JP2008286551A - Voltage measurement circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage measurement circuit for measuring voltage without errors with a measuring device having input impedance connected to a signal source having output impedance. <P>SOLUTION: This voltage measurement circuit has input impedance Z<SB>1</SB>and is used to measure a voltage v<SB>2</SB>impressed on an external load with the external load connected to a voltage signal source DS or AS. This measurement circuit is characterized in that it is connected in parallel with the external load and that a negative impedance circuit NL is connected thereto to supply the external load with a current i<SB>3</SB>substantially equal to an influent current i<SB>2</SB>into the external load. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a voltage measurement circuit, and more particularly to a voltage measurement circuit capable of performing measurement without measurement errors due to output impedance of a voltage signal source.

The state in which the measuring instrument is connected to the signal source when the voltage is measured by the voltage measuring circuit can be drawn as shown in FIG. That is, the output impedance is connected an external load Z ₂ is the configured voltage signal source SS the output voltage of the voltages V ₁ as a signal source VS generated by Z _1, current i ₁ flows to the output impedance Z _1, external load _Z is ₂ current _i 2 (= _{i 1)} flows, the voltage _{V 2} generated across the external load _{Z 2.}

Therefore, the voltage _{V 2} appearing at the load _{Z 2} is
V ₂ = V ₁ −Z ₁ i ₁
= V ₁ -Z ₁ i ₂ (1)
It is. Then, the second term (Z ₁ i ₁ , Z ₁ i ₂ ) of the above equation (1) is an error.

In order to reduce the voltage change due to the presence or absence of the load, there is a circuit configuration using an impedance converter A using an operational amplifier as shown in FIG. This is obtained by inserting the impedance converter A in series between the circuit of Figure 6, the output impedance Z ₁ and the external load Z _2.

The configuration shown in FIG. 7, the voltage appearing at the external load Z ₂ will be consistent with high accuracy a voltage V ₁ of the signal source. However, a differential voltage that limits the performance of the operational amplifier A is generated.

  The limit of the performance of the operational amplifier is that an input offset voltage is superimposed in the case of a DC voltage, and that it is affected by frequency dependence in the case of an AC voltage.

  The present invention has been made in consideration of the above points, and an object thereof is to provide a voltage measurement circuit capable of measuring a voltage without error by connecting a measuring instrument having an input impedance to a signal source having an output impedance. To do.

In order to achieve the above object, in the present invention,
In a voltage measurement circuit that has an output impedance and connects an external load to a voltage signal source and measures the voltage applied to the external load,
A voltage measuring circuit, connected in parallel with the external load, and connected to the external load a negative impedance circuit that supplies a current substantially equal to an inflow current to the external load;
Is to provide.

  In the present invention, as described above, a negative impedance circuit is connected in parallel with the external load so as to supply a current substantially equal to the inflow current to the external load, so that the current from the signal source to the external load is reduced. An error caused by energizing the output impedance of the signal source can be suppressed.

FIG. 1 is a circuit diagram showing a basic configuration of the present invention. This circuit is obtained by connecting the negative impedance Z ₃ in parallel with the external load Z ₂ in the conventional voltage measurement circuit shown in FIG.

  The negative impedance is “when a voltage is applied, a current having a magnitude proportional to the voltage and inversely proportional to the magnitude of the impedance flows toward the given voltage”.

Negative impedance Z ₃ is 1, the voltage shown in FIG. 2, when represented by the current,
Z ₃ = −V ₂ / i ₂ (2)
It becomes.

Negative impedance Z ₃ generates a current toward the voltage V ₂ is applied to the voltage application direction. However, between the current flowing through the external load Z _2, the difference in amplitude and phase angle occurs.

This is the error of the negative load, phase error, notation divided into quadrature phase error, i.e. when the (α + jβ), current i ₃ flowing from the negative impedance Z ₃ is
i ₃ = i ₂ {1+ (α + jβ)} (3)
It becomes. The magnitude of the error is determined nominal value of the negative impedance Z _3, a frequency characteristic, the environment dependency of the temperature, due to aging or the like.

The circuit configuration shown in FIG. 1, when the differential current flowing through the output impedance Z ₁ of the voltage signal source SS and i _d,
i _d = i ₃ −i ₂
= I ₂ {1+ (α + jβ)} − i ₂
= I ₂ (α + jβ)
<< V ₂ / Z ₂ (4)
It becomes. Then, a voltage drop in the output impedance _{Z 1} When _{d v,}
d _v = i _d Z ₁
= I ₂ (α + jβ) Z ₁ (5)
This is the difference between the voltage v ₁ and the measured voltage v ₂ that could not be suppressed even when negative impedance was used.

However,
(Α + jβ) << 1 (6)
Therefore, in comparison with the above formula (1),
_dv << i ₂ Z ₁ (7)
Thus, the error is effectively suppressed.

Here, when implementing the negative impedance Z ₃ to the external load Z _2, if implemented by an element of the same format Z ₃ and Z _2, the voltage characteristics of the load, current characteristics, easily aligned and frequency characteristics or temperature characteristics More advanced characteristic improvement can be realized.

  2 to 6 show specific circuit configuration examples according to the present invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

Figure 2 is an exemplary configuration of a voltage measuring circuit of the DC voltage source DS having a resistive divider RD, a resistive divider RD connected to a DC voltage source VS, give divided output to the external load Z _2. On the other hand, the external load Z _2, are connected in parallel a negative load NL. The negative load NL gives the output voltage A · V ₂ of the operational amplifier A having an amplification degree “A” to a feedback circuit having a negative impedance Z ₃ {= (A−1) Z ₂ } as a feedback element. It is a configuration.

With this configuration, the external load _{Z 2} includes a DC power supply VS current _{i 3} of approximately equal size as the current _{i 2} by (≒ _{i 2)} for flow, the output impedance _{Z 1} forming part of a resistive divider RD The flowing current is the difference current i _d (= i ₃ −i ₂ ). As a result, the resistor divider RD is only flows difference current i _d, can be measured as a voltage close to the partial pressure accuracy of the voltage divider values.

Figure 3 is an example of the configuration of the voltage measuring circuit of the induction voltage divider ID AC voltage source AS having, connect the inductive divider ID to an AC voltage source VS, give divided output to the external load Z _2. On the other hand, the external load _{Z 2,} connecting the negative load NL. The negative load NL applies the output voltage of the power amplifier A (1) having the voltage amplification degree “1” to the step-up transformer T, and negatively increases the boosted output voltage kV ₂ (k is a step-up multiple). it is configured to provide sexual impedance Z ₃ to the feedback circuit having a feedback element. The negative impedance Z ₃ is Z ₃ = (k−1) Z ₂ (8) with respect to the value of the external load Z _2.
Has the value

With this configuration, the external load _{Z 2,} since the AC power source VS current _{i 3} of approximately equal size as the current _{i 2} by the (≒ _{i 2)} flows, the output impedance _{Z 1} forming part of the inductive divider ID Only a small current flows. As a result, the voltage can be measured as a voltage close to the voltage dividing accuracy of the induction voltage divider.

In the circuit of FIG. 3, if the external load Z ₂ is the resistance Z ₃ the resistance, Z ₃ if the parallel circuit of the external load Z ₂ is a resistor and a capacitor also assumes a parallel circuit of a resistor and a capacitor Yes. However, the external load Z ₂ can also be implemented as a series circuit, since the reverse is also there may, to the configuration of the Z ₃ for Z ₂ have the freedom degree.

If the voltage amplification factor of the power amplifier A (1) is not "1" but "A" times,
Z ₃ = (Ak-1) Z ₂ (9)
In addition, when using only an amplifier having an amplification degree of “A” and not using the step-up transformer T,
Z ₃ = (A-1) Z ₂ (10)
As a negative impedance circuit can be realized.

  FIG. 4 shows a configuration example for measuring a certain high-frequency voltage. The line connecting the induction voltage divider ID and the external resistance (load) R in FIG. 3 is configured by the coaxial cable C, and the feedback element in FIG. Is configured as a parallel circuit of a resistor (k−1) R ′ and a capacitor (k−1) C ′.

  Here, the coaxial cable C has a capacity of 10,000 pF, the capacity C ′ has a capacity substantially equal to that of the coaxial cable, the resistance R has a resistance value of 100 kΩ, and the resistance R ′ has a resistance value substantially equal to the resistance R. K is the transformation ratio of the step-up transformer T.

  FIGS. 5A and 5B are measured characteristic diagrams of frequency contrast error and frequency versus phase angle in the range of 10 Hz to 10000 Hz of the circuit shown in FIG. All the characteristics shown by the solid line are obtained by the circuit with the negative impedance shown in FIG. 4 connected, and the characteristics shown by the broken line are the coaxial cable C (10000 pF) and the external resistor R (100 kΩ) connected. It was obtained by the circuit of only.

  By comparing the characteristic of the solid line with the characteristic of the broken line, both the ratio error and the phase angle can be greatly improved.

Explanatory drawing which shows the basic composition of this invention. 1 is a circuit diagram showing a configuration of Embodiment 1 of the present invention. The circuit diagram which shows the structure of Example 2 of this invention. The circuit diagram which shows the structure of Example 3 of this invention. FIGS. 5A and 5B are characteristic diagrams showing frequency contrast error characteristics and frequency versus phase angle characteristics of the configuration shown in FIG. The circuit diagram which shows the structure of the conventional voltage measurement circuit. The circuit diagram which shows the structure of the voltage measurement circuit using the conventional operational amplifier.

Explanation of symbols

Z ₁ output impedance Z ₂ external load Z ₃ negative impedance VS voltage source SS voltage signal source RD resistance voltage divider NL negative impedance DS DC signal source A voltage amplifier A (1) power amplifier ID induction transformer R, R 'resistance C, C 'capacity v voltage i current

Claims (3)

In a voltage measurement circuit that has an output impedance and connects an external load to a voltage signal source and measures the voltage applied to the external load,
A voltage measurement circuit, connected in parallel with the external load, and connected to the external load a negative impedance circuit that supplies a current substantially equal to an inflow current to the external load. The voltage measuring circuit according to claim 1,
The negative impedance circuit is:
A voltage measuring circuit comprising a voltage amplifier having a negative impedance feedback circuit. The voltage measuring circuit according to claim 1,
The negative impedance circuit is:
A power amplifier having a voltage amplification factor of 1,
A step-up transformer that converts the output voltage of the power amplifier into a voltage boosted by a step-up ratio k;
A voltage measurement circuit comprising: a feedback circuit that feeds back the boost output of the step-up transformer.

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