JP3436342B2 - High frequency oscillation type proximity switch device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency oscillation type proximity switch device capable of optimizing a bias current for a transistor circuit for oscillating and driving an LC tank circuit, suppressing wasteful current and reducing current consumption. Regarding

[0002]

2. Related Background Art A high-frequency oscillation type proximity switch (electronic switching device) having a detection coil that forms a part of a high-frequency oscillation circuit in a detection section detects an electromagnetic induction action with an object to be detected (magnetic material). The proximity of an object to be detected is detected by utilizing the fact that the inductance and loss of the coil change and the oscillation amplitude and oscillation frequency of the high-frequency oscillation circuit change accordingly, and the detection sensitivity is high and the response speed is fast. It has the excellent characteristics of.

A two-wire type high-frequency oscillation type proximity switch sharing a pair of power supply lines with signal lines has a high-frequency oscillation circuit 1, an integration circuit 2, and a high-frequency oscillation circuit 1 as shown in FIG.
A sensor circuit unit 6 including a comparison circuit 3, a signal processing circuit 4, and a constant voltage source 5, a display circuit 7 that receives the output from the sensor circuit unit 6 and drives the LED 7a to light up, and a pair of power supply lines La and Lb. And an output circuit 8 interposed therebetween. The proximity switch having such a configuration operates by connecting the pair of power supply lines La and Lb to the internal power supply Vout of the monitoring device 10 including a microprocessor via the load 9 and being supplied with power from the internal power supply Vout. To do.

That is, the high frequency oscillating circuit 1 is equipped with a coil (detection coil) 1a forming an LC tank circuit and a capacitor 1b and oscillates at a predetermined frequency. ), The oscillation amplitude is detected. Then, the oscillation amplitude detected as the integrated voltage is compared with a predetermined threshold voltage in the comparison circuit 3, whereby a decrease in the oscillation amplitude due to the proximity of the object to be detected (magnetic material) to the coil 1a is detected. The signal processing circuit 4 outputs the proximity of the detection target detected in this way according to the setting state of the proximity switch. The constant voltage source 5 drives each of the circuits 1, 2, 3, 4 from a power source voltage Vcc supplied from an external power source via the pair of power source lines La, Lb based on a predetermined internal reference voltage. Drive voltage Vdrv is generated.

Thus, the display circuit 7 drives the LED 7a to light up, for example, when the proximity of an object to be detected is detected.
Also, an output circuit 8 consisting of a bipolar transistor, etc.
Is in a non-conducting state at all times and changes its voltage Vcc between the pair of power supply lines La and Lb by being driven in conduction (when proximity of a detection object is detected) in association with lighting of the LED 7a. Let The load 9 operates due to such a change in the voltage Vcc between the power supply lines La and Lb, and the monitoring device 10 detects the proximity of the detection target by the proximity switch from the operating state of the load 9.

[0006]

A high-frequency oscillator circuit 1 having an LC tank circuit composed of a coil 1a and a capacitor 1b has a constant current source 11 as shown in FIG. 4, for example.
From the pair of npn transistors Q1 and Q2 for operating the LC tank circuit in an oscillating drive by receiving a constant current Iref from the first current mirror circuit 12 and the output current of the transistor Q2 to operate and Second current mirror circuit 1 including a pair of pnp transistors Q3 and Q4 exhibiting a positive feedback action to the current mirror circuit 12.
3 and 3. By the way, the constant current source 11 is
Oscillation transistor Q that oscillates and drives the LC tank circuit
It also plays a role of supplying a bias current Ib for charging / discharging the capacitance between the substrate forming the base body of 1 and its collector.

On the other hand, the oscillation frequency in this type of high-frequency oscillation circuit 1 is set according to the specifications such as the object to be detected and its proximity detection distance. Generally, the oscillation frequency is several kHz.
And from low, Ru variety der up to a few MHz and high.
Above Chi par bias current Ib, the oscillation frequency requires many high <br/> Ihodo.

However, in the conventional high-frequency oscillator circuit 1, particularly when it is integrated into an IC, the bias current supplied from the constant current source 11 in anticipation of the oscillation frequency being set high. Ib is set to a large value. Therefore, when oscillating at a low frequency, it cannot be denied that an extra bias current Ib is flowing. Therefore, useless current consumption occurs, which is a factor for hindering the reduction of the current consumption.

The present invention has been made in consideration of such circumstances, and an object thereof is a high-frequency oscillation type proximity switch device provided with an oscillation circuit suitable for preventing unnecessary current consumption and achieving low current consumption. To provide.

[0010]

Means for Solving the Problems The above-mentioned high-frequency oscillation type proximity switch device according to the present invention in order to achieve the object, be those which example Bei transistor circuit for oscillating drive the LC tank circuit comprising a detection coil and a capacitor Especially
Bias current supply circuit for the transistor circuit
Is a constant current source that flows a specified current, and this constant current source
Driven current mirror circuit and this current mirror
For current regulation that is inserted in the circuit and controls the output current
It is characterized by consisting of resistance .

Further, as a preferred embodiment of the present invention, claim 2
The transistor circuit and constant current source
Also, the current mirror circuit is integrated into a circuit, and the current adjusting resistor is externally attached to a pair of transistors forming a current mirror circuit driven by the constant current source. And, as described in claim 3, the LC is generated by the bias current.
The feature is that the capacitance between the collector and substrate of the transistor that oscillates the tank circuit is charged and discharged.

That is, according to the present invention, a bias current is supplied to a transistor circuit which oscillates and drives an LC tank circuit through a current mirror circuit driven by a constant current source, and an output current ( It is characterized in that the bias current) can be adjusted by a resistor.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high frequency oscillation type proximity switch device according to an embodiment of the present invention, particularly a high frequency oscillation circuit, will be described below with reference to FIG. Note that in FIG. 1 are indicated by the same reference numerals are given to the conventional general high-frequency oscillator in the same portion shown in FIG. The feature of this high-frequency oscillator circuit is that the bias current I is applied to the first current mirror circuit 12 that drives the LC tank circuit.
A bias current supply circuit for supplying b is realized as a third current mirror circuit 15 which is composed of a pair of pnp transistors Q5 and Q6 and is driven by a constant current source 14.
The output current Iref of the constant current source 14 is current-amplified and output, and the output current (bias current Ib) can be adjusted by a resistor Rb incorporated in the third current mirror circuit 15. There is.

That is, the constant current source 14 which outputs a constant current Iref is connected to the collector of the diode-connected transistor Q5 of the third current mirror circuit 15 so as to drive the current mirror circuit 15 with a constant current. It has become. The current mirror circuit 15 outputs a current corresponding to the drive current as a bias current Ib for the first current mirror circuit 12, particularly for the transistor Q1 via the transistor Q6 having the base commonly connected to the transistor Q5. Has become. The emitter of the transistor Q5 is connected in series with a resistor Rb for adjusting the operating condition of the current mirror circuit 15 to adjust the output current from the transistor Q6, and thus the bias current Ib for the first current mirror circuit 12. Has been inserted in. Particularly, the resistor Rb is incorporated as a so-called external circuit element in the third current mirror circuit 15 which is integrated and integrated with the above-mentioned first and second current mirror circuits 12 and 13, for example. ing.

Thus, the current Iref from the constant current source 14
Is once received by the third current mirror circuit 15,
According to the high-frequency oscillator circuit configured to supply the output current from the third current mirror circuit 15 to the first current mirror circuit 12 that oscillates and drives the LC tank circuit, the current output from the constant current source 14 The bias current Ib for the transistor Q1 can be easily adjusted by the resistor Rb incorporated in the third current mirror circuit 15 while keeping Iref constant. In particular, the bias current Ib can be set only by selecting the resistance value of the externally attached resistor Rb.

Therefore, in the case of the high-frequency oscillation circuit having the bias current supply circuit having the above-mentioned configuration, even if the current mirror circuits 12 and 13 forming the main part of the high-frequency oscillation circuit are integrated (integrated circuit), the oscillation frequency is specified. Accordingly, the bias current Ib can be easily changed only by changing the value of the resistor Rb.
Can be adjusted. In other words, it is not necessary to set the bias current Ib for the transistor Q1 large in anticipation that the oscillation frequency is set high as in the conventional case, and it is possible to set an appropriate bias current Ib according to the oscillation frequency. It will be possible. As a result, even when the oscillation frequency is set low, the excessive bias current Ib is not supplied to the transistor Q1 that drives the LC tank circuit, so that waste of current is eliminated and low current consumption is achieved. It becomes possible.

As described above, the bias current I can be simply
Transistor Q1 that adjusts b and drives the LC tank circuit
Since it is possible to flow only the minimum bias current Ib necessary for charging and discharging the capacitance between the collector and the substrate, a plurality of types of high-frequency oscillation circuits to be integrated into IC are prepared by changing the bias current Ib. In addition, it is possible to eliminate the trouble of selectively using these high-frequency oscillation circuits (ICs) according to the oscillation frequency.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 2, resistors Rb1 and Rb2 are respectively inserted in the emitters of the transistors Q5 and Q6 that form the third current mirror circuit 15, and the bias current Ib is adjusted by externally connecting the resistor Rb2 on the transistor Q6 side. You may be allowed to do so. In this case, both the resistors Rb1 and Rb2 can be externally attached. Further, here, the case of incorporating in a two-wire type proximity switch has been described, but it goes without saying that the same can be applied to a high frequency oscillation type proximity switch device provided with a power supply line and a signal line separately, and a discrete circuit. Needless to say, it can be applied to the case where it is realized by using parts (elements). In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0019]

As described above, according to the present invention, L
A current supply circuit that supplies a bias current to the transistor circuit that oscillates and drives the C tank circuit is configured by a current mirror circuit driven by a constant current source, and its operation is performed by using a resistor incorporated in the current mirror circuit. Since the bias current is adjusted so that the bias current can be adjusted, the optimum bias current according to the oscillation frequency can be easily set to reduce the current consumption.

In particular, by externally providing a resistor for adjusting the bias current, a great effect in practical use can be obtained such that the bias current can be easily set by adjusting the resistance value.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a high-frequency oscillation circuit showing a characteristic portion of a high-frequency oscillation type proximity switch device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a modified example of the high-frequency oscillator circuit according to the present invention.

FIG. 3 is a schematic configuration diagram showing the entire two-wire high-frequency oscillation type proximity switch device.

FIG. 4 is a diagram showing a configuration example of a conventional general high-frequency oscillator circuit.

[Explanation of symbols]

1 High frequency oscillator 1a coil 1b capacitor 11 constant current source 12 First current mirror circuit 13 Second current mirror circuit 14 constant current source 15 Third current mirror circuit Rb Bias current adjustment resistor

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Claims (3)

(57) [Claims] 1. An LC comprising a detection coil and a capacitor
A high frequency oscillation type proximity switch comprising a transistor circuit for driving the tank circuit to oscillate, and detecting the proximity of the detection target in a non-contact manner from a change in the oscillation operation due to an electromagnetic induction action between the detection target and the detection coil. A device for supplying a bias current to the transistor circuit
Is a constant current source for flowing a predetermined current, a current mirror circuit driven by this constant current source, and an output current which is inserted in this current mirror circuit to control its output current.
A high-frequency oscillation type proximity switch device comprising a resistor for controlling a current . 2. A high-frequency oscillation type proximity switch according to claim 1.
The switch device consists of the transistor circuit, constant current source and
The rent mirror circuit is formed as an integrated circuit, and the current adjusting resistor is externally attached to a pair of transistors forming the current mirror circuit.
That high-frequency oscillation type proximity switch device. 3. The high frequency oscillation type proximity switch device according to claim 1, wherein the bias current is used for charging and discharging the collector-substrate capacitance of a transistor that oscillates and drives an LC tank circuit.