JPH0360515A - Voltage detecting circuit - Google Patents

Abstract

PURPOSE:To operate a current mirror circuit with a simple circuitry and further with a low power supply voltage by composing the current mirror circuit of the first and second transistors and further setting the driving capacity of the second transistor larger than that of the fourth transistor. CONSTITUTION:When a voltage VIN to be detected is lower in comparison with a set voltage VD only a fine current flows to transistors N1 and N2. How ever, according to a ratio between the capacity of the N1 and N2, a current to flow to the N1 is larger than a current to flow to the N2. Thus, since a current to flow to the current mirror circuit is larger than the current to flow to the N2, an output voltage Vout is the almost same potential as the potential of a potential supply terminal 1. When the voltage VIN to be detected is higher in comparison with the set voltage VD, the output voltage Vout is almost the same potential as the potential of a potential supply terminal 2 by operation reverse to the above mentioned operation. Accordingly, the current mirror circuit can be operated with the voltage lower in comparison with the conven tional voltage.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a voltage detection circuit that detects a magnitude relationship between a voltage applied to a detection terminal and a predetermined voltage, and particularly relates to a voltage detection circuit suitable for integration into an integrated circuit. Regarding.

[Prior Art] Generally, when detecting the voltage at a specific point in a semiconductor integrated circuit, a reference voltage source whose output is set to a predetermined voltage by a constant voltage element such as a Zener diode is used, and the This is done by comparing the voltage of the detection section and the voltage of this reference voltage source using a comparison circuit such as a differential amplifier.

FIG. 5 is a circuit diagram showing a conventional voltage detection circuit of this type.

This type of voltage detection circuit consists of a comparator 5 with two inputs.
It is made up of. A reference voltage source 6 is connected to one input of the comparator 5, and the other input is connected to the detection terminal 4. In the voltage detection circuit configured in this way, an inverted output voltage is output to the output terminal 3 when the detected voltage applied to the detection terminal 4 exceeds the potential of the reference voltage source.

[Problems to be Solved by the Invention] However, the voltage detection circuit described above operates normally only when the reference voltage source and the power supplied to the comparator are in a steady state. For example, in a transient state such as when the power supply is turned on or when the power supply is cut off, this voltage detection circuit cannot operate normally. In addition, when the power supply voltage is low and the reference voltage source cannot maintain a predetermined voltage, or when the comparator cannot perform normal operation, normal comparison and detection of the detected voltage cannot be performed. Can not.

On the other hand, it is possible to configure a reference voltage source and a comparator that can perform predetermined operations even when the supply voltage is low. However, such a reference voltage source and a comparator have a complicated circuit configuration, and thus require a large number of integrated circuit elements.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a voltage detection circuit that has a simple circuit configuration and operates reliably even when the power supply voltage is low.

[Means for Solving the Problems] A voltage detection circuit according to the present invention includes: a first transistor of a first conductivity type connected between a first potential supply terminal and a second potential supply terminal; a first series circuit configured by connecting a second transistor of the same type and a resistor in series; a third transistor of the first conductivity type and a third transistor of the second conductivity type connected in parallel to the first series circuit; a second series circuit configured by connecting fourth transistors in series, and a connection point between the first and second transistors and the third
and one of the connection points of the fourth transistor is connected to each control electrode of the first and third transistors, and one of the connection points of the first and second transistors and the third and fourth transistors are connected to each control electrode of the first and third transistors. The other of the connection points of the transistors is connected to an output terminal, each control electrode of the second and fourth transistors is connected to a detection terminal, and the second transistor is connected to the fourth transistor. It is characterized by a greater driving capacity than the

[Action] If the potentials applied to the first and second potential supply terminals are the first level and second level, then a potential on the second level side with respect to the set potential is applied to the detection terminal. Sometimes, the current flowing through the second and fourth transistors is so small that the potential drop across the resistor is small. At this time, the current value flowing through the second transistor is smaller than the current value flowing through the fourth transistor, so the current flowing through the current mirror circuit consisting of the first and third transistors and the transistor connected to its output are Since a predetermined magnitude relationship occurs in the flowing current, the level of the output terminal becomes the first level or the second level.

Furthermore, when a potential on the first level side with respect to the set potential is applied to the detection terminal, the current flowing through the second and fourth transistors is large, so the voltage drop across the resistor becomes large. As a result, the current flowing through the current mirror circuit is suppressed, or the effect of the voltage drop due to the resistance is directly reduced, and the output terminal becomes the second level or the first level.

According to the present invention, there is no need to provide an external reference voltage source, and the setting to be compared with the voltage to be detected is determined by the amplification factor of the current mirror circuit, the element dimensions of the second and fourth transistors, and the resistance value of the resistor. The potential is determined. Therefore, since this voltage detection circuit operates normally as long as the voltage between the first and second potential supply terminals is a voltage at which the first series circuit can operate, the lower limit of its operable voltage is extremely low.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a voltage detection circuit according to a first embodiment of the present invention.

P-type MO8 is connected between potential supply terminal 1 and potential supply terminal 2.
? I! A field effect transistor P, , an N-type MO8 field effect transistor N, and a resistor R1 are connected in series. Similarly, a P-type MO8 field effect transistor P2 and an N-type MOS field effect transistor N2 are connected in series between the potential supply terminal 1 and the potential supply terminal 2. Here, the driving ability of the transistor N1 is set larger than that of the transistor N2. Then, P-type MO8) transistor Pl and P-type MO8) transistor P
2 has its gate short-circuited to the drain of a P-type MO transistor P1 to form a current mirror circuit. In addition, N-type MOS) transistor N1 and N-type MOS
) Each gate of the transistor N2 is short-circuited and led out to the detection terminal 4. Furthermore, a connection point between the P-type MOS transistor P2 and the N-type MOS transistor N2 is connected to the output terminal 3.

Next, the operation of this voltage detection circuit will be explained.

In FIG. 2, the horizontal axis represents the detected voltage V□, and the vertical axis represents the output voltage V. It is a graph diagram showing the relationship between the two in this example, taking UT. Detected voltage VtS is set voltage VD
, only a small current flows through the transistors Nl and N2, but the current flows through the transistors N1. The current flowing through the transistor N1 is larger than the current flowing through the transistor N2 from the capability ratio of N2. Therefore, the current flowing through the current mirror circuit becomes larger than the current flowing through transistor N2, so that the output voltage V. 1. , T is the potential between the potential supply terminal l and the potential between the path -.

Furthermore, when the detected voltage VIN is higher than the set potential VD, a large current flows through the transistors N, N2,
The voltage drop caused by the resistor R8 suppresses the current value of the current mirror circuit, and the current flowing through the current mirror circuit becomes smaller than the current flowing through the transistor N2. Therefore, the output voltage VOUT becomes a potential between the potential of the potential supply terminal 2 and the line.

Here, the set potential VD is the P-type MO8 field effect transistor P1. It is determined by the current amplification factor of the current mirror circuit constituted by P2, the element dimensions of N-type MO8 field effect transistor Nr, N2, and the resistance value of resistor R1. Therefore, if the voltage between the potential supply terminals 1 and 2 is higher than the voltage at which the series circuit consisting of the MO3 field effect transistors Ps and Nt and the resistor R1 can operate, it will operate normally. Such a voltage detection circuit can operate at a lower voltage than conventional ones.

Incidentally, the inventor used an enhancement type MOS field effect transistor as each transistor, set the current amplification factor of the current mirror circuit to l, and set the value of the gate width to the gate length of the MOS transistor N1 as MOS
) 2 of the gate width value for the gate length of transistor N2
0 times, and the value of the resistor R1 was set to IMΩ, and a voltage detection circuit according to this example was actually produced. the result,
The set potential Vo of this voltage detection circuit was 0.5v or less.

In addition, as described above, this set voltage V. The operating voltage at which it is possible to obtain, i.e. the voltage between the potential supply terminals l and 2, is
It is sufficient that the voltage range is higher than the voltage at which the series circuit consisting of the MOS transistors Pt, Nt and the resistor R1 is in a normal operating state. Therefore, the voltage between the potential supply terminals 1 and 2 can be set to a low voltage, for example, it can be set to an extremely low voltage comparable to the set potential (■.: 0.5V) in the above example. It is possible.

Furthermore, it is also possible to easily configure the voltage detection circuit to have a characteristic opposite to that shown in FIG. 2 described above. In this case, in FIG. 1, the gates of MOS transistors P and P2 are connected to the connection point of MOS transistors P2 and N2, and the connection point of MOS transistors Pt and N□ is connected to output terminal 3. Thereby, when the detected voltage Vxs is lower than the set voltage Vo, the output voltage V. The potential of LJT is near the potential supply terminal 2, and the detected voltage VXS is the set voltage V. If the output voltage v out is higher than
is approximately equal to the potential of the potential supply terminal 1.

FIG. 3 is a circuit diagram showing a voltage detection circuit according to a second embodiment of the present invention.

The difference between this embodiment and the first embodiment is that a new resistor R2-
R3 and R4 are provided, and the other configuration is basically the same as the first embodiment, so in FIG. 3, the same parts as in FIG. Detailed explanation will be omitted.

In this embodiment, a resistor R2 is interposed between the potential supply terminal 2 and the connection point between the resistor R1 and the N-type MOS field effect transistor N2. In addition, potential supply terminals l and 2
Resistors R3 and R4 are connected in series between the detection terminals, that is, N-type MOS field effect transistors N1 and N
Each gate of 2 is connected to the connection point of the resistors R3 and R4.

In Figure 4, the horizontal axis shows the power supply voltage ■DD, and the vertical axis shows the output voltage V. It is a graph diagram showing the relationship between the two in this example, taking UT. As is clear from FIG. 4, the output voltage V. N7 is the power supply voltage V. It rises as D rises, and when the power supply voltage VOO reaches the set potential Vo, it rapidly inverts to a low voltage (L level).

When the element dimensions of the MOS transistors N1 and N2 are set so that they operate in the weak anti-transfer region, the set voltage Vo becomes as shown in equation (1) below.

Vo” (1+R3/R4) @ (Vossz+(
1+P2/Pi)・(R2/R1)・(KT/q)fn
((NI IPl)/ (N2・P2)))...(
1) However, R1 to R4 are the resistance values of each resistor R, to R4, and V
O1lIN□ is the gate-source voltage of transistor N2, PL, P2. Nl and N2 are transistors P,,P
Gate width values for gate lengths of Q, N, and N2, q
is the electron charge, K is Boltzmann's constant, and T is the absolute temperature.

As is clear from equation (1), the set voltage Vo is generally determined by the gate-source voltage of the transistor having a negative temperature coefficient and the voltage drop across the resistor R2 having a positive temperature coefficient. Between this gate and source? By setting each parameter so that the U voltage and the voltage drop across the resistor R2 cancel each other out, a voltage detection circuit with low temperature dependence can be obtained.

For example, the transistor N at an absolute temperature T of 300K
2 gate-source voltage V. SN□ is 0.4V, and this gate-source voltage V. The temperature coefficient of SN2 is -
When 2.7mV/”C, Nl/N2=Io, P2
/P1=2, R1=IMΩ, R2=3.5MΩ, R3
When each constant is set such as /R4=1, the set voltage VD becomes 2.4v, and this set voltage V. shows excellent stability against temperature changes.

By forming each component as described above, it is possible to obtain a voltage detection circuit that has excellent stability against temperature and can operate normally even at a low supply voltage.

[Effects of the Invention] As explained above, according to the present invention, the first series circuit consisting of the first and second transistors and the resistor, and the third
and a second series circuit consisting of a fourth transistor are connected in parallel, and a current mirror circuit is configured by the first and second transistors, and the driving ability of the second transistor is applied to the fourth transistor. The voltage detection circuit is configured by setting the drive capacity to be larger than the drive capacity of the voltage detection circuit. Therefore, the voltage detection circuit according to the present invention can be operated with a low power supply voltage. Further, this voltage detection circuit has a small number of constituent elements, has a simple circuit configuration, and is suitable for integration into an integrated circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the voltage detection circuit according to the first embodiment of the present invention, FIG. 2 is a graph diagram showing the relationship between the detected voltage and the output voltage, and FIG. FIG. 4 is a graph diagram showing the relationship between the power supply voltage and the output voltage, and FIG. 5 is a circuit diagram showing a conventional voltage detection circuit. 1.2; Potential supply terminal, 3: Output terminal, 4; Detection terminal,
5; Comparator, 6; Reference voltage source

Claims (1)

[Claims] (1) A first transistor of a first conductivity type, a second transistor of a second conductivity type, and a resistor are connected in series between a first potential supply terminal and a second potential supply terminal. a first series circuit connected in parallel to the first series circuit, and a third transistor of the first conductivity type and a fourth transistor of the second conductivity type connected in series. a series circuit, and one of the connection points of the first and second transistors and the connection point of the third and fourth transistors is connected to each control of the first and third transistors. connected to an electrode, said first and second
The connection point of the transistor and the other of the connection points of the third and fourth transistors are connected to an output terminal, and each control electrode of the second and fourth transistors is connected to a detection terminal, The voltage detection circuit is characterized in that the second transistor has a larger driving capability than the fourth transistor.