JPH01167679A - Impedance measuring instrument - Google Patents

Abstract

PURPOSE:To obtain a high speed, highly accurate and low cost device by using a waveform read-out from sinusoidal waveform memory. CONSTITUTION:An output of an oscillator 37 is divided for the frequency by 1/m at a variable frequency divider 38, then a clock of the frequency fs is inputted into a phase accumulator 32. On accumulating the addition of numeric value (n) for every clock, the accumulator 32 outputs a numerical waveform 33 into the terminal 34 and a pulse 36 into the terminal 35 for every over-flow. The numerical waveform 33 is given to the waveform memory 41-43 of a numerical sine wave generating means, then first, second numerical sine wave and the numerical cosine wave are generated in the latches 44-46. The first numerical sine wave is given to a material 53 to be measured through a D/A converter 47, low-pass filter 48, amplifier 49, DC bias 51 and an adder 52. The output current Ix of the material 53 is converted to a voltage Vout by a current voltage converter 54 and given to a multiplication shape D/A converters 55, 56. The multiplication output deriving from the Vout which is outputted from the converters 55, 56 and the second sine wave or the cosine wave is converted to a conductance component Rl and receptance component Im by the integrator 61, 62.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an impedance measuring device that can measure the impedance transfer function of a measured object at high speed and with high precision even at low frequencies and very low frequencies.

"Prior Art" A conventional synchronous detection type impedance measuring device outputs a square wave with a 0° phase from the terminal 12 of the square wave oscillator 11 and a square wave with a 90° phase from the terminal 13, as shown in FIG. Then, the O° phase square wave at the terminal 12 is passed through a low-pass filter 14 to become a sine wave output, amplified by an amplifier 15, and then supplied to an object to be measured 16. Current output of the object to be measured 16 1. is converted into a voltage signal by the current-voltage converter 17, and the voltage signals are supplied to the synchronous detectors 18 and 19, respectively, and the terminals 12゜1
The outputs of these synchronous detectors 18 and 19 are integrated by integrators 21 and 22, respectively, to obtain integral outputs R and III, which are output by switch 23. The signal is switched and supplied to the AD converter 24, where it is converted into a digital signal. Feedback resistor 25 of current-voltage converter 17
Assuming that the resistance value of is R, a digital vector voltage R-1,=R,+j I is obtained from the AD converter 24.

The output Sit of frequency fc from the low-pass filter 14 is the fifth
Assuming that the results are obtained as shown in FIG. 5A, the strain sty, as shown in FIG.
St3... occurs. On the other hand, the spectrum of the square wave includes relatively large odd-order harmonics as shown in FIG. In other words, this conventional measuring device has a problem in that the distortion of the object to be measured 16 and the current-voltage converter 17 directly causes measurement errors.

Further, as an impedance measuring device, the one shown in FIG. 6 can be considered. That is, the output voltage of the sine wave oscillator 26 is supplied to the object under test 16, and the current output I of the object under test 16 is
A current-voltage converter 17 converts one into a voltage signal, and an AD converter 27 converts the voltage signal into a digital signal. The digital signal is Fourier-transformed by a Fourier transformer 28 to obtain S corresponding to -R1°. On the other hand, sine wave oscillator 2
6 is converted into a digital signal by an AD converter 29, and the digital signal is Fourier transformed by a Fourier transformer 31 to obtain S corresponding to V's. Therefore Z−−■=
, /1. - R-S-/Sb can be determined.

This impedance measuring device is not affected by the distortion of the object to be measured 16 and the current-voltage converter 17;
29 converts a waveform into a digital signal, so high speed and high precision are required, making it expensive. Furthermore, since it requires Fourier transform numerical processing, it is difficult to execute it at high speed.

According to the present invention, a numerical sine wave generating means including at least one sine wave waveform memory is read out at the output of a phase accumulator and generates a first digital sine wave, a second digital sine wave, and a second digital sine wave. wave, generates a digital cosine wave.

The first digital sine wave is converted into an analog signal by a DA converter and supplied to the object under test. The output of the object to be measured and the second digital sine wave are multiplied by the first multiplier type OA converter, and the output of the object to be measured and the digital cosine wave are multiplied by the second multiplier type OA converter.
Multiplied by converter. The respective outputs of the first multiplier type DA converter and the second multiplier type DA converter are integrated over an interval of an integer multiple of the sine wave period by the first integrator and the second integrator, respectively.

"Embodiment" FIG. 1 shows an embodiment of the present invention. In this invention a phase accumulator 32 is provided. The phase accumulator 32 accumulates a given numerical value n every clock, outputs a numerical waveform 33 to a terminal 34, and outputs a pulse 36 to a terminal 35 every time the internal accumulator overflows. The frequency is divided by m by the variable frequency divider 38, and the clock having the frequency r1 is input to the accumulator 32.

The output 33 of the terminal 34 of the accumulator 32 is output to numerical sine wave generating means 39. In this example, the numerical sine wave generating means 39 includes a first sine wave waveform memory 41, a second sine wave waveform memory 42, and a cosine waveform memory 43, and these memories 41, 42, and 43 use the numerical value from the terminal 34 as an address. The latch circuits 44, 45 .
46.

The output of the latch circuit 44 is converted into an analog signal by a DA converter 47, and the analog signal is passed through a low-pass filter 48, amplified by an amplifier 49 as necessary, and further outputted from a terminal 51 as necessary. DC biases are added by an adder 52, and the added output ViM is supplied to the device under test 53. The output current I8 of the object to be measured 53 is transferred to the current-voltage converter 54.
are converted into voltage outputs vl and llL.

This voltage output ■. □ is the first. Second multiplication type DA converter 55
．． 56 as reference voltages. 1st. Each output of the latch circuit 45.46 is supplied to the data input terminal of the second multiplier type DA converter 55.56. 1st. Second
The respective outputs of latch circuits 45 and 46 are supplied to data input terminals of multiplier type DA converters 55 and 56. 1st. The outputs of the second multiplication type DA converters 55 and 56 are respectively connected to the switches 5 and 5.
1st through 7°58. It is fed to a second integrator 61,62. 1st. The outputs of the second integrators 61 and 62 are supplied to the 7AD converter 64 through the changeover switch 63.

The pulses at terminal 35 of phase accumulator 32 are counted by cycle counter 65 and output 66 of counter 65
According to the 1st. The reset switch 67.68 of the second integrator 61.62 is turned on for a short time so that the reset switch 67.68 of the second integrator 61.62 is turned on for a short time. Second integrator 61
．． 62 is reset. During a predetermined period after the reset, /f (fc is the frequency of the pulse 36, k is an integer), the switch 57.58 switches the output 69 of the counter 65 to the first .f. Second
Multiplying type 1) Connect the output side of the A converter 55, 56 to the first. Connected to second integrator 61,62. Between the trailing edge of the output 69 and just before the reset pulse 66, the first . Second integrator 61
．． The outputs of 62 are each converted into digital values by an AD converter 64.

1st. The outputs of the second multiplier DA converters 55 and 56 are V, , (t)Sin(ωt>Vout(t)Cos(ωt), and ω=2πfcs.The outputs of the 2nd πfcs divider 61 and 62 are as follows. , respectively. tz -tl- has 7/fc, that is, V
Output R,,! out is Fourier transformed. , is obtained. This observed output R, +j1. is the current 1. flowing through the object to be measured 53. is proportional to.

Vout = RI * = J + J I mR is the resistance value of the feedback resistor 71 of the current-voltage converter 54.

Therefore, the impedance ZX of the object to be measured 53 is R, +j'l.

It can be found by V in is the amplitude of the sine wave applied to the object to be measured 53, and V is the correction vector of the measurement system.

The spectrum of the signal detecting v0□, that is, the output of the latch circuit 45°46, is as shown in FIG. 5C. The spectrum Sb+ that matches the measurement target spectrum S1 becomes an effective component for detection. Spectrum S. , S, 3... This matches the distortion spectrum of the object to be measured 53 and the current-voltage converter 54, resulting in a measurement error, but it is generally extremely small.
Since it is less than 1/1000, the influence is small. Spectrum S CI r SC! is mf.

This is a sample-free spectrum generated at ±fc (m=1.2...). r, /rC is a non-integer, for example 10
．． 24, this spectrum corresponds to the object to be measured 53,
Since it does not match the distortion spectrum of the current-voltage converter 54,
This is not a measurement error. Integral interval 1, -1. 1/f,
and an integer multiple of 1/f, e.g. 40 o7rc
=4096/r, if not selected, the spectrum S
The C1+scz component is observed as a Fourier transform truncation error. This error is in the integral interval Ltt+=/fc
For example, f, /fc=10.24, k=1
0, the cutting error is 0.1% or less.

If a voltage-voltage converter is used in place of the current-voltage converter 54 in FIG. 1, the transfer function of the object to be measured 53 can be measured.

The numerical sine wave generating means 39 in FIG. 1 may be constructed as shown in FIG. 2. That is, the output of the phase accumulator 32 is supplied to the phase shifter 72, and the 0° output and the 90° output are alternately outputted as shown in FIG. 3a.
These outputs read out the sine wave waveform memory 73, that is, a 0° sine wave and a 90° sine wave, that is, a cosine wave, are alternately read out from the sine wave waveform memory 73.

When the cosine wave is read out, it is latched in the latch circuit 74 by the pulse shown in Figure 3, and when the sine wave is read out, the third
The output of the latch circuit 74 is latched by the latch circuit 75 by the pulse shown in FIG. C, and the output of the latch circuit 74 is latched by the latch circuit 76. The output of the latch circuit 75 is supplied to the DA converter 47 and the first multiplication type DA converter 55, and the output of the latch circuit 76 is supplied to the second multiplication type DA converter 56.

The output R of the first integrator 61 in FIG. 1 is the conductance component of the impedance to be measured Z.
The output I7 of 2 is a resbutance component, and these R, ,
1, may be directly observed with an oscilloscope.

“Effects of the Invention” As stated above, this invention provides high-speed, high-precision A
Since no D converter is used, the structure can be constructed at a lower cost than that shown in FIG. Digital Fourier transform Operates at high speed without requiring numerical processing. Highly accurate measurement is possible because it is not affected by distortion of the object to be measured or the current-voltage converter. Furthermore, in the conventional device shown in FIG. 4, it is necessary to change the pass characteristics of the low-pass filter 14 in order to change the measurement frequency, and it is difficult to make the frequency variable. In the invention, even if the frequency is changed, the spectrum S C1+ sci in FIG.
Since there is only a slight change in fc, there is no need to vary the filtering characteristics of the filter for removing this, and the measurement frequency fc can be easily changed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a modification of the numerical sine wave generating means, Fig. 3 is a waveform diagram for explaining its operation, and Fig. 4 is a conventional one. FIG. 5 is a diagram showing a spectrum for explaining the present invention, and FIG. 6 is a block diagram showing another conventional impedance measuring device. Patent applicant: Atopan Test Co., Ltd.

Claims (1)

[Claims] (1) A numerical sine waveform comprising a phase accumulator and at least one sine wave waveform memory, read out at the output of the phase accumulator to generate a first digital sine wave, a second digital sine wave, and a digital cosine wave. a wave generating means, a DA converter that converts the first digital sine wave into an analog signal and supplies it to the object to be measured, and a first multiplier that multiplies the output of the object to be measured and the second digital sine wave. a DA converter; a second multiplication type DA converter that multiplies the output of the object to be measured by the digital cosine wave; and a second multiplication type DA converter that integrates the output of the first multiplication type DA converter over an interval of an integral multiple of the sine wave period. An impedance measuring device comprising: a first integrator; and a second integrator that integrates the output of the second multiplier type DA converter over an integral multiple of the sine wave period.