JPH0786958B2 - Signal generator - Google Patents

Description

The present invention relates to a signal generator using a potentiometer.

<Conventional Technology> A conventional technology will be described below with reference to the drawings.

FIG. 3 is an electric circuit diagram showing an outline of a conventional signal generator.

In FIG. 3, the variable signal output voltage signal V ₀ is taken out from the movable terminal P _{1b of the} 4-wire potentiometer P ₁ with a center tap. The fixed terminal P _1a of the potentiometer P ₁ has one end of the variable resistor VR ₁ for adjusting the positive span of the variable signal output voltage signal V ₀ connected to the other end of + V, and the fixed terminal P _1c of the potentiometer P ₁ One end of the variable resistor VR ₂ for adjusting the negative span of the variable signal output voltage signal V ₀ , to which the other end is connected to -V, is connected. The center tap terminal P _1d is connected to the reference level (0V) so that the zero point position is not affected by the span adjustment, and the zero point position is fixed.

<Problems to be Solved by the Invention> However, a 4-wire potentiometer with a center tap is more expensive than a 3-wire type potentiometer, and also includes a dead zone element in the center tap P _1d portion as shown in FIG. I'm out. That is, it is electrically connected to the resistor with the center tap P _1d width T. This width T becomes a factor that causes a dead zone. A dead zone of 0.3 to 1.4% occurs in a commercially available conductive potentiometer.

Further, the 3-wire type potentiometer has a problem that the zero point position is displaced by the span adjustment.

The present invention has been made in view of the problems of this conventional technique, and an object of the present invention is to provide a signal generator using an inexpensive 3-wire potentiometer that does not cause a shift of the zero point position due to span adjustment. And

<Means for Solving Problems> In order to achieve such an object, according to the present invention, one end is connected to a positive potential and the other end is connected to a negative potential, and a variable terminal that moves on a resistor is used. A three-wire potentiometer that obtains a voltage signal, a polarity determination circuit that compares the variable voltage signal with a reference potential and determines a positive / negative polarity, the variable voltage signal is input, and the variable voltage is input for each different polarity. A span adjustment circuit that amplifies the signal at an arbitrary ratio to perform span adjustment, and a selection circuit that selects the variable voltage signal span-adjusted by the span adjustment circuit for each polarity based on the polarity determined by the polarity determination circuit are provided. The feature is that the span can be adjusted arbitrarily for each different polarity.

<Examples> Examples of the present invention will be described in detail below with reference to the drawings.
In the following drawings, the same parts as those in FIGS. 3 and 4 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a circuit diagram of a signal generator showing a specific embodiment of the present invention.

In FIG. 1, P ₂ has a fixed terminal P _2a to which + V is connected, a fixed terminal P _2c to which −V is connected, and a movable terminal P _2c outputs a variable voltage signal V _p having positive / negative polarities 3 It is a wire potentiometer. 1, first circuit variable resistor VR _1, VR ₂ to perform span adjustment in accordance with the positive / negative polarity of the variable voltage signal V _p of 3-wire potentiometer P ₂
It is a span adjustment circuit composed of a pair of operational amplifier circuits 1a and 1b as constituent elements. That is, the operational amplifier circuit 1a includes an operational amplifier Q ₁ for inputting a variable voltage signal V _p to the non-inverting terminal, the operational amplifier Q output of the operational amplifier Q ₁ via the variable resistor VR _1
The feedback is provided to the _1- inverting input terminal, and the non-inverting input terminal is connected to the reference potential via the resistor R ₁ . Similarly, the operational amplifier circuit 1b includes an operational amplifier Q ₂ that inputs the variable voltage signal V _p to the non-inverting terminal, and the output of this operational amplifier Q ₂ is fed back to the inverting input terminal of the operational amplifier Q ₂ via the variable resistor VR _2. At the same time, the non-inverting input terminal is connected to the reference potential via the resistor R ₂ . Here, the span adjusting circuit 1 is a pair of operational amplifier circuits.
1a and 1b consist of variable resistors VR ₁ and VR ₂ which are respectively
This is because the span adjustment can be performed according to the negative polarity. That is, with this configuration, the resistance R ₁
(R ₂ ) and variable resistance VR ₁ (VR ₂ ) make amplification {1+ (VR ₁ /
R ₁ )} (or {1+ (VR ₂ / R ₂ )}) is obtained. If the internal resistance of the variable resistor VR ₁ (VR ₂ ) changes from 0 to R _max ,
The span can be adjusted within the range of ₁ to {1+ (R _max / R ₁ )}. 2 is a movable terminal of 3-wire potentiometer P ₂
A variable voltage signal V _p having positive / negative polarities from P _2c is input, the positive / negative polarities of this signal are discriminated, and gate signals G ₁ and G ₂ corresponding to the polarities are selected by a selection circuit (for example, an analog circuit). A pair of switch elements consisting of switches SW ₁ ,
SW ₂ ) This is a polarity discrimination circuit that outputs to 3, and the variable voltage signal V
_It is composed of a comparator Q ₃ for discriminating the polarity of _p and an inverter Q ₄ for inverting the output of this comparator Q ₃ . Here, the inverter Q ₄ is provided because the pair of switch elements SW ₁ and SW ₂ are not turned off (closed) at the same time. The switch elements SW ₁ , SW
Here, ₂ operates to turn off when the gate signal G ₁ or G ₂ is at a low level. At this time, the pair of operational amplifier circuits 1a and 1b of the span adjusting circuit 1 are respectively connected to one of the contacts, and as described above, the selection operation is performed by the signal from the polarity discriminating circuit 2 according to the polarity. Reference numeral 4 is a low-pass filter, in which the resistor R ₃ is connected to the other contact of the switch element SW ₁ , the resistor R ₄ is connected to the other contact of SW ₂ , and the resistor R ₃
And R ₄ are connected to one end of a capacitor C ₁ whose other end is connected to a reference potential, and serve to eliminate distortion during switching. 5 is a buffering circuit, and the signal from the low pass filter 4 is an operational amplifier Q ₅
Type of the non-inverting input terminal, the operational amplifier Q ₅ output resistor R ₅
It is fed back to the inverting input terminal via, and one end of the resistor R ₆ whose other end is connected to the reference potential is connected to the inverting input terminal. With such a structure, a signal generator having a structure capable of reproducing plus / minus signals after span adjustment can be obtained. That is, the same variable signal output voltage signal V ₀₁ can be obtained as a signal without a dead zone from the buffering circuit 5 as shown in FIG. 3 when it is taken out from the movable terminal P _{1b of the} 4-wire potentiometer P ₁ with a center tap. it can.

FIG. 2 is a diagram showing the output characteristic of each part of FIG.

FIG. 2 (a) is a voltage output characteristic diagram of the output V _p with respect to the movement amount θ of the movable terminal P _2b of the potentiometer. The output characteristic on the left side of the figure represents the time when the switch element SW ₁ is on, and the right side of the figure. Represents the time when the switch element SW ₂ is on (the same applies to FIG. 2 below). FIG. 2 (b) is a voltage output characteristic diagram of the operational amplifier circuit 1a of the span adjusting circuit 1 with respect to the movement amount θ of the movable terminal P _2b of the potentiometer, which is indicated by an arrow α.
₁ indicates that it can be changed by changing the variable resistance VR ₁ . FIG. 2 (c) is a voltage output characteristic diagram of the operational amplifier circuit 1b of the span adjustment circuit 1 with respect to the movement amount θ of the movable terminal P _2b of the potentiometer, and the arrow α ₂ can be changed by the variable resistor VR _2. Indicates. FIG. 2D is a voltage output characteristic diagram of the buffering circuit 5 with respect to the movement amount θ of the movable terminal P _2b of the potentiometer, and the outputs of the operational amplifiers Q ₁ and Q ₂ depend on the polarity of the variable voltage signal V _p. Switch element SW ₁
Alternatively, it can be seen that the output V ₀₁ that changes with the arrows α ₁ and α ₂ is obtained by turning on the SW ₂ and changing the variable resistors VR ₁ and VR ₂ .

<Effects of the Invention> As described above in detail with reference to the embodiments of the present invention,
According to the present invention using a 3-wire potentiometer without a center tap, it is possible to inexpensively provide a signal generator capable of independently adjusting spans of positive / negative polarities without dead zones. There is.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a signal generator showing a specific embodiment of the present invention, FIG. 2 is a diagram showing output characteristics of each part of FIG. 1, and FIG.
FIG. 4 is an electric circuit diagram showing an outline of a conventional signal generator, and FIG. 4 is a diagram for explaining problems of the conventional technique. P ₁ ... 4-wire potentiometer with center tap, P ₂
...... 3-wire potentiometer, 1 ... span adjustment circuit,
2 ... Polarity discrimination circuit, 3 ... Selection circuit, 4 ... Low-pass filter, 5 ... Buffering circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01D 5/16

Claims (1)

[Claims] 1. A three-wire potentiometer for obtaining a variable voltage signal from a movable terminal that moves on a resistor, one end of which is connected to a positive potential and the other end of which is connected to a negative potential, and a reference of the variable voltage signal and zero V. A polarity discriminating circuit that compares the electric potential and discriminates positive / negative polarities; a span adjusting circuit that inputs the variable voltage signal and arbitrarily amplifies the variable voltage signal for each different polarity to perform span adjustment; A signal generator characterized in that a selection circuit is provided for selecting, for each polarity, a variable voltage signal whose span has been adjusted by the span adjustment circuit based on the polarity determined by the polarity determination circuit, so that the span can be adjusted for each different polarity.