JPH06188707A - Voltage detection circuit - Google Patents

Abstract

PURPOSE:To obtain the circuit of simple circuit constitution which has good temperature characteristics of a detected voltage and is suitable for IC- implementation by applying the set voltage of a detected voltage setting circuit to the bases of two transistors(TR) of a band gap type reference voltage circuit. CONSTITUTION:The connection point of resistances R4 and R5 of the detected voltage setting circuit 2 is connected to the bases of the TRs Q1 and Q2 of the band gap type reference voltage circuit 1. When a source voltage VDD is applied, the output OUT of an operational amplifier circuit 3 rises while the emitter voltage V1 of the Q2 is lower than the voltage V2 at the connection point of the resistances R1 and R2 and then falls when the VDD rises until the V1 becomes as high as the V2. In this case, the value of the DDD when V1=V2 is the detected voltage. This constitution makes the temperature characteristics of the detected voltage similar to those of a normal circuit and the pattern occupation area at the time of the IC-implementation is reducible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detection circuit formed in a semiconductor integrated circuit, and is used, for example, in a power-on-clear circuit which detects a power-on time and generates a reset signal.

[0002]

2. Description of the Related Art A conventional voltage detection circuit used in a power-on / clear circuit is constructed as shown in FIG. 5 or 7. That is, the voltage detection circuit shown in FIG. 5 includes one NPN transistor Q, three resistors R1 to R3, and one operational amplifier circuit OP, and the divided voltage by the resistors R2 and R3 (detection voltage setting voltage ) Is compared with the base-emitter voltage VBE of the NPN transistor Q to detect whether or not the power supply voltage VDD has risen to a predetermined detection voltage and invert the detection output OUT.

However, in the voltage detection circuit of FIG.
Although the divided voltage has almost no temperature characteristic, VBE has a negative temperature characteristic, so that the detection voltage VDD has a negative temperature characteristic as shown in FIG.

On the other hand, the voltage detection circuit shown in FIG. 7 has two NPN transistors Q1 and Q2 and three resistors R1 to R3.
And a feedback control type operational amplifier circuit OP1 and a feedback control type bandgap type reference voltage circuit, two resistors R4 and R5 for setting a detection voltage, and a detection voltage setting by these two resistors R4 and R5. It comprises an operational amplifier circuit OP2 for comparing the voltage with the output voltage of the bandgap type reference voltage circuit, and the temperature characteristic of the detection voltage VDD can be made almost zero. The operational amplifier circuits OP1 and O
A circuit example of P2 is shown in FIG. 8, P1 to P4 are P channel MOS transistors, and N1 to N3 are N channel MO.
It is an S transistor.

However, the voltage detection circuit shown in FIG. 7 has a large number of circuit elements and requires two operational amplifier circuits OP1 and OP2, and the pattern occupied area of the operational amplifier circuit is particularly large when integrated into an integrated circuit. Therefore, it is not suitable for integrated circuits.

[0006]

As described above, in the conventional voltage detection circuit, many circuit elements and operational amplifier circuits are used in order to improve the detection voltage so as not to have a negative temperature characteristic.
However, the number of patterns required is large and the pattern occupying area is considerably large when integrated into a circuit. Therefore, there is a problem that it is unsuitable for integration into a circuit.

The present invention has been made to solve the above problems, and its object is to have a good temperature characteristic of a detection voltage, to have a simple circuit configuration, and to compare pattern occupying areas when integrated circuits are formed. The object of the present invention is to provide a voltage detection circuit which is small in size and suitable for integration into an integrated circuit.

[0008]

According to the voltage detecting circuit of the present invention, the collectors of a first transistor and a second transistor of the same type are connected to a first potential terminal, and the collector of the first transistor and the collector of the first transistor are connected to the first potential terminal. A bandgap in which a first resistor and a second resistor are connected in series with a second potential end, and a third resistor is connected between the emitter of the second transistor and the second potential end. A fourth reference voltage circuit, and a fourth reference voltage circuit between the first potential end and the second potential end.
And a fifth resistor are connected in series, and the series connection point is connected to each base of the first transistor and the second transistor, and the detection voltage setting circuit,
One input end is connected to the emitter of the transistor of
The other input end is connected to the connection point of the first resistor and the second resistor, the two inputs are voltage-compared to detect when the two inputs become equal, and an operational amplifier circuit for inverting the detection output is provided. It is characterized by having.

[0009]

The temperature characteristic of the detection voltage can be improved by applying the set voltage of the detection voltage setting circuit to each base of the two transistors of the bandgap type reference voltage circuit, and the circuit configuration is very simple. Since only one operational amplifier circuit is required for voltage comparison, the pattern occupying area is relatively small when integrated into an integrated circuit, which is suitable for integrated circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a voltage detection circuit used in a power-on-clear circuit which is formed in a semiconductor integrated circuit and detects a power-on time of the semiconductor integrated circuit to generate a reset signal. Bandgap type reference voltage circuit,
Reference numeral 2 is a detection voltage setting circuit, and 3 is an operational amplifier circuit.

The bandgap reference voltage circuit 1 is
The collectors of a first transistor Q1 and a second transistor Q2 of the same type (NPN in this example) are connected to a first potential terminal (power supply potential VDD in this example), and are connected to the emitter of the first transistor Q1. A first resistor R1 and a second resistor R2 are connected in series with a second potential end (ground potential GND in this example), and between the emitter of the second transistor Q2 and the second potential end. The third resistor R3 is connected.

In the detection voltage setting circuit 2, a fourth resistor R4 and a fifth resistor R5 are connected in series between the first potential end and the second potential end, and the connection point thereof is the first potential. Are connected to the respective bases of the transistor Q1 and the second transistor Q2.

Further, in the operational amplifier circuit 3, one input terminal (-input terminal in this example) is connected to the emitter of the second transistor Q2, and the first resistor R1 and the second resistor are connected.
The other input end (+ input end in this example) is connected to the connection point of the resistor R2 of, and both inputs are voltage-compared to detect when both inputs are equal to detect the detection output OUT (auto clear signal). Invert. Next, the operation of the voltage detection circuit having the above configuration will be described with reference to FIG.

The voltage at the connection point of the fourth resistor R4 and the fifth resistor R5 is VREF, the base-emitter voltage of the first transistor Q1 is VBE1, the base-emitter voltage of the second transistor Q2 is VBE2, The emitter voltage of the second transistor Q2 is V1, the first resistor R1 and the second resistor
When the voltage at the connection point of the resistor R2 of FIG. 2 is represented by V2, the change of each part voltage with respect to the change of the power supply voltage VDD is as shown in FIG. That is, the voltage VREF is obtained by dividing the voltage VDD by the fourth resistor R1 and the fifth resistor R5, the voltage V1 is lower than the voltage VREF by VBE2, and the voltage V2 is lower than the voltage VREF by VBE1. Is the first resistance R
The voltage is divided by the first and second resistors R2.

In the above voltage detection circuit, the power supply voltage V
When DD is turned on, the output OUT of the operational amplifier circuit 3 rises while V1 <V2, and the output OUT of the operational amplifier circuit 3 when the power supply voltage VDD rises until V1 = V2.
Falls. In this case, the value of the power supply voltage VDD when V1 = V2 is the detection voltage VACL.

Next, the characteristics of the voltage detection circuit will be analyzed. The emitter area ratio of the first transistor Q1 and the second transistor Q2 is N: 1, the current flowing through the second resistor is I1, the current flowing through the third resistor R3 is I2, and the current flowing through the fifth resistor R5 is When expressed by I3, the following equation (1
-1) and (1-2) are established.

[0018]

[Equation 1]

However, V _T is a thermal voltage expressed by V _T = kT / q, and k is Boltzmann's constant (1.38 × 10
^{-twenty three} j /), T is the absolute temperature, q is the electron charge (1.6
0 x 10 ^-19 Coulomb). Here, when V1 = V2, I1 · R2 = I2 · R3 ... (2-1), I2 / I1 = R2 / R1 ... (2-2), and equation (2-2) becomes (1-2 (3) is obtained by substituting in the equation).

[0020]

[Equation 2] Next, the detection voltage VACL is obtained.

[0021]

[Equation 3] The expression (3) is substituted into the expression (4-2).

[0022]

[Equation 4] Next, the temperature characteristic of the detection voltage VACL is obtained.

[0023]

[Equation 5] It is assumed that the variations in the resistances (for example, diffusion resistances) R4 and R5 and the temperature characteristics are almost negligible.

[0024]

[Equation 6] In order to

[0025]

[Equation 7] It should be designed to. FIG. 3 shows the result of actual measurement of the temperature characteristic of the detection voltage VACL in the case of designing in this way.
It has a slight negative temperature characteristic.

That is, according to the voltage detection circuit of the above embodiment, the temperature characteristic of the detection voltage is conventionally obtained by applying the set voltage of the detection voltage setting circuit to each base of the two transistors of the bandgap type reference voltage circuit. The circuit can be improved to the same extent as the circuit of FIG. 7 of the example, the circuit configuration is extremely simple compared to the circuit of FIG. 7 of the conventional example, and only one operational amplifier circuit is required for voltage comparison. The pattern occupying area is relatively small when integrated into a circuit, which is suitable for an integrated circuit.

In the above embodiment, the resistors R1 to R are used.
By adjusting the value of 3 and the emitter area ratio N of the transistors Q1 and Q2, the temperature characteristic of the detection voltage VACL can be set to be positive or negative.

FIG. 4 shows a modification of the voltage detection circuit shown in FIG. 1, in which N of the voltage detection circuit shown in FIG.
Replace the PN transistors Q1 and Q2 with the PNP transistor Q.
1'and Q2 'are changed and the connection relation between the power supply voltage VDD and the ground potential GND is reversed, and the same portions as those in FIG. 1 are denoted by the same reference numerals.

[0029]

As described above, according to the present invention, the temperature characteristic of the detection voltage is good, the circuit configuration is extremely simple, and the pattern occupying area is relatively small when integrated into a circuit. It is possible to realize a suitable voltage detection circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a voltage detection circuit of the present invention.

2 is a characteristic diagram shown to explain the operation of the circuit of FIG. 1;

3 is a diagram showing an example of a detection voltage characteristic of the circuit of FIG.

FIG. 4 is a circuit diagram showing a modified example of the circuit of FIG.

FIG. 5 is a circuit diagram showing a conventional voltage detection circuit.

6 is a diagram showing a detection voltage characteristic of the circuit of FIG.

FIG. 7 is a circuit diagram showing a conventional voltage detection circuit.

8 is a circuit diagram showing an example of an operational amplifier circuit in the circuit of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Bandgap type reference voltage circuit, 2 ... Detection voltage setting circuit, 3 ... Operational amplifier circuit, Q1, Q1 '... 1st transistor, Q2, Q2' ... 2nd transistor, R1 ... 1st resistance, R2 … Second resistor, R3… Third resistor, R4
… Fourth resistance, R5… Fifth resistance.

Claims (2)

[Claims] 1. A collector of a first transistor and a collector of a second transistor of the same type are connected to a first potential terminal, and an emitter of the first transistor and a second transistor of the second transistor are connected.
A bandgap type reference in which a first resistor and a second resistor are connected in series with the potential end, and a third resistor is connected between the emitter of the second transistor and the second potential end. A fourth resistance and a fifth resistance are connected in series between the voltage circuit and the first potential end and the second potential end, and the series connection point is the first connection point.
Detection voltage setting circuit connected to the bases of the transistor and the second transistor, and one input terminal connected to the emitter of the second transistor, at the connection point of the first resistor and the second resistor. A voltage detection circuit, comprising: an operational amplifier circuit having the other input terminal connected thereto, comparing both inputs to detect the time when both inputs become equal, and inverts the detection output. 2. The voltage detection circuit according to claim 1, wherein the voltage detection circuit is formed in a semiconductor integrated circuit and is used in a power-on-clear circuit that detects a power-on time of the semiconductor integrated circuit and generates a reset signal. Characteristic voltage detection circuit.