JPS5864821A - Threshold circuit - Google Patents

Abstract

PURPOSE:To avoid malfunction due to noise, by splitting a resistor connected between an input resistor and a power supply terminal, providing a capacitor between the split point and another power supply terminal, and giving a bias to a positive feedback means from the split point. CONSTITUTION:A signal of a signal source S is applied to an input of an inverting amplifier (a) through resistors R1, R3, inverted at an inverting amplifier (b) and a common mode signal is picked up from an output terminal (c). A resistor R4 is a positive feedback resistor, a resistor R5 is a bias resistor for the resistor R4 and a bias is applied to the resistor R4 through the resistor R5 from a filter circuit consisting of a resistor R6 and a capacitor C2 and a power supply terminal (d). Further, a resistor R2 changes the threshold value of a threshold circuit in response to a voltage at the said terminal (d) and is connected between a connecting point of R1 with R2 and a connecting point of the resistor R6 and the filter circuit of the capacitor C2. Thus, even if noise is superimposed on the terminal (d), the noise is eliminated with the resistor R6 and the C2, then no malfunction is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a threshold circuit, and an object of the present invention is to provide a threshold circuit that operates stably against noise that is superimposed on a power supply by 1%.

An example of using a threshold circuit is an ignition system for an internal combustion engine. That is, as in the example of the first WA, the distributor 1 has a magnetic circuit installed therein, which is one method of this type of ignition device.
An output approximated to a sawtooth wave corresponding to the rotation speed is obtained from the ignition coil, and a predetermined ignition energy is obtained on the secondary side of the ignition coil of the output circuit 3 after the threshold circuit 2 such as a Shemitt circuit is used. be.

In such applications, a circuit as shown in FIG. 2 has conventionally been used as the threshold circuit 2 shown in FIG. 1. In the same figure, S is a signal source (distributor), Rt
, Rs, Rsl R4, Rs.

are resistors, a and b are each an inverting amplifier, C is an output terminal of a threshold circuit, and dl is one end of a voltage supply source.

The operation of the threshold circuit having such a configuration will be explained using the signal waveform diagram shown in FIG. Assuming that a signal as shown in FIG. 3(a) is given from a signal source S, zero-inverting amplifiers a and b have resistances R1, '&1, BS, ]a4 and Rs as shown in FIG. 3 (Hata). It has a threshold value vtm shown as . Therefore, a rectangular wave as shown by the solid line in FIG. 1(b) is obtained at the output terminal C, and the ignition coil included in the output circuit 3 in FIG. A current as shown by the solid line in FIG. 3(C) flows due to a time constant determined by the inductance of the coil. In the case of the circuit shown in FIG. 2, if noise such as that shown by the broken line in FIG. 3(a) is superimposed on the input signal and becomes less than the threshold value Vtx.

Output is inverted. When state C occurs, the output is held due to the positive feedback effect of resistor R4, and as a result, the output waveform at terminal - becomes as shown by the broken line in FIG. 3(b). Therefore,
At that time, a current as shown in FIG. 3(C) flows through the ignition coil.

This type of noise is particularly the noise superimposed on the power supply terminal d, which is added to the input of the inverting amplifier @a through the resistors B1, R1, and R4. As shown in , the power consumption of the output transistor that drives the ignition coil and the power consumption of the ignition coil increase. This makes it extremely difficult to thermally design components such as the output transistor and ignition coil in the threshold circuit 2 and the output circuit 3, as well as the package, and also causes damage to the ignition coil and output transistor.

Conventionally, as a countermeasure for this type of noise, a capacitor CI is inserted at the connection point of the resistor R1°Rs on the input end side of the inverting amplifier 1, as shown by the dotted line in FIG. 2, to remove noise.

However, due to the signal source impedance of the signal source S and the integration circuit of the resistor R1 and the capacitor C1, the phase of the signal from the signal source S is delayed and transmitted to the inverting amplifier, resulting in a delay in the ignition timing. Particularly, when the period of the signal is short, the delay becomes more noticeable.

Therefore, it was not possible to increase the value of the ζ capacitor C1 to a value sufficient to eliminate noise.

The present invention has been made to improve the above-mentioned drawbacks, and its purpose is to eliminate noise superimposed on the power supply from other electronic devices installed in the automobile, and to prevent pulsating voltage from the generator when one terminal of the battery is disconnected. , it is an object of the present invention to provide a threshold circuit that operates stably even if a power supply terminal of the threshold circuit is applied to the power supply terminal in an insufficiently compressed state.

According to the present invention, positive feedback is applied to the input from the output of an amplifier that produces an output signal that is in phase with the input signal, and the input is connected to the other end of an input resistor whose one end is connected to the signal source, and the resistor is connected to the other end of the input resistor. Instruct the threshold circuit connected to the power supply terminal through
Divide the resistance connected between the input resistance and the power supply terminal,
A capacitor is provided between the dividing point and another power supply terminal, and the positive feedback means is biased from the dividing point via a resistor, which will be explained below with reference to the drawings.

FIG. 4 shows an example of a circuit specifically implementing the present invention.

In FIG. 4, a signal from a signal source S is applied to the input of an inverting amplifier 1 through resistors Rs and Rs, and further inverted by the inverting amplifier 1, and an in-phase signal is taken out from an output terminal C. Resistor R4 is a positive feedback resistor, and resistor R1 is a resistor R
4 bias resistor from the power supply terminal d to the resistor B.
A bias is supplied to the resistor R4 from the filter circuit of the capacitor Cm and the resistor R+I. Further, the resistor R2 adjusts the threshold value Vtm of the threshold circuit in response to the voltage of the power supply terminal d.
It is connected between the connection point of resistors R1 and Rj and the connection point of the filter circuit of resistor R- and capacitor CI. Therefore, even if noise is superimposed on the power supply terminal d, the resistor R@ and the capacitor C! Since the noise is removed by the capacitor Cm, the malfunction shown by the dotted lines in FIG.
Even if the value of is increased, the phase delay unlike the conventional circuit described above does not occur, so an effect of 3 times to 10 times or more can be expected.

FIG. 5 shows another example in which the present invention is specifically implemented.

In FIG. 5, a resistor R and a Zener diode D1 are used as a circuit that changes the threshold value in response to fluctuations in the power supply terminal d.
It is made up of. The signal of the input signal source S is transmitted through the resistors Rt, R
, is inverted by an inverting amplifier Q. The load resistor R of the inverting amplifier Q is connected to the second power supply terminal g in order to reduce the voltage drop across the resistor R of the filter circuit 1.
The output of the 0 inverting amplifier Qs connected to K is inverted by the inverting amplifier 1iiQsj via the resistor R and outputted to the output terminal cK. Furthermore, in order to reduce the output impedance, an emitter follower circuit of transistor Q4 is connected to the output terminal C, and positive feedback is applied to the input from the emitter through resistor R4, and the output from transistor Qs is connected to the base of transistor Q4 and series number ζ. A transistor Qs supplied through a resistor B$ is provided to drive the signal to a sufficiently low level. Similar to Figure 4, the noise superimposed on the power supply terminal d is caused by the resistance B- and the capacitor C1.
As a result, the noise that is removed and added to the base of the transistor Q2 through the bias resistors of the resistor Rs, the resistor R4, and the resistor B is extremely small, and the transistor operates stably against noise. Further, since there is sufficient margin against noise from the resistor B1, the power supply terminal g of the stripe 2 does not require a noise filter.

As described above, according to the present invention, it is possible to configure a threshold circuit that prevents the output transistor and the first coil from being destroyed due to malfunction due to noise without causing a phase lag in the threshold circuit, and by sharing the bias circuit, one circuit can be configured. We were able to achieve a sufficiently large noise removal effect using this capacitor. This has a great effect in reducing the size of the package and the cost when converting it into a hybrid IC.

[Brief explanation of drawings]

Figure 1 is a block diagram for explaining the internal combustion feedback ignition system.
Figure 2 is a circuit diagram showing a conventional threshold circuit, and Figure 3 is a signal waveform diagram to explain its operation, where (a) is the input signal waveform, (b) is the output voltage waveform, and (C) is the Ignition ■
FIG. 3 is a waveform diagram of a current flowing through the coil. Fig. 4 is a circuit connection diagram showing one embodiment of the present invention, and Fig. 5 is a circuit connection diagram showing another side of the invention. Inviting to the diagram, A... Distributor, B...
...Threshold circuit, C...Output circuit, R1,
Rs, R8R4, R1, R 藝, B y, Rs, R
e "" resistance, Qtm Qxs Qss Q4% Qt
m Transistor, ClCl...Curved capacitor, a, b
... Quaternary inverting amplifier, S ... signal source, C ... output terminal, 4% g ... voltage supply source, f ... ignition coil. #1 Figure 2 Figure 3 Figure 4 Figure #5 Flash

Claims (1)

[Claims] A first circuit that applies positive feedback to the input of the amplifier SS from the output of the amplifier that produces an output signal in phase with the input signal through a positive feedback 11 circuit, and has one end connected to the signal source and the other end connected to the input of the amplifier. and a second resistor connected between the input of the amplifier and one power supply terminal, the second resistor is divided, and the dividing point is connected to the other power supply terminal. A threshold circuit characterized in that a filter circuit is formed by connecting a function number ζ capacitor to the positive feedback circuit, and ζ is supplied to the positive feedback circuit from the dividing point.