JPH0567082B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to an electronic circuit that converts a voltage signal into a current signal, and particularly to a voltage/current conversion circuit suitable for being incorporated into a semiconductor integrated circuit, and which is capable of controlling the voltage/current conversion ratio. This type of conversion circuit is incorporated as a basic circuit element for handling analog signals in electronic devices and integrated circuit devices having various complex functions.

[Prior art and its problems]

The voltage/current conversion circuit described above converts a relatively small analog input voltage into an analog output current with a relatively large conductance.
Since they are often used as part of more complex electronic circuits for measurement and detection purposes, the voltage-to-current conversion ratio must be accurate. In principle, a circuit suitable for this purpose is the base of a transistor.
This can be achieved relatively easily by combining this with an emitter resistor using the voltage/emitter current characteristics and taking the converted output current from the collector side, but the voltage/current conversion ratio depends on the resistance value of the emitter resistor. The resistance value of the emitter resistor must be carefully controlled to maintain an accurate voltage/current conversion ratio. Therefore, even if the voltage/current conversion circuit is incorporated into a bipolar IC,
The emitter resistor is normally formed as a so-called external element, such as a thick film resistor.
In order to control the current conversion ratio to a predetermined value, the resistance value of the thick film resistor for the emitter resistor is usually adjusted by means such as trimming after the electronic circuit is assembled. In addition, voltage/current conversion circuits are often required to be able to control or switch the voltage/current conversion ratio, and conventionally used voltage/current conversion circuits that can switch the voltage/current conversion ratio are The basic circuit is shown in Figure 4. Transistor 1 shown in the figure is a conversion transistor, and the input voltage is applied to its base.
Take the VI. Two emitter resistors 2 and 3 are connected in series to the emitter, and a transistor 4 is connected so that one of the emitter resistors 3 can be short-circuited. The collector current of the conversion transistor 1 is the output current I0, and by turning on and off the transistor 4 using the switching signal SS applied to the base of the transistor 4, the voltage/current conversion ratio I0/VI of the circuit shown in the figure can be changed. can be switched. However, both emitter resistors 2 and 3 in the area surrounded by the dashed-dotted line in the figure need to be external resistors as mentioned above, and their respective resistance values must be adjusted by trimming etc. after the circuit is assembled. It won't happen. At this time, it is necessary to simultaneously adjust the combined resistance value of the emitter resistors 2 and 3 and the individual resistance value of the emitter resistor 2 to a predetermined value. In addition, in many applications, these resistance values not only determine the conversion ratio, but also serve as a type of load or impedance for other circuits in the electronic circuit that incorporates the voltage/current conversion circuit. In other words, resistance value management is becoming more important. As can be easily imagined, it is quite troublesome to strictly adjust the two types of resistance values to predetermined values by trimming, and in practice, a failure in trimming is likely to result in a defective circuit.

[Purpose of the invention]

The present invention solves the above-mentioned problems of the conventional circuit, simplifies the adjustment of the resistance value of the emitter resistor, and makes it possible to control the conversion ratio, which reduces the occurrence of defective products when manufacturing electronic circuits. The purpose is to obtain a voltage/current conversion circuit.

Summary of the Invention According to the present invention, the above-mentioned object is to provide a voltage-to-current conversion circuit with a conversion transistor that receives an input voltage to be converted into a current at its base, an emitter resistor that receives an emitter current of the conversion transistor; A current mirror circuit receives a collector current of a conversion transistor and generates first and second currents proportional to the collector current, and injects the first current into an emitter resistor so as to be the sum of the emitter current from the conversion transistor. and a shunting means connected to be able to shunt the first current injected into the emitter resistor via the connecting means, and take out the second current as an output current, and output the second current as an output current. This is achieved by making the conversion ratio for the input voltage controllable by varying the shunting ratio of the first current by means of shunting means. The above-described configuration of the present invention will be explained in more detail with reference to FIG. A single emitter resistor 5 is connected to the emitter of the conversion transistor 1, and its collector current IC is passed through a current mirror circuit 6 composed of three transistors 60 to 62 in the figure.
flows through transistor 60 of. As can be seen from its emitter-base connection, this transistor 60 is a reference transistor in the current mirror circuit, and as is well known, the first current I1 and the first current I1 generated from the other two transistors 61 and 62 are connected to each other. The value of the current I2 in 2 is the collector current IC.
is proportional to the value of The first current I1 is injected into the emitter resistor 5 through the diode 7, so that a current equal to the sum of the emitter current of the conversion transistor 1 and the first current flows in the emitter resistor 5. The diode 7 is the connection means according to the present invention, and in the illustrated example, it guides the first current I1 only in the direction in which it is injected into the emitter resistor 5, and conversely prevents the emitter current of the conversion transistor 1 from flowing in the opposite direction. A diode is used as this connection means 7. FIG. 1 shows a case where the voltage/current conversion ratio of the voltage/current conversion circuit is switched to two stages, and the illustrated transistor 8 is the shunting means according to the present invention,
When turned on by a voltage/current conversion ratio control signal, in the case of the figure, a switching signal SS, all of the first current I1 injected into the emitter resistor 5 is shunted. Even if the shunt means 7 is short-circuited in this way, the emitter current of the conversion transistor is blocked by the diode 7, so that it does not flow into the shunt, and all of it flows to the emitter resistor 5. Now, let us assume that the resistance value of the emitter resistor 5 is R. If there is no shunt as described above, this resistance value R will be equal to the emitter current of the voltage/current conversion ratio (since the base current is small, the collector The sum of the current IC (equal to IC) and the first current flows,
Considering that only the emitter current flows when there is a shunt, the emitter resistance 5 when shunted is
The equivalent resistance Re of is Re=R・IC/(IC+I1). The voltage/current conversion ratio I0/EI has a reciprocal relationship with this equivalent resistance. As can be seen from the above description, the switching width of the voltage/current conversion ratio in the present invention is determined by the proportional constant of the first current I1 to the collector current IC of the conversion transistor, that is, the ratio of the collector current of the transistor 61 to the collector current of the transistor 60. Depends on. As is well known, the collector current of a transistor is determined by the area or perimeter of the collector region (more precisely, the length facing the emitter region), and as shown in FIG.
In the case of pnp transistors, ie so-called lateral transistors, it is determined by the perimeter. Furthermore, as is well known, with current semiconductor wafer processing technology, it is possible to control pattern dimensions with micron or submicron precision, so the perimeter can be achieved with high precision as designed. Furthermore, as can be seen from the above equation, in the present invention, the switching width or ratio of the voltage/current conversion ratio is determined by the ratio of the collector currents of the two transistors, that is, the ratio of the circumferential lengths of the collector regions, so it is extremely accurate. control is possible. The above-mentioned configuration of the present invention was made with attention to this point, and the switching width or ratio of the voltage/current conversion ratio of the circuit of the present invention can be manufactured accurately as designed, without any post-adjustment. Not needed. In addition, for convenience of explanation, the first current shunt by the shunting means 8 is assumed to shunt all of the current, but of course only a part of it is shunted and the voltage
The current conversion ratio can be switched within the above-mentioned switching width. Furthermore, if the specific structure of the shunt means 8 is slightly modified, it is easy to continuously control the voltage/current conversion ratio. See the next section for other desirable aspects of the invention.

[Embodiments of the invention]

Hereinafter, embodiments of the circuit of the present invention and their operations will be described with reference to the application examples of the present invention shown in FIGS. 2 and 3. The example shown in FIG. 2 is a case where the circuit of the present invention is applied to a circuit of a mass-produced proximity switch. 2
0, and the judgment output circuit 30 is shown on the right side thereof. The center of the detection circuit 20 is a high-frequency parallel resonant circuit consisting of a coil 21 and a capacitor 22, and when the object B is away from the coil 21, it is in a normal resonance state, but when the object B is within a certain distance D. When it approaches, the resonance state is removed, and the determination output circuit 30 determines this and issues a detection output T0. As is well known, it is necessary for this type of sensor to have a predetermined hysteresis width HS in its detection operation as shown in FIG. The voltage/current conversion ratio can be switched according to the state of the detection output T0. Oscillation energy is injected into the resonant circuit consisting of the coil 21 and the capacitor 22 by the second current I2 or the output current I0 of the voltage/current conversion circuit, and the output transistor 62 is a transistor as shown in the figure. 61 may be incorporated into one current mirror circuit 6, or if the required output current value is large, it may be separated as a transistor of another current mirror circuit. In this embodiment, since the potential e2 at the point of energy injection into the resonant circuit fluctuates between positive and negative with respect to the ground potential, the emitter resistor 5 in the voltage/current conversion circuit 10
The connection point potential e1 to the emitter of the conversion transistor 1 is always made equal to this. A diode 24 supplied with a constant DC current by a constant current source 23 in the detection circuit 20 is a so-called level shift diode and provides a forward voltage drop equal to the base-emitter voltage of the conversion transistor 1. Therefore, when considering the base potential of the conversion transistor as a reference, its emitter potential e1 is always equal to the energy injection point potential e2 into the resonant circuit. Since this potential e2 and therefore the emitter potential e1 vary over time, the collector current IC of the conversion transistor also varies over time. However, this collector current IC becomes a pulsating direct current, more precisely a half-wave rectified wave-like direct current, due to the rectifying characteristics of the conversion transistor 1, which is an npn transistor. Of course, depending on the characteristics of the current mirror circuit, the first current I1 and the second current I2 generated by it have similar waveforms, and the latter of these is injected into the resonant circuit as the output current I0, so this is a kind of waveform. This has a positive feedback effect of 100%, thereby maintaining the oscillating conditions of the resonant circuit. Further, the second current I2 maintains the conversion ratio of the output current I0 to the input voltage EI constant over time based on the basic operation of the voltage/current conversion circuit described above. The voltage/current conversion circuit according to the present invention includes:
Of course, it operates as a pure DC circuit, but it can also be applied to a so-called semi-AC circuit in which the voltage and current values fluctuate over time. When the object B approaches the coil 21, the resonant circuit is detuned and its apparent impedance is drastically reduced, so that the potential e2, and therefore the emitter potential e1 of the conversion transistor, decreases. The judgment output circuit 30 sees this based on the base potential of the conversion transistor 1,
This is received at one input of a comparator 32 via a smoothing circuit 31. The smoothing circuit 31 is a normal one having, for example, resistors 31b and 31c and a capacitor 31a, and smoothes the pulsating component in the input voltage e1, which is the aforementioned potential e1, that is, the base potential of the conversion transistor, and supplies it to the comparator 32. A reference potential RV is given to the other input of the comparator 32, and when the value of the smoothed signal to one input falls below this, this is detected and the detection output T0
emits. This detection output T0 is, for example, a resistor 33
Since the voltage is applied to the base of the transistor 8 as a shunting means through the voltage dividing circuit 33 consisting of a and 33b, when the detection output T0 is generated, the transistor 8 is turned on and the voltage/current conversion circuit 1
0 conversion transistor I0/VI is switched,
In the present example the conversion ratio is increased. As a result, the output current I0 as the current injected into the resonant circuit is increased, so that the object B approaches the coil 21 and is further away from the coil 21 than the distance D when the detection output T0 is generated. Detection output T unless
0 is not turned off, and a hysteresis width HS as shown in FIG. 3 is obtained. As can be seen from the above explanation, this hysteresis width HS is determined by the switching width of the voltage/current conversion ratio of the voltage/current conversion circuit 10. Although it is necessary to keep this hysteresis width HS uniform in terms of control in manufacturing the proximity switch, since the collector current ratio of the transistor 60 and the transistor 61 in the current mirror circuit 6 can be accurately controlled as described above, the present invention According to this, it is possible to mass produce products with a constant hysteresis width HS, and there is no need for post-adjustment. However, the resistance value of the emitter resistor 5, which is an external resistor, is
Since it is necessary to match the parallel resonance impedance (resistance) between the capacitor 1 and the capacitor 22, it is necessary to adjust the resistance by trimming or the like. The present invention is not limited to the embodiments described above, and can be implemented in various ways. For example, as the connection means, the diode 7 is not always used, and it may change depending on the type and form of the electronic circuit combined with the circuit of the present invention. This should be understood as one of the advantageous embodiments as a means for injecting into the emitter resistor.

【Effect of the invention】

As can be seen from the above explanation, the switching width or control width of the voltage/current conversion ratio in the circuit of the present invention is essentially determined by the current ratio between the reference transistor and the first current generating transistor in the current mirror circuit. Since this current ratio can be accurately controlled by the perimeter ratio and area ratio of the collectors of both transistors, the switching width can be manufactured accurately, eliminating the need for post-adjustment. However, depending on the form of the electronic circuit combined with the circuit of the present invention, it is often necessary to adjust the resistance value of the emitter resistor after assembly, such as by trimming, but there is a risk that a single resistance adjustment will fail. There are very few
Such failures rarely result in defective products. In addition, since the switching width is determined by the ratio of the basic dimensions within the two semiconductor elements, there is no deviation even when ambient conditions such as temperature change, and as can be seen from the above explanation, the output It is dynamically stable even when used in applications where current fluctuates over time. The voltage/current conversion circuit according to the present invention is particularly suitable for being incorporated into an integrated circuit, and can exhibit the above-mentioned effects as a basic circuit in which various circuits are combined.

[Brief explanation of the drawing]

Figures 1 to 3 are for explaining the present invention, of which Figure 1 is a circuit diagram showing the basic configuration of the voltage/current conversion circuit according to the present invention in comparison with the conventional circuit shown in Figure 4; Figure 2 is an example circuit diagram showing an example in which the circuit of the present invention is applied to an electronic circuit for a proximity switch, and Figure 3 is a circuit diagram showing an example of the operation of the proximity switch using the voltage/current conversion ratio control function of the circuit of the present invention. FIG. 2 is a diagram showing the hysteresis characteristics of FIG. FIG. 4 is a basic configuration circuit diagram of a voltage/current conversion circuit having a voltage/current conversion ratio switching function according to the prior art. In the figure, 1: conversion transistor, 5: emitter resistance, 6: current mirror circuit, 60 to 62: transistors constituting the current mirror circuit, 7: connection means or diode, 8: shunt means or transistor, 10: voltage Current conversion circuit, 2
0: Detection circuit, 30: Judgment output circuit, B: Object,
HS: Operation hysteresis width of proximity switch, I
1: first current, I2: second current, I0: output current, SS: switching signal as a control signal for the shunt means, T0: detection output of the proximity switch.

Claims (1)

[Claims] 1. A conversion transistor whose base receives an input voltage to be converted into a current, an emitter resistor which receives an emitter current of the conversion transistor, and a resistor which receives a collector current of the conversion transistor and is proportional to the collector current. a current mirror circuit for emitting first and second currents; a connecting means for injecting and guiding the first current to the emitter resistor so as to be the sum of the emitter current from the conversion transistor; and a shunt means connected so as to be able to shunt the first current injected into the emitter resistor, outputting the second current as an output current and converting the conversion ratio of the output current to the input voltage into the second current. A voltage/current conversion circuit, characterized in that control is possible by changing the shunting ratio of the first current using shunting means. 2. In the voltage/current conversion circuit according to claim 1, the shunt means is a switching means capable of intermittent injection of the first current into the emitter resistor, and the voltage is - A voltage/current conversion circuit characterized by being able to switch the current conversion ratio. 3. The voltage/current conversion circuit according to claim 2, wherein the switching means is a transistor. 4. The voltage/current conversion circuit according to claim 1, wherein the connection means is a diode that guides the first current only in the direction toward the emitter resistor.