JP3314411B2 - MOSFET constant current source generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a MOSFET (Met
al Oxide Semiconductor Fi
More particularly, the present invention relates to a MOSFET constant current source generating circuit suitable for facilitating control of temperature characteristics.

[0002]

2. Description of the Related Art A MOSFET has a characteristic that a constant current flows between a drain and a source even when a voltage between the drain and the source changes. For example, "Transistor Technology" (CQ Publishing Co., Ltd., February 1992, As described on page 394, the circuit described on page 390 of CQ Publishing Company)
Used as a constant current element for supplying a constant current. Furthermore, when a constant current source generation circuit is configured using MOSFETs, it is common to obtain a constant current using the saturation characteristics of MOSFETs, using the constant voltage obtained using the constant voltage generation circuit as the gate voltage. is there.

FIG. 2 is a circuit diagram showing a configuration of a conventional constant current source generating circuit using MOSFETs. A current source (Iref) operated in a saturation region is obtained by short-circuiting between the gate and the source of the depletion type MOSFET 21, and two enhancement type MOSFETs having the same characteristics.
The current source (Iref) is multiplied by a constant (n) by a so-called current mirror circuit 24 in which the gates 22 and 23 are short-circuited between the gates and between the sources, and the constant current source (Icc) is reduced. generate.

However, in the case of this circuit, the constant current value (Ic
c) is a depletion type MOS as shown in the following equation.
The square characteristic of the FET 21 is obtained. Icc = n × Iref = n × Kd × (Wd / Ld) × | Vtnd | ² where Vtnd and Kd, and Wd and Ld are the threshold voltage and conduction coefficient of the depletion-mode MOSFET 21 and the effective channel width, respectively. Value and effective channel length.

Since the wafer manufacturing process of Vtnd has a large variation, the variation in the lot of the constant current value (Icc) and the temperature characteristic (ΔIc)
c / ΔT) also becomes large among lots. (∂Icc / ∂T) = {Ke × (We / Le) × | Vtnd | ² } / ∂T = (We / Le) × [｛| Vtnd | ² × (∂Ke / ∂T)} + ｛ 2 × | Vtnd | × Ke × ({| Vtnd | / {T)}] (a) where Ke, Wd and Ld are the conduction coefficient of the enhancement type MOSFETs 22 and 23, the effective channel width, and the channel length, respectively. Effective value.

[0006]

The problem to be solved in the prior art is that the current value (Icc) and temperature characteristic (∂cc) of the MOSFET constant current source generating circuit are caused by variations in the MOSFET manufacturing process. The point is that the variation between lots (Icc / ΔT) cannot be reduced.
An object of the present invention is to solve these problems of the prior art, and
Unaffected by variations in the SFET manufacturing process,
An object of the present invention is to provide a MOSFET constant current source generating circuit that can supply a constant current with high reliability.

[0007]

In order to achieve the above object, a MOSFET constant current source generating circuit according to the present invention comprises:
Three enhancement-type MOSFETs and a depletion-type one M formed by only one donor ion implantation from these three MOSFETs
An OSFET is a constant current source generating circuit that connects a source and a substrate.
MOSFET, and an enhancement type second MOSFET having a gate and a drain connected to the source of the first MOSFET.
And an enhancement-type third MOSFET in which the gate and the drain are connected to the source of the second MOSFET and the source is connected to the negative power source, the source is the negative power source, and the gate is the source of the first MOSFET. A fourth MOSFET of an enhancement type that is connected to each other and outputs a constant current to the drain, and a second MOSFET corresponding to a channel coefficient of the first MOSFET, which is a product of a ratio of a width to a length of a channel and a conductivity coefficient. MOSF
By connecting the ET channel coefficient and the channel coefficient of the third MOSFET in a pattern of physical dimensions in which the sum of the square roots of the respective ratios is 1 , the fourth MOS
The constant current flowing through the drain of the FET is
2nd to 4th MO that can be accurately controlled as a total
The threshold voltage Vtne of the SFET and the first M
Absolute value of OSFET threshold voltage Vtnd
Is determined by the sum of

[0008]

According to the present invention, first to fourth MOSFETs are provided.
, As shown in the following equation:
The first consisting of the product of the ratio of the width to the length of the channel and the conductivity coefficient;
The second MOS for the channel coefficient of the MOSFET
The physical dimension is such that the sum of the square roots of the respective ratios of the channel coefficient of the FET and the channel coefficient of the third MOSFET is 1. {(Kd × W1 / L1)} (Ke × W2 / L2)｝ + {(Kd × W1 / L1) ÷ (Ke × W3 / L3)} = 1 where Kd, W1, and L1 are respectively First MOSF
The conductivity coefficient of ET, the effective value of channel width and the effective value of channel length, and Ke and W2, L2, and W3, L3 are:
These are the conductivity coefficient of the second and third MOSFETs, the effective value of the channel width, and the effective value of the channel length, respectively.

As a result, the constant current value (Icc) of the MOSFET constant current source generation circuit is determined by the threshold voltage (Vtnd) of the first MOSFET and the fourth MOSFET.
The following equation is made up of the threshold voltage (Vtne) and the conductivity coefficient (Ke) of T, the effective channel width (W4), and the effective channel length (L4). Icc = Ke × (W4 / L4) × (| Vtnd | + Vt
ne) ² Then, the first MOSFET is connected to the second to fourth MOSFs.
By making only one implantation of donor ions from ET, the total number of implanted ions can be accurately controlled, and variations in the manufacturing process of “| Vtnd | + Vtne” can be reduced.
In addition, since the variation in the manufacturing process of the constant current value (Icc) is reduced, the temperature characteristics (∂Icc
/ ∂T) changes in proportion to (∂Ke / ∂T), making it easier to control the characteristics.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a configuration according to the present invention of a MOSFET constant current source generating circuit of the present invention. In the figure, reference numeral 1 denotes an N-channel type MOSFE as a depletion type first MOSFET of the present invention.
T is the MOSF as the second to fourth MOSFETs of the present invention of the N-channel type and the enhancement type.
ET. MOSFET1 and MOSFET2
To 3 are the gate voltages V when operated in the saturation region.
1 and V2 are constant voltages irrespective of the voltage Vdd between the drain and the source of the MOSFET1.

As a result, the current (I ₁ ) flowing through the MOSFETs _{1 to 3} is calculated as follows: I ₁ = Kd × (W1 / L1) × | Vtnd | ² I ₁ = Ke × (W2 / L2) × (V1-V2- Vtn
e) ² I ₁ = Ke × (W3 / L3) × (V2-Vtne) ² However, Kd and W1 and L1 are MOS
The conductivity coefficient of FET1, the effective value of channel width and the effective value of channel length, and Ke and W2, L2 and W3, L3
Are the conductivity coefficients of the MOSFETs 2 and 3, the effective channel width, and the effective channel length, respectively. Vtn
d and Vtne are MOSFET1 and MOSF, respectively.
These are the threshold voltages of ET2 to ET4.

Solving this, V1 = [{(Kd × W1 / L1) ÷ (Ke × W2 / L2)} + {(Kd × W1 / L1) ÷ (Ke × W3 / L3)}] × | Vtnd | + 2 × Vtne V2 = [{(Kd × W1 / L1)} (Ke × W3 / L3)}] × | Vtnd | + Vtne

Here, the pattern size is set as follows: {(Kd × W1 / L1)} (Ke × W2 / L2)} + {(Kd × W1 / L1)} (Ke × W3 / L3)} = Assuming that 1, V1 = | Vtnd | + 2 × Vtne.

Thus, when the MOSFET 4 is used in the saturation region, the current value (Icc) is: Icc = Ke × (W4 / L4) × (V1-Vtne) ² = Ke × (W4 / L4) × ( | Vtnd | + Vtne)
It becomes ² . However, W4 and L4 are MOSFETs, respectively.
4 are the channel width effective value and the channel length effective value.

Here, the process of forming the threshold voltage Vtnd of the MOSFET 1 and the threshold voltage Vtne of the MOSFETs 2 to 4 is as follows. MOSFET2 using surface concentration of p-well itself
Then, a threshold voltage Vtne of 4 is formed, and then a threshold voltage Vtnd of the MOSFET 1 is formed in one step of implanting donor ions. If you do this,
Since the control of the total number of implanted ions can be performed very accurately, the variation of “| Vtnd | + Vtne” can be controlled to be small. Therefore, the current value (Ic
Variations in the manufacturing process c) can be reduced.

Further, the variation in the temperature characteristic (∂Icc / ∂T) expressed by the following equation (b) in the manufacturing process can be reduced. (∂Icc / ∂T) = (W4 / L4) × [(| Vtnd | + Vtne) ² × (∂Ke / ∂T) + 2 × (| Vtnd | + Vtne) × Ke ｛(∂ | Vtnd | / ∂T ) + ({Vtne / {T)}] (b)

When the temperature characteristic (∂Icc / ∂T) is obtained from the experimental data according to the equation (b), for example, (V
When tnd = −0.4 v and Vtne = 0.2 v), (W4 / L4) × (∂Icc / ∂T) = (0.6) ² × (−1.0 ÷ 10 ⁶ ) + 2 × 0. 6 × 204 ÷ 10 ⁶ × (+ 1.5 ÷ 10 ⁴ -1.3 ÷ 10 ⁴ ) = − 3.6 ÷ 10 ⁷ + 7.3 ÷ 10 ⁹ ≒ −3.6 ÷ 10 ⁷ (A / ° C.) Become. This value is the same regardless of whether Vtnd is the standard (−0.4 V), the maximum (−0.25 V), or the minimum (−0.55 V).

Here, the temperature characteristic of a constant current source generating circuit using a conventional MOSFET under the same conditions is calculated using the conventional equation (a). First, Vtnd = −0.4v
In the case of (Type / standard), (Le / We) × (∂Icc / ∂T) = (0.4) ² × (−1.0 ÷ 10 ⁶ ) + 2 × 0.4 × 204 ÷ 10 ⁶ × (+ 1.6 ÷ 10 ⁴ ) = − 1.6 ÷ 10 ⁷ + 2.6 ÷ 10 ⁸ ≒ 1.3 ÷ 10 ⁷ (A / ° C.).

Next, Vtnd = -0.55v (Min /
In the case of (minimum), (Le / We) × (∂Icc / ∂T) = (0.55) ² × (−1.05 ÷ 10 ⁶ ) + 2 × 0.55 × 213 ÷ 10 ⁶ × (+1. 7 ÷ 10 ⁴ ) = − 3.2 ÷ 10 ⁷ + 4.0 ÷ 10 ⁸ ≒ −2.8 ÷ 10 ⁷ (A / ° C.).

Further, Vtnd = -0.25v (Max
/ Max), (Le / We) × (∂Icc / ∂T) = (0.25) ² × (−0.95 ÷ 10 ⁶ ) + 2 × 0.25 × 195 ÷ 10 ⁶ × (+1 5.5 ÷ 10 ⁴ ) = − 5.9 ÷ 10 ⁸ + 1.5 ÷ 10 ⁸ ≒ −0.44 ÷ 10 ⁷ (A / ° C.). As can be seen from this result, the MOS of the present embodiment
Although the temperature characteristic of the current value (Icc) generated by the FET constant current source generation circuit becomes large, it changes substantially in proportion to “∂Ke / ∂T”, which makes it easy to control the characteristics.

As described above with reference to FIG. 1, the MOSFET constant current source generating circuit of this embodiment
The pattern of T1-4 is set to a specific size, MOSFET
1 is made from MOSFETs 2 to 4 by only one implantation of donor ions. As a result, the total number of implanted ions can be accurately controlled, and variations in the manufacturing process of the constant current value (Icc) can be reduced. In addition, its temperature characteristics ({Icc / ∂
T) changes in proportion to (∂Ke / ∂T), which facilitates control of characteristics.

Note that the present invention is not limited to the embodiment described with reference to FIG. For example, in this embodiment,
Although the description is made using an n-channel MOSFET,
A p-channel MOSFET may be used.

[0023]

According to the present invention, the current value (Icc) and the temperature characteristic ({Icc /}) of the MOSFET constant current source generating circuit due to the variation in the manufacturing process of the MOSFET.
T) the variation between lots can be reduced, and MO
Unaffected by variations in the SFET manufacturing process,
It is possible to supply a highly reliable constant current.

[0024]

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a configuration according to the present invention of a MOSFET constant current source generating circuit of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional constant current source generation circuit using MOSFETs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 N-channel depletion type MOSFET 2-4 N-channel enhancement type MOSFET 21 Depletion type MOSFET 22, 23 Enhancement type MOSFET 24 Current mirror circuit

Claims (1)

(57) [Claims] 1. An enhancement-type three MOSFE
T and a depletion-type MOSFET formed by only one implantation of donor ions from the three MOSFETs, each of which is a constant current source generating circuit connecting a source and a substrate. A depletion-type first MOSFET for connecting a gate and inputting a positive power supply to a drain
The enhancement-type second MOSFET having a gate and a drain connected to the source of the first MOSFET.
The enhancement-type third MOSFET in which a gate and a drain are connected to the source of the second MOSFET, and the source is connected to a negative power source; the source is the negative power source, and the gate is the first MO.
The enhancement-type fourth MOSFET connected to the source of the SFET and outputting a constant current to the drain.
T is calculated by multiplying the channel coefficient of the first MOSFET by the product of the ratio of the width to the length of the channel and the conductivity coefficient.
Channel coefficient of the MOSFET and the third M
By connecting them in a pattern of physical dimensions in which the sum of the square roots of the respective ratios of the channel coefficients of the OSFET is one .
And the constant current flowing through the drain of the fourth MOSFET is
Accurate control of the total number of implanted ions
Threshold voltage of the second to fourth MOSFETs
And the threshold voltage of the first MOSFET.
A MOSFET constant current source generating circuit, wherein the MOSFET constant current source generating circuit is configured to be determined by the sum of the absolute value of the threshold voltage Vtnd and the absolute value of the threshold voltage Vtnd .