JPH0251281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an offset voltage trimming circuit for operational amplifiers in various measurement circuits, etc., and in particular, to a trimming circuit that adjusts the value of a polysilicon resistor installed for offset voltage adjustment along with an operational amplifier. It relates to something that can be adjusted by a circuit.

Conventionally, in operational amplifiers for measuring instruments that require high accuracy, the offset voltage has been adjusted by laser trimming a thin film resistor or by destroying a Zener diode (Zener zap). In adjusting such offset voltage, laser trimming requires an expensive laser trimmer and has the disadvantage that it must be done before packaging. Zenerzap trimming requires a trimming terminal on the operational amplifier, but this type of trimming has the disadvantage that only stepwise adjustment values can be obtained.

In this invention, a polysilicon resistor for offset adjustment and a trimming circuit for adjusting the resistance value are installed inside a semiconductor integrated circuit constituting an operational amplifier, making it easy to adjust the offset voltage and achieving high precision. The object of the present invention is to provide an offset voltage trimming circuit for an operational amplifier that allows adjustment.

This invention relates to a polysilicon resistor for offset voltage adjustment provided in an operational amplifier having a pair of signal input terminals, a voltage applied between a reference potential terminal and one signal input terminal, and a voltage applied to the base. a first transistor that becomes conductive based on a drive voltage, and a base current that is applied to the first transistor by the conduction of this transistor, which becomes conductive, and trimming from a current source that is applied between the reference potential terminal and the other signal input terminal; and a second transistor that allows current to flow through the polysilicon resistor.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows an embodiment of an offset voltage trimming circuit for an operational amplifier according to the present invention. In the figure, two constant current sources 4 and 6 are provided in the main circuit section 3 of the operational amplifier 2, and each constant current source 4 and 6 consists of diodes 8 and 10 and a polysilicon resistor for adjusting the offset voltage. Reference potential terminals 16A and 16B are formed via resistors 12 and 14. Further, in the main circuit section 3 of the operational amplifier 2, a pair of signal input terminals 18A and 18B are formed, and a power supply terminal 20 to which a driving voltage V _CC is applied is formed.

In this operational amplifier 2, each resistor 12, 1
Trimming circuits 22A and 22B including the resistors 12 and 14 are provided in order to adjust the offset voltage by individually trimming the resistors 12 and 14. That is, in the trimming circuit 22A, the first
The emitter of the transistor 24 is connected to the signal input terminal 18A via a resistor 26, and the base of this transistor 24 is connected to the power supply terminal 20. Further, the collector of this transistor 24 is connected to the base of a second transistor 28,
The collector of this transistor 28 is connected to the signal input terminal 18B, and the emitter is connected to the resistor 1.
It is connected to the high potential side terminal of No.2. Furthermore, in the trimming circuit 22B, the emitter of the first transistor 30 is connected to the signal input terminal 18B via the resistor 32.
The base of this transistor 30 is connected to the power supply terminal 20 similarly to the transistor 24.
It is connected to the. The collector of this transistor 30 is connected to the base of a second transistor 34, the collector of the transistor 34 is connected to the signal input terminal 18A, and the emitter is connected to the high potential side terminal of the resistor 14.

Based on the above configuration, trimming of the offset voltage of the operational amplifier 2 will be explained. When trimming the offset voltage of the operational amplifier 2 by adjusting the resistance value of the resistor 12, a voltage source 36 is connected between the signal input terminal 18A and the reference potential terminal 16A, as shown in FIG. The voltage of this voltage source 36 is V _IN
Then, this voltage V _IN is the sum of the drive voltage V _CC , the reference potential V _EE of the reference potential terminal, and the forward drop voltage V _F of the first transistor (V _CC + V _EE + V _F )
Set to . On the other hand, a constant current source 38 for flowing a trimming current is connected between the signal input terminal 18B and the reference potential terminal 16B, and a drive voltage V _CC is applied to the power supply terminal 20. In this way, the first transistor 24 becomes conductive, and the base current is applied from the first transistor 24 to the base of the second transistor 28, so that the transistor 28 becomes conductive. As a result, the resistor 1 is connected from the constant current source 38 through the transistor 28.
A trimming current flows through 2. By arbitrarily setting the time during which this current flows, the value of the resistor 12 can be arbitrarily set by utilizing the properties of the polysilicon resistor.

In addition, when trimming the value of the resistor 14, a constant current source 38 is connected between the signal input terminal 18A and the reference potential terminal 16A, and
It is assumed that a voltage source 36 is connected between B and the reference potential terminal 16B to adjust the resistance. In this way, a desired offset voltage can be set in the operational amplifier 2 based on the adjustment of the resistance value of the resistor 12 or 14.

According to such a configuration, in adjusting the resistance value of the resistor 12 or 14, there is no need to separately provide a trimming terminal on the circuit, and there is no need for an expensive trimming device such as a laser trimmer. In particular, an operational amplifier with a low offset voltage can be realized at a minimum cost, and trimming can be performed with high precision even after the product is completed (packaged). Moreover, the current for trimming is determined by the drive voltage V _CC and the reference potential V _EE
It can be set to any value within the range of (V _CC + V _EE ) and does not require a special power supply. In addition, resistors 12 and 14
Since the setting can be adjusted using continuous values, the offset voltage can be set with extremely high precision.

FIGS. 3 and 4 show specific embodiments of the invention. The operational amplifier 2 shown in FIG.
42, transistors 44 and 46 and a diode 48 forming a current inverting circuit as the constant current source;
It is composed of. And transistor 4
A signal input terminal 18A is formed at the base of the transistor 0, a signal input terminal 18B is formed at the base of the transistor 42,
A power supply terminal 20 is formed at the common emitters of the transistors 40 and 42 to apply a driving voltage V _CC through a diode 48 .

When the operational amplifier 2 is configured in this manner, the trimming circuits 22A and 22B can be configured in the same manner as in the embodiment described above, and the offset voltage can be arbitrarily adjusted by trimming the resistors 12 and 14. The circuit shown in FIG. 3 is designed to trim the resistor 12. For this purpose, a voltage source 36 is connected between the signal input terminal 18A and the reference potential terminal 16A, and the voltage source 36 is connected between the signal input terminal 18A and the reference potential terminal 16A.
A constant current source 38 is connected between 8B and the reference potential terminal 16B.

Figure 4 shows the PNP transistor 4 of the above embodiment.
NPN type transistor 50,5 instead of 0,42
2, and further includes a PNP type transistor 54,
56 and constant current sources 58, 60, and 62 are applied. Even when such NPN transistors 50 and 52 are included in the main circuit section 3,
The trimming circuits 22A and 22B can be constructed in the same way, and the offset voltage adjustment resistors 12 and 14 can be similarly trimmed to adjust the offset voltage of the operational amplifier 2 with high precision.

As explained above, according to the present invention, a trimming circuit for adjusting the offset voltage is provided inside the operational amplifier 2, so there is no need to form a special trimming terminal, and trimming using an expensive laser trimmer or the like is not required. without requiring any operation.
An operational amplifier with a low offset voltage can be realized at a minimum cost, and the offset voltage can be adjusted to a desired value.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an offset voltage trimming circuit for an operational amplifier according to the present invention, FIG. 2 is a circuit diagram showing its trimming state, and FIGS. 3 and 4 are diagrams showing a specific embodiment of the present invention. FIG. 2...Operation amplifier, 12, 14...Polysilicon resistor for offset voltage adjustment, 22A, 22
B...Trimming circuit, 24...First transistor, 28...Second transistor.

Claims (1)

[Claims] 1 A polysilicon resistor for offset voltage adjustment provided in an operational amplifier having a pair of signal input terminals, a voltage applied between the reference potential terminal and one signal input terminal, and a drive voltage applied to the base. The first transistor becomes conductive based on the voltage, and the first transistor becomes conductive due to the conduction of this transistor, which is supplied with a base current and becomes conductive. 1. An offset voltage trimming circuit for an operational amplifier, comprising: a second transistor that supplies voltage to a silicon resistor;