JP2010217963A - Constant current circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant current circuit for adjusting a current mirror ratio to obtain a high-accuracy output current, in a constant current circuit including a built-in current mirror circuit having large current mirror ratio. <P>SOLUTION: A correction circuit MCC is arranged between a current reference part CRS 1 and a current output COS 1. The correction circuit MCC is provided with: a transistor M01 configuring a current mirror circuit with a transistor M11 in the current reference part CRS 1; and a transistor M02 configuring the current mirror circuit with a transistor M12 in the current output part COS 1. Transistors M03 and M04 are serially connected to each of the transistors M11 and M12. A trim element (for example, MA1 and TA1) is paired with the serially connected transistors to form a trim circuit, and m trim circuits are connected to main currents of the transistor M03. In the same way, m trim circuits are connected to the main currents of the transistor M04. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a constant current circuit incorporating a current mirror circuit having a large current mirror ratio.

The constant current circuit is widely used as a bias supply source and a load inside the IC, and as a driver such as an LED or a motor outside the IC.
FIG. 2 shows the configuration of the most basic constant current circuit.

In FIG. 2, a transistor M21, a transistor M22, a transistor M23,..., A transistor M2n using P-channel MOSFETs have their gate terminals and source terminals connected in common to form a current mirror circuit. Here, the gate and source of the transistor M21 are short-circuited, and the main current path is connected in series with the resistor R2 between the power supply line V _DD and the ground. On the other hand, in the transistors M22 to M2n, the common connection point of each source terminal is connected to the power supply line _VDD, and the common connection point of each drain terminal is connected to an external current supply destination. The transistor M21 and the resistor R2 form a current reference part CRS2, and the transistors M22 to M2n form a current output part COS2.

In the constant current circuit of FIG. 2, if the voltage of the power supply line V _DD is constant, the input current I _in2 flowing through the transistor M21 and the resistor R2 is also constant. The value of the input current I _in2 is determined by the gate-source voltage of the transistor M21, the voltage of the power supply line V _DD , and the electric resistance of the resistor R2. Assuming that the transistors M21 to M2n are all formed in the same shape, the output current I _O2 obtained from the common connection point of the drain terminals of the transistors M22 to M2n is theoretically the current reference unit CRS2 and the current output unit COS2 It becomes a value according to the ratio of the number of each transistor.

Specifically, in the case of the circuit of FIG. 2, the output current I _O2 is (n−1) times larger than the input current I _in2 . The ratio (n−1) of the number of transistors is treated as a current mirror ratio indicating the ratio between the input current and the output current for convenience in the design stage of the semiconductor device. The current mirror ratio at the design stage is not originally in the form of the ratio of the number of transistors, but is calculated from the channel shape (particularly, the length L and width W) in each of the transistors M21 and M22 to M2n. It is obtained from the numerical ratio. (See Non-Patent Document 1) (Hereinafter, the number of transistors having the same channel shape will be discussed for easy understanding.)

In the constant current circuit configured as shown in FIG. 2, the magnitude of the output current I _O2 varies depending on the supply voltage from the power supply line V _DD . Therefore, when it is desired to keep the output current I _O2 constant regardless of the supply voltage, a constant current circuit having a configuration as shown in FIG. 3 is used.

In FIG. 3, a transistor M31, a transistor M32, a transistor M33,..., A transistor M3n using P-channel MOSFETs have their gate terminals and source terminals connected in common to form a current mirror circuit. The gate of the transistor M31 is connected to the output terminal of the error amplifier 31, and its main current path is connected in series with the resistor R3 between the power supply line V _DD and the ground. The non-inverting input terminal of the error amplifier 31 is directly connected to the transistor M31 side terminal of the resistor R3, and the inverting input terminal of the error amplifier 31 is connected to the ground side terminal of the resistor R3 via the reference voltage source _Vref3 .

On the other hand, in the transistors M32 to M3n, the common connection point of each source terminal is connected to the power supply line V _DD, and the common connection point of each drain terminal is connected to an external current supply destination. More transistors M31, the resistor R3, the current reference portion CRS3 is formed by the error amplifier A31 and the reference voltage source V _ref3, the current output section COS3 is formed by transistors M32～M3n.

In the constant current circuit of FIG. 3, the input current I _in3 flowing through the transistor M31 and the resistor R3 is controlled to a value that equalizes the voltage across the resistor R3 and the output voltage of the reference voltage source _Vref3 . When the transistors M31 to M3n are all formed in the same shape, the output current I _O3 is (n−1) times as large as the input current I _in3 , as in the constant current circuit of FIG.

JP-A-2005-173741 JP 2001-148468 A

Gray / Meyer co-authored by Nagata Satoshi, “Analog Integrated Circuit Design Technology for VLSI / Lower” Baifukan, December 15, 1990, first edition, P284

  When a constant current circuit is actually formed on a semiconductor chip, each transistor element constituting the constant current circuit is two-dimensionally arranged on the chip for convenience of pattern layout. At that time, the transistors constituting the current mirror circuit are usually formed in the same island region. However, even within the same island region, among the transistors (M22 to M2n and M32 to M3n) in the current output section, there are transistors that are close to and far from the current reference transistors (M21 and M31). It is inevitable that it is formed.

  A transistor at a far physical distance is less paired with a current reference transistor (M21 or M31) than a transistor at a near physical distance. Specifically, even if the shape and size of each part of each transistor are all the same, the current flowing through the transistor at a distant position is slightly different from the current flowing through the transistor at a distant position.

  For example, when a large current is required and the current mirror ratio is desired to be increased to several tens of times, the number of transistors in the current output unit is naturally increased. At this time, many transistors having a physical distance from the transistors (M21 and M31) in the current reference portion are formed. As a result, there is a problem that the actual output current value differs from the input current multiplied by the ratio of the number of transistors. In other words, there is a problem that an error between the value of the current mirror ratio at the design stage and the value of the current mirror ratio at the product stage becomes large.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a constant current circuit capable of adjusting a current mirror ratio and obtaining a highly accurate output current in a constant current circuit having a built-in current mirror circuit having a large current mirror ratio.

  In order to solve the above problems, the present invention provides a current reference unit for supplying a reference input current to the first transistor, and a current for obtaining an output current of several tens of times the input current from the output side of the second transistor An output unit, and a correction circuit disposed between the current reference unit and the current output unit, wherein the correction circuit forms a current mirror circuit with the first transistor as an output side transistor of the current mirror circuit A third transistor; a fourth transistor constituting a current mirror circuit with the second transistor as an input side transistor of the current mirror circuit; a fifth transistor connected in series with the third transistor; and a fourth transistor. Is connected in series to form a current mirror circuit with a fifth transistor as the output transistor of the current mirror circuit. A sixth transistor, at least one first trimming circuit connected in parallel to the main current of the fifth transistor, and at least one second trimming circuit connected in parallel to the main current of the sixth transistor; Characterized by comprising

  According to the present invention, by appropriately trimming the trimming element provided in the correction circuit, the current transmitted from the current reference unit to the current output unit can be adjusted, and the current mirror ratio of the constant current circuit can be adjusted. As a result, it is possible to provide a constant current circuit that can obtain a highly accurate output current.

Circuit diagram of constant current circuit according to the present invention The circuit diagram of an example of the conventional constant current circuit. The circuit diagram of another example of the conventional constant current circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of a constant current circuit according to an embodiment of the present invention.

In FIG. 1, the transistor M11 and the resistor R1 connected in series between the power supply line V _DD and the ground, the output terminal is connected to the gate of the transistor M11, and the non-inverting input terminal is connected to the transistor M11 side terminal of the resistor R1. The current reference unit CRS is configured by the error amplifier A11 and the reference voltage source V _ref1 connected to the inverting input terminal of the error amplifier A11. Further, the transistor M12, the transistor M13,..., The transistor M1n (where n is an integer exceeding 10) constitutes a current output unit COS1 in which the gate terminal and the source terminal are commonly connected.

  The circuit configurations of the current reference unit CRS1 and the current output unit COS1 are substantially the same as the current reference unit CRS3 and the current output unit COS3 of the conventional constant current circuit shown in FIG. 3, and the operations of the respective units are also substantially the same. . In the circuit of FIG. 1, a correction circuit MCC is disposed between the current reference unit CRS1 and the current output unit COS1. The inside of the correction circuit MCC is configured as follows.

First, a P-channel transistor M01 having a gate connected to the gate of the transistor M11 and a source connected to the source of the transistor M11 is provided so as to form a current mirror circuit with the transistor M11 in the current reference unit CRS1. The main current path of the transistor M03 by an N-channel MOSFET is connected between the drain of the transistor M01 and the ground, and the gate of the transistor M03 is connected to the output terminal of the error amplifier A01. The non-inverting input terminal of the error amplifier 01 is connected to the transistor M01 side terminal (= drain) of the main current path of the transistor M03, and the inverting input terminal of the error amplifier A01 is connected to the reference voltage source V _ref1 in the current reference unit CRS1. .

  In order to form a current mirror circuit with the transistor M03, the gates of the transistors MA1, MA2,..., MAm are commonly connected to the gate of the transistor M03, and the sources thereof are commonly connected to the source of the transistor M03. The drains of the transistors MA1 to MAm are commonly connected to the drain of the transistor M03 via trim elements TA1 to TAm, respectively. Thus, a trim circuit is formed in which a transistor and a trim element (for example, MA1 and TA1) connected in series are paired, and m trim circuits are connected in parallel to the main current of the transistor M03.

Further, a P-channel type in which the gate is connected to the gates of the transistors M12 to M1n and the source is connected to the sources of the transistors M12 to M1n so as to form a current mirror circuit with the transistors M12 to M1n in the current output unit COS1. The transistor M02 is provided. The gate of the transistor M02 is further connected to the output terminal of the error amplifier A02. The non-inverting input terminal of the error amplifier 02 is connected to the drain of the transistor M02, and the inverting input terminal of the error amplifier A02 is connected to the reference voltage source V _ref1 in the current reference unit CRS1. The main current path of the transistor M04 by an N-channel MOSFET is connected between the drain of the transistor M02 and the ground, and the gate of the transistor M04 is commonly connected to the gate of the transistor M03 so as to form a current mirror circuit.

  In order to form a current mirror circuit with the transistor M04, the gates of the transistors MB1, MB2,..., MBm are commonly connected to the gate of the transistor M04, and the sources thereof are commonly connected to the source of the transistor M04. The drains of the transistors MB1 to MBm are commonly connected to the drain of the transistor M04 via trim elements TB1 to TBm, respectively. Thus, a trim circuit is formed in which a transistor and a trim element (for example, MB1 and TB1) connected in series are paired, and m trim circuits are connected in parallel to the main current of the transistor M04.

In the constant current circuit of FIG. 1 having the above circuit configuration, a current corresponding to the input current I _in1 is (1) a current mirror circuit including a transistor M11 and a transistor M01.
(2) A parallel circuit of the transistor M03 and the transistors MA1 to MAm connected in series with the transistor M01 (3) a current mirror circuit including the transistor M03, the transistors MA1 to MAm, the transistor M04, and the transistors MB1 to MBm,
(4) a transistor M02 connected in series with a parallel circuit of the transistor M04 and the transistors MB1 to MBm;
Is transmitted to the current output unit COS1. Finally, an output current I _{O1 that} is several tens of times the input current I _in1 is obtained from the common connection point of the drains of the transistors M12 to M1n that constitute the current mirror circuit with the transistor M02.

Specifically, assuming that the transistors M11 and M12 to M1n have the same shape, the transistors M01 and M04 have the same shape, and the transistors M03, MA1 to MAm, MB1 to MBm, and M04 have the same shape, theoretically, the output current I _O1 is (n-1) times larger than the input current _Iin1 as in the circuit of FIG.

Here, when the output current I _O1 of the actually created constant current circuit is a value deviating from (n−1) times the input current I _in1 , the trimming elements TA1 to TAm and TB1 to TBm are appropriately disconnected or connected. By maintaining the output current I _O1 , the output current I _O1 is adjusted to a value (n−1) times the input current I _in1 . The specific procedure is as follows.

First, the input current I _in1 and the output current I _O1 are measured by inspection, and the current mirror ratio of the actual product is calculated from the two current values. Then, the ratio of the numbers of the transistors MA1 to MAm and the transistors MB1 to MBm is determined from the amount of deviation between the actual current mirror ratio and the current mirror ratio at the design stage. At that time, for example, when the actual current mirror ratio appears smaller than the current mirror ratio in the design stage, the number of transistors MA1 to MAn is relatively reduced.

In accordance with the previous determination of the number of transistors, it is determined which one of the trimming elements TA1 to TAn and TB1 to TBn is to be cut and cut by a laser trimming method or the like. As a result, the actual current mirror ratio is approximated to the current mirror ratio at the design stage, and the output current I _O1 is adjusted to a value (n−1) times the input current I _in1 with high accuracy.

  When the adjustment is performed by the correction circuit MCC in which a plurality of trimming circuits are connected to the transistors M03 and M04 as in the present invention, there are the following advantages over the conventional trimming method.

As an example of a conventional trimming method, there is one in which a trimming circuit is provided in the portion of the resistor R3 in FIG. In the case of this conventional method, the current mirror ratio deviation (= the actual current mirror ratio in the product stage and the current mirror ratio deviation in the design stage) generated in the transistors M31 to M3n remains as it is. _{When in3} is changed, the value of the output current I _O3 may deviate from the target value depending on the variable means of the input current I _in3 . On the other hand, in the present invention, since the actual current mirror ratio approximates to the design stage current mirror ratio by trimming, the value of the output current I _O3 is set to the target value regardless of the means of changing the input current I _in3. Can be adapted to

As another example of the conventional trimming system, as disclosed in Patent Document 2, a trimming circuit such as the transistor MA1 and the trimming element TA1 in FIG. 1 is directly connected in parallel to the transistors M32 to M3n in FIG. There is something to provide. In the case of this conventional example, if the current mirror ratio is as large as several tens of times, depending on the formation position of the transistor constituting the trimming circuit and which one is to be cut, the positional relationship and current of the transistor are disturbed and the trimming is performed. There is a possibility that the current mirror ratio and the output current I _O3 will not be as large as planned.

Further, in another example of the conventional method, in terms of variations in each product was also considered, as is intended to adjust the output current I _O3 to the target value by trimming, a constant current circuit output current I _O3 while higher than the target value Must be made. In other words, the product must be trimmed, and the difference between the value of the output current I _{O3 at} the time of inspection and the target value becomes large, so it is not easy to adjust the output current I _O3 to the target value with high accuracy.

On the other hand, in the present invention, the relative positional relationship and current between the transistor M02 and the transistors M12 to M1n in FIG. 1 depend on the positions where the transistors MA1 to MAn and MB1 to MBn constituting the trimming circuit are formed and whether or not they are disconnected. Not disturbed. Further, the current mirror ratio between the transistors MA1 to MAm and the transistors MB1 to MBm is low (1 in the embodiment), and the physical distance is obtained by dispersing the formation positions of the MA1 to MAm and MB1 to MBm. It is possible to easily prevent the formation of transistors that are close to and distant from each other. For this reason, the current mirror ratio and the output current I _O1 of the actual product after the trimming process can be set to the sizes planned before the process with high accuracy.

Furthermore, in the present invention, a constant current circuit can be manufactured from the beginning so that the output current I _O3 becomes a target value, and some of the products do not require trimming, and the amount of work required for trimming can be reduced. Further, since the difference between the value of the output current I _{O1 at} the time of inspection and the target value is small, it is easy to adjust the output current I _O3 to the target value with high accuracy. Therefore, according to the present invention, it is possible to provide a constant current circuit that can obtain an output current with high accuracy.

  In the embodiment of the present invention described above (FIG. 1), the drains of the transistors M03 and M04 are directly connected to the drains of the transistors M01 and M02. However, the drains of the transistors M03 and M04 may be connected to the drains of the transistors M01 and M02 via trim elements, and the transistors M03 and M04 may be used as one of the trimming circuits.

In the embodiment of the present invention shown in FIG. 1, biases for the transistors M11, M03, and M02 constituting the current mirror circuit are supplied from error amplifiers A11, A01, and A02, respectively. When the output current I _O1 does not require a very high stability, the error amplifiers A11, A01, A02 are not used, but instead the gates and sources of the transistors M11, M03, M02 as in the transistor M21 of FIG. You may make it short-circuit between.

COS1: current output unit CRS1: current reference unit I _in1 : input current I _O1 : output current M01: transistor (third transistor)
M02: Transistor (fourth transistor)
M03: Transistor (fifth transistor)
M04: Transistor (sixth transistor)
M11: transistor (first transistor)
M12 to M1n: transistors (second transistors)
MA1 to MAn: transistors (transistors constituting the first trimming circuit)
MB1 to MBn: transistors (transistors constituting the second trimming circuit)
MCC: correction circuits TA1 to TAn: trim elements (transistors constituting the first trimming circuit)
TB1 to TBn: Trim elements (transistors constituting the second trimming circuit)

Claims (3)

A current reference section through which a reference input current is passed to the first transistor, a current output section that obtains an output current of several tens of times the input current from the output side of the second transistor, the current reference section, A correction circuit disposed between the current output units,
Here, the correction circuit
A third transistor that forms a current mirror circuit with the first transistor as an output-side transistor of the current mirror circuit;
A fourth transistor constituting a current mirror circuit with the second transistor as an input side transistor of the current mirror circuit;
A fifth transistor connected in series with the third transistor;
A sixth transistor connected in series with the fourth transistor and forming a current mirror circuit with the fifth transistor as an output side transistor of the current mirror circuit;
At least one first trimming circuit connected in parallel to the main current of the fifth transistor;
A constant current circuit comprising: at least one second trimming circuit connected in parallel to a main current of the sixth transistor. The first trimming circuit includes a seventh transistor that forms a current mirror circuit with the fifth transistor, and a first trim element connected in series to a main current path of the seventh transistor,
The second trimming circuit includes an eighth transistor constituting a current mirror circuit with the sixth transistor, and a second trim element connected in series to the main current path of the eighth transistor. The constant current circuit according to claim 1, wherein:   3. The constant current circuit according to claim 2, wherein the fifth transistor is shared with one of the seventh transistors, and the sixth transistor is shared with one of the eighth transistors. .

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