JPH0738547B2 - Operational amplifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an LSI for an operational amplifier, and particularly to an operational amplifier using a MOS transistor.

[Conventional technology]

FIG. 3 shows a circuit diagram of an operational amplifier using a CMOS transistor which is commonly used. In the figure, V _IN ⁺ is a normal input terminal V _IN ⁻ is an inverting input terminal, V _OUT is an output terminal, BIAS is a bias power supply input terminal, V _DD is the first power supply, V _SS is the second power supply, M1, M2, M5 , M7 is a first conductivity type (hereinafter referred to as P channel) transistor, M3, M4, M6 are second conductivity type (hereinafter referred to as N channel) transistor, and C is a capacitor.

Conventional operational amplifiers using CMOS transistors have a wide variety of transistor sizes. Therefore, in order to reduce the chip area when integrated into an LSI, the transistors are arranged regardless of the current axis direction.

An example of a conventional operational amplifier is shown in FIG. 4, and FIG. 4 is a pattern of the circuit diagram shown in FIG. In the figure, the size of the transistor is an arbitrary value.

S ₁ in _{FIG, S 2, S 3, S} 5, S 6, S 7 is the source of each transistor, but S ₃ is the source of the transistors M3 and _{M4, G 1, G 2,} G 3, G 4, G ₅ , ₅ , G ₆ and G ₇ are the gates of the respective transistors, D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ and D ₇ are the drains of the respective transistors, and C ₁ is the upper part of the capacitance C. , C ₂ is the lower part of the capacitance c, and SUB is the substrate of the transistors M1 and M2.

In this operational amplifier, the current axis directions of the transistors M1 and M2 are different from the current axis directions of the transistors M5 and M7 for the P channel transistor, and the current axis directions of the transistors M3 and M4 are different from the transistor M for the N channel transistor.
6 Current axis direction is different. Transconductance (hereinafter referred to as gm) of a transistor is given by the following equation.

Where μ is the charge mobility, C _OX is the gate oxide film capacity per unit area, W is the gate width, L is the gate length, I _D is the drain current, λ is the channel length modulation coefficient, and V _DS is the drain capacitance.
It is the voltage between the sources.

Normally, the simulation in the circuit design of an operational amplifier is performed by setting the charge mobility μ for each channel, but the value of μ differs depending on the direction of the current axis of the transistor. In the conventional operational amplifier, the charge mobilities of the transistors M1 and M2 are different from those of the transistors M5 and M7 for the P-channel transistor, and the charge mobilities of the transistors M3 and M4 and the transistor M6 are different for the N-channel transistor.
Since the charge mobilities of the two are different, the characteristics of the operational amplifier obtained by the simulation cannot be obtained.

Further, if the pair of differential input stage transistors M1, M2 and M3, M4 have different current axis directions, the transistor M
The gm of 1 and M2 become equal, which causes an offset voltage.

[Problems to be Solved by the Invention]

The conventional operational amplifier described above has a drawback in that the current axis direction of the transistors forming the operational amplifier is not constant in the same channel, so that it affects gm and the characteristics as simulated in circuit design cannot be obtained. .

[Means for Solving the Problems]

In the operational amplifier of the present invention, the transistors constituting the operational amplifier have the same current axis direction in the same channel and the same charge mobility μ.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the operational amplifier of the present invention. All symbols in FIG. 1 are the same as in FIG. The operational amplifier shown in FIG. 1 is an example in which the current axis direction of the transistors forming the operational amplifier is constant in the same channel, and the charge mobility of the same channel transistors is equal. Therefore, the characteristics as simulated in the circuit design can be obtained, and the offset can be minimized.

FIG. 2 shows an operational amplifier according to another embodiment of the present invention. Second
All symbols in the figure are the same as in FIG. In the operational amplifier of the embodiment shown in FIG. 2 as well as in the embodiment shown in FIG. 1, the current axis directions of the transistors constituting the operational amplifier are constant within the same channel, and the charge mobilities are equal.

〔The invention's effect〕

As described above, according to the present invention, by making the current axis direction of the transistors forming the operational amplifier constant in the same channel, the charge mobility μ of the same channel transistors is made equal, and the operational amplifier is integrated into an LSI. It has the effect of preventing the deterioration of the characteristics of and further minimizing the offset voltage.

[Brief description of drawings]

FIG. 1 is a pattern diagram of a circuit element showing an embodiment of an operational amplifier according to the present invention, FIG. 2 is a pattern diagram of a circuit element showing another embodiment of the present invention, and FIG. 3 is commonly used.
FIG. 4 is a circuit diagram of an operational amplifier using CMOS transistors, and FIG. 4 is a pattern diagram of a circuit element of a conventional operational amplifier. V _IN ⁺ ...... non-inverting input terminal, V _IN ^- ...... inverting input terminal, V _OUT ...
… Output terminal, BIAS …… Bias power supply, M1, M2, M5, M6 ……
P-channel transistor, M3, M4, M6 ...... N-channel transistor, C ...... _{capacity, S 1, S 2, S} 3, S 5, S 6, S 7 ...... transistor sources, G _1, G _2, G ₃ , G ₄ , G ₅ , G ₆ , G ₇ ...... Transistor gate, D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ , D ₇ ...... Transistor drain, C ₁ ...... Capacity C upper electrode, C ₂ ... lower electrode of capacitance C, SUB ... substrates of transistors M1 and M2.

Claims (1)

[Claims] 1. A plurality of first conductivity type MOS transistors and a plurality of second conductivity type M, each formed on a common semiconductor substrate.
In an operational amplifier configured by an OS transistor, all the first conductivity type MOS transistors have the same current flow direction, and the plurality of second conductivity type MOS transistors are the same.
The current flowing directions of the conductivity type MOS transistors are the same, and the source regions of the paired transistors in the operational amplifier among the plurality of first conductivity type transistors are arranged close to or common to each other, and The operational amplifier circuit is characterized in that the source regions of the paired transistors in the operational amplifier among the second transistors of the second conductivity type are arranged close to or common to each other.