JP2002374131A - Automatic correction circuit of operational amplifier offset voltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically correct an offset voltage by using an input offset voltage of an operational amplifier. SOLUTION: When an input offset voltage Voffset of the operational amplifier OP is generated, the voltage of a non-inverted input terminal of the operational amplifier is a reference voltage VREF, the input offset voltage is applied to an inverted input terminal, and (1+RF/RG)×Voffset appears as the output voltage of an inversion amplification circuit. When the voltage of the non-inverted input terminal of the operational amplifier is corrected as VREF-Voffset by using this circuit, the voltage of the inverted input terminal become equal to the reference voltage VREF and the inverted amplification circuit can obtain an output voltage which is not related to the input offset voltage Voffset .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an automatic offset voltage calibration circuit for an operational amplifier used in an analog signal processing circuit such as an inverting amplifier circuit and an active filter.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional offset voltage adjusting circuit of an operational amplifier. Normally, these techniques detect an input offset voltage of an operational amplifier, convert the voltage to a current, make adjustments to match the input offset voltage, and pull the output by the input offset voltage at an input terminal.

[0003]

Here, in order to accurately adjust the voltage, it is difficult to overcome the input offset voltage of the input offset voltage detection circuit itself, and high accuracy is required. Is also difficult.

Further, when an input offset voltage V _offset of an operational amplifier used in an analog signal processing circuit occurs, the conventional technique needs to use an external circuit to set and adjust external parameters and the like.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to adjust and adjust the non-inverting input voltage of an operational amplifier irrespective of manufacturing variations and temperature characteristics without performing any of these settings and adjustments. is to obtain a stable output signal is equal to the ideal output regardless _{V o} ffset.

According to the present invention, in a circuit with a built-in chip, which detects an offset voltage V _offset of an operational amplifier and inverts and amplifies it, and operates only with a positive power supply VDD, the inverting input terminal and non-inverting input terminal of the operational amplifier are used. Voltage is VDD / 2 and VD respectively
In the case of a circuit that operates with the positive power supply VDD and the negative power supply VSS at D / 2−V _offset , the voltage of the inverting input terminal and non-inverting input terminal of the operational amplifier is automatically adjusted to GND and −V _offset , and the ideal output is obtained. An offset voltage automatic calibration circuit for obtaining an equal output signal is provided.

[0007]

FIG. 1 shows a specific circuit configuration of the automatic offset voltage calibration according to the present invention. In the analog signal processing circuit is connected to the input V _in to the reference power supply V _REF,
The output _Vout is connected to a non-inverting input terminal of an operational amplifier used in an analog signal processing circuit.

According to the present invention, there is provided a first inverting amplifier having one input terminal for inputting an input voltage and the other input terminal for inputting a reference power supply voltage, for detecting an offset voltage, and the first inverting amplifier. An operational amplifier voltage calibration circuit comprising a second inverting amplifier having a non-inverting input terminal connected to the output of the amplifier.

Here, as the resistor connected to the first inverting amplifier or the second inverting amplifier, a basic cell or a resistor in which basic cells are connected in series can be used.

In the present invention, the input terminal is connected to the reference power supply V _REF , the offset voltage of the operational amplifier is detected by the inverting amplifier of the first stage, the offset voltage is adjusted by the second stage, and the output terminal is connected. An operational amplifier offset voltage built in a chip, comprising a circuit connected to a non-inverting input terminal of an operational amplifier used for an analog signal processing circuit such as an inverting amplifier circuit and an active filter, and for automatically calibrating an offset voltage of the operational amplifier. An automatic calibration circuit was used.

The resistor connected to the operational amplifier offset voltage automatic calibration circuit with built-in chip is connected in series with the basic cell with a resistance of a positive multiple of the basic cell and the basic cell. Operational amplifier offset voltage automatic calibration circuit.

[0012]

An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 shows a circuit according to an embodiment of the present invention, _in which an operational amplifier O to which a circuit input voltage Vin and a reference power supply voltage _VREF are inputted.
And P1, resistor R _s1 connected in series to the circuit input voltage V _in
And a resistor R connected between the input and output terminals of the operational amplifier.
_This is a cascade connection of _F1 and an inverting amplifier circuit as shown in FIG. 2 connected to a resistor R _F1 . When the circuit operates, the non-inverting input terminal of the operational amplifier is connected to the reference power supply V _REF . This circuit will be analyzed as an example. When the operational amplifier OP the ideal ones, the voltage V _B of the voltage V _A of the inverting input and non-inverting input terminal of the formula (1)

[0013]

(Equation 1)

## EQU1 ## The relationship between the input signal V _in and the output signal V _OUT represented by the formula (2).

[0015]

(Equation 2)

In an actual application, the operational amplifier OP is non-ideal, and when an input offset voltage V _offset occurs, the relationship between the input signal and the output signal taking into account the input offset voltage V _offset is expressed by equation (3).

[0017]

(Equation 3)

The input terminal voltage V _A and V _B is a formula (4).

[0019]

(Equation 4)

Here, V _B = V _REF , therefore, V _A = V _REF + V
_offset . The relationship between the input signal V _in and the output signal V _out is expressed by the equation (5).

[0021]

(Equation 5)

As can be seen from equation (5), the operational amplifier
Input offset voltage V_offsetTo (1 + R _F/ R_S) Amplify twice
Output. Also, compared to equation (2), the input offset voltage V
_{offse t}Causes an output error.

From the analysis of FIG. 2, the input offset voltage V
The circuit of FIG. 1 considering the _offset is analyzed. As mentioned above, the circuit of FIG. 1 is a cascade connection of the circuit of FIG. As shown in FIG. 1, the input voltage of the inverting amplifier circuit in the first stage V _in, the output voltage and V _o1, the respective input and output voltages of the second stage V _o1, V _o2. Then, equation (5)
The relationship between the input and output of the entire circuit is expressed by equation (6).

[0024]

(Equation 6)

Here, similarly to FIG. 2, V _B = V _REF and V _A = V _REF
+ V _offset . The Substituting input voltage V _in = V _REF in equation (6), the output voltage V _o2 becomes Equation (7).

[0026]

Equation 7

Comparing equations (2) and (3), if the voltage _VA at the inverting input terminal of the operational amplifier is set to the reference voltage V _REF , regardless of the input offset voltage V _offset as in equation (2) An ideal output voltage V _OUT can be obtained. Equation (4)
Accordingly, in order to make V _A = V _REF , the voltage V _{B at} the non-inverting input terminal of the operational amplifier may be obtained by subtracting the offset voltage from the reference voltage instead of the reference voltage V _REF (Equation (8)).

[0028]

(Equation 8)

Furthermore, from equations (7) (8), if the output voltage V _o2 of Figure 1 circuit to V _B, the equation (9) is obtained.

[0030]

[Equation 9]

From equation (9), there is only a proportional relationship between the resistance values irrespective of the input offset voltage. It is equation (10)
Can be expressed as

[0032]

(Equation 10)

From Equation (10), each resistance value is given by Equation (11).

[0034]

[Equation 11]

Then, equation (12) is obtained.

[0036]

(Equation 12)

Is as follows. Where R₀The resistance of the basic cell and
Equation (11) and (12) show that the resistance R_S1, R _S2, R_F1, R_F2Is all
Base cell R₀If it is composed of
Regardless, the proportionality as shown in equation (10) can be maintained.
And stable output that is resistant to variations in temperature characteristics and resistance
A voltage is obtained.

[0038]

As described above, the present invention uses an operational amplifier similar to that used in an analog signal processing circuit.
This is a simple circuit configuration using a basic resistance cell _R0 . Also,
The operational amplifiers and resistors are made on the same semiconductor substrate, and the operational amplifiers are the same, and the precision is not particularly required. Further, from equation (10), only the proportional relationship is required regardless of the accuracy of the resistance value. Finally the input voltage of the circuit has an excellent effect of so stable reference voltage V _{R EF,} strong stable output voltage by variations in the temperature characteristics and parameters can be easily realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an inverting amplifier circuit according to an embodiment of the present invention.

FIG. 3 is a block diagram of an adjustment circuit according to a conventional technique.

FIG. 4 is a circuit diagram showing an example for confirming the effect of the present invention.

FIG. 5 is a diagram showing DC output characteristics of the circuit of FIG.

FIG. 6 is a diagram showing another embodiment according to the present invention.

[Explanation of symbols]

OP, OP1, OP2 Operational amplifiers R ₀ , R _S , R _F , R _S1 , R _F1 , R _S2 , R _F2 Resistance V _in Circuit input voltage V _out , V _OUT , V _o1 , V _o2 Circuit output voltage V _A calculation inverting input terminal voltage V _B operational amplifier input offset voltage VDD positive power supply voltage VSS negative supply voltage V _REF reference source voltage GND ground the non-inverting input terminal voltage V _offset operational amplifier in amplifier

Claims (4)

[Claims] A first input terminal for inputting an input voltage;
An operation comprising a first inverting amplifier having another input terminal for inputting a reference power supply voltage and detecting an offset voltage, and a second inverting amplifier having a non-inverting input terminal connected to the output of the first inverting amplifier. Amplifier voltage calibration circuit. 2. The operational amplifier voltage calibration circuit according to claim 1, wherein the resistor connected to the first inverting amplifier or the second inverting amplifier is a basic cell or a resistor in which basic cells are connected in series. 3. An input terminal is connected to a reference power supply V _REF , an offset voltage of an operational amplifier is detected by an inverting amplifier of a first stage, the offset voltage is adjusted by a second stage, and an output terminal is connected to an inverting amplifier circuit and an active amplifier. An on-chip operational amplifier offset voltage automatic calibration circuit, comprising: a circuit connected to a non-inverting input terminal of an operational amplifier used for an analog signal processing circuit such as a filter, for automatically calibrating an offset voltage of the operational amplifier. 4. A chip built-in chip wherein the resistor connected to the chip built-in operational amplifier offset voltage automatic calibration circuit is connected in series with the base cell and a resistance of a positive multiple of the base cell. Operational amplifier offset voltage automatic calibration circuit.