respectively.

Here, the control input voltage V _C1 is “H” level, V
When _C2 is inputted becomes "L" level, transistors _{Q 2} and _{Q 4} are turned on, the transistor _{Q 1,} and _{Q 3} are turned off. At this time, the multi-constant current source circuit 1 is in a state that can be represented as an equivalent circuit shown in FIG. 1 (b).

That is, the transistors Q ₂ and Q ₄ act as current sources according to the control input voltage V _C1 , and the output currents become 2I ₀ and I ₀ due to the resistors R and 2R. Then, the current 2I ₀ is supplied to the differential amplifier 2A, the differential amplifier 2A operates, and the voltage V ₀ is output.

Conversely, when the control input voltage V _C1 is “L” level, V _C2
Is at "H" level, its equivalent circuit is shown in Fig. 1 (c).
Then, the transistors Q ₁ and Q ₃ are turned on, the differential amplifier 2B operates, and the voltage V ₀ is output.

In this circuit, as described above, the currents I ₀ and 2I ₀ are determined by the ratio of the resistors R and 2R. Therefore, even if the “H” voltage of V _C1 or V _C2 varies, the resistance ratio of the resistors R and 2R is Since the ratio is constant on the IC substrate, the current ratio rarely fluctuates, the offset voltage also decreases, and the characteristics of the switch circuit also improve. Also,
A circuit for independently generating the current I ₀ is unnecessary, and the number of elements can be reduced as compared with the conventional one.

Furthermore, unlike the circuit shown in FIG. 6, it is not necessary to apply a bias voltage separately from the control input voltage, and the lower limit of the control input voltage can be extended.
It is also effective when you want to lower the operating voltage of the current output terminal.

FIG. 2A shows a case where there are four current operating circuits such as a differential amplifier. 1A is a multi-constant current source circuit of the present invention, and 2A to 2D are current operating circuits such as a differential amplifier. Indicates.

Again, in response to each control input voltage (V _C1 ~V _C4), the transistor pair _{(Q 21, Q 25),} (Q 22, Q
₂₆ ), (Q ₂₃ , Q ₂₇ ), (Q ₂₄ , Q ₂₈ ), and further, the emitters of Q _{21 to} Q ₂₄ , which are the first transistor group, are commonly connected to the resistor R, and the second transistor group Becomes Q
_By commonly connecting the emitters of _{25 to} Q ₂₈ to the resistor 2R and commonly connecting the collectors thereof, it is possible to obtain the same effect as in the case of two inputs in FIG.

For example, when the control input voltage V _C1 is “H” level,
When V _{C2 to} V _C4 are at “L” level, only Q ₂₁ and Q ₂₅ are turned on, the current ratio is determined by the resistors R and 2R, the current 2I ₀ is supplied to the differential amplifier 2A, and the voltage is increased. V
₀ is output. The multi-constant current source circuit 1A at this time is
It will be shown as an equivalent circuit in FIG.

Since the current ratio is determined by the resistance ratio of the two resistors to which the respective emitters of the first and second transistor groups are connected, the current ratio can be changed by changing the resistance ratio n.

For example, as shown in FIGS. 3 (a) and 3 (b), the second
By setting the resistance of the transistor group connected to nR to nR, the current sent to each differential amplifier can be set to nI ₀ having a predetermined coefficient n with respect to I ₀ .
By setting the resistance connected to the transistor group of n as nR and the resistance connected to the second transistor group as R,
It is also possible to output the current I ₀ / n.

It should be noted that in the above-described embodiments, the description has been made by using the current source of the NPN type transistor, but it goes without saying that the current source of the PNP type transistor as shown in FIG. 4 may be used. Nor.

Further, the current operation circuit selected by this multi-constant current source circuit is not limited to the differential amplifier, but may be a multiplier or an oscillation circuit.

[Effect of device]

As explained above, the multi-constant current source circuit of the present invention is
Since the current ratio is determined by the resistors R and nR, there is an effect that the variation in the current ratio is small and the offset voltage can be reduced. Further, there is also an effect that the restriction is reduced when it is desired to lower the operating voltage of the current output terminal, and the utility to low voltage devices is expanded.

[Brief description of drawings]

1 (a), (b) and (c) are circuit diagrams showing one embodiment of the present invention, and FIGS. 2 (a) and (b) are circuit diagrams showing another embodiment of the present invention. 3 (a) and 3 (b) are circuit diagrams for explaining the current ratio setting according to the present invention, and FIG.
A circuit diagram when a P-type transistor is used, FIG. 5 is a circuit diagram of an amplifier with a switch, FIGS. 6 (a) and 6 (b) are circuit diagrams showing a conventional example, and FIG. 7 is another conventional example. It is a circuit diagram shown. In the figure, 1A indicates a multi-constant current source circuit, and 2A to 2D indicate differential amplifiers.

Claims (1)

[Scope of utility model registration request] 1. A plurality of first current source transistors whose emitters are commonly connected to one end of a first resistor and whose collectors are connected to a plurality of current operating circuits;
A plurality of second current source transistors that are commonly connected to one end of the resistor and whose collectors are commonly connected,
The other ends of the first resistor and the other end of the second resistor are grounded, the plurality of first current source transistors connected to each of the plurality of current operating circuits, and the plurality of first current source transistors. The respective base electrodes of the plurality of second current source transistors which are controlled in correspondence with the respective current source transistors to form a plurality of common inputs, and select the current operating circuit for the common inputs. A multi-constant current source circuit, which is supplied with a control signal for operating the same.