DE2128920A1 - Electronic switch for logic circuits - Google Patents

Description

Dr. Herbert Seh ο U

Note: NV PMLiPS ' GwOElLLAMPENFABMEIStt Va / RV.

File: PHU- I 3

Registration of u t)

Electronic switch for logic circuits,

The invention relates to an electronic switch for logic circuits with a first and a second transistor, wherein the collector of the first transistor is coupled to the base of the second transistor, the emitters are coupled to one another, and a trigger signal is applied to the base of the first transistor. In logic circuits, the output signal must depend on the Values of a number of input signals one of two possible discrete Assume values which values represent a 0 or 1 in the bimeric code. To achieve this behavior, many logical steps are taken Circuits uses a differential amplifier, one of the input terminals representing the connection point of the inputs of the logic circuit and a constant voltage is applied to the second input terminal «Depending on the voltage applied to the input terminal of the differential amplifier

167 1

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When the voltage is applied, one of the two stages of this amplifier is conductive. The disadvantage of such circuits is the need for a constant reference voltage at the second input terminal of the differential verse tSrkers.

The necessity of this reference voltage can be avoided by _f that instead of a differential amplifier, a threshold circuit is used _for the already known under the name "Schmitt" circuit or "Schmitt-trigger circuit". In this circuit of the type mentioned at the beginning, when the input signal exceeds the response value of the circuit, the output signal changes from one binary value to the other at a rate that is only dependent on the circuit. As a result of the coupling between the collector of the first transistor and the base of the second transistor, the switching state of this second transistor is determined directly by that of the other transistor, so that a reference voltage is superfluous. The Auspreohwert is determined by the dimensioning of the circuit

"The circuit are not the same, εο that a hysteresis phenomenon occurs.

This hysteresis phenomenon is undesirable for logic circuits ^ because this increases the sensitivity to interfering signals will. The StSrspannungsabstend is due to this hysteresis phenomenon namely reduced.

The invention h.at the 2%? Eck to create an electronic switch for logic circuits, in which the hysteresis phenomenon can be suppressed more easily, which can have a large signal-to-noise ratio and in which the output has considerable currents for control

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can be taken from the following stages.

The invention is characterized in that in the collector circuit of the first transistor, a first voltage divider is added, the tap point of which with the base of a third as an emitter follower

switched transistor is connected, and that in the emitter circuit a second voltage divider is added to this third transistor, the tap point of which is connected to the base of the second transistor

The combination of the voltage divider and the emitter follower in the connection line between the collector of the first and the base of the second transistor results in great freedom with regard to the setting the switching characteristic. As will be set out in more detail in the description of the figures, correct setting of the Voltage divider can be achieved that the response value of the switch for the two directions of signal change are the same, i.e. that the Switching characteristic shows no hysteresis phenomenon, while nevertheless there is sufficient freedom with regard to the size of the pickup value remain.

Positive feedback can be achieved in that into the common emitter line of the first and second transistor a resistance is added. Instead, however, a current source or the series connection of a number of diodes can also be included will.

In order to achieve a faster operation of the circuit, the first voltage divider by an ^n-powered forward direction diode can be bridged, which then acts as a overdriving of the first transistor preventing diode.

The output signal can be sent to the collector of the first transistor

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tors can be taken from the point at which the circuit will be well loaded can"

A complementary output signal can be sent to the collector of the second transistor, for what purpose an impedance must be added to the collector circuit of this transistor. To the Increasing the switching speed of the circuit * can increase this impedance in turn bridged by a diode operated in the forward direction will.

"In order to obtain a logic circuit can be arranged parallel und.können J, the bases of these transistors are used, including the base of the first transistor" as the input terminals of the logic circuit a number of transistors to the first transistor. The output signal can be taken from the emitter of a transistor whose base is connected to the collector of the third transistor, whose collector is connected to one of the terminals of the supply source and whose emitter is connected via an impedance to the other terminal of the supply source.

The base of the first transistor can also be connected to the common emitter of a number of parallel-connected transistors whose common collector is connected to one of the terminals of the supply source and whose bases are supplied with the input signals of the logic circuit. The base of the first transistor must be connected via a resistor to a terminal of the supply source or to the emitter of this first transistor. This structure of the circuit results in advantages in terms of integration, as can be seen from the description of the figures .

Soft implementation fora of the invention are in the drawing

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and are described in more detail below. Show it:

Piguren 1 and 2 two embodiments of a logic circuit with an electronic switch according to the invention,

Fig. 3 shows the characteristic of the circuit according to the invention in Compared to that of a Schmitt flip-flop circuit, and

FIGS. 4-7 an integrated version of the circuit according to FIG. 2,

Fig. 1 shows a first embodiment of a logical

Circuit with an electronic switch according to the invention. The circuit contains three input transistors T., T_ and T, connected in parallel, whose bases can be supplied with input signals V. It is evident, however, that the number of input transistors can easily be increased. The common collector of these input transistors is connected to the ground terminal _{via a first voltage divider S 1} with the partial resistors R ₁ and R _9. The tapping point of this voltage divider S is connected to the base of a transistor T connected as an emitter follower, the emitter of which in turn has a second voltage divider S _? with the partial resistors R, and R. is connected to the common emitter of the input transistors. The tapping point of this second voltage divider S ″ is connected to the base of a transistor T. whose collector is connected to the ground terminal and whose emitter is connected to the common emitter of the input transistors.

The electronic switch can therefore be constructed from each of the input transistors (T ₁ , T _?, T), the voltage dividers S ₁ and S ″ and the transistors T and T ₁ . The switching state of the transistor T is determined by the switching state of the input transistors, namely by the coupling of the common collector of these transistors

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with the base of T via the voltage divider S, the transistor T and the voltage divider S-. This structure of the coupling makes it possible through a correct setting of the voltage dividers S and S_ a hysteresis-free To achieve the switching characteristic, while there is also sufficient freedom to set the switching voltage to a required value, as will be demonstrated by a calculation on the basis of FIG.

To increase the switching speed, the first voltage divider S. can be bridged by a diode T ", which prevents that the input transistors get into the saturation state. The common one Emitter resistance R_ of the transistors T, T, T and T carries contributes to a quick switching effect. But this resistance can also be replaced by a power source or by the series connection of a number of diodes, although the use of a resistor is considered with consideration has advantages on temperature stability. The output signal V can be connected to the emitter of a transistor Tg connected as an emitter follower whose base is connected to the common collector of the input transistors. This extraction of the output signal via a Emitter follower is required in this circuit so that the output can be connected again to the inputs of the following logic circuits can. A complementary output signal can be provided via an emitter follower taken from the collector of T, for what purpose in the collector circuit This transistor has an impedance to be recorded, which in turn is bridged by a diode to increase the switching speed can be.

The circuit described can be integrated in a semiconductor body in the usual way. Can be advantageous with integration but a modification of this circuit can be used (see Fig. 2).

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This circuit also contains three input transistors T ₁₁ , T ₁₂ , T ₁₅ connected in parallel, the common collector of which is now directly connected to the ground terminal. The common emitter of these input transistors T. connected to the base of the transistor. and about one

Resistor R ₁₁ connected to the negative terminal (-V) of the supply source. The transistor T ₄ . forms part of the electronic switch according to the invention, which further comprises the transistors T, T, and the voltage dividing p and S _15th Instead of using a diode connected in parallel to the voltage divider S _{11 , the transistor T 1} - is provided with an additional emitter which is connected to the collector of T 1. In this way, practically the same effect is achieved, because in practice the partial resistance R ₁ - of S _{11 is} considerably smaller than the partial resistance R ₁ .

The output signal V can in the circuit according to FIG

directly to the collector of T. can be taken, while the complementary output signal can be taken directly from the collector of the transistor T ₁ ^, for which purpose, of course, an impedance is to be taken up again in the collector circuit of this transistor.

By a suitable choice of the setting of the voltage dividers S and S _1? a hysteresis-free switching characteristic can be achieved again, as will be explained in more detail using a simplified calculation of the response values of the circuit.

It is assumed that the transistors used are all identical. Partial resistances R ₂ and R_ are used for the voltage divider S ₁₁ and partial resistances R ₁₄ and R ^ are used _{for the voltage divider S 12.}

If βηβ · ηο · β · & becomes that 4's Baei »from M ₁₁ ei»

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2T2892Q

signal V. is fed, the following equation can be found:

V ₄ -V, - V, = - V _D -V, -V ₁₃ -V,, i be be R _{1 p} be "R be ,,,

T ₁₁ T ₁₄ 12 T ₁₅ 14 T ₁₆

where Vp is the voltage across resistor R ₁₉ and V-. the tension It ₁₂ \ d K ₁₄

represents across the resistor R ...

When determining the response value for an increasing input signal, it is assumed that T. is still just in the blocked state (base-emitter voltage V ""), while the transistor T ₁ - is in the conductive state (base-emitter voltage k V __ + / JT,). The following is then found for the response value for an increasing input signal:

/ ^V of f - ^

Rj ι
^V off ^V t ^ ^{1 +;} ·

R ₁₅ R ₁₅

It is assumed that the base-emitter voltages of the transistors T and T ₁ are equal to one another at this transition.

Purely for determining the response value with a decreasing input signal it is assumed that T,., - is still blocked

(V, = V "") and that T .. is in the conductive state be "off 14

»Be"
^T 16

V
14th

It is also assumed that the voltage between the base of T ₁ j. and its additional emitter V "_. The response value is then found »

R R

v '= v + Αν- v - ν - ν

^V i off ^{a V} t ^ - off R ₄ - off off

R ₁₅ 15

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It is again assumed that V, «V, is.

te "be",

11 15 In order to obtain a hysteresis-free characteristic, the following must apply

A 1

i " ^Y i

^V i - ^V i ^ ^V off 2 & - ^{Δ V} t <* _ ^E 13 ^R 15

From this equation it is clear that with a suitable choice of the Partial resistors a hysteresis-free switching characteristic can be obtained. It can also be seen that sufficient freedom with regard to the ' The choice of the size of the pickup value remains. A suitable choice of the response value can ensure that the St6 "rvoltage distance is the same half of the minimum permissible voltage swing of the input signal. This is illustrated in Fig. 3, in which the switching characteristic of a Schmitt flip-flop (dashed line) over that of the Circuit according to the invention (full line) is applied. The input signal is plotted as the abscissa and the output signal as the ordinate. If a minimum voltage swing V is assumed and the connection

Speaking value is \ V, it can be seen from the figure that the interference voltage spacing for the so-keeping according to the invention is also £ V Integrate output transistors together with the switch. These transistors then have a common base and a common collector, which is connected to the collector of the transistor T. This module can then be used to build the same logical system as the circuit shown, with the input transistors for the following modules now being integrated with the preceding modules.

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As already mentioned, the design of the circuit according to FIG. 2 has advantages in terms of integration. These advantages are primarily due to the fact that the collectors of all but one of the transistors are directly connected to the earth terminal. Furthermore, the additional emitter of the transistor T. _c can be integrated more easily than an additional diode.

The advantage of the circuit is that in this circuit an integration method can be used in which only a particularly small semiconductor surface is required. Such an integrated design is described below with reference to FIGS. 4-7. wrote.

It should be noted that the integration method used here in itself the subject of the Dutch patent application ITr. 09 089 forms.

Fig. 4 shows a topology or "layout" of a particular one Integrated design of the circuit according to FIG. 2. The different circuit elements with the the same reference numerals as in FIG.

The semiconductor arrangement contains a semiconductor body 70,

h which has a low-resistance substrate 1Λ , on which an epitaxial layer 72 of the same conductivity type and with a higher specific resistance is applied. (Fig. 5) · The substrate 71 and the epitaxial layer 72 together form the collector zone of the transistor T ₁₁ , the can be connected to a reference potential, e.g. to earth. In the present exemplary embodiment, the positive terminal of the supply voltage source is also connected to this collector zone, so that the substrate carries the most positive potential that occurs in the circuit,

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The input _{transistors T 11} -T each have a base zone 73 and an emitter zone 74. _{Input signals can be fed to the transistors T 11} , T ₁₂ and T via metal tracks 76 lying on the insulating layer 75 and connected to the base zones 75 in an opening in the insulating layer.

A metal track 77 also connects the three emitter zones 74 of the base zone 78, 79 of the isolated transistor T .. This base zone has an intermediate part 78 which forms an emitter zone in the semiconductor body 80 surrounds, while this base zone further has a bowl-shaped insulating part 79, which with the common collector zone 71t72 one the transistor T surrounding the insulating pn junction 81 forms. the The collector zone 82 of the transistor T, which is provided with a contact zone 83, is completely surrounded by the base zone 78, 79 in the semiconductor body. The intermediate part 78 of the base zone is connected to the semiconductor surface 84 with the insulating part 79, the intermediate Part 78 extends in a direction parallel to the surface 84 up to the vicinity of the insulating part 79 and there on the Part 79 follows. As a result, the intermediate part 78 forms one the extension or extension of the insulating part 79 adjoining the semiconductor surface 84, which extension protrudes beyond the collector zone 82.

The insulating part 79 is designed in the shape of a ring on the semiconductor surface or has at least a closed geometry on. This ring can be used to contact the base zone 78, 79. At a suitably chosen location, the insulating layer 75 be provided with an opening 85 above the insulating part 79, via which the conductor track 77 is connected to the base zone 78, 79.

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As can be seen from the circuit diagram (Fig. 2), the resistance is R .. connected to the base of the transistor T. This fact is used to create a conductor track and the space for the associated Saving contact openings in the insulating layer. The second zone 78, 79 of the transistor T has a locally isolated surface 84 from the insulating Part 79 outstanding part 86 on which is attached to the common collector zone 71 »72 borders and extends in a direction perpendicular to the semiconductor surface 89 over a smaller distance than the cup-shaped insulating Part 79 extends in the semiconductor body. This excellent

. For example, part 86 can be attached at the same time as intermediate part 78 will. The intermediate lying within the shell-shaped part 79 Part 78 forms the actual effective part of the base zone of the Transistor T, i.e. a part in which, in the operating state, the charge transport, which participates in the actual transistor effect of the structure is, at least substantially. The resistor R. is at least largely due to the protruding from the shell-shaped part 79 Part 86 is formed .. The insulating part 79 thus not only serves as an insulation for the transistor, but also as a low-resistance connection of the active part of the base zone and as a low-resistance connection

ψ between the active part and the resistor R ₁₁ *

The resistance R. is also connected to the negative terminal of the supply voltage source. For this purpose, the zone is 86 ^m via an opening in the insulating layer 75 is connected it the metal layer 87th

The resistor R. ^ is formed by the zone 88 and is connected via an opening in the insulating layer to a metal track 89 which leads to the emitter zone 80 of the transistor T. and leads to the emitter zone 90 of the transistor T ^. The resistance R _1C - is determined by the

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Zone 91 is formed, which on one side with the zone 88 and on the other side with the base zone 92 of the transistor T ₁ , - is related. The resistor R .. is formed by a zone 93 connected to the base zone 92. By using a metal layer 94f which lies in the opening 95 in the insulating layer next to the emitter zone 90 and the opening 96 opposite on the semiconductor surface, the resistance value of the resistor R. more precisely defined. Via the opening 96 and the metal track 97, the resistor R is connected to a first of the two emitters 98 of the reverse emitter transistor T ^. The two emitter zones 98 are surrounded by a base zone 99 in the semiconductor body. Zones 100 and 101 are connected to this base zone 99 and form the resistors R ₁₂ and R._ With these resistors too, the resistance values are more precisely defined by a metal layer 102 lying on the semiconductor surface. A metal track IO3, the second emitter 98 of the transistor T,. connects with the collector zone 82 of the transistor T and with the resistor R., forms the electrical output of the gate circuit. The resistor R _{1 9} is connected via an opening IO4 in the insulating layer with a metal layer 105, which is connected by means of a contact zone IO6 to the common collector region 71 »72nd

The transistors T - T ^ are further buried with one each low-resistance part IO7 to reduce the collector series resistance provided which low-resistance parts 107 are on and in the Proximity of the interface between the substrate 71 and the epitaxial Layer 72 extend.

The transistor T. takes up much less space than a transistor mounted in an isolated island in the usual way. These Space saving is due to the fact that the active part 78 of the base

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zone is applied to the insulating zone 79. With the usual structures must on the other hand, the base zone and the isolation zones are at a certain distance from one another this distance is also due to the factors to be taken into account Tolerances in connection with the mutual orientation of the different diffusion masks and, for example, with this orientation occurring deviations must be relatively large.

A further space saving is obtained in that for the transistors with a common collector do not require an isolated island. In addition, these transistors are also in bonded in place to a lesser extent, which may make the metallization pattern for the interconnections simpler. The places of these transistors can easily be adapted to the metallization pattern.

It is also important that the substrate has a grounding surface, i.e. an area with reference potential, for the circuit, whereby the electrical effect of the circuit is favorably influenced.

The gate circuit described has a particularly simple metallization pattern with short connecting tracks. A considerable one Number of connections is made without metal tracks, while the circuit elements can be further arranged so that too thanks to the relatively large freedom in terms of contacting the base of the self-isolating transistor, for the rest internal connections short conductor tracks are sufficient.

The semiconductor arrangement described can be made with the aid of the methods customary in semiconductor technology, or also those of the methods already described mentioned Dutch patent application. No. 70 09 089 Way to be made.

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Claims (8)

-15-. PHN. 4915 PATENT CLAIMS : mJ Electronic switch for logic circuits with a first and a second transistor, the collector of the first transistor being coupled to the base of the second transistor, the PJmitter are coupled together and a trigger signal to the base of the first Transistor is applied, characterized in that in the collector circuit of the first transistor, a first voltage divider is added, the tap point of which is connected to the base of a third as an emitter follower Transistor is connected and that a second voltage divider is included in the emitter circuit of this third transistor, its Tap point is connected to the base of the second transistor. 2. Electronic switch according to claim 1, characterized in that that the impedance ratios of the voltage dividers are such that a step-like switching characteristic with a symmetrical modulation range and negligible hysteresis is obtained. 3. Electronic switch according to claim 1 or 2, characterized in that that the third transistor is provided with an additional emitter which is connected to the collector of the first transistor. 4. Electronic module for logic circuits with an electronic switch according to one of the preceding claims, characterized characterized in that the output terminal of the circuit is connected to the collector of the first transistor of the electronic switch. 5. Electronic module for logic circuits with a Electronic switch according to claim 1, 2 or 3, characterized in that that one of the input terminals of the logic circuit is connected to the base of the first transistor of the electronic switch and the other input terminals with the bases of a number to this first 1098B3 / 1671 -16- PHN. 4913 Transistor of transistors connected in parallel are connected. 6. Electronic component for logic circuits with a Electronic switch according to claim 1, 2 or 3, characterized in that that the base of the first transistor is connected to the common emitter of a number of transistors connected in parallel, the common Collector is connected to the collector of the third transistor and whose bases are connected to the input terminals. 7 · Electronic module for logic circuits according to claim 4j, characterized in that the circuit elements of the elec-. tronic switch together with a number of transistors connected in parallel with a common collector connected to the collector of the third transistor is connected, are integrated in a semiconductor body, the circuit elements in a surface layer of a first conductivity type are attached, which extends over a substrate from first conductivity type extends that a lower specific Has resistance as the surface layer, wherein the semiconductor zones of the first transistor in the semiconductor body of a shell-shaped Isolation zone of the second conductivity type are surrounded and the substrate serves as the common collector connection of the remaining transistors. 8. Electronic component according to claim 7 »characterized in that that the base zone of the first transistor is related to the shell-shaped insulating zone. 109853/1671