JP2008009710A - Constant current source and integrated circuit device for proximity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant current source and an integrated circuit device for a proximity sensor having an excellent temperature characteristic in a smaller circuit area. <P>SOLUTION: The constant current source formed as an integrated circuit is composed of a current mirror circuit 11 having a master side transistor QO to which a collector and a base are connected, and a slave side transistor Q1. In the current mirror circuit, an emitter of the master side transistor and an emitter of the slave side transistor are connected to a first power supply line X1 supplied with a first predetermined voltage, respectively through an implanted resistor RH and a base diffusion resistor RB, and the resistance value of the implanted resistor RH is set larger than the resistance value of the base diffusion resistor RB. Further, the collector of the master side transistor is connected to a second power supply line X2 supplied with a second predetermine voltage, through a limiting implanted resistor RHO for limiting the flowing current, and the supply current of the constant current source is set to a current I1 flowing to the slave side transistor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a constant current source and an integrated circuit device for proximity sensors.

  2. Description of the Related Art Conventionally, for example, a high frequency oscillation type integrated circuit device for a proximity sensor is shown in FIG. That is, this integrated circuit device includes a current mirror circuit, and a constant current source 91 as a master is connected to the transistor Q91 connected between the base and the collector. The slave current obtained by turning back the current I91 supplied from the constant current source 91 by the current mirror is used as the reference voltage generating current I92 of the reference voltage source 92 connected to the transistor Q92 or the oscillation circuit 93 connected to the transistor Q93. Is supplied as a bias current I93. The reference voltage source 92 generates a predetermined reference voltage Vth based on the reference voltage generation current I92. The oscillation circuit 93 generates a bias voltage Voffset for voltage shifting the sine wave voltage Vosc oscillated by the LC resonance circuit 93a based on the bias current I93. The oscillation circuit 93 is shifted in voltage by the bias voltage Voffset and generates the detection voltage Vs based on the sine wave voltage Vosc.

  Here, the variation due to the temperature of the reference voltage generation current I92 related to the generation of the reference voltage Vth and the bias current I93 related to the generation of the bias voltage Voffset has a great influence on the temperature characteristics (detection characteristics) of the proximity sensor. Therefore, when a resistor is employed as the constant current source 91, for example, as described in Patent Document 1, among base diffusion resistors or implant resistors that can be applied in an integrated circuit device, temperature characteristics with better stability. It is preferable to employ a base diffusion resistor having

That is, as shown in FIG. 4 showing the temperature characteristics of the slave currents (I92, I93), when the base diffusion resistor RB is adopted as the constant current source 91, the slave current is compared with the case where the implant resistor RH is adopted. Is more stable against temperature changes. That is, it is confirmed that the current (I91) supplied from the base diffusion resistor RB with the slave current turned back is more stable against temperature changes. In this case, the reference voltage source 92 and the oscillation circuit 93 generate the reference voltage Vth and the bias voltage Voffset in which fluctuation due to temperature is suppressed, respectively.
Japanese Patent Laid-Open No. 11-122195

  By the way, when the base diffusion resistor RB is adopted as the constant current source 91, the stability of the current I91 supplied from the constant current source 91 with respect to a temperature change is excellent, but the base diffusion resistor RB is compared with the implantation resistor RH. It takes a very large area to build in. Specifically, it is known that when compared with the same resistance value, the size of the base diffusion resistor RB is about 10 times the size of the implantation resistor RH. In this case, the chip size of the integrated circuit device must be increased.

  An object of the present invention is to provide a constant current source and a proximity sensor integrated circuit device which have a smaller circuit area and excellent temperature characteristics.

  In order to solve the above problem, the invention according to claim 1 is an integrated circuit constant current source, wherein the constant current source is a master side transistor in which one of a pair of transistors is connected to a collector and a base. And the other of which is a slave-side transistor, wherein the emitter of the master-side transistor and the emitter of the slave-side transistor are connected to a first predetermined resistor via an implant resistor and a base diffusion resistor, respectively. Connected to a first power supply line to which a voltage is supplied, a resistance value of the implantation resistor is set to be larger than a resistance value of the base diffusion resistor, and the collector of the master side transistor generates a current flowing through the master side transistor. The second predetermined voltage is supplied via the limiting implantation resistor for limiting. Is connected to the second power supply line, the supply current of said constant current source, and summarized in that the current flowing through the slave transistor.

  According to this configuration, the supply current of the constant current source is a current flowing through the slave transistor, that is, a current flowing through the base diffusion resistor. The current flowing through the base diffusion resistor is formed by folding the current flowing through the master side transistor, that is, the current flowing through the implantation resistor, with a current mirror. However, the temperature characteristic of the base diffusion resistor is dominant. It has been confirmed by the applicant. Therefore, the supply current of the constant current source can be further stabilized against temperature changes. In addition, the resistance value of the base diffusion resistor that contributes to an increase in the area required for the entire constant current source (current mirror circuit) by setting the resistance value of the implantation resistor larger than the resistance value of the base diffusion resistor. The circuit area of the constant current source can be reduced by reducing the value. And the chip size as an integrated circuit of a constant current source can be further reduced.

  According to a second aspect of the present invention, in the integrated circuit device for a proximity sensor including the constant current source according to the first aspect, the proximity sensor integrated circuit device includes an oscillation circuit having a detection coil as an oscillation element, and the bias current of the oscillation circuit is It is generated based on the supply current of the constant current source.

  According to this configuration, since the supply current of the constant current source, that is, the bias current of the oscillation circuit can be further stabilized against temperature change, detection characteristics as a proximity sensor can be further stabilized. In addition, since the circuit area of the constant current source can be reduced, the chip size of the proximity sensor integrated circuit device can be further reduced.

  According to a third aspect of the present invention, in the integrated circuit device for proximity sensors according to the second aspect, the detection target object is detected by comparing a detection voltage based on the oscillation amplitude of the oscillation circuit with a predetermined reference voltage. The gist is provided with detection means, and the predetermined reference voltage is generated based on a supply current of the constant current source.

  According to this configuration, since the predetermined reference voltage is generated based on the supply current of the constant current source, the reference voltage can be further stabilized against a temperature change. And the detection characteristic of the to-be-detected target object by the said detection means can be stabilized more with respect to a temperature change.

  According to the first to third aspects of the present invention, it is possible to provide a constant current source and a proximity sensor integrated circuit device having a smaller circuit area and excellent temperature characteristics.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing an electrical configuration of the proximity sensor integrated circuit device according to the present embodiment. As shown in the figure, this integrated circuit device for proximity sensor includes a current mirror circuit 11 constituting a constant current source, and the current mirror circuit 11 is connected to a collector and a base (so-called diode connection). An NPN type master side transistor Q0 and an NPN type slave side transistor Q1 having the same characteristics as the master side transistor Q0 are configured. In the current mirror circuit 11, the emitter of the master-side transistor Q0 and the emitter of the slave-side transistor Q1 are connected to the first power supply line X1 via the implant resistor RH and the base diffusion resistor RB, respectively. The first power supply line X1 is grounded to the ground GND and supplied with a first predetermined voltage (for example, 0 V) on the low potential side. In the present embodiment, the resistance value of the implantation resistor RH is set larger than the resistance value of the base diffusion resistor RB. Specifically, the resistance value (for example, 10 kΩ) of the implantation resistor RH is set to about twice the resistance value (for example, 5 kΩ) of the base diffusion resistor RB.

  The bases of the master side transistor Q0 and the slave side transistor Q1 are connected to each other. The collector of the master side transistor Q0 is connected to a second power supply line X2 to which a second predetermined voltage (for example, 3.5 V) VREG on the high potential side is supplied via the limiting implant resistor RH0. The limiting implantation resistor RH0 has a sufficiently large resistance value (eg, 92 kΩ) with respect to the resistance value of the implantation resistor RH, and limits the current flowing through the master side transistor Q0.

  In the current mirror circuit 11, a current I0 is supplied to the implantation resistor RH through the original limiting implantation resistor RH0, and a current I1 obtained by folding the current I0 by the current mirror flows to the base diffusion resistor RB. A current I1 flowing through the base diffusion resistor RB (slave side transistor Q1) is a supply current of a constant current source (current mirror circuit 11).

  The collector of the slave transistor Q1 is connected to the collector of a PNP transistor Q11, the emitter of the transistor Q11 is connected to the second power supply line X2, and the collector and base of the transistor Q11 are further connected. ing.

  The first power supply line X1 is connected to the collector of a PNP transistor Q12 via a reference voltage generating circuit 12, and the emitter of the transistor Q12 is connected to the second power supply line X2. Furthermore, the collector of a PNP transistor Q13 is connected to the first power supply line X1 through the oscillation circuit 13, and the emitter of the transistor Q13 is connected to the second power supply line X2.

  The bases of the transistors Q11 to Q13 are connected to each other. Therefore, these transistors Q11 to Q13 constitute a current mirror circuit, and a reference voltage generating circuit in which a slave current obtained by turning back the current I1 that is the current supplied to the current mirror circuit 11 by the current mirror is connected to the transistor Q12. 12 is supplied as a reference voltage generation current I2 or as a bias current I3 of the oscillation circuit 13 connected to the transistor Q13. The reference voltage generating current I2 and the bias current I3 have the same magnitude and temperature characteristics.

  The reference voltage generation circuit 12 generates a predetermined reference voltage Vth based on a reference voltage generation current I2. That is, the reference voltage generating circuit 12 includes a resistor R having one end connected to the collector of the transistor Q12, and the other end of the resistor R is forward with the first power supply line X1. Two diodes D2 are connected in series. Each diode D2 is configured by, for example, connecting the collector and base of an NPN transistor, and when the reference voltage generating current I2 flows, the voltage between the base and emitter of the transistor is shifted by a PN junction. The voltage is a predetermined voltage Vbe. Therefore, the reference voltage generation circuit 12 adds the voltage obtained by multiplying the reference voltage generation current I2 by the resistance value of the resistor R and the voltage obtained by doubling the predetermined voltage Vbe at the connection point C2 between the transistor Q12 and the resistor R. A reference voltage Vth (= I2 × (resistance value of R) +2 Vbe) is generated and output.

  The oscillation circuit 13 generates a sine wave voltage Vosc in the LC resonance circuit 13a serving as an oscillation element, and generates a bias voltage Voffset for voltage shifting the sine wave voltage Vosc based on the bias current I3. That is, in the oscillation circuit 13, two diodes D3 are connected in series so as to be in the forward direction between the collector of the transistor Q13 and the LC resonance circuit 13a, and also connected to the first power supply line X1 in the LC resonance circuit 13a. ing. The connection point C31 between the transistor Q13 and one diode D3 and the connection point C32 between the other diode D3 and the LC resonance circuit 13a are connected via an oscillation current feedback circuit 13b.

  Accordingly, the LC resonance circuit 13a configured by connecting the detection coil Losc and the detection capacitor Cosc in parallel is supplied with a feedback current through the oscillation current feedback circuit 13b, so that a sine of a resonance frequency corresponding to the inductance and the capacitance thereof. A wave voltage Vosc is generated. Each diode D3 is configured by connecting the collector and base of an NPN transistor having the same characteristics as the diode D2, and the voltage between the base and emitter of the transistor when the bias current I3 flows. Becomes the predetermined voltage Vbe. Therefore, the oscillation circuit 13 generates a voltage (= Vosc + Voffset) obtained by adding a voltage (= 2Vbe) obtained by doubling the predetermined voltage Vbe to the sine wave voltage Vosc as a bias voltage Voffset. The oscillation current feedback circuit 13b generates and outputs a detection voltage Vs by, for example, rectifying and smoothing the sine wave voltage Vosc that has been shifted by the bias voltage Voffset. The oscillation amplitude of the sine wave voltage Vosc is set to a predetermined amplitude. For example, when a metal detection target object W comes close to the detection coil Losc, an induced current is generated in the detection target object W and heat is generated. When the loss occurs, the oscillation amplitude of the sine wave voltage Vosc is attenuated and the level of the detection voltage Vs is lowered. That is, the level of the detection voltage Vs is set to a predetermined level when the detection target object W is not close to the detection coil Losc, and varies so as to decrease as the detection target object W approaches the detection coil Losc. To do. The predetermined level set for the detection voltage Vs is set larger than the level of the reference voltage Vth.

  A connection point C2 of the reference voltage generation circuit 12 is connected to a non-inverting input terminal (+) of a comparator 14 serving as a detection unit, and an inverting input terminal (−) of the comparator 14 is connected to the oscillation circuit 13. The oscillation current feedback circuit 13b is connected. The comparator 14 compares the levels of the reference voltage Vth and the detection voltage Vs input from these input terminals, and outputs a detection signal corresponding to the comparison result of these levels. Specifically, when the detection object W is not close to the detection coil Losc and the detection voltage Vs is at a predetermined level, the comparator 14 indicates that the level of the detection voltage Vs is higher than the level of the reference voltage Vth. Then, a detection signal that is turned off is output. On the other hand, when the level of the detection voltage Vs decreases and falls below the level of the reference voltage Vth as the detection target object W approaches the detection coil Losc, a detection signal that is turned on is output.

  Here, temperature characteristics of slave currents (reference voltage generation current I2 and bias current I3) related to generation of the reference voltage Vth and the detection voltage Vs will be described. FIG. 2 is a graph showing the temperature characteristics of the slave current when the resistance value of the implantation resistor RH is varied in a range of ± 25% with the same base diffusion resistor RB connected to the current mirror circuit 11. It is. In the figure, the second predetermined voltage VREG is 3.5 V, the resistance values of the limiting implantation resistor RH0, the implantation resistor RH, and the base diffusion resistor RB are 92 kΩ, 10 kΩ, and 5 kΩ, and a slave current of about 50 μA flows. The case characteristics are shown. That is, when the predetermined voltage Vbe between the base and the emitter is 0.7 V, the slave current is obtained by the following equation.

I0 = (3.5−0.7) / (92k + 10k)
I1 = 10k · I0 / 5k = 55 μA≈slave current As shown in the figure, the temperature characteristic of the slave current is dominated by the temperature characteristic of the base diffused resistor RB regardless of variations in the resistance value of the implant resistor RH. It is confirmed that That is, the current I1 (supply current of the current mirror circuit 11) that flows through the base diffusion resistor RB that is the source of the slave current is the current mirror that is the current that flows through the master transistor Q0, that is, the current I0 that flows through the implant resistor RH. Although it is folded, it is indirectly confirmed that the temperature characteristic of the base diffusion resistor RB is dominant. As can be seen from the figure, the slave current, in which the temperature characteristic of the base diffusion resistor RB is dominant, is more stabilized against temperature changes. Accordingly, the reference voltage generation circuit 12 and the oscillation circuit 13 generate the reference voltage Vth and the bias voltage Voffset, respectively, in which fluctuations due to temperature are suppressed, based on the slave current (reference voltage generation current I2 and bias current I3). .

  Incidentally, when a slave current of about 50 μA is passed in the conventional mode (see FIG. 3) in which the base diffusion resistor RB is employed as the constant current source (91), the resistance value of the base diffusion resistor RB is set to a magnitude of about 56 kΩ. Must be set.

I91 = (3.5−0.7) / (56k) = 50 μA≈slave current That is, in the present embodiment, in the current mirror circuit 11 including the base diffusion resistor RB having a very small resistance value as compared with the conventional embodiment. The stability of the supply current (I1) and the slave current with respect to temperature changes can be improved.

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) In the present embodiment, the supply current of the current mirror circuit 11 as a constant current source is the current flowing through the slave transistor Q1, that is, the current I1 flowing through the base diffusion resistor RB. The current I1 flowing through the base diffusion resistor RB is formed by folding the current flowing through the master side transistor Q0, that is, the current I0 flowing through the implantation resistor RH with a current mirror, and its temperature characteristic is the temperature characteristic of the base diffusion resistor RB. Has become dominant. Therefore, the supply current of the current mirror circuit 11 can be further stabilized against temperature changes. In addition, since the resistance value of the implantation resistor RH is set to be larger than the resistance value of the base diffusion resistor RB, the base diffusion that contributes to an increase in area required for the entire constant current source (current mirror circuit 11). As the resistance value of the resistor RB is reduced, the circuit area of the current mirror circuit 11 can be reduced. Further, the chip size as the proximity sensor integrated circuit device can be further reduced, and as a result, the cost can be reduced.

  (2) In the present embodiment, the supply current (I1) of the current mirror circuit 11, that is, the bias current I3 of the oscillation circuit 13 that is a slave current based on the supply current (I1) can be more stabilized against temperature changes. The oscillation amplitude of the voltage Voffset and the sine wave voltage Vosc can be stabilized, and the detection characteristic (temperature characteristic) as a proximity sensor can be further stabilized. Further, since the circuit area of the current mirror circuit 11 can be reduced, the chip size as the proximity sensor integrated circuit device can be further reduced.

  (3) In the present embodiment, the supply current (I1) of the current mirror circuit 11, that is, the reference voltage generation current I2, which is a slave current based on the supply current (I1), can be more stabilized against temperature changes. The reference voltage Vth generated based on the generation current I2 can be further stabilized against a temperature change. And the detection characteristic of the to-be-detected target object W by the said comparator 14 can be stabilized more with respect to a temperature change.

  (4) In the present embodiment, the voltage shift (2 Vbe) of the reference voltage Vth is generated by the diode D2 having the same characteristics as the diode D3 composed of an NPN transistor that generates the bias voltage Voffset of the oscillation circuit 13. Therefore, for example, even if the characteristics of the diodes D2 and D3 fluctuate due to a temperature change or the like, the respective voltage shifts of the reference voltage Vth and the detection voltage Vs are equal to each other. Therefore, the fluctuation of the comparison result by the comparator 14, that is, the detection accuracy of the detection target W can be suppressed by the characteristic fluctuation of the diodes D2 and D3.

In addition, you may change the said embodiment as follows.
In the embodiment, if the detection coil is an oscillation element, the circuit configuration of the oscillation circuit 13 may be changed as appropriate.

  In the above embodiment, the master side transistor and the slave side transistor of the current mirror circuit 11 may be configured by a pair of PNP transistors.

The circuit diagram which shows the electrical constitution of one Embodiment of this invention. The graph which shows the temperature characteristic of a slave current. The circuit diagram which shows the electrical constitution of a prior art form. The graph which shows the temperature characteristic of a slave current.

Explanation of symbols

  Losc ... Detection coil, Q0 ... Master side transistor, Q1 ... Slave side transistor, RB ... Base diffusion resistor, RH ... Impulse resistor, RH0 ... Limiting implant resistor, W ... Detected object, X1 ... First power line, X2 2nd power supply line 11 Current mirror circuit constituting constant current source 12 Reference voltage generating circuit 13 Oscillating circuit 14 Comparator as detecting means

Claims (3)

In an integrated circuit constant current source,
The constant current source is composed of a current mirror circuit in which one of a pair of transistors has a collector side and a base side transistor connected to a base, and the other a slave side transistor.
The current mirror circuit is:
The emitter of the master side transistor and the emitter of the slave side transistor are respectively connected to a first power supply line to which a first predetermined voltage is supplied via an implant resistor and a base diffusion resistor,
The resistance value of the implantation resistor is set larger than the resistance value of the base diffusion resistor,
A collector of the master-side transistor is connected to a second power supply line to which a second predetermined voltage is supplied via a limiting implantation resistor for limiting a current flowing through the master-side transistor;
A constant current source characterized in that a supply current of the constant current source is a current flowing through the slave side transistor. In the integrated circuit device for proximity sensors comprising the constant current source according to claim 1,
An oscillation circuit having a detection coil as an oscillation element is provided.
2. The proximity sensor integrated circuit device according to claim 1, wherein the bias current of the oscillation circuit is generated based on a supply current of the constant current source. The integrated circuit device for a proximity sensor according to claim 2,
A detection means for detecting a detection target object by comparing a detection voltage based on an oscillation amplitude of the oscillation circuit and a predetermined reference voltage;
The integrated circuit device for a proximity sensor, wherein the predetermined reference voltage is generated based on a supply current of the constant current source.

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