JPS5916378B2 - Proximity switch - Google Patents

Description

[Detailed description of the invention] The present invention relates to a high frequency oscillation type proximity switch.

Most conventional proximity switches consist of circuits made of discrete components.

In order to save space and cost, we simplified the circuit configuration as much as possible, put the oscillator in a hard oscillation state (a state where the oscillation amplitude increases and stops rapidly), and obtains a step characteristic, and the subsequent circuit is simplified. It consists of a detection and amplification circuit.

IC circuits such as bipolar and monolithic IC circuits
If this is done, space and cost constraints can be avoided, there is no need to use a circuit with a simple circuit configuration as described above, and a circuit that is stable in terms of temperature characteristics and other aspects can be realized.

In view of the above, the present invention is a proximity switch circuit suitable for converting into an IC such as a bipolar monolithic IC, and which stably performs a voltage comparison operation when comparing the output of an oscillator with a reference voltage. The purpose is to provide

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, a detection coil 1 and a capacitor 2 constitute a parallel resonant circuit, and this parallel resonant circuit is connected to an oscillator 3.

When a nearby object (generally a magnetic metal) approaches the detection coil 1, the loss of this resonant circuit increases, and as a result, the oscillation amplitude of the oscillator 3 decreases and oscillation stops.

As a circuit for detecting a change in the oscillation amplitude of the oscillator 3, there are circuits in subsequent stages.

The output of the oscillator 3 is sent via a level shift circuit 4 to a first voltage comparator 5 which compares it with a first reference voltage, and further passes through an integration circuit 6 to a second voltage comparator which compares it with a second reference voltage. Sent to 7.

The output of this second voltage comparator 7 is outputted from an output circuit 8 as a detection signal.

Note that the power supply circuit 9 supplies direct current of a predetermined voltage to each circuit.

Specifically, the level shift circuit 4 and the first voltage comparator 5 are configured as shown in FIG. 2, for example.

That is, the level shift circuit 4 does not include a plurality of diodes, but allows current to flow through the resistor 41 to shift the output voltage of the oscillator 3 by the forward voltage drop thereof.

The voltage comparator 5 includes a differential amplification type comparison circuit composed of transistors 51 and 52 and a constant current circuit 53, and a resistor 54.
．． 55 and a plurality of diodes 56 connected in series thereto.

Here, the number of diodes 56 connected in series to the reference voltage generating resistive voltage divider circuit is assumed to be equal to the number of diodes in the level shift circuit 4.

In this way, the oscillation amplitude of the oscillator 3 is raised by a certain level by the level shift circuit 4 and applied to the base of the transistor 51.

When the input voltage applied to the base of the transistor 51 is much lower than the reference voltage applied to the base of the transistor 520, the transistor 51 is turned off and the transistor 52 is turned on. However, when the input voltage exceeds the reference voltage, the transistor 51 and 52 are inverted, transistor 51 is turned on and transistor 52 is turned off.

As a result, OUT, 1 goes from the low level to the Karabye level, and 0UT2 goes from the NO level to the low level.

In this case, since the input voltage is shifted by a predetermined voltage by the level shift circuit 4 and the reference voltage is also shifted by the same voltage by the plurality of diodes 56, the voltages shifted by the level shift circuit 4 are canceled out. , voltage comparison of only the oscillation amplitude of oscillator 3 is performed, and when this oscillation amplitude is small, 0UTI is low level, 0UT2 is bi level,
When the oscillation amplitude is large, 0UT1 is bilevel, 0tJT
2 becomes low level, and this voltage comparison is performed in a voltage range where the voltage comparison circuit has good linearity and stable operation, making it easy to compare voltages.

By connecting the level shift circuit in this way, for example, the oscillation amplitude cannot be increased when the power supply voltage is low, and there are also limits to the linearity and stability of the amplifier gain. This makes it possible to deal with cases where it is difficult to increase the oscillation amplitude input to the voltage comparator 5.

However, if the oscillation amplitude is small, voltage comparisons must be made within this small voltage range, and the device must be operated in a region where there are problems with linearity and stability. By level-shifting the oscillation amplitude, stable voltage comparison operation can be performed in a region where linearity is good and voltage comparison is easy.

Furthermore, in consideration of the temperature drift in this level shift circuit, a similar diode is inserted in the reference voltage generating resistor voltage dividing circuit of the voltage comparator 5 in order to cancel it.

In particular, proximity switches have become increasingly sensitive in recent years, and it is necessary to grow or stop the amplitude of the oscillator with a slight change in constant, and there is a certain limit to the linearity of the gain when viewed as an amplifier. When a large amplitude cannot be obtained due to power supply voltage constraints, etc., use the voltage comparator 5.
The above-mentioned configuration is extremely important in that the level of the input voltage is matched and the detected voltage level does not change even if the temperature changes.

FIG. 3 shows a second embodiment in which an emitter follower stage consisting of a transistor 57 with a resistor 58 connected to its emitter is inserted at the base of transistor 51.

The other configurations are the same as in FIG. 2.

In this case, after the oscillation amplitude of the oscillator 3 is raised by a certain level by the level shift circuit 4, it is lowered by the base-emitter voltage through the base-emitter junction of the transistor 57 in the emitter follower stage, and is applied to the base of the transistor 51. It will be done.

Therefore, the number of diodes 56 that level shift the reference voltage is determined by adding the base-emitter voltage of this transistor 57 to the shift voltage in the level shift circuit 4.

Voltage comparison is performed in this way, but the input voltage is shifted by a predetermined voltage by the level shift circuit 4, further shifted by the transistor 57, and the reference voltage is also shifted by the same voltage as the total shifted voltage by the plurality of diodes 56. As a result, the voltages shifted by the level shift circuit 4 and the transistor 57 are canceled out.
A voltage comparison is made only for the oscillation amplitude of the oscillator 3, and if the oscillation amplitude is small, IUTI will be at low level and 0UT2 will be at bi level, and when the oscillation amplitude is large, 0UT1 will be at bi level and 0UT2 will be at low level. The voltage comparison is performed in a voltage range where the voltage comparison circuit has good linearity and stable operation, making it easy to compare voltages.

Note that in FIGS. 2 and 3, the resistors 41, 54 can be replaced with current sources.

FIG. 4 shows a third embodiment, in which the current flowing through the level shift circuit 4 is changed so that the same current as that flowing through the level shift circuit 4 also flows through the reference voltage generation resistor voltage divider circuit. A current source 42 for supplying current and a current source 59 for supplying a current to the reference voltage generating circuit are provided so that the currents (2) of both types of current sources are the same.

In this way, the error in the forward voltage drop of the diode is reduced.

The other configurations and operations are exactly the same as in FIG. 2.

FIG. 5 shows a fourth embodiment, and the embodiment shown in this figure is exactly the same as FIG. 4 except for the polarity.

That is, the output voltage of the oscillator 3 is shifted by the level shift circuit 4 using the power supply voltage Vcc as a reference, and the output voltage of the oscillator 3 is shifted by the level shift circuit 4.
The signal is shifted by the effective voltage and sent to the base of the transistor 51.

The reference voltage is determined by a plurality of diodes 56 based on the power supply voltage Vcc.

Here, the reason why the resistor r is not placed on the reference voltage side like the resistor 53 in Figure 4, but on the input side is because the current I is the same on the input side and the reference voltage side, so no matter where it is placed, there is no difference. This is because they are the same.

When the input voltage applied to the base of the transistor 51 is higher than the reference voltage applied to the base of the transistor 52, the transistor 51 is turned on and the transistor 52 is turned off; when the input voltage is lower than the reference voltage applied to the base of the transistor 52, the transistor 51 is turned off and the transistor 52 is turned on. If the oscillation output is large, the input voltage will be low; if the oscillation output is small, the input voltage will be high.

Therefore, different from each of the above embodiments, when the oscillation amplitude is small, 0UT1 is a bi level and 0UT2 is a low level, and when it is large, 0UT1 is a low level and 0UT2 is a bi level.

In addition, in FIGS. 3, 4, and 5, the same parts as in FIG. 2 are designated by the same numbers, and explanations thereof are omitted.

As described above with respect to the embodiments, according to the present invention,
When comparing the oscillation output of the oscillator with the reference voltage, the oscillation output is level-shifted with a diode, and the reference voltage is also level-shifted with the corresponding diode, making voltage comparisons stable and reliable. be able to.

In other words, when the oscillation amplitude is small, voltage comparisons must be made within this small voltage range, and operation must be performed in a region where there are problems in terms of linearity and stability. Since the amplitude is level-shifted, stable voltage comparison operation is possible in a region where linearity is good and voltage comparison is easy.

Furthermore, since the diode for level-shifting the oscillation output and the diode for level-shifting the reference voltage are made to correspond to each other, their respective temperature drifts can be canceled out, and the influence of temperature drift can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of the present invention, FIG. 2 is a circuit diagram specifically showing the level shift circuit 4 and voltage comparator 5 of FIG. 1, and FIG. , 4 and 5 are circuit diagrams corresponding to FIG. 2 showing the second, third and fourth embodiments, respectively. 1...detection coil, 3...oscillator, 4
...Level shift circuit, 5,7...Voltage comparator, 6...Integrator circuit, 8...Output circuit, 9... power circuit.

Claims (1)

[Claims] 1. An oscillator formed including a detection coil, a first voltage comparator that compares the oscillation output of this oscillator with a first reference voltage, and an output of this first voltage comparator. , and a second voltage comparator that compares the output of the integration circuit with a second reference voltage, and outputs the output of the second voltage comparator as a detection signal. The switch includes a level shift circuit made of a diode for l/bell shifting the output of the oscillator, and the diode of the level shift circuit is connected to a resistive voltage divider circuit for generating a first reference voltage of the first voltage comparator. A proximity switch characterized in that a diode corresponding to the above is connected. 2. The first voltage comparator has a current source, and the same current as the current flowing through the diode of the level shift circuit is caused to flow through the first reference voltage generating resistive voltage divider circuit and the diode. A proximity switch according to claim 1, characterized in: