JPH0831751B2 - Amplifier - Google Patents

Description

TECHNICAL FIELD The present invention relates to an amplification device suitable for use in, for example, a measuring instrument.

(Prior Art) As an amplification device in a conventional measuring instrument, an operational amplifier OP having a configuration as shown in FIG. 3 is generally used. In the figure, Vs is the voltage source to be measured, Rs is its internal resistance, and Ri is the input resistance of the operational amplifier OP. The output of the voltage source Vs to be measured is applied to the non-inverting input terminal of the operational amplifier OP via the series circuit of the internal resistance Rs of the voltage source and the input resistance Ri. Assuming that the gain of the operational amplifier OP is A, the output voltage Vo is applied to the resistance (A-1) at the inverting input terminal of this operational amplifier OP.
A voltage divided by R and resistance R is applied.

(Problems to be Solved by the Invention) In the amplification of such a configuration, the output voltage Vo is expressed by Vo = A (Vs + Eerr) ... (1) Eerr = Vo S + (Rs + Ri) I B ... (2) It (2) In the formula, Vo _S is input referred offset voltage of the operational amplifier OP, I _B are those also showing the bias current of the operational amplifier OP. These offset voltage Vo
Those _S and the bias current I _B is present necessarily in the operational amplifier OP, the Vo _S in amplifying apparatus shown in FIG. 3
And I _B cause an error Eerr as shown in equation (1).
A high-precision amplifier is required for the measuring instrument, and the measurement error Eerr caused by Vo _S and I _B needs to be corrected by some means. Moreover, the offset voltage
If Vo _S is large, the amplifier OP may be saturated and measurement may be impossible.

The present invention has been made to solve such a problem, and an object thereof is to provide an offset voltage component Vo _S
The present invention also provides an amplifying device which is corrected with an error due to the bias current component I _B and has a very high accuracy without causing the amplifier to be saturated and which is suitable for use in a measuring instrument.

(Means for Solving the Problems) The amplification device of the present invention is an input switching means for selectively applying a measurement signal, a ground signal not via a resistor and a ground signal via a resistor to the amplifier, and an output from the amplifier. A / D converter that converts a measurement signal, a ground signal that does not pass through a resistor, and a ground signal that passes through a resistor into a digital signal respectively, and supports the ground signal that does not pass through the resistor converted by this A / D converter The offset voltage component of the amplifier obtained based on the digital signal and the bias current component of the amplifier obtained based on the digital signal corresponding to the ground signal via the resistor converted by the A / D converter A microprocessor that calculates correction data for correcting each of these offset voltage and bias current components, and the offset voltage obtained by this microprocessor. A first D / A converter that converts the minute correction data into an analog signal and feeds back to the inverting input terminal of the amplifier; and the bias current component correction data obtained by the microprocessor is converted into an analog signal, A second D / A converter that feeds back to the non-inverting input terminal of the amplifier. Hereinafter, examples of the present invention will be described in detail.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the device of the present invention. In the figure, 9 is a switch used as an input switching means, and in addition to the measurement signal M, a ground voltage Z is directly or indirectly as a R via a resistor 10 having a resistance value R _B , a non-inverting input of an amplifier 11. Switch to pin and output.

The output terminal of the amplifier 11 is connected to the A / D converter 12, and the resistor 13 having the resistance value R ₁ and the resistor 14 having the resistance value R 2 are connected.
It is connected to the ground potential point via a resistance voltage dividing circuit constituted by. The connection point between the resistors 13 and 14 which form the resistance voltage dividing circuit is connected to the inverting input terminal of the amplifier 11.

The digital signal converted by the A / D converter 12 is added to the microprocessor 15 which performs various arithmetic controls. 16
Is a first D / A converter that converts a digital signal output from the microprocessor 15 into an analog signal and feeds it back to the inverting input terminal of the amplifier 11 via a resistor 17 having a resistance value Rcv; and 18 is a microprocessor 15 Resistor 1 with resistance value RcI that converts the digital signal output from
The second D that feeds back to the non-inverting input terminal of the amplifier 11 via 9
/ A converter. The microprocessor 15 also controls switching of the switch 9. The operation of the device of the present invention having such a configuration will be described below.

Now, assuming that the gain of the amplifier 11 is A, it is expressed by A = (R ₁ + R ₂ ) / R ₂ (3). The output voltage of the amplifier 11 when the switch 9 is set to the position of the ground voltage Z when the outputs of the D / A converters 16 and 18 are zero is VAz1, and the input conversion offset voltage of the amplifier 11 is
Assuming Vos, VAz1 is represented by VAz1 = A · Vos (4). Output voltage VA of amplifier 11 expressed by equation (4)
z1 is converted into a digital signal by the A / D converter 12 and then given to the microprocessor 15 to store its value. The microprocessor 15 determines whether or not this measured value VAz1 exceeds the allowable error voltage range ± Ve max shown in FIG. If it exceeds ± Ve mex, a sufficient voltage VD is generated so that the measured value VAz1 falls within the allowable error voltage range ± Ve max based on the design data stored in advance in the microprocessor 15. The correction data of is calculated and output to the D / A converter 16.

The output VD of the D / A converter 16 is supplied to the amplifier 11 via the resistor Rcv.
It is fed back to the inverting input terminal of as correction voltage. If the conversion output of the A / D converter 12 in this state is VAz2, this VAz2
Falls within the allowable error voltage range ± Ve max, and the microprocessor 15 stores this converted output VAz2 as correction data at the time of calculation.

Thus, the conversion output VAz2 of the A / D converter 12 when the switch 9 is set to the ground voltage Z position is within the allowable error voltage range ± V.
If the switch 9 is switched to the M position and the output signal Es of the measurement signal source 1 is measured (with the measured value being VAM) while being within e max, the microprocessor 15
Performs the operation of Es = VAM-VAz2 (5) using the stored operation correction data VAz2, and performs the operation corrected so that the offset voltage Vos is within the allowable error voltage range.

As described above, in the amplifying device of FIG. 1, the offset voltage component Vo is changed by the D / A converter 16 as shown in the equation (5).
Since s is corrected, the offset voltage component Vo
High-accuracy measurement can be performed using an inexpensive amplifier with large s.

Even if the offset voltage component Vos is large, the amplifier 11 will not be saturated.

And so on.

On the other hand, the output signal V A _R of the amplifier 11 when the switch 9 is set to the R position with the outputs of the D / A converters 16 and 18 being zero is V A _R = A (I _B · R _B + Vos) ( 6) becomes. In (6), I _B shows a bias current component of the amplifier 11 as described in Figure 3. (6)
After the output signal VA _R shown in Equation is converted into a digital signal by the A / D converter 12 is supplied to the microprocessor 15. Microprocessor 15, the signal VA _R and had been stored in the microprocessor (4) V _C2 = the offset voltage component Vos based on gain-multiplied value VA _Z1 shown in formula VA _R -VA _Z1 = A・ I _B · R _B … (7) is calculated.

The output of the microprocessor 15 causes the D / A converter 18 to output a voltage corresponding to this V _C2 , and this output voltage causes the amplifier 11 to cancel the bias current I _B via the resistor RCI.
It is fed back to the non-inverting input terminal of. That is, by the output V _C2 of the D / A converter 18 as the correction data of the bias current I _B ,
This D / A converter outputs a current I _C having a relationship of −I _B = −I _C (8). As a result, the bias current I _B is corrected.

Here, for example, | I _B | <1nA, and the sensitivity of V _C2 is 1mV / 1nA.
Assuming that the microprocessor 15 corresponds to ±
Digital setting value of 4-bit resolution (maximum voltage is 1 mV) is D
Output to the / A converter 18. As a result, the D / A converter 18
With the 4-bit resolution, the correction current I _C having the relationship of −I _B = −I _C as described above is output. Signal source 1 to be measured
Has an internal resistance Rs. As shown in the following equation (8), the internal resistance Rs has a current difference between the bias current I _B and the correction current I _C.
I _B ′ flows.

I _B ′ = I _B −I _C (9) In the conventional device shown in FIG. 3, there is no means for correcting the bias current I _B , and therefore the error due to the bias current component represented by I _B × Rs Get out. On the other hand, also in the present invention, I _B ′ ×
An error due to the bias current represented by Rs appears, but the value of I _B ′ as the error is ± ± of the D / A converter 18 with respect to the value of I _B.
It can be reduced to ± (1/16) nA determined by 4-bit resolution.

The output of the D / A converter 18 may be a current output or a voltage output, and a constant current source such as a current mirror may be interposed if necessary.

As mentioned above, the microprocessor 15, a digital signal corresponding to the direct input Z of the ground signal output from the amplification system, the bias current component based on the resistance value R _B of the digital signal and the indirect input corresponding to the indirect input R obtains the offset voltage component Vos based on the digital signal corresponding to the direct input Z of the ground signal with obtaining the I _B, these bias currents I
It calculates the data for correcting these bias current component I _B and the offset voltage component V _OS based on _B and the offset voltage component V _OS. Then, the offset voltage component correction data is added to the D / A converter 16, and the bias current component correction data is added to the D / A converter 18. This allows the D / A converter
The offset voltage correction analog signal is fed back from 16 to the inverting input terminal of the amplifier 11 via the resistor 17, and D /
The bias current correction analog signal Ic is fed back from the A converter 18 via the resistor 19 to the non-inverting input terminal of the amplifier 11. Therefore, if the input switching means 9 is switched to the M position and the output signal Es of the measurement signal source 1 is measured in this state,
The measured value VAM is the offset voltage component V _OS due to the amplifier 11.
And the bias current component I _B is corrected, and the measurement signal Es can be accurately measured.

(Effect of the Invention) As described above, according to the present invention, the influence of an error caused by an offset voltage and a bias current component of an amplification system including an amplifier and an A / D converter can be removed with a relatively inexpensive component. As a result, it is possible to realize an amplifying device capable of highly accurate measurement, and the practical effect is extremely large.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the device of the present invention, and FIG.
FIG. 3 is an operation explanatory view of the device of the present invention, and FIG. 3 is a block diagram showing an example of a conventional device. 1 ... Signal line, 2 ... Signal source resistance, 3 ... Internal resistance of device, 9 ... Switch, 10,13,14,17,19 ... Resistance, 11 ...
Amplifier, 12 …… A / D converter, 15 …… Microprocessor, 16,18 …… D / A converter.

Claims (1)

[Claims] 1. An input switching means for selectively applying a measurement signal, a ground signal without a resistance and a ground signal with a resistance to an amplifier, a measurement signal output from the amplifier, a ground signal without a resistance, and An A / D converter that converts a ground signal via a resistor into a digital signal, and an offset of the amplifier obtained based on the digital signal corresponding to the ground signal not passing through the resistor converted by the A / D converter To correct the offset voltage and the bias current component respectively by the voltage component and the bias current component of the amplifier obtained based on the digital signal corresponding to the ground signal via the resistor converted by the A / D converter. A microprocessor that calculates the correction data of, the offset voltage component correction data obtained by this microprocessor is converted into an analog signal A first D / A converter which feeds back to the inverting input terminal of the amplifier; and a first D / A converter which converts the bias current component correction data obtained by the microprocessor into an analog signal and feeds it back to the non-inverting input terminal of the amplifier. An amplification device characterized by comprising two D / A converters.