GB2031678A

GB2031678A - Pulse forming circuit

Info

Publication number: GB2031678A
Application number: GB7926142A
Authority: GB
Original assignee: Ducellier et Cie
Current assignee: Ducellier et Cie
Priority date: 1978-08-01
Filing date: 1979-07-26
Publication date: 1980-04-23
Also published as: FR2432797B1; NL7905907A; GB2031678B; FR2432797A1; IT1122286B; IT7924588A0; DE2931300A1; ES483769A1

Abstract

The input stage of a linear integrated circuit intended to receive at A an alternating input signal, and shape it into rectangular form, includes a diffused resistor R1, a current limiting resistor R2, an NPN transistor T1 strapped as a diode and a PNP transistor T2 the base of which is polarised by a reference voltage VR, connected substantially as shown. As applied, Fig. 2 (not shown), to ignition control for an IC engine both negative and positive half cycles of the signal are clipped, the latter at an adjustable level equal to VBE+VR, where VBE=0.8 volts. <IMAGE>

Description

SPECIFICATION Improvement to the input stage of linear integrated circuits intended to receive an alternating input signal The present invention concerns an improvement of the input stage of a linear integrated circuit intended to receive an alternating input signal, for example, a circuit for shaping the alternating input signal into rectangular form, for use in an electronic ignition control device of an internal combustion engine including a magnetic generator delivering an alternating signal.

In such devices, the use of a magnetic generator for triggering the ignition leads to the formation of parasitic transistors at the inputs of the shaping means during the clipping of the negative half cycles of the signals from the magnetic generator. This formation of parasitic transistors disturbs the operation of the integrated circuit and can lead to its destruction. The conduction of the parasitic transistor depends on the currents which supply the inputs of the shaping circuit. It is possible to provide external input resistors of which the very high ohmic value will limit the supply currents to a value less than that necessary to render the parasitic transistors operative.However, the use of high ohmic value external resistors at the input of circuits such as amplifiers, comparators, shapers, formed by linear integrated technology, diminishes the precision of these circuits by reason of input currents which produce potential differences across these resistors which are not negligible.

The object of the present invention is to remedy the aforesaid disadvantages and concerns to this effect an improvement to the input stage of linear integrated circuits receiving an alternating input signal, characterised in that a diffused resistor is connected at one of its ends, firstly to one of the ends of an external current limiting resistor receiving the alternating signal, secondly to the emitter of an NPN type transistor of which the collector and the base are connected to the negative pole of said circuit and thirdly to the emitter of a PNP type transistor of which the collector is connected to the negative pole and of which the base is polarised by a reference voltage; the other end of the diffused resistor being connected to the input stage in a manner such that the predetermined ohmic value of the diffused resistor limits the emitter currents of parasitic transistors included in said input stage to a value which cannot disturb the operation of the integrated circuit.

The following description with reference to the accompanying drawings will facilitate a better understanding of howthe invention can be carried out.

Figure 1 is the diagrammatic representation of the improvement forming the subject of the invention.

Figure 2 is the representation of a preferred embodiment of the invention, of the input of the shaping means of a linear integrated circuit forming part of an electronic ignition control device for an internal combustion engine, particularly for motor vehicles.

The improvement of the input stage according to the invention and represented diagramatically by Figure 1 comprises a diffused resistor R1 connected at one of its ends firstly to one of the ends of an external current limiting resistor R2 receiving the alternating signal A from a generator such as, for example, a magnetic generator, said end of the diffused resistor is connected secondly to the emitter of a transistor T1 of the NPN type of which the collector and the base are connected to the negative pole of said circuit and thirdly to the emitter of a transistor T2 of the PNP type of which the collector is connected to the negative pole and of which the base is polarised by a reference voltage Vr, the other end of the diffused resistor R1 being connected to the input stage B in such a manner that the predetermined ohmic value of the diffused resistor R1 limits the emitter currents of parasitic transistors, created by the isolating regions and sidewalls of the integrated circuit, to a value which cannot disturb the operation of the integrated circuit.

In the British Patent Application No. 7903401, the electronic ignition control device includes a magnetic generator for triggering ignition signals, a voltage step-up coil including a primary winding connected in series with an electronic contact breaker and a monolithic circuit including first supply means, shaping means, anti-interference means, second supply means, an integrator, a comparator, a mixer, filtering and delay means, current regulating means such that in association with external capacitive and resistive elements there is obtained a constant energy spark at the elecrodes of the plug selected by the ignition distributor.In such a device, the use of a magnetic generator for the ignition triggering signals leads to the formation of parasitic transistors at the inputs of the shaping means during the clipping of the negative half cycles of the signals from the generator. This formation of parasitic transistors disturbs the operation of the monolithic circuit and can lead to its destruction.

The embodiment of the shaping means represented by Figure 2 enables this disadvantage to be overcome.

According to the present invention, the shaping means 200, for which the reference numerals of Application 7903401 are maintained to facilitate understanding, comprise two complementary inputs 6 and 7 of which one, input 7, is connected directly to the negative pole of the device and of which the other input 6 is connected to one of the ends of the inductive winding of the magnetic generator by a voltage bridge divider composed of external resistors, including the resistor R2 (see Figures 1 and 2).

The bases of the PNP type transistors 201 and 203 (see Figure 2) are connected to the emitters of the transistors T1, T1', by means of diffused resistors R1, R1' of P type base. Their ohmic value is determined in such a manner as to ensure the limitation of the emitter current of the parasitic transistors, of which the emitters are constituted by the bases of transistors 201 and 203, to a value which cannot disturb the operation of the shaping means. The emitters of transistors T2, T2' are connected to the ends of the diffused resistors R1, R1', connected on the one hand to the emitters of the transistors T1,T1', and on the other hand to the inputs 6,7. The collectors of transistors r2, T2' are connected to the negative pole of the device by means of the connection 109.

The bases of the transistors T2, T2' are polarised by a reference voltage VR, which in this embodiment is equal to 1.6 volts, the reference voltage VR being fixed by the two transistors 213 and 214 connected as a diode. The clipping of the negative half cycles of the signal from the magnetic generator is carried out by the emitter-base ju nction of the transistors T1, T2', but these transistors do not clip the positive half cycles. This clipping is carried out by the transistors T2, T2' when the emitter potential of said transistors is greater by a value of 0.8 volts than the potential VR.

The value VR is not limitative and the clipping of the positive half cycles could be carried out at a potential between 0.8 volts, that is to say the value of the emitter base junction of the transistors T2, T2' the base being then connected to the negative pole and for the value 4.8 volts the value of the supply voltage of 4 volts, of the monolithic circuit, plus the value of 0.8 volts of the emitter base junction of the transistors T2, T2'.

It will be understood that the invention is not limited to the embodiment described above and illustrated, other embodiments being possible without departing from the scope of the invention.

Claims

1. An improvement to the input stage of a linear integrated circuit intended to receive an alternating input signal characterised in that a diffused resistor is connected at one of its ends firstly to one of the ends of an external current limiting resistor receiving the alternating signal, secondly to the emitter of an NPN type transistor of which the collector and the base are connected to the negative pole of said circuit and thirdly to the emitter of a PNP transistor of which the collector is connected to the negative pole and of which the base is polarised by a reference voltage, the other end of the diffused resistor being connected to an input stage, such that the predetermined ohmic value of the diffused resistor limits the emitter currents of the parasitic transistors included in said input stage to a value which cannot disturb the operation of the integrated circuit.

2. A linear integrated circuit input stage substantially as hereinbefore described with reference to the accompanying drawings.