JPH06303033A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain an oscillation circuit by which a stable coin detection distance against a change in ambient temperature is obtained without decreasing a positive feedback current by providing a temperature compensation circuit of a current addition system to the oscillation circuit. CONSTITUTION:An LC circuit A is an LC parallel resonance circuit consisting of a capacitor 22 and a coil 23 (equivalent to sensor coil). Then a constant current is supplied from a constant current circuit B to the LC circuit A. In this case, the LC parallel resonance circuit A is stably resonated by amplifying an output of the LC parallel resonance circuit A to use the amplified signal for positive feedback. When a Q of the LC parallel resonance circuit A is changed due to ambient temperature, a compensation current applied from a temperature compensation circuit E is adjusted according to a change, resulting that a loop gain is not decreased but stable against ambient temperature. Furthermore, the temperature characteristic is set optionally by only revising a resistance constant and then the circuit is easily adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator circuit which can be used as an inductive proximity switch circuit using a transistor element. In particular, the present invention relates to an output of a LC parallel resonant circuit which is positively feedback-amplified to cause the LC parallel resonant circuit to oscillate, and relates to improvement of an oscillator circuit including a temperature compensation circuit that adjusts a loop gain according to an ambient temperature. .

[0002]

2. Description of the Related Art A conventional oscillation circuit of this type is shown in FIG. The oscillation circuit in the illustrated example constitutes a part of the inductive proximity switch circuit equipped in the vending machine, and has a function of detecting the presence or absence of a coin inserted in the vending machine.

The LC circuit A is a resonance circuit in which a capacitor and a coil (corresponding to a sensor coil) are connected in parallel, and a constant current from the constant current circuit B is supplied. The bias circuit C is connected to one end of the LC circuit A, and the positive feedback amplifier circuit D is connected to the output stage of the bias circuit C. The output terminal T is provided at the output of the bias circuit C.

That is, the output of the LC circuit A is biased by the bias circuit C and further the positive feedback amplifier circuit D.
Is amplified by positive feedback, and a stable oscillating voltage is obtained from the output terminal T. Then, in this state, if a coin, which is a metal body, approaches the LC circuit A,
This transmission condition is broken and the circuit oscillation stops. In other words, whether or not a coin is inserted can be detected depending on whether or not the voltage appearing at the output terminal T has a vibration component.

Further, a temperature compensating circuit E for compensating for a change in the positive feedback current due to temperature is connected to the positive feedback amplifying circuit D. The larger the current flowing into the temperature compensating circuit E, the more the positive feedback amplifying circuit. The output current of D becomes small. The current flowing into the temperature compensating circuit E is proportional to the base-emitter voltage of the NPN transistor, and is large at low temperature and small at high temperature. Therefore, by combining the negative temperature coefficient of the temperature compensation current and the positive temperature coefficient of the parasitic series resistance of the coil of the LC circuit A,
Even if the ambient temperature changes, the loop gain can be kept constant and the distance for detecting the presence or absence of a coin does not change.

The above conventional oscillation circuit is disclosed in Japanese Patent Application Laid-Open No. 4-70120 filed by the applicant of the present application.

[0007]

However, the above conventional oscillation circuit with temperature compensation circuit has the following problems.

That is, since the positive feedback current is reduced by adding the temperature compensation circuit, there is a problem that the gain of the entire circuit is reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a coin detection distance that is stable against changes in ambient temperature without reducing the positive feedback current (gain). It is to provide an oscillation circuit that can obtain.

[0010]

The oscillator circuit of the present invention is L
An oscillator circuit for amplifying the output of the C parallel resonance circuit by positive feedback to oscillate the LC parallel resonance circuit, which comprises a temperature compensation circuit for adjusting the loop gain according to the ambient temperature. The above temperature compensation circuit is provided.

[0011]

When the output of the LC parallel resonance circuit is amplified and positive feedback is applied, the LC parallel resonance circuit resonates stably.
When the Q value of the LC parallel resonance circuit changes depending on the ambient temperature, the compensation current applied from the temperature compensating circuit is adjusted according to the change, and as a result, the loop gain is stabilized against ambient temperature without decreasing. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an oscillator circuit according to the present invention will be described below with reference to FIG.

This circuit constitutes a part of an inductive type proximity switch circuit equipped in a vending machine or the like, and is connected to stable oscillation in a normal state.
When a coin passes near, the oscillation condition is broken and the oscillation stops, and the presence or absence of the oscillation allows the presence or absence of the coin inserted in the vending machine or the like to be detected.

The circuit of this embodiment comprises an LC circuit A, a constant current circuit B, a bias circuit C, a positive feedback amplifier circuit D and a temperature compensation circuit E.

The LC circuit A is an LC parallel resonance circuit,
It is composed of a capacitor 22 and a coil 23 (corresponding to a sensor coil). The constant current from the constant current circuit B is supplied to the LC circuit A.

The constant current circuit B includes a PNP transistor 5,
6 and 7 and resistors 1 and 2, and a constant current source 24 connected to the input side of the current mirror circuit, and a stable current is supplied to the LC through the bias circuit C. It is supplied to the circuit A.

The bias circuit C is an NPN transistor 1
A V _D multiplier circuit composed of 2 and resistors 13, 14 and 15, wherein the oscillation voltage of the LC circuit A is level-shifted based on the output current of the constant current circuit B, and the NPN transistor 11 in the positive feedback amplifier circuit D is used. The bias potential of is given. An output terminal T is provided at the output of the bias circuit C. The bias provided by the V _D multiplier circuit is stable with respect to temperature due to the negative temperature characteristic of the base-emitter voltage of the NPN transistor 12 and the constant current circuit B that outputs a current proportional to the absolute temperature. ing.

The positive feedback amplifier circuit D is a circuit composed of the PNP transistors 8 and 9 and the NPN transistor 11 and the resistor 16, converts the oscillation voltage of the LC circuit A into a current, amplifies the current, and biases it. The basic configuration is such that the LC circuit A is stably transmitted by returning to the input of the circuit C and performing positive feedback. A resistor 16 for loop gain adjustment is connected to the emitter side of the transistor 11 for voltage / current conversion. Also, the transistor 1
A temperature compensating circuit E is connected to the collector side of No. 1, and a current that cancels a change in the parasitic resistance value of the coil due to a temperature change is added to the feedback current.

Next, the temperature compensation circuit E will be described.
A current mirror circuit composed of NPN transistors 17 and 18 and resistors 19 and 20 is connected to the base and collector of the PNP transistor 8 in the positive feedback amplifier circuit D. On the base / collector side of the transistor 18,
The collector of the PNP transistor 10 is connected.
On the other hand, the emitter side of the transistor 10 is connected to the power supply potential V _cc = 3V via the resistor 3. The base potential of the transistor 10 is given by the resistors 4 and 21.

The operation of the temperature compensating circuit E thus constructed will be described. The collector current of the transistor 17 is determined by the collector current of the transistor 10, the area ratio of the transistors 17 and 18, and the ratio of the resistors 19 and 20. Further, the collector current of the transistor 10 is proportional to the voltage applied across the resistor 3. Here, the base potential of the transistor 10 is V _10B , the base −
Assuming that the voltage between the emitters is V _BE , (V
voltage _cc -V _10B -V _BE) is to be applied. If the sizes of resistors 4 and 21 are R ₄ and R ₂₁ , respectively, V
_10B is determined by the following equation.

V _10B = V _CC × R ₂₁ / (R ₄ + R ₂₁ ) That is, V _CC -V _10B -V _BE = (V _CC × R ₄ / (R ₄ + R ₂₁ ))-V _BE .

Therefore, the collector current I _10C of the transistor 10 is I _10C = ((V _CC × R ₄ / (R ₄ + R ₂₁ ))-V _BE / R ₃ .

However, when the ambient temperature of the circuit changes, the current also changes accordingly. That is, when the ambient temperature becomes low, V _BE F becomes high, the voltage applied across the resistor 3 becomes small, and the collector current of the transistor 10 also becomes small. The collector current of the transistor 10 is proportional to the collector current of the transistor 17, and a decrease in this current means a decrease in the loop gain of the positive feedback amplifier circuit D.

On the contrary, when the ambient temperature increases, V _BE decreases, the voltage applied across the resistor 3 increases, and the collector current of the transistor 10 also increases. Therefore, the loop gain of the positive feedback amplifier circuit D becomes large.

The positive temperature coefficient of this temperature compensation current and LC
By incorporating the positive temperature coefficient of the parasitic series resistance of the coil of the circuit A, an oscillation circuit in which the distance for detecting the presence / absence of a coin does not change even if the ambient temperature changes.

The temperature coefficient of the temperature compensation current is dI _10C / dT =-(1 / R ₃ ) × dV _BE / dT, which is determined by R ₃ .

Therefore, since the temperature compensating circuit E operates even if the ambient temperature changes, the loop gain of the positive feedback amplifying circuit D becomes stable. In other words, as the ambient temperature rises, L
Even if the Q value of the C circuit A decreases, it is canceled by the temperature compensation circuit E, and the entire loop gain does not change,
As a result, the distance at which the presence or absence of coins can be detected does not change due to the change in ambient temperature.

By changing the constant of the resistor 3, the temperature characteristic of the oscillation loop gain can be set arbitrarily.

Therefore, there is a merit in improving the performance of the inductive proximity switch circuit.

The oscillator circuit according to the present invention is not limited to the application of the inductive proximity switch circuit only.

[0031]

As described above, according to the oscillator circuit of the present invention, the loop gain as a whole does not change even if the ambient temperature changes. Therefore, the Q value of the LC parallel resonant circuit is Even if it changes due to changes in temperature,
Any inconvenience caused by this change can be eliminated. Moreover, since the current addition method is used for temperature compensation, the gain does not decrease. Further, it is possible to set the temperature characteristic to an arbitrary value only by changing the constant of the resistance, and there is an advantage that the circuit adjustment becomes very easy.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional oscillator circuit.

[Explanation of symbols]

 A LC circuit B Constant current circuit C Bias circuit D Positive feedback amplifier circuit E Temperature compensation circuit

Claims (1)

[Claims] 1. An oscillator circuit for amplifying the output of an LC parallel resonance circuit by positive feedback amplification to oscillate the LC parallel resonance circuit,
An oscillator circuit comprising a temperature compensating circuit for adjusting a loop gain according to an ambient temperature, wherein the temperature compensating circuit according to a current addition method is provided.