Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
2002-04-02
2004-06-01
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Parameter related to the reproduction or fidelity of a...
C324S613000
Reexamination Certificate
active
06744261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a method and a device for determining the relative value (ratio) of the amplification factor before changing and after changing the amplification factor of a signal normalizer, and in particular, relates to a method and a device for determining the ratio of the amplification factor of a signal normalizer used in determination devices in order to improve the determination accuracy.
2. Discussion of the Background Art
The method whereby an analog-digital converter (A/D converter hereafter) is set up as an alternating-current voltage determination device and after the signals that are the subject of determination have been converted to discrete values, the signal components of the desired frequency are calculated by numeric operation, which is widely used as a method of determining the voltage amplitude of alternating-current signals that are the subject of determination in determination devices such as alternating-current volt-ammeters and LCR meters, etc. Determination errors in this case are attributed mainly to quantization errors, linearity errors due to bit weighting errors, and thermal noise, and there is particularly an increase in errors when the voltage amplitude of a signal that is input to the A/D converter is small. For example, errors of as much as 108 ppm are produced when signals are input where the maximum input voltage to an A/D converter with an accuracy of 18 bits is {fraction (1/10)}
th
the full-scale voltage of the A/D converter. On the other hand, as a result of the increased accuracy needed for components that are the subject of determination, etc., the determination accuracy of the above-mentioned LCR meter must be 10 ppm or less when determining the alternating-current signal amplitude.
The method whereby a voltage converter that raises or lowers the signal voltage by a predetermined ratio is set up in front of the A/D converter and fluctuations in the voltage amplitude of signals that are input to the A/D converter are kept within a predetermined range in order to reduce the effects of linearity errors is a method for reducing the effects of linearity errors of the A/D converter on the determination values when determining the voltage amplitude of input signals within a broad voltage range. If the voltage amplitude of the signals that are the subject of determination is large enough, it is directly determined by an A/D converter, while if this voltage amplitude is so small that it will cause linearity errors of the A/D converter, voltage conversion by a voltage converter is performed on the signals that are the subject of determination. The voltage amplitude of the signals that are the subject of determination during voltage conversion can be obtained by multiplying the voltage amplitude of the signals input from the voltage converter to the A/D converter as determined by the A/D converter by the inverse of the conversion ratio of this converter. Consequently, it is necessary to know the conversion ratio with an accuracy that is superior to the accuracy of the A/D converter and the voltage converter is generally made so that this accuracy requirement is satisfied to the utmost, or a standard signal source is generally set up and the voltage amplitude of signals obtained through the voltage converter is determined by the A/D converter and the error in the conversion ratio is corrected by calculation after the determination.
When a transformer is used as an example of a voltage converter, transformers of large shape are more expensive, depending on the frequency band that is used, and except when at ½ partial pressure, there is a problem with accuracy because of coil resistance and leakage inductance.
The method whereby amplifier
12
(signal normalizer hereafter) having multiple amplification factors in stages is set up in front of the input part of A/D converter
11
is another method that does not have the above-mentioned restrictions, as in the case of the alternating-current voltage determination device
10
in FIG.
1
. Signal normalizer
12
has the function of amplification and output so that the voltage amplitude of signals that are input by signal generator
13
stays within a predetermined range. As a result, the maximum input voltage to A/D converter
11
is always close to the full-scale voltage of A/D converter
11
, regardless of the size of the voltage amplitude of the input signals, and the effect of linearity errors due to A/D converter
11
is reduced. However, although an amplifier is used in this method, progress has been made in terms of high integration and high performance, even with popular amplifiers on the market, and space-saving effects are marked, regardless of the frequency used.
Depending on the width of the voltage range to be determined, there are cases in which multiple amplification factors of the normalizer are set up in stages in order to finely divide this voltage range. In this case, unless the ratio of the amplification factor before the amplification factor of the signal normalizer is changed and the amplification factor after it has been changed (simply amplification factor ratio hereafter) is known within a desired range of accuracy, the linearity of the determination value will be interrupted by the time when the amplification factor of the signal normalizer is changed as the dividing line, and new linearity errors will be produced. Therefore, the effect of improving errors with a normalizer will not be obtained.
For instance, when the amplification factor of signal normalizer
12
is set using a popular type of network resistance for the part comprising signal normalizer
12
, an accuracy of only 100 ppm at the most can be realized. Therefore, by setting up normalizer
12
, the effect of linearity errors of A/D converter
11
on the determination values is reduced, but a new linearity error is produced due to the insufficient accuracy of the amplification factor ratio in signal normalizer
12
. Consequently, in order to obtain appropriate results when using a signal normalizer for the purpose of reducing the effect of linearity errors of the A/D converter on determinations, it is necessary to precisely determine the amplification factor ratio of the signal normalizer so that linearity of the determinations is maintained.
The method in which only the amplification factor of signal normalizer
12
is changed while keeping constant the amplitude of signals input to input normalizer
12
, the output amplitude of signal normalizer
12
is determined by A/D converter
11
before and after this change is determined, and determinations are performed based on this determination ratio is a method for determining the amplification factor ratio of the signal normalizer
12
. For instance, when determinations of the signal normalizer are performed with an amplification factor of 1× and 10×, first, the amplification factor of signal normalizer
12
is set at 1× and signals are input from signal generator
13
to signal normalizer
12
so that the maximum input voltage to A/D converter
11
is {fraction (1/10)}
th
the full-scale voltage of A/D converter
11
. The voltage of the determination frequency component is calculated from the determination results with A/D converter
11
at this time and serves as V
1
. Then the amplification factor of signal normalizer
12
is set at 10×. The voltage amplitude of the signals input to signal amplifier
12
is not changed and therefore, the maximum input voltage to A/D converter
11
is the full-scale voltage of A/D converter
11
. The voltage of the determination frequency component is calculated from the determination results with A/D converter
11
at this time and serves as V
2
. As a result, the amplification factor ratio obtained from the determination results is found as V
2
/V
1
.
By means of the above-mentioned method, the maximum input voltage to A/D converter
11
during V
1
determination is {fraction (1/10)}
th
the full-scale voltage of the A/D conver
Agilent Technologie,s Inc.
Benson Walter
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