JPH05312849A - Transient voltage alteration detecting circuit - Google Patents

Abstract

PURPOSE:To provide a transient voltage alteration detecting circuit which has high detection sensitivity of the transient voltage alteration, and a wide detection range and with which the capacity of a capacitor can be made small and input signal offset voltage of a comparator can be made small. CONSTITUTION:The circuit is composed of transistors 3, 4 which form a circuit to convert standardized voltage into current and current mirror circuits 1, 2 and the current different of the transistors 2, 4 is sent to a comparator 13. Corresponding to the transient standardized voltage alteration, current output is generated transiently in the comparator 13 by a resistor 12 and a capacitor 6 connected with the transistor 1 and the transient standardized voltage alteration is detected. Also, the same circuit excluding the capacitor 6 is connected to the other input side of the comparator 13 and the input signal offset voltage of the comparator 13 can be made small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transient voltage change detection circuit having high sensitivity and wide detection voltage range.

[0002]

2. Description of the Related Art Generally, when detecting the presence or absence of a voltage that transiently changes, the voltage signal to be directly detected should be held for a certain period of time and compared with the detected voltage signal. Requires a voltage signal. FIG. 2 shows a conventional example having such a configuration. Resistance R between the equivalent voltage source and ground
27, R28 and R29, R30 are directly connected,
Output terminal 1 at each midpoint of R29, R30 and R27, R28
Connected to the positive and negative input voltage terminals of comparator 13 having 6. Further, the capacitor 6 is connected to the negative input terminal.

In this configuration, the positive and negative input voltages Vin + and Vin- of the comparator 13 are Vin + = V5 × R29 / (R29 + R30) (1) Vin- = V5 × R27 / (R27 + R28) (2) ) Becomes. R29 = R27 = Ra, R30 = R
If the condition of 28 = Rb is set, Vin + = Vi in the steady state
Since n- = V5 × Ra / (Ra + Rb), the output of the comparator becomes zero.

If V5 transiently changes, the value of the capacitor 6 is made sufficiently large, and if the charging / discharging time of the capacitor 6 is made sufficiently longer than the change of V5, the voltage difference Vci generated at the input of the comparator is Vci = ΔV5 × Ra / (Ra + Rb) (3) Here, ΔV5 is a transient change voltage of V5.

In a large-scale semiconductor integrated circuit,
It is desirable to simplify each functional block as much as possible. In addition, due to demands for low voltage operation, simplified comparator circuits are often used. Such circuits often have low sensitivity to the input voltage, and may not operate unless the voltage expressed by the equation (3) is sufficiently high. In addition, the comparator input voltage Vin +,
Since Vin− is limited by the power supply voltage Vcc of the comparator circuit, V5max = Vcc × (Ra + Rb) / Rb (4), which limits the detection voltage range.

[0006]

As described above, the conventional circuit has a problem that the transient voltage change detection sensitivity is low and the detection voltage is limited by the power supply voltage of the comparator.

The present invention is intended to solve such a problem, and provides a transient voltage change detection circuit which improves the detection sensitivity of a transient voltage change and has a wide detection voltage range.

[0008]

The present invention has a pair of so-called current mirror circuits in which the base and collector of one of the PNP transistors having a resistor between the power supply terminal and the emitter are connected to each other, which is a so-called current mirror circuit. Each collector of the transistors connected to the mirror circuit is connected to the collector of an NPN transistor that has an equivalent voltage source at its base, has a common base, and has a ground resistance at its emitter. However, a resistor is connected between the connection point of the base and collector of the current mirror circuit and the collector of the NPN transistor, and one connection point is grounded via the capacitor. In addition, the transient voltage change detection circuit has a configuration in which the collector connection points of the other transistors are connected to positive and negative input / output terminals of a comparator having an output terminal, and the terminals are connected to the power supply terminal via resistors.

[0009]

With the above-mentioned structure, the present invention can enhance the detection sensitivity of the transient voltage change and realize a wide detection range.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention in which the sensitivity of detecting a transient voltage change is increased, the detection voltage range is wide, the value of a capacitor can be reduced, and the offset voltage of an input signal of a comparator is reduced. It is intended for.

In the figure, transistors 3 and 4 are circuits for converting a reference voltage into a current. The collectors of the circuits are connected to the collectors of a current mirror circuit composed of PNP transistors 1 and 2 having a common base. Is a circuit for determining the time constant of the current change of the transistors 1 and 2,
The resistor 12 is a circuit for increasing the time constant of current change,
Transistors 17, 18, 19, 20 are circuits for reducing the input offset of the comparator, resistors 7, 21
Is the load resistance. The operation will be described below.

The bases of the transistors 3, 4, 19 and 20 are commonly connected to the equivalent voltage source 5, and when the emitter resistors 10, 11, 24 and 25 are made equal, the currents IC3, IC4 and IC19 flowing into the respective collectors. IC20 will be equal. Transistors 1, 2 and 17, 18 respectively form a current mirror circuit, and by setting the mirror ratio to 1: 1 respectively, the currents IC2, I flowing out from the transistors 2, 18 are
C18 is IC2 = IC3, IC1 respectively when the equivalent voltage source 5 is constant.
8 = IC19, IC3 = IC4 = IC19 = IC20, and IC2 =
IC4, IC18 = IC20.

If the voltage V5 of the equivalent voltage source 5 changes transiently, IC3, IC4, IC19 and IC20 change,
IC3 + ΔIC3, IC4 + ΔIC4, IC19 + ΔIC1 respectively
9, IC20 + ΔIC20. In this case transistor 18
The more flowing current IC18 also changes to IC18 + ΔIC18,
IC18 = ΔIC20. On the other hand, IC1 and IC2 are capacitors 6
Therefore, when the time constant is changed with a time constant and the time constant is set to be sufficiently larger than the transient change of V5, the transient changes ΔIC1 and ΔIC2 of IC1 and IC2 are sufficiently smaller than ΔIC4, and the load resistance is A current of ΔIC4 will flow.

As described above, when the value of the capacitor 6 is sufficiently large, the current ΔIC4 flows according to the transient voltage change ΔV5 of V5, and VCin = ΔIC4 × R7 (5) between the inputs of the comparator 13. Voltage is generated. Here, R7 is the resistance value of the resistor 7. Since the value of R7 can be set to an appropriate value according to the detection sensitivity of the comparator, a sufficiently high transient voltage detection circuit can be realized. Further, in the steady state, the current flowing through the load resistance becomes zero regardless of the value of V5, so that it is not necessary to consider the reference operating voltage of the comparator, and the detection range is wide.

Next, the time constant of the change of IC1 and IC2 by the capacitor 6 will be considered. The capacitance of the capacitor 6 is C6,
When the voltage across the capacitor 6 is VC6, when ΔIC3> 0, ΔVC6 = C6 × (−ΔIC3 × Δt) (6) On the other hand, when ΔIC3> 0, ΔVC6 is the value of C6, the resistors 8 and 12, and the diode-connected transistor 1
It changes with a time constant determined by the impedance of. That is, the voltage change of V6 when C6 is discharged is ΔIC3
The voltage change of V6 when C6 is charged varies depending on the values of the resistors 8 and 12 and the time constant determined by C6 when the diode impedance is considered to be sufficiently small. Further, the change amount of IC1 becomes ΔIC1≅−ΔV6 / (R8 + R12) (7) when the voltage change of the capacitor is ΔV6. From these, the value of ΔIC1 is C6, R8,
Determined by the value of R12. Generally, it is difficult to form a large capacitance in a semiconductor integrated circuit, and an individual capacitor is often used externally. It is desirable that the capacity value is small in view of space and cost merit. Even when a constant time constant is realized as described above, R8,
By increasing R12, it becomes possible to reduce the capacitance of the capacitor.

Next, the offset voltage of the comparator input will be described. In an actual transistor, IC3 and IC4 are due to the existence of finite current amplification factor hFE and Early effect.
There is a slight difference between IC1 and IC2. Therefore, even when there is no change in the voltage of V5, the offset current I01 exists, and Vin- = V15 + I01 * R7 (8), where Vin- is the negative input terminal voltage of the comparator and V15 is the reference voltage. ..

A current mirror circuit composed of PNP transistors 17 and 18, a current conversion circuit of a reference voltage composed of NPN transistors 19 and 20, and resistors 22, 23, 24 and 2.
The circuit constituted by 5, 26 has the same configuration as the circuit connected to the negative input side of the comparator in the steady state. In a semiconductor integrated circuit, since almost the same characteristics can be realized by arranging each element adjacent to each other on a silicon chip, the voltage at the positive input side of the comparator Vin + = V15 + I02 × R21 ...... (9) Then, if R7 = R21, then I02≈I01 can be satisfied, so that the offset voltage generated at the comparator input can be made substantially zero.

[0018]

As described above, according to the present invention,
Has a high detection sensitivity for transient voltage changes, has a wide detection range,
This is extremely useful because the capacitance value of the capacitor can be reduced and a transient voltage change detection circuit with a small input signal offset voltage of the comparator can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a transient voltage change detection circuit according to an embodiment of the present invention.

FIG. 2 is a conventional transient voltage change detection circuit diagram.

[Explanation of symbols]

1, 2, 3, 4, 17, 18, 19, 20 Transistor 5 Equivalent voltage source 6 Capacitor 7, 21 Load resistance 8, 9, 10, 11, 12, 22, 23, 24, 25,
26, 27, 28, 29, 30 Resistor 13 Comparator 14 Power supply terminal 15 Reference voltage terminal 16 Output terminal

Claims (3)

[Claims] 1. A first and a second transistor in which an equivalent voltage source is commonly connected to a base and each emitter is grounded directly or through a resistor, and a collector of the first transistor is an input side transistor. A first current mirror circuit connected to a common connection point of the collector and the base, and a collector of the second transistor connected to a collector of an output side transistor; and the first transistor and the first current mirror circuit common A first capacitor connected between the connection point and ground, a first load connected between a common connection point of the collector of the second transistor and the first current mirror circuit, and a first reference power supply terminal Resistance,
It is characterized by comprising a first comparator having both ends of the first load resistor as an input, and outputting a positive or negative signal from the comparator according to a transient increase / decrease change of the first equivalent voltage source. Transient voltage change detection circuit. 2. A first resistor is provided between a common connection point of the collector of the first transistor and the first capacitor and a common connection point of the collector and base of the input side transistor of the first current mirror circuit. The transient voltage change detection circuit according to claim 1, wherein the transient voltage change detection circuit is provided. 3. The third and fourth transistors whose bases are commonly connected to the equivalent voltage source and whose emitters are grounded directly or via a resistor, and the collector and base common connections of the third transistor. A second current mirror circuit connected to a point, the collector of the fourth transistor being connected to the collector of the output side transistor, and a common connection point of the collector of the fourth transistor and the second current mirror circuit. 2. The transient voltage change detection according to claim 1, wherein the second comparator is connected to a reference power supply side input of the first comparator, and a second load resistor is provided between the reference power supply side input and the first reference power supply. circuit.