JPS5837596B2 - Conversion circuit with nonlinear characteristics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conversion circuit used to obtain an output that approximates a nonlinear function of an input.

The output Ex of the detector of the physical variable X is approximately nonlinear with respect to X.

In order to convert such detection output Ex into a signal proportional to X, a conversion circuit with a non-linear relationship between input and output is required.

Conventionally, as a circuit for approximating the characteristics of an input/output conversion circuit with such nonlinear characteristics, a so-called broken line characteristic circuit has been used, which approximates a given nonlinear characteristic by a broken line characteristic.

When approximating a nonlinear characteristic using such a polygonal characteristic, if you divide the given nonlinear characteristic into many sections and use a circuit that approximates the nonlinear characteristic using a polygonal characteristic with a large number of divisions, the approximation characteristics will be better, but on the other hand, the circuit configuration The disadvantage is that it becomes complicated.

The present invention uses a polygonal characteristic circuit with a relatively small number of divisions, and aims to realize a conversion circuit that has input/output characteristics that approximate the nonlinear characteristics given with high accuracy over a wide range of input changes. be.

FIG. 1 is a block connection diagram showing the principle structure of an embodiment of the present invention.

In the figure, 1 is an input terminal to which input ex is applied from the outside.

FG1 and FG2 are voltage/current conversion circuits having first and second broken line characteristics, respectively.

Input ex applied to input 1 is converted into currents Ix' and IL' according to the polygonal characteristics of FG and FG2, respectively.

PWM is a pulse width modulation circuit, and the input terminal 2 of the modulation circuit is the output current Ix' of FG1, and the input terminal 3 of the reference current is a variable reference current Is that can add the output current IL' of FG2 to the constant reference current Is. ' is given, and the input current Ix at output 4
This circuit generates a pulse width modulation signal corresponding to the ratio of ' and reference current Is'.

FIG. 2 shows the structure of an example of PWM in more detail.

To explain the action of Ix' using the diagram, when input current signal Ix' and reference current Is' are applied to this circuit, I
s' is switched between positive and negative according to the conditions described later, and Ix'
It is also applied to input 5 of operational amplifier A.

In the figure, Os is a power source for obtaining a constant current Is, and 8 is a current converter that generates +Is' and -Is' from a variable reference current Is' that can add the current IL' from FG2 to Is.

Amplifier A constitutes a summing integrator together with capacitor C,
In addition to Ix' and ±Is', the input 5 of the integrator is supplied with a drive current ±Ic that is inverted at a constant repetition period, and the output of the integrator is supplied with input currents Ix' and ±Is supplied to input terminal 2.
Voltage e by integrating s' and ±lc.

occurs and e0? It is compared with zero level by comparator CO.

The output of comparator CO is e.

Switches S1 and S are set so that +Is' is fed back to the integrator power 5 when e < 0, and -Is' is fed back to the integrator power 5 when e < 0.
Drive 2.

The reference voltages +Is' and -Is' fed back at this time are pulse width modulated according to the input current Ix', and the average value over one cycle of each cancels out the input current Ix' at the summing point 5 of the summing integrator. Equilibrium is maintained at zero.

Note that the average value of the clock current +Ic over one cycle is zero.

Now, if the period in which +Is' is fed back to the integrator input in the equilibrium state is tl, the period in which -Is' is fed back is t2, and the period of the pulse width modulated wave is T, the period T is equal to the clock current ±Ic. It is determined by the period T, and the following equation holds true.

If equation (1) is modified and the coefficient of Is' on the right side is set as Tp, FIG. 3 is a waveform diagram of a pulse modulated wave generated by PWM.

Here, the output current IL of FG2 is added to the reference current Is.
If the ratio of ' and Ix' is set to K, the following equation holds true.

Therefore, the PWM is a conversion circuit with nonlinear characteristics that converts the input current Ix' into the output signal Tp.

Tp is determined by counting the period ΔT with a counter.

(2) is a circuit that calculates Tp by counting ΔT.

Let Tp be the output of PWM. Now, FG in Figure 1
, and FG2 with a relatively small number of break points, and if output currents Ix' and IL' for converting ex by these circuits are given to the PWM, the relationship between the PWM output Tp and the input ex can be expressed as follows: It is possible to construct an input/output conversion circuit whose characteristics closely approximate the desired nonlinear characteristics.

Hereinafter, the effects of the present invention will be explained with reference to specific examples.

FIG. 4 shows a specific configuration of an embodiment of the present invention.

In this embodiment, a portion including a first broken line characteristic circuit corresponding to FG1 and a second broken line characteristic circuit corresponding to FG2 in FIG. 1 is shown within a chain line I.

The pulse width modulation circuit PWM and the circuit section (2) for measuring the output Tp of the PWM are the same as those shown in FIG.

The circuit shown in Fig. 4 is characterized by the fact that the break point in the input/output characteristic of the first broken line characteristic circuit matches the break point in the second broken line characteristic circuit, and the structure of circuit I is simplified. be.

In FIG. 5, only the first broken line characteristic circuit included in the broken line characteristic circuit portion (2) is extracted and shown.

In FIG. 5, the first broken line characteristic circuit I is an operational amplifier A1.
This is a circuit with a third broken line characteristic including two breaking points: a first idealized diode centered on A2 and a second idealized diode centered on operational amplifier A2.

Now, for convenience of explanation, if the resistors R1, R4 and Rs1 included in the first idealization diode are chosen to have equal values, A1 is inactive in the range below the bias voltage El31, and e
e to the output 11 of the first diode only in the range x>EB1
An output voltage FEe1 having a polarity opposite to x is generated.

Also, e) (A2 is inactive in the range of > EB2, and the output of the second diode is 1 only in the range of eX < EB2.
2, an output voltage e2 of opposite polarity to eX is generated.

Therefore, the characteristic of the output current Ix' with respect to the input ex becomes a broken line characteristic whose breaking points are <EBI and -EB2, as shown in FIG.

Resistance Rxy△Rx1 in the broken line characteristic circuit portion of Fig. 5
+△Rx2 to other resistors RL and △RLI
If you change it to +△RL2, the break point E B 1 p E B2
It is possible to realize a second broken line characteristic circuit whose broken line characteristic coincides with the bending point of the first broken line characteristic circuit and differs only in the slope of the broken line.

The broken line characteristic circuit portion I shown in FIG. 4 is such that the first and second idealization diodes included in the lth broken line characteristic circuit are shared by the second broken line characteristic circuit.

The relationship between the input ex and the output Tp of the embodiment shown in FIG. 4 is shown in the characteristic diagram of FIG. 7, and the Tp/ex characteristic will be explained using this diagram.

Now, if we look into the FG2 circuit part in Fig. 4 and assume that its output current IL' is zero, the relationship between ex and Tp is expressed by the dotted line (1
) is a broken line characteristic.

This broken line characteristic is the input/output characteristic of FG1 (e
x vs. I x' ).

When IL' is actually added to the PWM reference current Is by FG2, the input/output characteristics (ex vs. Tp) will draw a curve as shown by the solid line (2), for example, when ex is -E B
The ex vs. Tp curve in the range 2<e

The slope of the characteristic curve (2) at ex=O is determined by Rx, and the curvature rate (e) of the curve (the ratio of the increment ΔT in Tp to the increment Δex in ex at each point of ΔTpAe) is RL Determined by

Moreover, the characteristic curve (2) in the range of ex>EB1 is e
At the point where x exceeds EB1, its slope and curvature change in relation to ΔRx1 and ΔRL1.

Further, e) (In the range <-EB2, the slope and curvature change in relation to ΔRx2 and ΔRL2 at the point where ex becomes less than -EB2.

Therefore, when constructing a conversion circuit with characteristics approximating desired nonlinear characteristics using the embodiment circuit of FIG.
Two broken line voltages EB1 and -EB2 of G1 and FG2 are determined, and the input characteristic (Tp/e x ) in this intermediate range is determined to approximate the desired nonlinear characteristic by Rx and RL, e X > E B 1, and e X <
E B The input/output characteristics in the range of 2 are △Rx1 y△RL
1, and ΔRx2 yΔRL2 to approximate the desired nonlinear characteristics.

In this method, the circuit element R that determines the characteristics of FG1
The values of the circuit elements RL, ΔRL1, and ΔRL2 that determine the characteristics of x tΔRxl vΔRx2 and FG2 are selected to arbitrary desired values to construct a conversion circuit with characteristics that approximate the target nonlinear characteristics. Therefore, a conversion circuit with good approximation can be easily realized.

In addition, since some of the circuit elements constituting FG1 can be shared with some of the circuit elements of FG2, it is possible to convert a characteristic that closely approximates the desired non-characteristic characteristic by using a circuit with a broken line characteristic with a relatively small number of break points. The circuit can be realized.

Note that the circuit with the broken line characteristic, which is the circuit element of the present invention, has the fourth
The present invention is not limited to the broken line characteristic circuit I shown in the figure.

It is also possible to arbitrarily select the circuit elements that determine the broken line characteristics and the number thereof.

Further, the pulse width modulation circuit may be of another type.

Any circuit may be used as long as it generates the output signal Tp corresponding to the ratio between the input signal Ix and the reference signal Is.

[Brief explanation of the drawing]

FIG. 1 shows the basic configuration of an embodiment of the present invention. FIG. 2 shows a pulse width modulation circuit included in an embodiment of the present invention. FIG. 3 shows a waveform diagram of the output of the pulse width modulation circuit. FIG. 4 shows a specific configuration of an embodiment of the present invention. FIG. 5 shows the structure of the main part of the broken line characteristic circuit part of the embodiment of the present invention. FIG. 6 is a characteristic line diagram showing the relationship between input and output of the differential line characteristic circuit shown in FIG. FIG. 7 is a characteristic diagram for explaining the input/output relationship of the embodiment of the present invention. FG1...first voltage-current conversion circuit, FG2...
Second voltage-current conversion circuit, PWM...pulse width conversion circuit, ■...output signal counting circuit.

Claims (1)

[Claims] 1. The ratio between the input current and the reference current is determined by a first voltage/current conversion circuit having a first broken line characteristic, a second voltage/current conversion circuit having a second broken line characteristic, and a reference current whose polarity is reversed to positive or negative with respect to the input current. a pulse width modulation circuit that generates a corresponding pulse width modulation signal, a first output current for converting the input voltage by the first voltage/current conversion circuit is provided to the input of the pulse width modulation circuit, and the input voltage is A variable current capable of adding a second output current converted by the second voltage/current conversion circuit to a constant current is used as the reference current, and the first output current and the variable reference are added to the output of the pulse width modulation circuit. A conversion circuit with nonlinear characteristics that can be configured to obtain an output signal corresponding to the ratio of the current.