JP3410351B2 - 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 integrates an output current of an oscillating circuit having a detection coil, and detects the proximity of an object to be detected from the integrated voltage as a change in the operating state of the oscillating circuit. The present invention relates to a high-frequency oscillation type proximity switch device with high precision operation.

[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 that shares a pair of power supply lines La and Lb with a signal line has a high-frequency oscillation circuit 1, an integration circuit 2, and a schematic configuration 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 connects the pair of power supply lines La and Lb to the internal power supply V of the monitoring device 10 including a microprocessor via the load 9.
connected to out (external power supply for proximity switch),
Power is supplied from the internal power supply Vout to operate.

That is, the high frequency oscillation circuit 1 includes a detection coil 1a forming a LC tank circuit and a capacitor 1b, and oscillates at a predetermined frequency. The integration circuit 2 integrates (smooths) the output of the oscillation circuit 1. Therefore, 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 uses the pair of power supply lines La, L based on a predetermined internal reference voltage.
Drive voltage Vdrv for driving each of the circuits 1, 2, 3, and 4 from a power supply voltage Vcc supplied from an external power supply via b.
To generate.

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]

The high-frequency oscillator circuit 1 having the LC tank circuit has a constant current Iref (bias current Iref) from a constant current source 11 as shown in FIG. 4, for example.
b) A first current mirror circuit 12 composed of a pair of npn transistors Q1 and Q2 which operates in response to the above operation to drive the LC tank circuit, and a first current mirror which operates by receiving the output current of the transistor Q2. A pair of pnp transistors Q3 and Q4 which have a positive feedback effect on the circuit 12.
And a second current mirror circuit 13. Incidentally, the bias current Ib also plays a role of charging / discharging the capacitance between the substrate which is the substrate of the oscillating transistor Q1 for oscillating and driving the LC tank circuit and its collector.

However, the output of the high frequency oscillation circuit 1 is
For example, via the transistor Q5 whose base is commonly connected to the first current mirror circuit 12, it is taken out as a mirror current corresponding to its drive current (oscillation operation current). Then, this current is output through the third current mirror circuit 14 driven by the transistor Q5 and integrated by, for example, the capacitor C forming an integrating circuit. The third current mirror circuit 14 has a pair of p
It is composed of np transistors Q6 and Q7.

Therefore, the output current Iin of the high frequency oscillation circuit 1
It is unavoidable that the component of the bias current Ib is superposed on t. For example, even if the oscillating operation of the high frequency oscillation circuit 1 is stopped due to the proximity of the detection target, the output current Iint
Does not become zero (0). Therefore, the bias current Ib
In order to remove the influence of the bias current Ib, a constant current source 15 is used to generate a cancel current Ic as shown in FIG. 4, and the cancel current Ic is added to the transistor Q5.
It is considered to offset the components of.

On the other hand, the oscillation frequency in the 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 as low as several KHz to as high as several MHz. Vary. For example, when the detection target is metal powder such as aluminum powder or the proximity detection distance is short, the oscillation frequency is set to be relatively low. However, the higher the oscillation frequency, the more the bias current Ib is required.

Therefore, in the conventional high-frequency oscillator circuit 1, particularly when it is integrated into an IC, the bias current Ib supplied from the constant current source 11 in anticipation that the above-mentioned oscillation frequency is set high. Is set to a large value. However, when the high-frequency oscillator circuit is oscillated at a low frequency, an extra bias current Ib is flowing. Therefore, recently, various attempts have been made to reduce the current consumption by setting the bias current Ib according to the oscillation frequency.

However, when the bias current Ib in the high frequency oscillating circuit 1 is thus optimized and set according to its oscillation frequency, even if the oscillating amplitude of the high frequency oscillating circuit 1 is the same, the output current of the integrating circuit 2 is the same. Iint
Since it depends on the bias current Ib, a difference occurs in the integrated voltage. When the bias current Ib is very large, the output current Iint of the integrating circuit 2 becomes too large,
Even if the oscillation amplitude of the high-frequency oscillator circuit 1 changes, the line segment voltage may remain high. Therefore, it is difficult to set the proximity detection distance of the detection target to the specification value according to these states, and it is difficult to satisfy the performance as the high frequency oscillation type proximity switch.

The present invention has been made in consideration of such circumstances, and an object thereof is to reliably cancel a bias current component in an output current from the oscillation circuit according to the bias current in the oscillation circuit. It is an object of the present invention to provide a high-frequency oscillation type proximity switch device having a simple structure capable of improving the accuracy of integration operation in an integrating circuit. That is, according to the present invention, the cancel current corresponding to the bias current in the oscillator circuit is simply generated, the bias current component in the current output from the oscillator circuit is reliably canceled, and the output current to be integrated is zero-point compensated. It is an object of the present invention to provide a high-frequency oscillation type proximity switch device including a cancel circuit that can be used.

[0013]

In order to achieve the above-mentioned object, a high-frequency oscillation type proximity switch device according to the present invention is provided with a detection coil and an oscillating circuit which oscillates when a predetermined bias current is applied, and this oscillating circuit. An integrating circuit that integrates the output current of the circuit to detect a change in the operating state of the oscillation circuit due to the proximity of the detection target to the detection coil, and a bias current in the current mirror circuit driven by a constant current source. And a current cancel circuit for generating a corresponding cancel current and canceling the bias current component from the output current of the oscillation circuit.

Particularly, as described in claim 2, the current mirror circuit forming the current canceling circuit has a configuration in which the resistance for setting the current amplification factor is adjustable, and the oscillation is set according to the oscillation frequency. The resistance can be adjusted according to the bias current of the circuit, and the resistance is externally attached to the transistor forming the current mirror circuit as described in claim 3, thereby facilitating the adjustment. It is characterized by the fact that

Alternatively, as described in claim 4, the current mirror circuit is configured by providing a plurality of mirror transistors whose bases are commonly connected to the transistors driven by the constant current source, and is set from the outside. It is characterized in that each of the mirror transistors is selectively operated in parallel according to the bias current by a possible switch means.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high frequency oscillation type proximity switch device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a main part of a high-frequency oscillation circuit 1 and an integration circuit 2 which are characteristic parts of the high-frequency oscillation type proximity switch device according to this embodiment, and is the same as the conventional general circuit configuration shown in FIG. The parts are denoted by the same reference numerals.

The feature of this device is that the high frequency oscillation circuit 1 having an LC tank circuit is constructed so that the bias current can be adjusted according to its oscillation frequency, and the integration circuit 2 cancels according to the bias current. It is configured to include a current cancel circuit that generates a current and cancels a bias current component in the output current of the high frequency oscillation circuit 1.

That is, the high frequency oscillation circuit 1 is provided with a bias current supply circuit for supplying the bias current Ib corresponding to the oscillation frequency to the first current mirror circuit 12 which drives the LC tank circuit. The bias current supply circuit is composed of a pair of pnp transistors Q8 and Q9, and is driven by the constant current source 21 to serve as a fourth current mirror circuit 22 which current-amplifies and outputs the output current Iref1 of the constant current source 21. Will be realized. Further, the emitter of the transistor Q8 of the fourth current mirror circuit 22 is
A resistor Rb for adjusting the bias current Ib that is the output current is inserted in series.

That is, the constant current source 21 that outputs a constant current Iref1 is connected to the collector of the diode-connected transistor Q8 of the fourth current mirror circuit 22 so that the current mirror circuit 22 is driven with a constant current. It has become. The current mirror circuit 22 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 a transistor Q9 having a base commonly connected to the transistor Q8. Has become. Further, a resistor Rb for adjusting the operating condition of the current mirror circuit 22 to adjust the output current from the transistor Q9, and consequently the bias current Ib to the first current mirror circuit 12, is connected in series to the emitter of the transistor Q8. Has been inserted in. In particular, the resistor Rb is incorporated as a so-called external circuit element in the fourth current mirror circuit 22 integrated and integrated with the above-described first and second current mirror circuits 12 and 13, for example. ing.

Thus, the current Iref1 from the constant current source 21
Is temporarily received by the fourth current mirror circuit 22,
According to the high-frequency oscillator circuit configured to supply the output current from the fourth current mirror circuit 22 to the first current mirror circuit 12 that oscillates and drives the LC tank circuit, the current output from the constant current source 22 The bias current Ib for the transistor Q1 can be easily adjusted by the resistor Rb incorporated in the fourth current mirror circuit 22 while keeping Iref1 constant. In particular, the bias current Ib is set only by selecting the resistance value of the external resistor Rb according to the oscillation frequency.

On the other hand, the integrating circuit 2 is provided with a transistor Q5 for taking out the current flowing through the first current mirror circuit 12 as a mirror current, and the emitter of the transistor Q5 has a cancel current for canceling the bias current component. Current cancel circuit 3 for supplying Ic
Is equipped with. The lever current cancel circuit 3
A constant current source 31 for generating a constant current Iref2 and a pair of pnp transistors Q1 driven by the constant current source 31.
The fifth current mirror circuit 32 is composed of 0 and Q11. In particular, resistors Re1 and Re2 are serially inserted in the respective emitters of the transistors Q10 and Q11 that form the current mirror circuit 33.
The current amplification factor for the constant current Iref2 in the current mirror circuit 33 is adjusted by Re2, and the cancel current Ic corresponding to the bias current Ib is generated and output.

In particular, each of the resistors Re1 and Re2 is incorporated in the fifth current mirror circuit 32 as an external circuit element for the fifth current mirror circuit 32 integrated and integrated with the above-described high frequency oscillation circuit 1, for example. It is like this. The resistors Re1 and Re2 may be integrated and integrated with the transistors Q10 and Q11, and an auxiliary resistor Re3 may be externally connected in parallel to the resistors Re1 and Re2 to adjust the resistance value. It is possible.

That is, the fifth driven by the constant current source 31.
In the current cancel circuit 3 configured as the current mirror circuit 32, the current amplification factor is set by adjusting the resistors Re1 and Re2 incorporated in the fifth current mirror circuit 32, and the constant current output from the constant current source 31 is constant. The cancel current Ic corresponding to the bias current Ib is output without changing the current Iref2. Specifically, a cancel current Ic that cancels out a bias current component in the output current of the high-frequency oscillation circuit 1 that is taken out as a mirror current via the transistor Q5 is generated, and this is output to the resistor Re4 connected to the emitter of the transistor Q5. It is supposed to do.

Thus, such a current cancel circuit 3
According to the integrator circuit 2 provided with, the bias current Ib of the high-frequency oscillator circuit 1 is incorporated in the current mirror circuit 33 even when the current consumption is reduced by adjusting the bias current Ib according to the oscillation frequency. Since the cancel current Ic can be easily changed by adjusting the resistors Re1 and Re2 and can be made to correspond to the bias current Ib, the bias current component included in the output current from the high frequency oscillation circuit 1 can be effectively used. It becomes possible to offset.

Therefore, the integrating circuit 2 integrates the output current of the oscillating circuit 1 in which the bias current component is canceled as described above, so that the oscillating of the high frequency oscillating circuit 1 is independent of the bias current Ib. It is possible to obtain an integrated voltage that accurately reflects the state (oscillation amplitude). In particular, even when the oscillating operation of the high frequency oscillating circuit 1 is stopped due to the proximity of the object to be detected, the influence of the bias current Ib does not affect the operation of the integrating circuit 2, and the integrated voltage when the oscillation is stopped is constant. Can be converted. As a result, the change in the oscillation amplitude with respect to the proximity distance of the detection target becomes constant, and high-precision proximity detection can be performed.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 2, a mirror transistor Q12 is further provided for the transistors Q10 and Q11 forming the fifth current mirror circuit 32, and the plurality of mirror transistors Q11, Q11, The output current (cancellation current Ic) from the current mirror circuit 33 may be adjusted by selectively operating Q12 in parallel. In this case, it is possible to provide three or more transistors for the mirror, and at the same time, it is also possible to provide resistors in the emitters of the respective transistors and to perform current adjustment in parallel. 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.

[0027]

As described above, according to the present invention, the current mirror circuit driven by the constant current source is used to generate the cancel current for canceling the bias current contained in the output current of the oscillation circuit. Therefore, even when the bias current in the oscillator circuit is variably set, a cancel current according to the bias current can be easily generated, the operation of the integrating circuit can be easily stabilized, and its accuracy can be improved. Can be planned.

Particularly, by externally attaching a resistor for adjusting the cancel current, the cancel current can be easily adjusted to improve the accuracy of the integration operation in the integrating circuit, and thus the accuracy of the proximity detection. Great effect can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a high frequency oscillation circuit and a current cancellation circuit showing a characteristic part 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 a current cancel 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 oscillation circuit and a current cancellation circuit.

[Explanation of symbols]

1 High frequency oscillator 1a coil 1b capacitor 2 integrating circuit 14 Third current mirror circuit 3 Current cancel circuit 31 constant current source 32 Fifth Current Mirror Circuit Re1, Re2 resistance for canceling current Q5, Q6, Q7, Q10, Q11, Q12 transistors

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-3-262323 (JP, A) JP-A-61-35620 (JP, A) JP-A-7-154226 (JP, A) JP-A-4- 261213 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03K 17/945 H01H 36/00

Claims (4)

(57) [Claims] 1. An oscillating circuit comprising a detection coil, which oscillates when a predetermined bias current is applied, and an output circuit of the oscillating circuit, which integrates an output current of the oscillating circuit to bring the detection target into proximity with the detection coil. An integrating circuit for detecting a change in the operating state, and a current canceling circuit for canceling the component of the bias current from the output current of the oscillating circuit, the current canceling circuit is driven by a constant current source, A high frequency oscillation type proximity switch device comprising a current mirror circuit which outputs a cancel current according to a bias current. 2. The bias current applied to the oscillation circuit is set according to the oscillation frequency thereof, and the current mirror circuit forming the current cancellation circuit comprises:
The high frequency oscillation type proximity switch device according to claim 1, further comprising an adjustable resistor for setting the current amplification factor. 3. The resistor for setting the current amplification factor of the current mirror circuit is externally attached to the current mirror circuit, and its resistance value is adjusted according to the bias current. 2. The high frequency oscillation type proximity switch device according to 2. 4. The current mirror circuit forming the canceling circuit comprises a plurality of mirror transistors each having a base commonly connected to a transistor driven by the constant current source, and the mirror transistors depending on the bias current. 2. The high frequency oscillation type proximity switch device according to claim 1, further comprising switch means for selectively operating in parallel.