Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2001-01-17
2003-04-15
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S713000
Reexamination Certificate
active
06549021
ABSTRACT:
BACKGROUND
1. Description of the Invention
The present invention pertains to electric measuring equipment in general and in particular to an apparatus that finds the ratio of electrical signals and measuring equipment that uses this apparatus.
2. Related Art
Technology for measuring the ratio between two electrical signals, such as network analyzers, apparatuses for measuring circuit elements, devices for measuring transmission or equipment for measuring phase and amplitude, etc., is used for many purposes. In particular, this ratio is a vector ratio when the electrical signals are alternating-current signals.
By means of prior art, two electrical signals to be determined are measured by separate measuring means and the ratio is found from the measurements that have been obtained where low precision is acceptable for the ratio measurement. Many network analyzers (for instance, Agilent 8715A marketed by Agilent Technology (Tokyo)) use this method.
Nevertheless, the conversion coefficient of the measuring means, that is, the ratio of the quantity to be measured and the measurement (usually a complex number), generally do not agree with the theoretical value due to differences in properties between the two measuring means. An error due to the above difference readily increases with an increase in frequency of the electrical signals to be measured.
One method of eliminating this difference is calibration, as long as the measuring means is linear. One method that is generally used for the calibration of the voltage ratio is the method whereby the output of one signal source is divided in two with a resistance-type distributor and the respective outputs are measured as input of the measuring means and the same measurements serve as the reference. However, by means of methods that use two measuring means, it is difficult to maintain 0.05% stability in terms of the amplitude of the measurements with changes in temperature of ±10° after calibration and stability of 0.03° in terms of phase due to differences in the properties of the respective structural parts.
The method whereby the same measuring means are used with the help of time division is employed as the ultimate method for minimizing and stabilizing the difference between the conversion coefficients of these measuring means. For instance, the method of time division is used with equipment for measuring impedance (for instance, Agilent 4294A made by Agilent Technology), which is one of the apparatuses used to measure circuit components, because stability of 0.05% in terms of the amplitude of the measurements (absolute value) and 0.03° or less in terms of phase is required.
The ratio meter of the prior art shown in
FIG. 1
comprises switch means
9
for time-division multiplexing of input signals, terminal resistance
16
connected in series to the output side of this switch means, measuring means
100
, and control and computation apparatus
30
. Switch means
9
comprises input switches
6
and
8
connected to input terminals
2
and
4
and connections that include junctions
10
and
12
. Junction
10
is also an input terminal of measuring means
100
. Terminal resistance
16
is connected to junction
12
.
Voltage U corresponding to the current that flows to the device under test is introduced to input terminal
2
. On the other hand, voltage V that corresponds to the voltage applied to the device under test is introduced to input terminal
4
.
Input switches
6
and
8
are in the first state, wherein input terminals
2
and
4
are exclusively connected to measuring apparatus
14
and terminal resistance
16
, respectively, (as shown by the solid switch lead lines) in the first time interval. Here, measuring apparatus
14
measures voltage V and measurement u is stored in memory
22
. Input terminal
4
terminates at terminal resistance
16
.
Input switches
6
and
8
are in the second state, where input terminals
4
and
2
are exclusively connected to measuring apparatus
14
and terminal resistance
16
, respectively, (as shown by the broken switch lead lines) in the next second time interval. Here, measuring apparatus
14
measures voltage V and measurement v is stored in memory
24
. Input terminal
2
terminates at terminal resistance
16
. Control and computation apparatus
30
obtains the operation timing of input switches
6
and
8
, output switch
20
, and other components, or accesses memories
22
and
24
in order to input measurements u and v and calculates their ratio v/u. The voltage ratio that is found from the corrected formula, which has been found during calibration of this ratio, is calculated.
In this case, even if the conversion coefficient of measuring means
100
changes with temperature, etc., for instance such that u and v become ku and kv, (kv)/(ku)=v/u then the ratio that is measured will not change. The hypothesis that the value of resistance R1 of input resistance (generally impedance, but resistance is used in the following discussion for purposes of clarity and understanding of the invention, and not as a limitation of the invention) of measuring apparatus
14
and the value of resistance R2 of terminal resistance
16
are equal must be valid in order to accurately calibrate and measure by this measuring method.
Nevertheless, it is difficult to keep R1 and R2 the same within a wide frequency range when the frequency of voltages U and V increases, and there are cases where input impedances looking into ratio measuring means
100
from input terminal
2
or
4
takes on different values, depending on the switching state. Therefore, voltage sources U and V changes and V/U itself also changes in accordance with the switch state.
The method has also been used whereby an attenuator is introduced in front of each of input terminals
2
and
4
so that the above-mentioned changes present in the connection state of the switches are attenuated. However, by means of this method, the undesirable effect often occurs wherein voltages U and V that are input to measuring means
100
are attenuated and their signal-to-noise ratio is reduced, resulting in a reduction in measurement precision.
SUMMARY OF THE INVENTION
The object of the present invention is an apparatus and a method for accurate calibration and stable measurement of the ratio of electrical signals without requiring an unnecessary attenuator, even if there is a difference in the input impedance.
Another object of the present invention is an apparatus for measuring electric components and a method of measuring electric components that uses these very stable ratio measurements.
The first apparatus for measuring the ratio of electrical signals pertaining to the present invention comprises a switch means that comprises a first input terminal that receives a first electrical signal, a second input terminal that receives a second electrical signal, and a first and a second output terminal, and that has a first state, wherein the first input terminal and the first output terminal are connected and the second input terminal and the second output terminal are connected, as well as a second state, wherein the first input terminal and the second output terminal are connected and the second input terminal and the first output terminal are connected; a first measuring means for measuring electrical signals received from the above-mentioned first output terminal having a first receiving terminal connected to the above-mentioned first output terminal; a second measuring means for measuring electrical signals received from the above-mentioned second output terminal having a second receiving terminal connected to the above-mentioned second output terminal; and a control and computation means, which is connected to the above-mentioned switch means and the above-mentioned first and second measuring means and receives the respective measurements of the above-mentioned electrical signals of the above-mentioned first and second measuring means with the above-mentioned switch means and the above-mentioned first and second state, respectively, and
Agilent Technologie,s Inc.
Benson Walter
Le N.
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