RU2556301C2 - Meter of parameters of multi-element rlc-dipoles - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to instrumentation. A meter comprises a voltage pulse generator, which varies according to a law of n extent, n serially connected differentiators on an operational amplifier each, a multi-element dipole of a measurement object, a differential converter "current-voltage", assembled on operational amplifiers, an n+1 adjustable resistor, n analogue switches, an (n+1) balance indicator. At the same time the first pole of the measurement object dipole and the first lead of the first of (n+1) adjustable resistors are connected, the second pole of the dipole is connected with the first inlet of the converter "current-voltage", the second lead of the first adjustable resistor is connected to the second inlet of the converter, the first leads of other adjustable resistors are connected to inlets of differentiators, and the second leads - to inlets of analogue switches, the outlets of which are connected to the inlets of the "current-voltage" converter, to the outlet of the latter a n-cascade differentiator is connected on RC-links, outlets of the differentiator and the converter are connected with the inlets of (n+1) zero-indicators. Serially connected differentiators are built on operational amplifiers with frequency correction.

EFFECT: increased accuracy of performed measurements.

4 dwg

Description

The invention relates to measuring technique, in particular to a technique for measuring the parameters of objects whose equivalent circuits are in the form of multi-element passive two-terminal devices with lumped parameters.

A device is known for determining the parameters of multi-element passive two-terminal devices (RF patent No. 2390787, G01R 27/02), in which the measured two-terminal device is subjected to voltage pulses, which varies according to the law of the nth time degree, and the two-terminal current is balanced by a compensating signal synthesized from current pulses having the form of power time functions with exponents from n to 0, leading to zero after the end of the transient voltage at the outputs of an n-cascade differentiator connected to the output of the converter difference of currents in voltage, as well as at the output of this converter; based on the found amplitudes of the current pulses mentioned above, the generalized conductivity parameters are calculated, and then the parameters of the two-terminal devices; the n-th voltage pulse shaper consists of a rectangular pulse generator and n series integrators; to form current pulses in the form of power functions, multiplying digital-to-analog converters (DACs) are used, the analog inputs of which are connected to the outputs of the pulse generator and integrators; the current-voltage converter generates a signal of the difference between the current of the two-terminal and the compensating current, which, with the help of an n-cascade differentiator, is brought to zero by adjusting the codes on the digital inputs of the DAC.

The disadvantages of the device are:

1. Limiting the maximum amplitude of the DAC output currents to the maximum permissible value for integrated circuits, for example, for the K572PA1 (PA2) series, this value is 1 mA, which creates an obstacle for balancing the two-terminal current and the compensating current if their amplitudes exceed the limit value for the DAC.

2. Measurement errors due to a wide range of amplitudes of all components of the compensating current, up to 10,000 times. To achieve an acceptable quantization error, DACs with at least 24 bits are required.

The closest in technical essence to the proposed one is a device for determining the parameters of multi-element passive two-terminal devices (RF patent No. 2466412, G01R 17/00), in which the measured two-terminal device is subjected to voltage pulses, changing according to the law of the nth degree of time, and the two-terminal current is balanced by a compensating signal synthesized from current pulses in the form of power time functions with exponents from n to 0, and from the found amplitudes of the component current pulses, generalized parameters are calculated conductivity, and then - the parameters of the elements of the bipolar; The n-th voltage pulse generator consists of a rectangular pulse generator and n series-connected integrators; to generate current pulses having the form of power functions, the output signals of the pulse generator and integrators are used, to which resistors with discretely tunable resistance are connected. The disadvantage of this device is the measurement error due to a wide range of resistance values of adjustable resistors, from hundreds of ohms to units of megohms, which is determined by the large range of amplitudes of all components of the compensating current, up to 10,000 times. To achieve an acceptable quantization error, a large set of switched resistors and switches with a bit depth of at least 24 are required, which significantly complicates the possibility of practical implementation of the device.

The problem to which the invention is directed, is to increase the resolution of the parameter meter of RLC two-terminal devices by reducing the range of resistance values of adjustable resistors.

The technical result is achieved by the fact that in the parameter meter of multi-element RLC two-pole, containing a voltage pulse generator having the form of a function of the nth degree of time, the first (signal) output of which is connected to the first terminal for connecting the measured multi-element two-pole, the general output of the generator is grounded; n series-connected voltage pulse shapers, varying according to the law of a power function with exponents from (n-1) to zero, a current-voltage differential converter, which includes two operational amplifiers, the first included in the feedback circuit of the first and second amplifiers and the second exemplary resistors, respectively, the output of the first operational amplifier is connected to the inverting input of the second operational amplifier through the third resistor, the inverting inputs of the first and second operations nnyh amplifiers form the first and second inputs of the converter, and the output of the second operational amplifier - the inverter output, said first inverter input coupled to a second terminal for connection of the measured multivariate bipole; (n + 1) null indicator and n-cascade differentiator on differentiating RC links, (n + 1) adjustable resistor and n analog switches, with one output of the first adjustable resistor connected to the first output of the pulse generator and the other output connected to the second the input of the current-voltage converter, the first output of the second adjustable resistor is connected to the output of the first pulse shaper, and the second output to the analog input of the first analog switch, the first output of the third adjustable resistor is connected to the output of w horn pulse shaper, and the second output with the analog input of the second analog switch, etc., ..., the first output of the (n + 1) th adjustable resistor is connected to the output of the nth pulse shaper, and the second output with the analog input n -th analog switch, the input of the first differentiating RC link is connected to the output of the current-voltage converter; the signal input of the first null indicator is connected to the output of the last, nth differentiating RC link, the signal input of the second null indicator is connected to the output of the penultimate, (n-1) th differentiating RC link, the signal input of the third null indicator is connected with the output of the (n-2) th differentiating RC link, etc., the signal input of the last, (n + 1) th null indicator is connected to the output of the current-voltage converter, the control inputs of the first, second, and t .d., n-th analog switch connected to the outputs of the switching signals of the second, third go, etc., ..., (n + 1) th null indicator, respectively, the first output of each analog switch is connected to the first input of the current-voltage converter, and the second output of each analog switch is connected to the second input of the converter current-voltage ”, the control inputs of the adjustable resistors are connected to the outputs of the control signals of the zero indicators, the synchronization inputs of the zero indicators are connected to the second output (synchronization output) of the pulse generator; n series differentiators, each of which contains an operational amplifier, the first resistor in the feedback circuit between the inverting input of the amplifier and its output, and also series-connected, are introduced as voltage pulse generators of the form of a power function with exponents from (n-1) to zero a capacitor and a second resistor in the input circuit of the amplifier.

The invention is illustrated by the example of a four-element two-terminal parameter meter. The device diagram is shown in FIG. 1. The meter contains a generator of 1 pulses of cubic shape

$$u_{g\mathrm{and}}(t)=\frac{U_m{t}^3}{t_{\mathrm{and}}^3}(\mathrm{one})$$

where U _m and t _and are the amplitude and duration, the first (signal) output of the generator is connected to the input of the first differentiator 2, the output of the differentiator 2 is connected to the input of the second differentiator 3, the output of the differentiator 3 is connected to the input of the third differentiator 4. To simplify the analytical expressions, we assume that all differentiators have the same transfer functions. In FIG. 2 is a diagram of an inverting differentiator, and FIG. 3 - non-inverting differentiator on an operational amplifier. To ensure stable operation, the frequency characteristic correction is introduced into the circuit using a resistor with a small resistance mR. The transfer function of one differentiator has the form

where p is the Laplace operator, τ = RC is the time constant, and the factor m << 1.

The transfer function of two differentiators is equal to the product of the functions of the first and second differentiators:

the transfer function of the three differentiators is equal to the product of the functions of the first, second and third differentiators:

The waveforms at the outputs of the first, second, and third differentiators found by the operator method have the form:

$$u_{d\mathrm{and}f\mathrm{one}}(t)=\frac{3\tau U_m{t}^2}{t_{\mathrm{and}}^3}-\frac{6m{\tau }^2{U}_{m}t}{t_{\mathrm{and}}^3}+\frac{6m^2{\tau }^3{U}_m}{t_{\mathrm{and}}^3};(5)$$

$$u_{d\mathrm{and}f2}(t)=\frac{6{\tau }^2{U}_{m}t}{t_{\mathrm{and}}^3}-\frac{12m{\tau }^3{U}_m}{t_{\mathrm{and}}^3};(6)$$

$$u_{d\mathrm{and}f3}(t)=\frac{6{\tau }^3{U}_m}{t_{\mathrm{and}}^3}.(7)$$

With the first (signal) output of the generator 1, a first terminal for connecting a multi-element bipolar (MOS) 5 of the measurement object is connected, as well as the first output of the adjustable resistor 6. Adjustable resistors 7, 8 and 9 are connected to the outputs of the differentiators 2, 3 and 4, respectively. Resistors 6, 7, 8, and 9 are designed to control the amplitude of current pulses of cubic, quadratic, linear, and rectangular shapes, from which a signal is formed that compensates all current components of the measured two-terminal device i _dp (t) after the end of the transition process:

$$i_{dP}(t)=\frac{Y_0{U}_m{t}^3}{t_{\mathrm{and}}^3}+\frac{3Y_{\mathrm{one}}{U}_m{t}^2}{t_{\mathrm{and}}^3}+\frac{6Y_2{U}_{m}t}{t_{\mathrm{and}}^3}+\frac{6Y_3{U}_m}{t_{\mathrm{and}}^3},(8)$$

where Y ₀ , Y ₁ , Y ₂ , Y ₃ are the generalized conductivity parameters of a multi-element two-terminal device of the measurement object.

The balancing of the two-terminal current and the compensating current is carried out using a current-voltage differential converter and a three-stage differentiator on differentiating RC links. The differential current-voltage converter is built on the first and second operational amplifiers 10 and 11 with resistors 12 and 13 included in the feedback circuits, respectively, the output of the first amplifier 10 is connected to the inverting input of the second amplifier 11 through a resistor 14. The voltage at the output of the second operational amplifier in proportion to the difference of the input currents in the circuits of the inverting inputs of the operational amplifiers 10 and 11:

. $$u_{\mathrm{at}sx}(t)=\frac{i_{\mathrm{at}x\mathrm{one}}{R}_{12}{R}_{13}}{R_{\mathrm{fourteen}}}-i_{\mathrm{at}x2}{R}_{13}=\frac{(i_{\mathrm{at}x\mathrm{one}}{R}_{12}-i_{\mathrm{at}x2}{R}_{\mathrm{fourteen}})R_{13}}{R_{\mathrm{fourteen}}}$$

.

With equal values of R ₁₄ = R ₁₂

u _o (t) = (i _in1 -i _in2 ) R ₁₃ .

The three-stage differentiator contains three sequentially differentiating RC links: a capacitor 15 and a resistor 16, a capacitor 17 and a resistor 18, a capacitor 19 and a resistor 20. All three RC links have the same RC time constant, but to reduce the duration of the transient in the differentiator, the capacitances of the capacitors and the resistances of the resistors in each cascade are chosen different: C ₁₅ = C / k, C ₁₆ = kR, C ₁₇ = C, R ₁₈ = R, C ₁₉ = kC, R ₂₀ = R / k, where k << 1 . Since the directions of the cubic component of the current of the two-terminal device and the current of the resistor 6 are always the same, the second terminal for connecting the multi-element two-terminal device is connected to the inverting input of the first operational amplifier 10, and the second output of the adjustable resistor 6 is connected to the inverting input of the second operational amplifier 11. The remaining components of the current of the two-terminal device from configurations equivalent circuits can have both a positive and a negative sign. The amplitudes of the components of the compensating current are regulated by the signals supplied to the control inputs of the adjustable resistors 6, 7, 8, and 9 from the corresponding outputs of the zero indicators 21, 22, 23 and 24. The free terminals of the adjustable resistors 7, 8 and 9 are connected to the analog inputs of the analog switches 25, 26 and 27, respectively. The inputs of the signals controlling the switching are connected to the outputs of the switching control of the null indicators.

Operational amplifiers 10 and 11 covered by parallel negative feedback have a low, near zero input

, где R_oc - сопротивление резистора в цепи обратной связи; К_{u оу} - коэффициент усиления операционного усилителя. Поэтому уравновешивающие токи через резисторы 6, 7, 8 и 9 определяются только выходным напряжением генератора 1 и дифференциаторов 2, 3 и 4 и значениями сопротивлений R_yp0, R_yp1, R_ур2 и R_ур3 регулируемых резисторов 6, 7, 8 и 9 соответственно:resistance $$R_{\mathrm{at}x\text{os}}=\frac{R_{\mathrm{about}\mathrm{from}}}{K_{u\text{OU}}}$$

where R _oc is the resistance of the resistor in the feedback circuit; To _{u oh} - the gain of the operational amplifier. Therefore, the balancing currents through the resistors 6, 7, 8 and 9 are determined only by the output voltage of the generator 1 and the differentiators 2, 3 and 4 and the resistance values R _yp0 , R _yp1 , R _ur2 and R _{ur3 of the} adjustable resistors 6, 7, 8 and 9, respectively:

Comparing expression (8) for the two-terminal current and expressions (9) - (12) for balancing currents, we can find the conditions for compensating the current i _dn (t) in the steady state after the end of the transient process:

1) for cubic current

2) for the quadratic component

3) for the linear component

4) for the constant component

Formulas (13) - (16) allow us to determine the generalized conductivity parameters of a two-terminal network. In order to separately control the process of balancing each current component of a two-terminal network by adjusting the amplitudes of the cubic, quadratic, linear and constant components of the compensating current, the output signal of the current difference converter to the voltage is fed to a three-stage differentiator on differentiating RC links.

The signal input of the first null indicator 21 is connected to the output of the third differentiating RC link (capacitor 19 and resistor 20), the signal input of the second null indicator 22 is connected to the output of the second differentiating RC link (capacitor 17 and resistor 18), the signal input of the third zero -indicator 23 - with the output of the first differentiating RC link (capacitor 15 and resistor 16), the signal input of the fourth zero indicator 24 - with the output of the current-voltage converter (second operational amplifier 11).

The balancing of currents is carried out in stages, starting with the senior (3rd) degree. The voltage pulse of a cubic shape (1) from the output of the generator 1 excites a current (8) in a two-terminal 5 in the steady state. As a result of three-fold differentiation of the output voltage of the current-voltage converter, a constant voltage pulse is established at the output of the third differentiating RC link, proportional to the difference between the cubic components of the current of the two-terminal network and the current through the resistor 6. Compensation of the cubic component of the current of the two-terminal network 5 is carried out by reducing the output voltage of the third differentiating device RC-unit by adjusting the resistance R of the resistor 6. The signal _ur0 resistor 6 regulating expression atyvaet null indicator 21.

Then, the second null indicator 22 analyzes the voltage at the output of the second differentiating RC link, proportional to the difference between the quadratic components of the current of the two-terminal network and the current through the resistor 7. Compensation of the quadratic component of the current of the two-terminal 5 is carried out by reducing the output voltage of the second differentiating RC link to zero by adjusting the resistance R _yp1 resistor 7. A null indicator 22 controls the switching of the analog switch 25 and generates a resistance control signal of the resistor 7.

After balancing the cubic and quadratic components of the two-terminal current and the compensating current, the linear component is balanced by bringing the output voltage of the first differentiating RC link to zero by adjusting the resistance - R _{ur2 of} resistor 8. Switching the analog switch 26 and adjusting the resistance of resistor 8 is controlled by the third zero indicator 23.

At the last stage, the DC component of the two-terminal 5 is balanced by a resistor 9. The fourth null indicator 24 determines the current sign and generates a switch signal 27 and a resistance regulation signal R _{yp3 of} resistor 9.

After four stages of balancing the two-terminal current i _dp (t) and the compensating current using the formulas (13) - (16), the generalized conductivity parameters of the two-terminal Y ₀ , Y ₁ , Y ₂ , Y _{3 are} determined. This concludes the unified part of the meter algorithm, the same for any two-terminal device with passive elements: RC, RL or RLC type.

Next, using the obtained values of the values Y ₀ , Y ₁ , Y ₂ , Y ₃ , calculate the electrical parameters of the elements of the bipolar.

As an example, consider the four-element bipolar RCL shown in FIG. 4. The operator image of the conductivity of the two-terminal network has the form

Y-parameters of a two-terminal device are equal [3]

These expressions allow you to determine the parameters of the elements R ₁ , C ₁ , R ₂ and L ₁ :

; квадратичной формы

; линейной формы

; постоянной составляющей

. Как видно, динамический диапазон амплитуд составляет 3436 раз. Если амплитуды импульсов напряжения, из которых формируются компенсирующие токи, имеют близкие значения, необходимо осуществлять регулировки сопротивлений резисторов в очень широком диапазоне, т.е. требуются многоразрядные схемы управления.A serious factor hindering the implementation of high accuracy measurements is a wide range of values of different current components of the two-terminal network. So, at nominal values of the parameters of the above example of a two-terminal device, R ₁ = 2 kOhm; C ₁ = 4 nF; R ₂ = 5 kΩ; L ₁ = 3 mH Y-parameters of a two-terminal device are equal: Y ₀ = 0.5 mS; Y ₁ = 4 mS · μs; Y ₂ = -80 mS · msec ² ; Y ₃ = 1552 mS · μs ³ . When the amplitude of the voltage pulse of the test signal is 10 V, and the pulse duration is 400 μs, the amplitudes of the components of the current of the two-terminal network according to (8) are equal to: cubic

; quadratic form

; linear shape

; constant component

. As you can see, the dynamic range of amplitudes is 3436 times. If the amplitudes of the voltage pulses from which the compensating currents are formed have close values, it is necessary to adjust the resistors in a very wide range, i.e. multi-bit control circuits are required.

; линейной формы

; постоянной составляющей

.In the considered example, for the given parameters of the two-terminal network and the value of the time constant of the differentiators 12 μs, the voltage amplitudes at the outputs of the first, second, and third differentiators are equal: quadratic

; linear shape

; constant component

.

It can be seen that the differentiators reduce the amplitudes of the voltage pulses from cascade to cascade in approximately the same proportions as the required amplitudes of the components of the current of the two-terminal network. As a result, to balance currents, resistance settings in a narrow range are required: R _ur0 = 2 kOhm; R _yp1 = 2.948 kΩ; R _yp2 = 1.8266 kΩ; R _ur3 = 1,092 kOhm. If you use 12-bit control signals, the quantization error in all channels is in the range of 0.27 ... 0.72 Ohms. In the case of using the same amplitudes of the output signals of the shapers, the value of the resistance quantum in the second stage would be 11 times greater than in the first stage, in the third - 185 times, and in the fourth - 6250 times, i.e. to increase the resolution to the level of the first stage, it would be necessary to increase the resolution of the control signals to 24, which is not acceptable for practical implementation.

Thus, the use of differentiators for the formation of voltage pulses of a power-law form allows us to narrow the control range of current-setting resistors by hundreds of times. Therefore, with a limited bit depth of digital signals, the price of one quantum of resistance, which determines the resolution of the meter, decreases significantly.

Claims (1)

Parameter meter for multi-element RLC diodes, comprising a voltage pulse generator having the form of a function of the nth time degree, the first (signal) output of which is connected to the first terminal for connecting the measured multi-element diode, the common output of the generator is grounded; a differential current-voltage converter, which includes two operational amplifiers, the first and second reference resistors are included in the feedback circuit of the first and second amplifiers, respectively, the output of the first operational amplifier is connected to the inverting input of the second operational amplifier through the third resistor, the inverting inputs of the first and the second operational amplifiers form the first and second inputs of the converter, and the output of the second operational amplifier is the output of the converter, the first input e is connected to a second terminal for connecting a measured multi-element bipolar; (n + 1) adjustable resistor, n analog switches, (n + 1) null indicators and an n-cascade differentiator on differentiating RC links, one of the terminals of the first adjustable resistor connected to the first output of the pulse generator, and the second terminal of the first adjustable a resistor is connected to the second input of the current-voltage converter, one of the terminals of the second, third, ..., (n + 1) -th adjustable resistors is connected to the analog input of the first, second, ..., n-th analog switch, the input of the first differentiating RC- Vienna converter connected to the output "current-voltage"; the signal input of the first null indicator is connected to the output of the last, nth differentiating RC link, the signal input of the second null indicator is connected to the output of the penultimate, (n-1) th differentiating RC link, the signal input of the third null indicator is connected to the output of the (n-2) th differentiating RC link, etc., ..., the signal input of the last, (n + 1) th null indicator is connected to the output of the current-voltage converter, the control inputs of the first, second , ..., of the nth analog switch are connected to the outputs of the switching signals of the second, third oh, ..., (n + 1) -th null indicator, respectively, the first output of each analog switch is connected to the first input of the current-voltage converter, and the second output of each analog switch is connected to the second input of the current-voltage converter the inputs of adjustable resistors are connected to the outputs of the control signals of the zero indicators, the synchronization inputs of the zero indicators are connected to the second output (synchronization output) of the pulse generator, characterized in that n are additionally introduced into it in series key differentiators, each of which is built on an operational amplifier with frequency correction, the input of the first differentiator is connected to the first output of the pulse generator, and the outputs of the first, second, ..., n-th differentiators are connected to the free terminals of the second, third, ..., (n + 1 ) th adjustable resistor, respectively.

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