JPH0514072A - Semiconductor device - Google Patents

Abstract

PURPOSE:To improve the noise immunity at the time of setting a standard current by integrating a voltage setting circuit, 1st and 2nd variable current sources and a current mirror circuit so as to set the standard current without any externally mounted component. CONSTITUTION:The device is formed by integrating an input terminal T being an external terminal for adjusting an output current, a voltage setting circuit (comprising a transistor(TR) Q3 and a constant current source I1) setting and outputting an optional voltage based on a potential of the external terminal T, 1st and 2nd variable current sources employing a setting output voltage for a current control voltage and having a specific current flowing start equivalent control age, and a current mirror circuit (comprising TRs Q4, Q5, Q6 and resistors R3, R4). Thus, the standard current is set without any externally mounted component, the noise immunity at the time of setting the standard current and fine-adjustment of the output current is easily implemented as required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device suitable as a bias current source for various semiconductor linear circuits, and more particularly to a semiconductor device which can be easily adjusted from the outside.

In manufacturing a linear IC, a user may demand extremely strict accuracy with respect to circuit characteristics. However, it is difficult to achieve such strict accuracy only by controlling the IC manufacturing process.

Therefore, in the case of such a linear IC, it is necessary to add an external adjustment terminal to the chip for fine adjustment.

[0004]

2. Description of the Related Art Conventionally, in manufacturing a linear IC, which requires extremely strict accuracy with respect to circuit characteristics, a variable current source is built in at a required portion of each circuit portion, and its output current value is passed through an external adjustment terminal. Fine tuning is being done.

FIG. 5 shows a conventional example of an IC incorporating such a variable current source. This IC is a transistor Q5
1, Q52, Q56, Q57, and a second current mirror circuit made up of transistors Q53, Q54, Q55, and a second current mirror circuit. By appropriately selecting the value of the external resistor R51 connected between the two, the specified current is supplied to the built-in load circuit (not shown) via the transistors Q55 and Q57.

However, according to such a circuit configuration, even if the IC manufacturing process is completed, no current flows in the built-in load circuit unless the external resistor R51 is connected.
C The manufacturing process causes a certain amount of standard current to flow through the built-in load circuit, and then is not suitable for applications in which fine adjustment of the current is performed while selecting the value of the external resistor R51 as necessary. Since all the accuracy is determined by the accuracy of the external resistor R51, there is a problem that it is difficult to finely adjust. In the figure, R52, R
53, R54, R55, and R56 are resistors with a built-in IC.

Another example of a conventional IC having a variable current source is shown in FIG. This IC has transistors Q58 and Q5
9. A current mirror circuit composed of Q61 and a built-in load circuit (not shown) is provided through the transistor Q61 by applying an appropriate potential to the base of the transistor Q58 by a bias circuit composed of built-in resistors R60 and R61. It is possible to finely adjust the load current value by supplying the standard current to the external adjustment terminal and appropriately selecting the value of the external resistor connected between the external adjustment terminal BIAS and the power supply terminal Vcc or GND. It is a thing.

According to such a circuit configuration, the built-in resistor R
Since it has a bias circuit of 60 and R61,
C. Since the current can be passed through the built-in load circuit from the completion of the manufacturing process, a certain amount of standard current is passed through the built-in load circuit by the IC manufacturing process, and then the value of the external resistor is selected if necessary. It is suitable for the application for which adjustment is intended.

However, according to such a circuit configuration, the value of the potential VB of the external adjustment terminal BIAS in the state where the external resistor is not connected is the intermediate value between the power source Vcc and GND or VEE, as shown in FIG. Since the input impedance is increased due to the influence of the bias circuit formed by the internal resistors R60 and R61, the external adjustment terminal B as shown in FIG.
There is a problem that noise is easily influenced by IAS. That is, the external adjustment terminal BIAS is connected to the power supply terminal Vc.
c or GND, the external adjustment terminal BIA
The potential VB of S can be stabilized to improve noise resistance,
This causes the inconvenience that the standard current cannot flow to the load circuit. In the figure, R57, R
58 and R59 are built-in resistors.

FIG. 9 shows another example of a conventional IC capable of finely adjusting the current from the external adjustment terminal. This IC is a first stage differential amplifier composed of transistors Q71 to Q77,
An internal load circuit is configured by cascade-connecting with an amplifier composed of transistors Q81 to Q89, and the emitters of a pair of transistors Q76 and Q77 interposed in a pair of current paths of the first stage differential amplifier are led out to the outside. The adjustment terminals (OFF SET NULL) are used. By connecting a variable resistor Rx to these external adjustment terminals, the operating current of the first stage differential amplifier is finely adjusted.

However, according to the circuit configuration for finely adjusting the bias current without using such a variable current source, two external adjustment terminals are required, and in addition, a variable resistor having a large dedicated space on the substrate is used. Since the resistor Rx is required and the standard current value is determined corresponding to a certain intermediate setting position of the variable resistor, the adjustment direction is opposite when the current value is increased and when the current value is decreased. There is a problem that it is difficult.

[0012]

As described above, as described above,
For ICs that allow fine adjustment of the current from the external adjustment terminal via the variable current source, a certain amount of standard current is applied to the internal load circuit by the IC manufacturing process, and then the value of the external resistor is selected if necessary. However, it is not suitable for the application for fine adjustment of the current, and in the case of the standard current and the IC that can finely adjust the standard current, the value of the potential of the external adjustment terminal when the external resistor is not connected is , Power supply Vcc
Has a relatively unstable potential between GND and VEE or VEE, and since the input impedance increases due to the effect of the bias circuit due to the internal resistance, there is a problem that the external adjustment terminal is easily affected by noise. ,
Further, in the case where the current is finely adjusted without using the variable current source, there are problems that the number of external adjustment terminals is increased, the external parts are enlarged, and the adjustment operation is difficult.

The present invention has been made in view of the above problems, and an object of the present invention is to set a standard current without external parts and to prevent noise when setting the standard current. It is another object of the present invention to provide a semiconductor device which is excellent in that the fine adjustment of the output current can be easily performed if necessary.

[0014]

In order to achieve the above object, the present invention provides an external terminal for adjusting output current, and a voltage setting circuit for setting and outputting an arbitrary voltage based on the potential of the external terminal. , First and second variable current sources, each having a set output voltage of the voltage setting circuit as a current control voltage and having a control voltage corresponding to a specific current outflow start, a first current terminal connected to a load, and a standard load A second current terminal connected to a corresponding current source, one of the first and second variable current sources is commonly connected to the first current terminal, and the second current terminal is connected to the second current terminal. Is characterized in that the other one of the first and second variable current sources is integrated with a current mirror circuit commonly connected.

[0015]

[Function] When the potential of the external terminal for adjusting the output current is fixed to the power supply or the ground, the voltage drop of the active element decreases and the set output voltage of the voltage setting circuit also decreases, which corresponds to the start of the current outflow of each variable current source. When the voltage becomes equal to or lower than the voltage, the output current value of each of these variable current sources becomes zero. Then, the current flowing through the reference side of the current mirror circuit is only from the current source corresponding to the standard load, and the current value flowing through the load circuit becomes the standard load current value. Further, in this state, the potential of the external terminal for adjusting the output current is fixed to the power supply or the ground, so that it is not affected by noise.

On the other hand, when the potential of the external terminal for adjusting the output current is changed from this state to the ground or the power source potential, the voltage drop of the active element increases and the set output voltage of the voltage setting circuit also rises. When this exceeds the voltage equivalent to the current outflow start of each variable current source, the output current value of these variable current sources starts to rise. At this time, the first variable current source and the second variable current source
Since the current outflow start timing is different from that of the variable current source of No. 3, the value of the current flowing through the load circuit changes its changing direction halfway over time. Therefore, by changing the potential of the external terminal for adjusting the output current in one direction,
Fine adjustment of the load current in the increasing and decreasing directions is possible.

[0017]

FIG. 1 shows an embodiment of a semiconductor device according to the present invention. As shown in the figure, this semiconductor device has an input terminal T which is an external terminal for adjusting an output current, and a voltage setting for setting and outputting an arbitrary voltage from the potential of the input terminal T using a transistor Q3 as a voltage dividing element. Circuit (transistor Q3
And a constant current source I1), and a first variable current source (transistor Q1 and diode D1) having current control voltages set as output voltages of the voltage setting circuit and respective control voltages corresponding to start of current outflow. , D2 and resistance R
1) and a second variable current source (composed of a transistor Q2 and a resistor R2), a first current terminal A connected to an internal circuit C which is a load, and a standard load equivalent current source I2. With a second current terminal B connected,
A transistor Q2, which is the second variable current source, is commonly connected to the first current terminal A, and a transistor Q2, which is the first variable current source, is connected to the second current terminal B.
A current mirror circuit in which 1 is connected in common (composed of transistors Q4, Q5, Q6 and resistors R3, R4)
And are integrally formed.

Next, the operation of the circuit having the above configuration will be described in detail. As shown in the figure, the output current of the transistor Q1 which is the first variable current source is I ′, the output current of the transistor Q2 which is the second variable current source is I, and the output current of the constant current source I ₂ is I _2, the current flowing through the internal circuit I _4, when the current flowing through the transistor Q6 of the current mirror circuit is denoted by I _3, by the action of the current mirror circuit, the following expression is established.

I ₃ = I ₄ + I ... I ₃ = I ₂ + I '... The current I flowing in the internal circuit C from the relation of these equations and equations.
₄ is calculated by the following equation.

I ₄ = I ₂ + I ′ −I ... Further, if the value of the output voltage of the voltage setting circuit is V _OUT ,
V _OUT is represented by the following equation: V _OUT = V _in + V _BE (V _BE = about 0.7V) Further, Vth1 (= 3) for the first variable current source and the second variable current source, respectively. × V _BE ; depends on the base-emitter voltage of the transistor Q1 and the diodes D1 and D2),
A threshold voltage corresponding to the current outflow start of Vth2 (= V _BE ; depending on the base-emitter voltage of the transistor Q2) is set.

Further, the following equation is set for the resistors R1 and R2 of the first variable current source and the second variable current source. R1 = r ... R2 = 2 * r ... Therefore, when the input terminal T is connected to the power supply Vcc, V _in = 0
Next, the V _{OU T} = V _BE from the equation. In this state,
Since the relationship of V _OUT ≦ Vth1 and Vth2 is established, the output currents of the first and second variable current sources are I ′ = I = 0. Therefore, as is clear from the equation, the value of the load current flowing in the internal circuit C is I ₄ = I ₂ . That is, when the input terminal T is connected to the power source Vcc, the internal circuit C
On the other hand, a specified current determined by the accuracy of the constant current source I ₂ can be supplied as a standard current. Also, in this state,
Since the potential of the input terminal T is fixed at Vcc, noise will not be mixed into the circuit via the input terminal T.

On the other hand, the potential of the input terminal T is set to Vcc.
As the value of V _in gradually increases from 0, the value of V _in gradually increases from 0 in FIG.
As shown in (a), a current I expressed by the following equation starts to flow.

I = V _in / (2 × r) ... On the other hand, the output current of the first variable current source is maintained at I ′ = 0 until V _in = 2 × V _BE is reached.

Therefore, as is apparent from the equation, the current flowing through the internal circuit C is I ₄ = I ₂ -I,
As shown in (b), the load current I ₄ flowing through the internal circuit C tends to decrease in the section of 0 ≦ V _in <2 × V _BE . That is, by gradually decreasing the potential of the input terminal T, the value of the load current flowing through the internal circuit C can be reduced below the standard value.

On the other hand, when the value of V _in exceeds 2 × V _BE , from the first variable current source, as shown in FIG.
A current I'shown by the following equation starts to flow. I'= V _in / r ... Therefore, as apparent from the equation, the current flowing through the internal circuit _{C I 4 = I 2 -I-} I' next, as shown in FIG. 2 (b), V _in ≧ In the section of 2 × V _BE, the load current I ₄ flowing through the internal circuit C tends to increase. That is, by lowering the potential of the input terminal T to Vcc−2 × V _BE or less, the value of the load current flowing in the internal circuit C can be increased more than the standard value.

In the circuit of the embodiment shown in FIG. 1, if the first variable current source is connected to the terminal A and the second variable current source is connected to the terminal B, as shown in FIG. It is also possible to reverse the increasing / decreasing tendency of the current I ₄ .

An example in which the circuit of the present invention shown in FIG. 1 is applied to the internal circuit C shown in FIG. 9 is shown in FIG. In this circuit, the polarities of the transistors are opposite to those in FIG. That is, this circuit has an external terminal (OF) for adjusting the output current.
FSET NULL), a voltage setting circuit that sets and outputs an arbitrary voltage by using the active element Q89 whose resistance value is controlled by the potential of the external terminal as a voltage dividing element, and a set output voltage of the voltage setting circuit as a current control voltage. And the first and second control voltages, each of which has its own current outflow start control voltage
Variable current sources (Q90, Q91), a first current terminal A connected to the internal circuit C that is a load, and a second current terminal B connected to the standard load equivalent current source I ₇₃ , and The first variable current source Q is connected to the first current terminal A.
90 is connected in common, and the second current terminal B is integrated with a current mirror circuit in which the second variable current source Q91 is connected in common.

According to this circuit configuration, although the number of elements is increased as compared with the case of FIG. 9, only one external terminal is required and the bias adjustment thereof is easy. In each of the above embodiments, a bipolar type transistor is used, but it goes without saying that a MOS transistor may be used.

[0029]

As is clear from the above description, according to the present invention, the standard current can be set without external parts, and the noise resistance at the time of setting the standard current is excellent.
Moreover, fine adjustment of the output current can be easily performed if necessary.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a graph showing changes in first and second variable current sources and an internal circuit current.

FIG. 3 is a graph showing another example of changes in the first and second variable current sources and the internal circuit current.

FIG. 4 is a circuit diagram showing a case where the present invention is applied to the conventional circuit of FIG.

FIG. 5 is a circuit diagram showing an example of a conventional IC incorporating a variable current source.

FIG. 6 is a circuit diagram showing an example of a conventional IC incorporating a variable current source.

7 is a bias voltage V _B and current I in the circuit of FIG.
₇ is a graph showing the relationship with _B.

FIG. 8 is an explanatory diagram showing a problem of the circuit of FIG.

FIG. 9 is an IC capable of finely adjusting a current from an external adjustment terminal.
FIG. 7 is a circuit diagram showing an example of a conventional example.

[Explanation of symbols]

C ... Internal circuit T ... Input terminal Q1 ... Transistor Q2 serving as first variable current source ... Transistor Q3 serving as second variable current source ... Transistors Q4, Q5, Q6 serving as active elements ... Transistors forming current mirror circuit D1, D2 ... threshold setting diodes I ₂ ... standard-current constant-current source set

Claims (2)

[Claims] 1. An external terminal for adjusting an output current, a voltage setting circuit for setting and outputting an arbitrary voltage based on the potential of the external terminal, a set output voltage of the voltage setting circuit as a current control voltage, and each of them is unique. The present invention has first and second variable current sources having a control voltage equivalent to a current outflow start, a first current terminal connected to a load, and a second current terminal connected to a standard load equivalent current source, and One of the first or second variable current sources is commonly connected to a first current terminal, and the other of the first or second variable current sources is commonly connected to the second current terminal. And a current mirror circuit integrated with each other. 2. The semiconductor device according to claim 1, wherein the first and second variable current sources have different current outflow start equivalent control voltages from each other.