GB1337992A - Voltage reference circuit or voltage threshold detection circuit incorporating such a reference circuit - Google Patents

Abstract

1337992 Ignition system R C A CORPORATION 4 Dec 1970 [18 Dec 1969] 57593/70 Heading F1B [Also in Division G3, H3] A voltage reference circuit comprises a common point, such as earth, first and second stacks D1, D3, D5 and D2, D4, D6 matched to each other and each of equal pluralities of series connected asymmetrically conductive devices, each stack being connected between the common point and a respective separate point and means R, R<SP>1</SP> to pass current and to predetermine a ratio between first and second currents passed through the stacks in their forward direction, the common point representing the same polarity of both stacks and the separate points delivering the difference between the voltages developed across the two stacks as the voltage reference. The voltage reference circuit may be used in a voltage threshold detection circuit which includes a differential amplifier Q10, Q12, Q14, Q16, having the stacks D1, D3, D5 and D2, D4, D6 providing the reference voltage and the differential amplifier provides a signal output at C when an input signal at A, B attains a predetermined threshold value.The reference voltages are selected by determining the current ratio through the diode stacks D1, D3, D5 and D2, D4, D6 by suitable selection of resistors R, R<SP>1</SP>. The diodes D1, D3, D5 determine the high threshold voltage of the circuit and the diodes D2, D4, D6 determine the low threshold voltage. The detection circuit may be formed as an integrated circuit so that diodes D1-6 can be formed of transistors connected like Q34. The diodes are matched with regard to their forward voltage drops and the stacks compensate for supply voltage and temperature variations. With zero input from pick up coil 39 of a pulse distributor of an automotive ignition system the detection circuit is in the low level state with transistors Q10, Q12, Q24, Q26, Q30, Q32 and Q34 off and Q14, Q16, Q20 and Q22 on. As the input at A, B increases towards the high threshold the state of these transistors begin to reverse and regenerative feedback from the output transistor Q26 via Q34 and Q32 cause transistor Q30 to shut the diodes D1, D3, D5 to change the state of the circuit so that transistors Q10, 12, 24, 26, 30, 32 and 34 are conductive and Q14, 20 and 22 are off. Transistor Q16 is kept from completely turning off by the biasing potential applied from Q18. When the input signal A, B decreases to zero the circuit flips back to its initial state. Constant current sources are provided by Q15, R17, D19 and Q25, R27, D29. As an alternative way of obtaining the required current ratio through the diode stacks, the junctions of the diodes D2, D4, D6 could be made larger. Transistor Q34 may be replaced by a diode.