JPS6040033Y2 - integrated filter circuit - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to integrated filter circuits.

In modern vehicle electrical systems, significant cost savings can be achieved by using integrated circuits in, for example, ignition systems and seat belt interlock systems.

However, the current state of automobiles is generally very harsh on semiconductor circuits.

As a result, unforeseen problems and requirements arise in the design of integrated circuits that work reliably within automotive electrical systems and other high noise environments.

Current automotive conditions result in wide temperature variations.

Additionally, a wide range of spurious signals are generated throughout the wiring of the vehicle electrical system.

Positive or negative high frequency spurious signals (hereinafter referred to as "noise multiplied signals") having a magnitude of, for example, several hundred volts are generated in the wiring connecting various sensors to the input terminals of the integrated circuit device.

Such noise signals can cause conventional integrated circuit devices to malfunction, become inoperable, and even destroy them.
Furthermore, there is a risk of destroying separate semiconductor devices such as power transistors controlled by integrated circuits.

Therefore, integrated circuits that work in noisy environments such as the electrical system of a car must be designed so that they do not respond to noise.
Preferably, the filter circuit is provided on the chip.

However, large capacitance and resistance values are required to obtain adequate filtering action.

However, large value capacitors and resistors are difficult to form on integrated circuit chips and are extremely expensive.

The object of the present invention is to provide an integrated filter circuit that does not include such large-value capacitors and resistors, and can therefore be easily and inexpensively integrated using ordinary integration techniques, and can effectively suppress the above-mentioned high-frequency noise. There is something to do.

The integrated filter circuit of the present invention includes a first transistor and a first transistor.
A capacitance multiplier circuit comprising an integrated capacitor connected between the base and collector electrodes of the transistor, and a second transistor having two base electrodes connected to a bias potential source and an emitter electrode connected to an input terminal and a current source of the filter, 1st
It is characterized in that the emitter electrode of the transistor is connected to a ground potential terminal, and its collector electrode is connected to the output terminal of the filter and the collector of the second transistor, so that all the elements are integrated.

The invention will be explained with reference to the drawings.

First, the problem of various noises and transient voltages occurring in the electrical system of an automobile will be explained.

FIG. 1 is a model diagram of an automobile's electrical system, and FIG. 2 is a graph showing noise and transient voltages occurring in this electrical system.

In FIG. 1, a vehicle electrical system 100 includes a 12-port storage battery 102 with a negative terminal 104 and a positive terminal 1
It has 06.

Negative terminal 104 connects to ground conductor 105 of electrical system 100 .

Ground conductor 105 includes the vehicle chassis and wires connected thereto at various points.

In Figure 1, the resistance value of the chassis is determined by several different resistors 1
08. Concentrated on 110, 112, 114, 116 and 118.

Their resistance increases as the chassis corrodes and its various mechanical connections weaken.

The positive terminal 106 of the battery 102 is connected to an alternator (current source 121
) and the output terminal of the alternator, and the other terminal of the alternator is grounded.

A power line 122 (hereinafter referred to as the B ten bus) is also connected to the positive terminal 106.

The B live bus 122 is routed through a wire collection fixture 124 along with many other wires of the electrical system.

The distributed inductance of the B raw bus bar 122 is concentrated in several inductances 126, 128, and 130 in the model diagram of FIG.

Positive power supply terminal 134, ground terminal 136 and input terminal 1
38 at point 13 of B raw bus 122.
9 and a point 140 of the ground conductor 105.

The input terminal 138 is connected to the bus bar 12 in the wiring collection fixture 124.
A conductive wire 142 connected to a through switch 143 adjacent to
Connect to.

When switch 143 closes, conductor 142 connects to ground conductor 10
It is connected to point 144 of 5.

The distributed inductance of conductor 142 is concentrated in several inductances 145, 146 and 147.

Concentrated capacitors 123, 125 and 127 are connected to B live bus 1
22 and signal line 142.

Electrical accessory 150 is connected between point 151 of B live bus 122 and point 152 of ground conductor 105.

A second electrical accessory 154 (which may be, for example, an air conditioning motor) is connected to a point 155 of the B live bus 122 and the ground conductor 10.
5 to point 156.

A third electrical accessory 158 (which may be, for example, a drive motor for a power seat or a power window) is connected between point 159 of the B live bus 122 and point 160 of the ground conductor 10.5.

The various inductances and couplings therebetween shown in FIG. 1 generate large electrical squeaks on conductor 142 and busbar 122 as the various electrical accessories switch on and off.

For example, when accessory 158 is in operation, a large current flows from terminal 106 through B live bus 122, infrastructure 126 and 128, and resistors 114, 112, 110, and 108 to negative terminal 104.

The resistance of ground conductor 105 is typically large and creates a significant voltage drop between point 160 and negative terminal 104.

When attachment 158 is suddenly switched off, the change in current flowing through inductors 126 and 128 causes point 159
A very large positive voltage transient also occurs above and on point 139.

Therefore, a large positive voltage is developed between terminals 134 and 136 of integrated circuit 132.

Furthermore, the mutual coupling between inductors 126 and 145 and between inductors 128 and 146 creates large positive transient pulses on conductor 142 and thus on terminal 138 of integrated circuit 132, especially when switch 143 is open. do.

Similarly, by switching on or off other electrical accessories 150 and 154, B live bus 122 and terminal 134;
Additionally, positive or negative voltage transients occur on conductor 142 and terminal 138.

Generally, the B live bus 1 is installed in the electrical system separated from the battery 102.
The integrated circuit connected between 22 and the ground conductor 105 is
It is subject to voltage transients that occur between terminals 134 and 136 when the accessory switches.

Also, due to the current flowing through the distribution resistors 108, 110, etc., an undefined ground reference potential exists.

Additionally, any input terminal connected to a conductor running within the wire consolidation fixture 124 will pick up noise due to mutual induction and capacitive coupling with the B live bus 122.

If the battery is removed from the positive terminal 106 while current is flowing through the field coil 120, other noises of a different type than those described above will be generated.

In this case, a high energy positive voltage transient, referred to as a "load dump" voltage, is generated on the B1 bus 122.

The two types of voltages mentioned above are shown in the graph of FIG.

The load dump voltage is shown between points A and 8 on the left hand portion of this graph.

As shown in FIG. 2, the load dump voltage can exceed 100 volts.

The duration between points A and 8 is typically 1/2 seconds.

This voltage transient on bus 122 is of sufficiently large amplitude and energy that it cannot be integrated into conventional integrated circuit devices and low cost discrete semiconductor devices such as power transistors without some method of capturing the integrated circuit. Destroy.

The waveform C shown on the right side of the graph in FIG.
2 and the high voltage, high frequency noise that can occur on conductor 142.

The amplitude of the noise shown in waveform C can be 300 volts or more and typically has a duration of about 1 to 50 microseconds.

These pulses also sometimes have sufficient energy to destroy conventional integrated circuits.

Moreover, spectral analysis of the noise waveform as shown in FIG. 2 shows the presence of very high frequency components with amplitudes of a few volts and frequencies on the order of 100 megacycles.

Because bipolar integrated circuits are generally high-frequency circuits, these circuits are susceptible to high-frequency noise, and when designing circuits for use in today's automobiles, various measures are taken to ensure that the circuits respond only to information input and not to such noise. Need to pay attention.

Chassis - Unlike integrated circuits that have an input terminal to which a switch or sensor is connected by a long conductor, where a significant voltage drop occurs across the ground conductor due to the high current (many amperes) flowing through the resistor. This causes a condition that becomes associated with the ground voltage.

In this way, in the current state of automobiles, high frequency noise is generated, so the integrated circuit's I
Preferably, the filter circuit is provided on the C chip.

However, large resistance and capacitance values are required to obtain adequate filtering action.

However, large capacitance and resistance capacitors and resistors are extremely expensive to fabricate on integrated circuit device chips.

The present invention aims to realize an integrated filter circuit that does not include resistors and capacitors with such large resistance and capacitance values, can therefore be manufactured easily and inexpensively, and can filter out the above-mentioned high frequency noise well. FIG. 3 shows an example of the integrated filter circuit of the present invention.

In FIG. 3, 316 is a circuit (
where β denotes the common emitter current gain of the NPN transistor, and this circuit 316 is separated from the capacitor 302 and the NPN transistor 304 having a base electrode 306, an emitter 308, and a collector 310.

The capacitor 302 has a first terminal 312 and a second terminal 314.
has.

Emitter 30B of transistor 304 is grounded and base 306 is connected to capacitor terminal 312.

Collector 310 connects to capacitor terminal 314.

When the voltage on the collector 310 increases by Δ■, the current I=
CΔV/Δt flows through capacitor 302.

Here, C is the capacitance value of the capacitor 302, and Δt is the time required for the voltage increment ΔV to occur.

Current I flows into the base of transistor 304, and the current flowing through collector 310 is βCΔ■/Δt.

Therefore, the total current flowing through capacitor 302 and collector 310 is (β+1)CΔ■/Δt.

Therefore, the capacitor 302 connected as shown in FIG.
and transistor 304 develops an equivalent capacitance having a value of (β+1)C between terminal 318 and ground during positive transitions of the voltage supplied to terminal 318 connected to terminal 314.

Terminal 322 is an external input terminal of filter circuit 300, at which both information and noise signals may be generated.

The emitter of a PNP transistor 320 is connected to this terminal.

The collector of transistor 320 is connected to terminal 318 and its base to a suitable bias voltage source (not shown).

Also shown in FIG. 3 are a diode 328 and an NPN transistor 330.

The anode of diode 328 is connected to terminal 318 and its cathode to the base of transistor 330, whose emitter is connected to ground and whose collector is connected to output terminal 322'.
This terminal can be connected to the next circuit stage (not shown).

The operation of this filter circuit is as follows.

First, when a negative high frequency noise pulse is applied to the input terminal, transistor 320 is turned off so that no negative high frequency noise pulse appears at the output terminal 322'.

A positive high frequency noise pulse is then applied to input terminal 322 and, when the bias voltage of base 326 is exceeded by a sufficient voltage, current is drawn from current source 324 and the external noise source to terminal 318.
This current must charge the effective capacitance of the capacitance multiplier circuit 316 in order to drive the transistor 330.

Initially, if base 306 is at ground potential, terminal 318
The voltage increases rapidly to about 0.75 volts (for a silicon device) until the emitter-base junction of transistor 304 becomes forward biased.

As the voltage at terminal 318 increases further, this voltage increase will increase (β+
1) Charge an equivalent capacity of C picofarad.

Therefore, the noise signal must have a duration long enough to charge the (β+1)C picofarad capacitance from about 0.75 volts to 1.5 volts to drive transistor 330 into conduction; Since the duration of the noise signal is too short to drive transistor 330 into conduction, no noise signal appears at output terminal 322'.

On the other hand, the information signal applied to terminal 322 has a duration long enough to drive transistor 330 into conduction, so that the information signal appears at output terminal 322'.

Since a typical value of C can be 10 picofarads and a typical value of β can be 100 or more,
An equivalent capacity of 1000 picofarad can be obtained,
This capacitance value is large enough for the above-described operation.

Thus, the integrated filter circuit of the present invention can filter both positive and negative high frequency noise well, and requires only a small capacitor such as 10 picofarad, a transistor and a diode, and a large value filter circuit. Since no capacitors or resistors are required, it can be formed very simply and inexpensively on an integrated circuit chip using conventional integration techniques.

That is, capacitors with small capacitances, such as 10 picofarads, can be easily obtained by conventional integration techniques, for example as MOS (metal-oxide-semiconductor) capacitors or as PN junction capacitors.

In particular, it is advantageous to configure this capacitor with the collector-base junction capacitance of the NPN transistor 304 with its base region extended as necessary, as its manufacture becomes simpler and space is saved.

FIG. 4 is a circuit diagram of an integrated circuit for an automobile electrical system comprising another example of the integrated filter circuit of the present invention.

In FIG. 4, integrated circuit 400 includes an interface circuit 405 having an input terminal 403. In FIG.

The interface circuit 405 is a circuit that converts an appropriate voltage signal at the input terminal 403 into a current signal at the output coupling point connected to the capacitance multiplier circuit 414. The upper transistor corresponds to the current source 324 in FIG. The transistor 320 corresponds to the transistor 320 in FIG.

Integrated circuit 400 in FIG. 4 corresponds to integrated circuit 132 in FIG. 1, and terminal 403 in FIG. 4 corresponds to terminal 138 in FIG.

Capacitance multiplier circuit 414 is an NPN circuit having a capacitor 415 and a collector connected to interface circuit 405.
It has a transistor 416.

Capacitor 415 is connected between the collector and base of transistor 416 and its emitter is grounded: the equivalent capacitance that needs to be charged with the current from interface circuit 405 is the capacitance value of capacitor 415
It is equal to the value multiplied by the common emitter current gain β of 16.

The effect of the capacitance multiplier circuit 414 in this example is that the high frequency noise signal passing through the interface circuit 405 is
and provides a filter capacitor in a small area that prevents transistor 419 from being biased conductive and prevents flip-flop 420 from making erroneous changes in response to such high frequency noise signals.

Integrated circuit 400 further includes a second input terminal 429 connected to circuit 428 .

The circuit 428 can be provided with a filter circuit consisting of an interface circuit and a capacitance multiplier circuit similar in configuration and operation to the circuits 405 and 414.

Flip-flop 420 is connected to the collector of transistor 419 and circuit 428, and input terminals 403 and 429
Stores logic states representing signals occurring at a given time.

The output terminal of flip-flop 420 is connected to a circuit 430 that senses the information stored in flip-flop 420 and converts it into a signal that controls output transistors 432 and 434.

By way of example, integrated circuit 400 may be part of a motor vehicle seat belt interlock system, with terminal 403 providing a seat input signal from the motor vehicle operator's seat indicating whether the driver is seated. do.

Terminal 429 is provided with an input signal from the seat belt indicating whether the seat belt is fastened.

If the driver is not in the driver's seat of the vehicle and the seat belt is not fastened, both the seat input terminal and the belt input terminal are ungrounded.

When the driver sits on the seat, the seat input terminal 403 is grounded.

When the seat belt was then fastened, belt input terminal 429 was grounded and 1L was stored in flip-flop 420 by circuits 405, 415 and 428.

If the seat belt is fastened and the driver then takes the seat, '0yo' is written to flip-flop 420.

The state of the flip-flop is detected from the emitter of transistor 422 by circuit 430, which detects the output from terminal 431 to transistor 432 if seat input terminal 403 and belt input terminal 429 are grounded in the correct order.
Generates a drive current to turn on.

If the seat and belt input terminals are not grounded in the correct order and O-Yo is stored, circuit 430 provides base current from terminal 433 to output transistor 434.

If 111 is stored in flip-flop 420, output transistor 432 turns on and drives start relay 436.

On the other hand, if 101 is stored in flip-flop 420, output transistor 434 is turned on and drives warning buzzer 437.

Circuits 445 and 450 include circuits for setting reference voltages for various current source devices within integrated circuit 400, and further circuits for replenishing transistors 432 and 434 and other transistors within integrated circuit 400 from overvoltage on bus 438. including.

Although the invention has been described with respect to specific examples, it will be apparent to those skilled in the art that the various parts may be modified to suit particular requirements without departing from the scope of the invention.

[Brief explanation of drawings]

Fig. 1 is a model diagram of an automobile electrical system, Fig. 2 is a graph showing load dump transient voltage and noise occurring in an automobile electrical system, Fig. 3 is a circuit diagram of an example of the integrated filter circuit of the present invention, and Fig. 4 is an automobile electrical system. 1 is a circuit diagram showing an example of an integrated filter circuit of the present invention installed in an electrical system; FIG. 300... integrated filter circuit, 302...
...Capacitor, 312...First terminal, 314
...Second terminal, 304...NPN transistor, 306...Base, 310...
... Collector, 308 ... Emitter, 318.
...Terminal, 400 ...Integrated circuit, 316
．． 414... Capacity multiplier circuit, 415...
・Capacitor, 416...NPN) transistor.

Claims (1)

[Claims for Utility Model Registration] A filter circuit that filters high-frequency noise voltage supplied to an input terminal to prevent high-frequency noise from appearing at an output terminal, comprising a first transistor 304 and a base of the transistor.
A capacitance multiplier circuit consisting of an integrated capacitor 302 connected between collector electrodes, and a second transistor whose base electrode is a bias potential source and whose emitter electrode is connected to an input terminal 322 and a current source 324 of the filter are provided. An integrated filter circuit characterized in that the emitter electrode of one transistor is connected to a ground potential terminal, the collector electrode of the transistor is connected to the output terminal of the filter and the collector electrode of the second transistor, and all of the above elements are integrated.