JPS62256505A - Voltage/current converting circuit - Google Patents

Abstract

PURPOSE:To decrease generation of defective electronic circuits in manufacturing them by controlling the conversion ratio of an output current to an input voltage through the change in the current ratio of the 1st current by a shunt means thereby simplifying the resistance adjustment of an emitter resistor. CONSTITUTION:A single emitter resistor 5 is connected to an emitter of a conversion transistor (TR) 1 and its collector current IC flows through a TR 60 of a current mirror circuit 6 comprising TRs 60-62. The 1st current 11 from the TRs 61, 62 and the 2nd current 12 are proportional to the collector current IC and the 1st current 11 is injected to the emitter resistor 5 via a diode 7. A TR 8 branches all the 1st injected current to the emitter resistor 5 when the TR 8 is turned on by a switching signal SS. Since the collector current ratio of the two TRs 60, 61, that is, the ratio of the surrounding length of the collector region decides the switching width of the voltage/current converting ratio or its ratio, the control is attained very accurately.

Description

[Detailed description of the invention]

1. Field of the Invention The present invention relates to an electronic circuit that converts a voltage signal to a current signal, particularly a voltage/current conversion circuit suitable for being incorporated into a semiconductor integrated circuit. This relates to a controllable F 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-to-current conversion circuit described above converts a relatively small analog input voltage into an analog output current with a relatively large conductance, but it is also used as part of a more complex electronic circuit for measurement or detection. Since the voltage/current conversion ratio must be accurate as it is often used as This can be achieved relatively easily by taking the conversion output current from the collector side, but since the voltage/current conversion ratio is almost determined by the resistance value of the emitter resistor, in order to maintain an accurate voltage/current conversion ratio, it is necessary to The resistance value must be carefully controlled. Therefore, even when a voltage/current conversion circuit is incorporated into a bipolar IC, the emitter resistor is usually formed as an external element, such as a thick film resistor. In order to control the voltage/IT 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 the conventionally used voltage/current conversion ratio is switchable voltage/1t2i! The basic circuit of the L conversion circuit is shown in Figure 4.
The illustrated transistor 1 is a conversion transistor and receives an input voltage Vl at its base. Its emitter has 2
Emitter resistors 2.3 are connected in series, 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 10, and the voltage/current conversion ratio IQ/Vl of the illustrated circuit is switched by turning on and off the transistor 4 using a switching signal SS given to the base of the transistor 4. It will be done. However, as mentioned above, it is necessary to use resistors externally for both the emitter resistors 2.3 in the part surrounded by the single point tl line in the figure, and the value of each of these resistances must be adjusted by trimming etc. after the circuit is assembled. Must be. At this time, it is necessary to simultaneously adjust the combined resistance value of the emitter resistor 2.3 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, managing the resistance value becomes 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, allows easy adjustment of the resistance value of the emitter resistor, reduces the occurrence of defective products when manufacturing electronic circuits, and enables control of the voltage and current conversion ratio. The purpose is to obtain a conversion circuit.

[Key points of the invention]

According to the invention, the above-mentioned object is to provide a voltage/Q fE conversion circuit with a conversion transistor whose base receives an input voltage to be converted into a current, an emitter resistance which receives an emitter current of the negative transistor, a current mirror circuit receiving the collector current of the conversion transistor and producing first and second currents proportional to the acid collector current, and a connection for directing the first current to be injected into an emitter resistor in parallel with 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, extracting the second current as an output current and adjusting the input voltage of the output current. This is achieved by making the conversion ratio of the first current controllable by changing the shunt ratio of the first current by the shunt 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 I
C flows through the transistor 60 of the current mirror circuit 6, which in the figure is made up of three transistors 60-62. 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 other two transistors 61
．． The first current 11 and the second current I2 emitted from 62
The values of are each proportional to the value of the collector current IC. The first current ItO is injected into the emitter resistor 5 through the diode 7, so that the emitter current of the conversion transistor 1 and the first current flow in the emitter resistor 5 in parallel. The diode 7 is the connecting means according to the present invention, and in the illustrated example, it guides the first current 11 only in the direction in which it is injected into the emitter resistor 5, and conversely prevents the emitter current of the conversion transistor l 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 into two stages, and the illustrated transistor 8 is the shunting means according to the present invention, and controls the voltage/current conversion ratio. In the case of signal 1, when turned on by the switching signal SS, the 0 shunting means 7, which shunts all of the first current ■1 injected into the emitter resistor 5 mentioned above, is in a short-circuited state like this. Even if the emitter current of the conversion transistor is blocked by the diode 7, it will not flow into the shunt side (all of it will flow to the emitter resistor 5. Now, if the resistance value of the emitter resistor 5 is R, then , as mentioned above, if there is no shunt, this resistance value R is the sum of the emitter current of the voltage/current conversion ratio (substantially equal to the collector current IC since the base current is small) and the first current. , and when there is a shunt, only the emitter current flows, so the emitter resistance 50 equivalent resistance Re when shunted is Re” R・IC/ (IC+11), which is the pressure-to-current conversion ratio. 10/El has a reciprocal relationship with this equivalent resistance.As can be seen from the above explanation, the switching width of the voltage/current conversion ratio in the present invention is determined by the collector current f of the conversion transistor.
The first current flowing into c is the proportional constant of 1. That is, it is determined by the ratio of the collector current of transistor 61 to the collector current of transistor 60. As is well known, the collector current of a transistor is determined by the area or circumference of the collector region (more precisely, facing the emitter region), and as shown in FIG.
, 61 f>< p n p ) In the case of a transistor, that is, a so-called lateral transistor, it is determined by the peripheral length. 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, what determines the switching width or ratio of the voltage/current conversion ratio in the present invention is the ratio of the collector currents of the two transistors, that is, the ratio of the circumferential lengths of the collector regions. 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 precisely controlled as designed. possible, fP A, i”-n) body mass w t
a menu s, W+-sr +,'sFor 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. By dividing the current, the voltage/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. The circuit 20. A determination output circuit 30 is shown on the right side thereof. The center of the detection circuit 20 is a coil 21 and a capacitor 22.
. A high-frequency parallel resonant circuit consisting of The output circuit 30 makes a determination and issues a detection output TO. As is well known, this type of sensor has a predetermined hysteresis width II in its detection operation as shown in FIG.
In order to provide this hysteresis width, the voltage/current conversion ratio of the voltage/current conversion circuit according to the present invention is switched in accordance with the state of the detection output TO. The 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 amount filo of the voltage/current conversion circuit, and the output transistor 2 is a transistor as shown in the figure. 6
1 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. Since the potential e2 at the energy injection point fluctuates between positive and negative with respect to the ground potential, the voltage
The connection point potential e1 of the emitter resistor 5 in the current conversion circuit 10 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 el is always equal to the energy injection point potential e2 into the resonant circuit. This potential e2, and therefore the emitter potential e1, fluctuate over time. The current flowing through the collector of the conversion transistor also changes over time. However, this collector current IC is npn)
Due to the MfL characteristic of the conversion transistor 1, which is a transistor, a pulsating direct current flows, more precisely a half-wave rectified wave-like direct current. Of course, depending on the characteristics of the current mirror circuit, the first current (1) and the second current (2) generated by the current mirror circuit have similar waveforms, and the latter of them is the output current (2).
Since it is injected into the resonant circuit as zero, it has a kind of positive feedback effect, thereby maintaining the oscillating condition of the resonant circuit. Further, the second current I2 is determined based on the basic operation of the voltage/current conversion circuit described above.
The voltage/current conversion circuit according to the present invention, which maintains the conversion ratio of the output amount 2itIO to l constant over time, also operates as a pure DC circuit, but in this way, the voltage/current conversion circuit
1! It can also be used in so-called semi-AC circuits where the current value varies over time. When the object B approaches the coil 21, the resonant circuit tunes and its apparent impedance drastically decreases, so that the potential e2. Therefore, the 0 judgment output circuit 30 in which the emitter potential e1 of the conversion transistor decreases sees this from the base potential of the conversion transistor 1, and receives this at one input of the comparator 32 via the 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 ripples in the input voltage el, which is the above-mentioned potential el, that is, the base potential of the conversion transistor, and supplies it to the comparator 32. A reference potential RV is applied to the other input of the comparator 32, and when the value of the smoothed signal to one input falls below this, it is detected and a detection output To is generated. This detection output To is given to the base of the transistor 8 as a shunting means via a voltage dividing circuit 33 consisting of resistors 33a and 33b, for example, so that when the detection output TO is generated, the transistor 8
is turned on to switch the conversion transistor 10/Vl of the voltage/T4 current conversion circuit 10, increasing the conversion ratio in this example. As a result, the output 1110 as the current injected into the resonant circuit is increased more than before, so it is detected as long as the object B approaches the coil 21 and does not move away from the coil 21 by more than the distance HD when the detection output To is generated. Output T
O 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 III
H5 is determined by the switching width of the voltage/current conversion ratio of the voltage/current conversion circuit 10. It is necessary to keep this hysteresis width H3 uniform in terms of management in manufacturing the proximity switch, but the transistor 60 and transistor 61 in the current mirror circuit 6
Since the collector current ratio of can be controlled accurately as described above, according to the present invention, 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 external resistor Emiso9 TIE resistor 5 is coil 21
Since it is necessary to match the parallel resonant impedance (resistance) between the capacitor 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, the diode 7 is not always used as the connection means, and the type of electronic circuit combined with the circuit of the present invention may be used. Therefore, in terms of the gist of the present invention, it should be understood that M11 is an advantageous means for injecting the first current into the emitter resistor.

【Effect of the invention】

As can be seen from the above explanation, how much voltage and electricity are used in the circuit of the present invention? The switching width or control width of the JL conversion ratio is essentially determined by the current ratio between the reference transistor and the first current generating transistor in the current mirror circuit, and this current ratio is determined by the perimeter ratio and area ratio of the collectors of both transistors. Since it can be controlled accurately, the switching width can be manufactured accurately! Jil! i! (Of course, depending on the form of the electronic circuit combined with the circuit of the present invention, the emitter resistor often requires adjustment of the resistance value after assembly, such as trimming work. Resistance adjustment has a very low risk of failure, and such failure will rarely result in defective products, and since the switching width is determined by the ratio of the basic dimensions in the two semiconductor elements, It does not become distorted even when ambient conditions such as temperature change, and as can be seen from the above explanation, it is dynamically stable even when used in applications where the output current fluctuates over time. The voltage/current conversion circuit is particularly suitable for being incorporated into an integrated circuit, and can provide the above-mentioned effects as a basic circuit that can be combined with various circuits.

[Brief explanation of drawings]

Figures 1 to 3 are for explaining the present invention, and Figure 1 of the inner cylinder 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 proximity switches, and Figure 3 is an example circuit diagram of the proximity switch using the voltage/current conversion ratio control function of the circuit of the present invention. FIG. 3 is a diagram showing operational hysteresis characteristics. Figure 4 is a basic configuration circuit diagram of a voltage/current conversion circuit with a voltage/current conversion ratio switching function according to the prior art. In Figure 0, 1: conversion transistor, 5: emitter resistor, 6: current mirror circuit, ~62: Transistor constituting the current mirror circuit, 7: Connection means or diode, 8: Shunt means or transistor, 10: Voltage/current conversion circuit, 20: Detection circuit, 30: Judgment output circuit, B: Object, U
S: operating hysteresis width of the proximity switch, l: first current, I2: second current, IO = output current, SS: switching signal as a control signal for the shunt means, TO: detection output of the proximity switch, It is. Figure 1 + Figure 4

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; connecting means for guiding the first current to be injected into the emitter resistor in parallel with the emitter current from the conversion transistor; and shunt means connected so as to be able to shunt the first current, which extracts the second current as an output current and determines the conversion ratio of the output current to the input voltage of the first current by the shunt means. A voltage/current conversion circuit characterized by being controllable by changing the shunt ratio. 2) In the 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/current conversion ratio is switched by intermittent operation of the switching means. A voltage/current conversion circuit that is characterized by making it possible. 3) A voltage/current conversion circuit according to claim 2, wherein the switching means is a transistor. 4) A voltage/current conversion circuit according to claim 1, wherein the connecting means is a diode that guides the first current only in the direction to the emitter resistor. 5) The circuit according to claim 1, characterized in that the current mirror circuit is provided separately into a first current generating current mirror circuit and a second current generating current mirror circuit. Voltage/current conversion circuit.