JPH0877282A - Analog arithmetic circuit - Google Patents

Abstract

PURPOSE: To provide the inexpensive, high-performance analog arithmetic circuit which does not require highly precise components. CONSTITUTION: This circuit consists of a 1st 1-bit D/A converter 11 which receives a DC voltage as the denominator of correction arithmetic, a subtracter 12 which receives the output of the 1-bit D/A converter 11 and a reference voltage and performs subtraction, an integrator 13 which receives and integrates the output of the subtracter 12, a comparator 14 which receives the output of the integrator 13 and decides the polarity, and a 2nd 1-bit D/A converter 15 which receives a DC voltage as the numerator of the correction arithmetic; and the output of the comparator 14 is used as a switching signal for the 1st and 2nd 1-bit D/A converters 11 and 15. The output of the 2nd 1-bit D/A converter 15 is used as a correction arithmetic output. Therefore, there is no place to be adjusted, so good precision and superior stability are obtained and neither special components nor severe selecting operation is required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog arithmetic circuit for correcting a detection signal of a differential transformer.

[0002]

2. Description of the Related Art A signal detection circuit of a differential transformer is a circuit for converting a positional displacement of a core in the differential transformer into an electric signal and taking out the electric signal. In FIG. 5, the oscillation circuit 41 is connected to the primary side of the differential transformer 40, and the addition circuit 42 and the subtraction circuit 43 are connected to both ends of the secondary side, respectively. The adder circuit 42
The voltage V _a on the secondary side and the voltage V _b that change according to the position displacement of the core 41 of the differential transformer 40 are added, and the subtraction circuit 4 is added.
3 subtracts the voltage V _a and the voltage V _b . Adder circuit 4
2, the subtraction circuit 43 includes synchronous rectification circuits 44 and 4 respectively.
5 is connected, and the summed signal voltage (V _a + V _b ),
Differential signal voltage (V _a -V _b) are output.

By the way, in this signal detecting circuit, the length of the cable connecting the differential transformer 40 and the oscillating circuit 41 and the differential transformer 40, the adding circuit 42 and the subtracting circuit 43, and the resistance value inside the differential transformer. An error occurs when is changed by temperature or the like. Generally, in order to correct this error factor, the signal voltage (V _a −V _b ) of the difference is calculated by the divider circuit.
Is divided by the summed signal voltage (V _a + V _b ).

FIG. 6 shows an example of a division circuit conventionally used.
Shown in The division circuit 46 is composed of a multiplication circuit 51, a subtraction circuit 52, and an amplification circuit 53, and uses an analog calculator that utilizes the exponential function characteristic of a semiconductor.

[0005]

However, in the above-mentioned conventional example, an analog calculator utilizing the fact that the diode forward current-voltage characteristic of a semiconductor can be approximated to an exponential function is used, and the characteristic error due to element variation is large. For this reason, in order to obtain a highly accurate product, it is necessary to use expensive components that have been rigorously selected. In addition, there are many adjustment elements and they are complicated, and there is a drawback that it takes a lot of adjustment time.

Therefore, an object of the present invention is to solve the problems of the conventional analog arithmetic unit as described above and to provide an inexpensive and high-performance analog arithmetic circuit which does not require highly accurate parts.

[0007]

According to the present invention, a first 1-bit D / A for receiving a DC voltage serving as a denominator of a correction operation.
A converter, an arithmetic unit that receives the output of the 1-bit D / A converter and a reference voltage to perform subtraction, an integrator that receives the output of the arithmetic unit to perform integration, and a polarity determination that receives the output of the integrator. And a second 1-bit D / A converter that receives a DC voltage that is the numerator of the correction operation,
The output of the comparator is the first and second 1-bit D / A
An analog arithmetic circuit is obtained which is used as a converter switching signal to obtain the output of the second 1-bit D / A converter as a correction arithmetic output.

[0008]

In the analog operation by the circuit of the present invention, a highly accurate multiplication / division analog voltage can be obtained by the effect of the integrator in the loop circuit while using the digital signal internally. Further, since no analog non-linear element is used, it is possible to perform calculation with excellent stability with respect to time, temperature, etc., with few characteristic change factors.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. With reference to FIG. 1, an analog operation circuit according to the present invention includes a first 1-bit D / A converter 11 that receives an input signal voltage V _B that is a denominator of a correction operation, and an output of the 1-bit D / A converter 11. Subtractor 12 that receives V ₁ and the input signal voltage V _A as the reference voltage to perform subtraction
, A circuit 10 including an integrator 13 that receives the output V ₂ of the subtractor 12 and performs integration, and a comparator 14 that receives the output of the integrator 13 to determine the polarity, and the numerator of the correction operation. Second 1-bit D / which receives the input signal voltage V _C
It has an A converter 15. The input signal voltages V _A , V _B and V _C are all DC voltages.

It is well known that the output of a D / A converter is generally the product of an analog voltage input as a reference voltage and a digital input. The waveform of each part when the input signal voltages V _A , V _B and V _C are applied to the circuit of FIG. 1 is as shown in FIG. That is, 1 to which the input signal voltage V _B is added
The output V ₁ of the bit D / A converter 11 is shown in FIG.
Of the input signal voltage V by the digital output D of the comparator 14 of
By swinging _B positively or negatively, the time T is changed as shown in Fig. 2 (b).
_The sign is reversed at ₂ . Negative input signal voltage V
The waveform of the output V ₂ of the subtractor 12 to which _A is added is shown in FIG.
It becomes like.

The average voltage of the output V ₂ is 0 by the integrator 13.
(V), the following equation is obtained.

(V _B −V _A ) × T ₁ − (V _B + V _A ) × T ₂ = 0 When deformed, V _B × (T ₁ −T ₂ ) = V _A × (T ₁ + T ₂ ) Therefore, Get the following formula.

V _A = V _B · (T ₁ −T ₂ ) / (T ₁ + T ₂ ) On the other hand, the digital output D is represented by the following equation using T ₁ and T ₂ .

D = (T ₁ -T ₂ ) / (T ₁ + T ₂ ) The following equation is obtained from the above equation and the equation.

V _A = D × V _{B When} transformed, the following equation is obtained.

D = V _A / V _{B The} output voltage V _{E obtained} by passing the input signal voltage V _C through the 1-bit D / A converter 15 is obtained by swinging the input signal voltage V _C positively or negatively by the digital output D. It is represented by V _E = D × V _C , and the following formula is obtained from the formula. In this way, the comparator 14
Digital output D of the 1-bit D / A converter 11,
Acts as a 15 switching signal.

V _E = V _C · V _A / V _B That is, the output voltage V _E is obtained by multiplying between V _A and V _C and dividing it by V _B.

FIG. 3 shows a circuit when the arithmetic circuit according to the present invention is applied to a differential transformer signal detection circuit. Since the polarity of the input signal voltage V _B (= V _a + V _b ) which is the sum signal output from the differential transformer signal detection circuit 10 is always positive, the 1-bit D / A converters 11 and 15 of FIG. , And can be replaced by the analog switches 31 and 35. The reference voltage V _A from the reference voltage generator 37 is a negative voltage. Further, the input signal voltage V _C is a DC voltage, but since it has a pulsating flow due to the analog switch 35, a low pass filter 36 is used to remove this ripple component.

The output V _o of the low-pass filter 36 is given by the following expression according to the above description.

V _o = K · (V _a −V _b ) / (V _a + V _b ), where K is an arbitrary constant and the above-mentioned input signal voltage V
Corresponds to _A.

The subtractor 12 shown in FIG. 1 has input signal voltages V _A and V
If the polarities between _B are opposite, they are replaced by the adder 32. Needless to say, the 1-bit D / A converters 11 and 15 can use various methods depending on the polarity and responsiveness of the signal to be calculated. That is, in the above embodiment,
Since the polarity of the input signal voltage V _B (= V _a + V _b ) is always positive, the 1-bit D / A converters 11 and 15 could be replaced by the analog switches 31 and 35, but the polarity is negative. If so, the configuration as shown in FIGS. 4A and 4B is required.

In FIG. 4A, the input signal voltage V _B and the voltage obtained by inverting the input signal voltage V _B by the inverting amplifier IA1 are compared with each other by the comparator 3
The output D of 4 is used for switching by the switch circuit S1. In FIG. 4B, the input signal voltage V _B is input to the inverting input terminal of the operational amplifier OP1. On the other hand, the input of the input signal voltage V _B to the non-inverting input terminal of the operational amplifier OP1 is switched by the switch S2 which is turned on / off by the output D of the comparator 34.

[0023]

As is apparent from the above description, since the analog arithmetic circuit according to the present invention has no portion requiring adjustment, it is not only accurate and excellent in stability, but also special parts or strict selection work. There is no need to pay, and the economic effect obtained is large.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an arithmetic circuit according to the present invention.

FIG. 2 is a diagram showing voltage waveforms of respective parts of FIG.

FIG. 3 is a diagram for explaining an example in which the arithmetic circuit according to the present invention is applied to correction of a differential transformer signal detection circuit.

FIG. 4 is a diagram showing a specific example of the 1-bit D / A converter shown in FIG.

FIG. 5 is a diagram showing an example of a differential transformer signal detection circuit.

FIG. 6 is a diagram showing a configuration of a conventional analog arithmetic circuit.

[Explanation of symbols]

 31, 35 Analog switch IA1 Inverting amplifier OP1 Operational amplifier

Claims (2)

[Claims] 1. A first 1-bit D / A converter for receiving a DC voltage serving as a denominator of a correction operation, and the 1-bit D / A.
An arithmetic unit that receives the output of the converter and the reference voltage to perform subtraction, an integrator that receives the output of the arithmetic unit to perform integration, a comparator that receives the output of the integrator to determine the polarity, and a correction operation Second 1-bit D / A that receives the DC voltage that becomes the numerator of
A converter, wherein the output of the comparator is used as a switching signal for the first and second 1-bit D / A converters, and the output of the second 1-bit D / A converter is obtained as a correction calculation output. Characteristic analog arithmetic circuit. 2. The analog arithmetic circuit according to claim 1, wherein an analog switch is used as the 1-bit D / A converter.