JPH11194844A - Self-correcting constant current circuit - Google Patents

Abstract

(57) [Problem] To provide a constant current flowing through a depletion type MOS transistor even if a threshold voltage varies. SOLUTION: A resistor for self-correction of a current variation due to a variation in threshold voltage is provided with a depletion type MO.
It was inserted between the gate and the source of the S transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current circuit capable of obtaining a stable constant current even if the threshold voltage of a MOS transistor fluctuates in a manufacturing process, and a circuit (for example, a reference voltage) using the constant current circuit. Circuit, constant current inverter circuit, etc.).

[0002]

2. Description of the Related Art FIG. 2 shows a conventional depression type MO.
1 shows a constant current circuit using a single S transistor. By connecting the gate, source and substrate of the depletion type MOS transistor 1 to the ground potential VSS and connecting the drain to the high potential VDD, a constant current flows between the source and drain of the depletion type MOS transistor.

[0003]

In a conventional constant current circuit using a single depletion type MOS transistor, it occurs in manufacturing processes such as thermal diffusion, gate oxidation, and ion implantation.
There has been a problem that the absolute value of the constant current and the temperature coefficient are greatly changed by the fluctuation of the threshold voltage of the MOS transistor.

[0004]

According to the present invention, in order to solve the above problems, a resistor is inserted between the source and the gate of a depletion type MOS transistor. By doing so, for example, when the threshold voltage is increased and the constant current is about to increase, the gate potential will not flow the constant current due to the voltage drop caused by the current flowing through the resistor inserted between the gate and source. , The constant current is stabilized. Conversely, if the threshold voltage decreases and the constant current tries to decrease, the gate
Since the voltage drop caused by the current flowing through the resistor inserted between the sources is reduced, the gate potential changes in the direction in which a constant current flows, and the constant current is stabilized.

[0005] The resistance is a depletion type MOS.
A more stable constant current can be obtained by using a resistor whose resistance value changes in a direction to stabilize the constant current in conjunction with a change in the threshold voltage of the transistor.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a constant current circuit in which a resistor 2 is inserted between the gate and the source of a depletion type MOS transistor 1. The resistor 2 may be a poly resistor or a diffused resistor. However, in conjunction with the threshold voltage of the depletion type MOS transistor 1 (hereinafter referred to as Vtnd), the resistance increases as the absolute value of Vtnd increases, and the resistance of Vtnd increases. It is desirable that the resistance value decreases as the absolute value decreases. By selecting such a resistor, Vtnd
, The absolute value of the constant current and the temperature characteristics are stabilized.

[0007]

FIG. 1 shows an embodiment of a self-correcting constant current circuit according to the present invention. Connect the source of the depletion type MOS transistor 1 to one end of the resistor 2 and connect the gate of the depletion type MOS transistor 1 to the other end of the resistor 2 with VSS.
By connecting the drain of the S transistor 1 to VDD, a constant current flows between the source and the drain of the depletion type MOS transistor 1.

As shown in FIG. 1, depletion type MOS
By inserting the resistor 2 between the source and the gate of the transistor 1, even if the threshold voltage (Vtnd) of the depletion type MOS transistor 1 varies in the manufacturing process, self-correction is applied by the following principle and the constant current is stable. Become [1] When Vtnd increases Vtnd increases → The current flowing through the depression type MOS transistor 1 increases.

(Amount of increase in current flowing through depletion type MOS transistor 1: ΔI) Constant current increases → The gate potential of depletion type MOS transistor 1 becomes “ΔI ×
R ”in the negative direction. (Resistance value of resistor 2:
R) The gate potential changes in the negative direction with respect to the source potential → It becomes difficult for a constant current to flow.

As described above, the constant current flowing through the depletion type MOS transistor 1 is self-corrected, and the constant current is stabilized with respect to the variation of Vtnd. [2] When Vtnd becomes small Vtnd becomes small → The current flowing through the depression type MOS transistor 1 decreases.

(Amount of decrease in current flowing through depletion type MOS transistor 1: ΔI) The constant current decreases. → The gate potential of depletion type MOS transistor 1 becomes “ΔI ×
R ”changes in the positive direction. (Resistance value of resistor 2: R) The gate potential changes in the positive direction with respect to the source potential → The constant current flows more easily.

As described above, the constant current flowing through the depletion type MOS transistor 1 is self-corrected, and the constant current is stabilized with respect to the fluctuation of Vtnd. The resistor 2 in FIG. 1 may be a poly resistor or a diffused resistor, but the resistor having the structure formed in the steps shown in FIGS. 3A to 3C has the greatest effect of stabilizing the constant current. 3 (a) to 3 (c)
FIG. 4 is a cross-sectional view of a manufacturing process of the depletion type MOS transistor 1 and the resistor 2. This is described below.

Depletion type MOS transistor 1
N-type impurities for adjusting the threshold voltage of the depletion type MOS transistor 1 (Phos or
As) is implanted (FIG. 3A), and an N-type conductive layer 7 is formed on the surface of the Pwell (FIG. 3B). Next, a gate 10 of the MOS transistor is formed, and a high-concentration N-type impurity is ion-implanted into the source and drain 8 to form a portion 9 serving as an electrode of the resistor 2.
A high-concentration P-type impurity is ion-implanted to complete the depletion type MOS transistor 1 and the resistor 2 (FIG. 3C).

As shown in FIG. 3C, "Ion implantation into the channel forming region for adjusting the threshold voltage of the depletion type MOS transistor 1" is also performed on the surface of the diffusion resistor portion of the resistor 2 as in the case of the resistor 2 in FIG. , The resistance value of the resistor 2 is linked with Vtnd, and the self-correction is applied to the variation of Vtnd. In the following, "Regarding resistor 2" and "Principle of self-correction of constant current when resistor 2 and depletion type MOS transistor 1 are combined" will be described.

The resistor 2 in FIG. 3C is a Pwell resistor formed inside the Nsub, and the same amount of impurities as the ion implantation into the channel forming region of the depletion type MOS transistor 1 is implanted near the surface of the Pwell resistor. ing. Fig. 3 (c)
In FIG. 7, the region into which ions are implanted is indicated as 7. The part that actually works as a resistor is 11 below 7. Pwell (P type)
Has an N-type layer 7 of opposite polarity on the surface of the resistor 2, the resistance value of the resistor 2 changes depending on the magnitude of Vtnd (the amount of ion implantation), and Vtnd
Increases, the resistance value of the resistor 2 increases. That is, Vtn
d and the resistance value of the resistor 2 are linked.

Next, the resistance 2 and the depletion type MOS
The principle that the constant current is self-corrected when the transistor 1 is combined will be described. FIG. 4 is a diagram showing “solid line a indicating the relationship between the ON resistance of the depletion type MOS transistor 1 and Vtnd” and “broken line b indicating the relationship between the resistance value of the resistor 2 and Vtnd”. When Vtnd increases, the on-resistance of the depression type MOS transistor 1 (the gate potential is fixed to 0 V) decreases, and the resistance value of the resistor 2 increases. Accordingly, by connecting one end of the resistor 2 to the source of the depletion type MOS transistor 1 and connecting the other end to the gate of the depletion type MOS transistor 1, the constant current is self-corrected according to the following principle.

[1] When Vtnd is large Vtnd is large → The current flowing through the depletion type MOS transistor 1 increases (depletion type M
Current flowing through OS transistor 1: I, increase in current flowing through depletion type MOS transistor 1: Δ
I) Vtnd large → resistance value of resistance 2 increases (resistance value of resistance 2: R, increase amount of resistance value of resistance 2: ΔR) As described above, the potential difference (Vgs) between the gate and source of the depletion type MOS transistor 1 is reduced. Decrease (Amount of decrease in potential difference between gate and source: ΔVgsΔ−I × Δ
R−ΔI × R) Vgs decrease → current flowing in the depletion type MOS transistor 1 decreases Self-correction is applied to the current flowing in the depletion type MOS transistor 1 as described above, and the constant current hardly fluctuates even if Vtnd fluctuates.

[2] When Vtnd becomes small Vtnd becomes small → The current flowing through the depletion type MOS transistor 1 decreases (depression type MO transistor 1).
Current flowing in S transistor 1: I, decrease in current flowing in depletion type MOS transistor 1: ΔI) Vtnd small → resistance of resistance 2 decreases (resistance of resistance 2: R, reduction of resistance of resistance 2) : ΔR) As described above, the gate-source potential difference (Vgs) of the depletion type MOS transistor 1 increases (the amount of increase in the gate-source potential difference: ΔVgs ≒ −I × Δ).
R−ΔI × R) Vgs increase → current flowing in depletion type MOS transistor 1 increases Self-correction is applied to the current flowing in depletion type MOS transistor 1 as described above, and the constant current hardly fluctuates even if Vtnd fluctuates.

FIG. 5 shows a temperature characteristic of Vgs-√Ids of the depletion type MOS transistor 1. Here, Vgs indicates a gate-source potential, and Ids indicates a source-drain current. MOS transistor has current (√Ids) against temperature change
There is a point P at which is hardly changed. The depletion type MOS transistor is located at the point P where the temperature change of the source-drain current of the MOS transistor becomes small.
By adjusting the resistance value R of the resistor 2 so that the gate potential of 1 (Vg = 0 V) comes (for example, by adjusting the size of the resistor and the constant current value), the absolute value is obtained according to the principle of self-correction described above. A constant current circuit with small variation and small variation in temperature coefficient can be obtained.

FIG. 6 shows the Vtnd dependence of the temperature coefficient of the constant current of the self-correcting constant current circuit of the present invention. The broken line d representing the relationship between the temperature coefficient of the constant current when the resistor 2 is inserted and the Vtnd is a constant current due to the Vtnd fluctuation, compared to the solid line c representing the relationship between the temperature coefficient of the constant current and the Vtnd when the resistor 2 is not inserted. Small variation in temperature coefficient. Further, by using the self-correcting constant current circuit of the present invention, it is possible to reduce variations in current consumption and temperature coefficient of the reference voltage circuit, the constant current inverter circuit, and the like. Hereinafter, embodiments of the reference voltage circuit (two types) and the constant current inverter circuit (one type) using the self-correcting constant current circuit of the present invention will be described.

FIG. 7 shows an embodiment of a reference voltage circuit using a self-correcting constant current circuit. Depletion type MOS transistor 1 and enhancement type MO of the same conductivity type
Consisting of S transistor 14 and resistor 2, the source, substrate and resistor of depletion type MOS transistor 1
2 is connected to the gate of the depletion type MOS transistor 1, the other end of the resistor 2 and the enhancement type.
By connecting the drain and gate of the MOS transistor 14, the reference voltage Vref is output to the OUT terminal.

FIG. 8 shows the Vtnd dependence of the temperature coefficient of the reference voltage of the reference voltage circuit using the self-correcting constant current circuit of the present invention. Temperature coefficient of reference voltage and Vtnd when resistor 2 is inserted
The dashed line f representing the relationship between Vtnd and Vtnd represents the relationship between the temperature coefficient of the reference voltage and Vtnd when the resistor 2 is not inserted.
The variation of the temperature coefficient of the reference voltage due to the variation is small. FIG. 9 shows an embodiment of a reference voltage circuit using a self-correcting constant current circuit and a current mirror circuit. Depletion type MOS transistor 1, enhancement type MOS transistor 14, resistor 2, and current mirror circuit 1 of the same conductivity type
5 and 16, connecting the source of the depletion type MOS transistor 1, the substrate and one end of the resistor 2,
The gate of the depletion type MOS transistor 1, the other end of the resistor 2, and the enhancement type MOS transistor 14
The source and substrate of the enhancement type MOS transistor 14 are connected to VSS, and a current having the same magnitude as the current flowing through the depletion type MOS transistor 1 is supplied to the drain of the enhancement type MOS transistor 14 by the current mirror circuits 15 and 16, and the Connect the drain and the gate, and output the reference voltage Vref to the OUT terminal.

The reference voltage Vref obtained here has a small variation in temperature coefficient even if the threshold voltage Vtnd varies in the manufacturing process, similarly to the reference voltage in FIG. FIG. 10 shows an example of a constant current inverter circuit using a self-correcting constant current circuit. It consists of a depletion type MOS transistor 1, an enhancement type MOS transistor 14, a resistor 2, and a current mirror circuit 15, 16 of the same conductivity type, and connects the source of the depletion type MOS transistor 1, a substrate, and one end of a resistor 2 to a depletion type MOS transistor. VSS connects the gate of MOS transistor 1, the other end of resistor 2, and the source and substrate of enhancement type MOS transistor 14.
The current mirror circuits 15 and 16 supply a current of the same magnitude as the current flowing through the depletion type MOS transistor 1 to the drain of the enhancement type MOS transistor 14, and a voltage input to the gate IN of the enhancement type MOS transistor 14. Output terminal OU
Construct a constant current inverter in which the voltage of T changes.

Although FIGS. 1 to 10 use Nch depletion type MOS transistors, it is also possible to create a self-correcting constant current circuit using Pch depletion type MOS transistors. It is also possible to use a resistor other than a Pwell resistor (for example, an Nwell resistor). Furthermore, in the case of insulator separation, the resistance can be made other than the Well resistance.

FIGS. 1 to 10 show a depletion type.
Although the source and the substrate of the MOS transistor are connected (represented by ●), the substrate may be connected to a source other than the source, for example, a ground terminal.

[0026]

According to the present invention, it is possible to obtain a constant current with small variation in absolute value and small variation in temperature coefficient. Further, by applying the self-correcting constant current circuit of the present invention to a reference voltage circuit, a constant current inverter circuit, or the like, a "reference voltage" or a "reversed voltage of a constant current inverter" having a small variation in temperature coefficient can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram of a self-correcting constant current circuit according to the present invention.

FIG. 2 is a diagram of a conventional constant current circuit.

FIGS. 3A to 3C are cross-sectional views in the order of manufacturing steps of a depletion type MOS transistor 1 and a resistor 2. FIGS.

FIG. 4 is a relationship diagram showing Vtnd dependence of “ON resistance of depletion type MOS transistor 1” and “resistance value of resistance 2”.

FIG. 5: ΔIds of a depletion type MOS transistor
FIG. 4 is a characteristic diagram showing a −Vgs characteristic.

FIG. 6 is a relationship diagram showing a relationship between a temperature coefficient of constant current and Vtnd of the self-correcting constant current circuit of the present invention.

FIG. 7 is a reference voltage circuit diagram using a self-correcting constant current circuit.

FIG. 8 is a relationship diagram showing a relationship between a temperature coefficient of a reference voltage and Vtnd of a reference voltage circuit using a self-correcting constant current circuit of the present invention.

FIG. 9 is a reference voltage circuit diagram using a self-correcting constant current circuit and a current mirror circuit.

FIG. 10 is a circuit diagram of a constant current inverter using a self-correcting constant current circuit and a current mirror circuit.

[Explanation of symbols]

Reference Signs List 1 Depletion type MOS transistor 2 Resistance 3 Phos or As ion implantation 4 Gate oxide film 5 Pwell 6 Nsub 7 N type diffusion region formed by ion implantation into depletion type MOS transistor 1 8 Form source / drain of Nch_MOS transistor High-concentration N-type diffusion region 9 High-concentration P-type diffusion region forming an electrode of resistance 2 10 Gate of MOS transistor 11 Resistance image of resistance 2 √lds Square root of source-drain current 14 Enhancement type MOS transistor OUT Output terminal 15, 16 Current mirror circuit IN input terminal VDD High potential VSS Ground potential

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Claims (2)

[Claims] 1. A self-correction circuit comprising a constant current circuit comprising at least one depletion type MOS transistor, wherein at least one resistor is inserted between a source and a gate of the depletion type MOS transistor. Type constant current circuit. 2. The depletion type, wherein the resistance is the depletion type.
2. A self-contained diffusion resistor of the same conductivity type as a substrate of a MOS transistor, wherein ions are implanted into a channel forming region of the depletion type MOS transistor also on a surface of a diffusion resistance part of the resistor. Correction type constant current circuit.