TWI522770B - Bandgap reference circuit - Google Patents

Description

Bandgap reference circuit

The present invention relates to a reference circuit; and more particularly to a bandgap reference circuit.

The bandgap reference circuit is used to generate an accurate output voltage. The output voltage generated by the bandgap reference circuit is not affected by process variations, power supply, and temperature variations. Therefore, the bandgap reference circuit can be widely used in various analog circuits and digital circuits, which require an accurate reference voltage during operation.

Figure 1 illustrates a conventional bandgap reference circuit 100. Referring to FIG. 1, the bandgap reference circuit 100 includes PMOS transistors M1, M2, and M3, an operational amplifier OP, resistors R1 and R2, and bipolar transistors Q1, Q2, and Q3. When the base current is ignored, the output voltage VOUT of the bandgap reference circuit 100 can be expressed as: VOUT = VEB3 + VT × lnN × R2/R1 (1)

Among them, VEB3 is the emitter-base voltage difference of bipolar transistor Q3, VT is the thermal voltage at room temperature, N is the current density of bipolar transistor Q2 and the current of bipolar transistor Q1. The ratio of density.

As shown in equation (1), adjust the resistance ratio of resistors R2 and R1 After the example, the bandgap reference circuit 100 can provide a stable output voltage VOUT having a zero temperature coefficient. The voltage level of the voltage VOUT is about 1.25V, which is close to the electron volt of the energy gap, that is, the 矽 energy gap reference voltage.

One of the objects of the present invention is to provide a bandgap reference circuit to provide a temperature dependent slope current and an output voltage having a zero temperature coefficient.

According to an embodiment of the invention, the gap reference circuit includes a first current source, a second current source, a third current source, an operational amplifier, a first bipolar transistor, a voltage dividing circuit, and a a second bipolar transistor, a third bipolar transistor, and a first resistor. The operational amplifier is electrically coupled to the first to third current sources. The first bipolar transistor has an emitter electrically coupled to the first current source and a base and a collector electrically coupled to a ground voltage. The voltage dividing circuit is electrically connected between the emitter of the first bipolar transistor and the base, and the voltage dividing circuit provides a ratio of an emitter-base voltage difference of the first bipolar transistor a first voltage and a second voltage. The second bipolar transistor has a base for receiving the first voltage, an emitter electrically coupled to the second current source, and a collector electrically coupled to the ground voltage. The third bipolar transistor has a base for receiving the second voltage and a collector having an electrical connection to the ground voltage. The first resistor is electrically connected to the third current source and the third bipolar Between one emitter of the crystal.

100‧‧‧Gap reference circuit

200,200’,200”‧‧‧Gap Reference Circuit

22,22’‧‧‧ Current source unit

24‧‧‧voltage circuit

M1, M2, M3, M4‧‧‧ PMOS transistors

OP‧‧‧Operational Amplifier

Q1, Q2, Q3, Q4‧‧‧ bipolar transistor

R1, R2, R3, R4 R5‧‧‧ resistance

Figure 1 illustrates a common bandgap reference circuit.

Figure 2 is a circuit diagram showing a bandgap reference circuit incorporating an embodiment of the present invention.

Figure 3 is a circuit diagram showing a bandgap reference circuit incorporating another embodiment of the present invention.

Figure 4 is a circuit diagram showing a bandgap reference circuit incorporating yet another embodiment of the present invention.

Figure 2 shows a circuit diagram of a bandgap reference circuit 200 incorporating an embodiment of the present invention. As shown in FIG. 2, the bandgap reference circuit 200 includes a current source unit 22, a voltage dividing circuit 24, an operational amplifier OP, a resistor R1 and a plurality of bipolar transistors Q1, Q2 and Q3. In the present embodiment, the current source unit 22 is composed of three PMOS transistors M1, M2, and M3. The transistors M1, M2 and M3 are electrically connected to a supply source VDD to provide currents I1, I2 and I3. Since the gates of the PMOS transistors M1, M2, and M3 are connected to each other, the current flowing through the PMOS transistors M1, M2, and M3 is proportional to the width to length ratio (W/L ratio) of the transistor.

In the present embodiment, the size ratio of the PMOS transistors M1, M2, and M3 in the current source unit 22 is set to 2:1:1. Therefore, currents I1, I2 and I3 The current value ratio is 2:1:1.

As shown in FIG. 2, the bipolar transistor Q1 has an emitter electrically connected to the drain of the PMOS transistor M1, and a base and a collector electrically connected to a ground. The bipolar transistor Q2 has an emitter electrically connected to the drain of the PMOS transistor M2, has a base electrically connected to a voltage VB3 from the voltage dividing circuit 24, and has an electrical connection to a ground. One episode of the end. The bipolar transistor Q3 has a base electrically connected to a voltage VB1 from the voltage dividing circuit 24, and a collector electrically connected to a ground. The resistor R1 is electrically connected between a drain of the PMOS transistor M3 and an emitter of the bipolar transistor Q3.

As shown in FIG. 2, the operational amplifier OP has a positive input terminal electrically connected to the drain of the PMOS transistor M3, and has a negative input terminal electrically connected to the drain of the PMOS transistor M2, and An output having a gate electrically connected to the PMOS transistors M1, M2 and M3. The amplifier OP and the PMOS transistors M2 and M3 form a negative feedback loop such that the input voltages VD1 and VD3 are substantially identical. Therefore, the voltages VD1 and VD3 can be expressed as: VD1 = VD3 = VB3 + VEB2 = VB1 + VEB3 + I3 × R1 (2)

Wherein, VEB2 is the emitter-base voltage difference of the bipolar transistor Q2, and VEB3 is the emitter-base voltage difference of the bipolar transistor Q3.

As shown in Fig. 2, the voltage dividing circuit 24 is electrically connected to the emitter of the bipolar transistor Q1. In the present embodiment, the voltage dividing circuit 24 is composed of three resistors R3, R4, and R5 connected in series. Therefore, the voltages VB1 and VB3 supplied from the voltage dividing circuit 24 are proportional to the emitter-base voltage difference of the bipolar transistor Q1. Therefore, the voltages VB1 and VB3 can be expressed as: VB3 = VEB1 × R5/(R3 + R4 + R5) (3)

VB1 = VEB1 × (R4 + R5) / (R3 + R4 + R5) (4)

Wherein, VEB1 is the emitter-base voltage difference of the bipolar transistor Q1.

Accordingly, equation (2) can be rearranged as: I3 × R1 = VEB2 - VEB3 + VB3 - VB1 = VT × lnN - VEB1 × R4/(R3 + R4 + R5) (5)

Wherein VT is a thermal voltage at room temperature, and N is a ratio of a current density of the bipolar transistor Q2 to a current density of the bipolar transistor Q1. In the present embodiment, the current flowing through the bipolar transistor Q1, the current flowing through the bipolar transistor Q2, and the current flowing through the bipolar transistor Q3 are adjusted to be substantially the same.

Therefore, the current I3 flowing through the resistor R1 can be expressed as: I3 = VT × lnN/R1 - VEB1 × R4/(R1 × (R3 + R4 + R5)) (6)

Since the thermal voltage VT has a positive temperature coefficient of 0.085 mV/° C., and the emitter-base voltage difference of the bipolar transistor Q1 has a negative temperature coefficient of -2 mV/° C., the current I3 has temperature dependence. The slope of. Due to the primary term -VEB1 x (R4/R3+R4+R5), the temperature dependent slope of this current I3 increases rapidly with temperature compared to the prior art.

As shown in equation (6), the net temperature coefficient of current I3 can be determined by selecting the resistances of resistors R1, R3, R4, and R5 and the current density of bipolar transistor Q2 and the current density of bipolar transistor Q1. N to adjust. Furthermore, as shown in FIG. 3, the base of the bipolar transistor Q2 can be electrically connected to the voltage VB1 from the voltage dividing circuit 24, and the base of the transistor Q3 can be electrically connected to the point. This voltage VB3 of the voltage circuit 24. The net temperature coefficient of this current I3 in this architecture will be smaller than that of the circuit configuration in Figure 2.

In order to provide a stable output voltage having a zero temperature coefficient, the bandgap reference circuit 200" further includes a resistor R2 and a bipolar transistor Q4, as shown in Fig. 4. Referring to Fig. 4, the current source unit 22' is It is composed of PMOS transistors M1, M2, M3 and M4, and the gates of the transistors are driven by the output terminal of the amplifier OP. In this embodiment, the PMOS transistor M4 and the PMOS transistor M3 have the same Therefore, the current I4 flowing through the resistor R2 is the same as the current I3 and can be expressed as: I4 = I3 = VT × lnN/R1 - VEB1 × R4/(R1 × (R3 + R4 + R5)) (7 )

According to the above circuit structure, the voltage VREF can be expressed as: VREF = VEB4 + I4 × R2 (8)

Wherein, VEB4 is the emitter-base voltage difference of the bipolar transistor Q4.

Substituting equation (7) into equation (8) yields : VREF = VEB4 + VT × lnN × R2/R1 - VEB1 × R2 × R4/(R1 × (R3 + R4 + R5)) (9)

Therefore, the appropriate resistance of resistors R1, R2, R3, R4, and R5 is selected. Value, the bandgap reference circuit 200" can obtain an output voltage having a zero temperature coefficient and low sensitivity to temperature.

Furthermore, the bandgap reference circuit 200" of Figure 4 can operate at a lower supply voltage level than the prior art. Return to equation (1): VOUT = VEB3 + VT × lnN × R2/R1 ( 1)

From equation (1), it can be found that to obtain a zero temperature coefficient, the output voltage level of a conventional bandgap reference circuit is limited to 1.25V. However, referring to equation (9), the output voltage level of the bandgap reference circuit disclosed in the present invention can be reduced by a ratio of a voltage of VEB1. In an example, if the ratio N is selected to be 32, the resistances of the resistors R1, R2, R3, R4, and R5 are selected to be 39KΩ, 225KΩ, 114KΩ, 4KΩ, and 84KΩ, respectively, and the gap reference circuit disclosed in the present invention The output voltage level can be as low as 1.11V. Therefore, in the present invention, the supply voltage level of the bandgap reference circuit can be as low as 1.35V.

In addition, the bandgap reference circuit disclosed in the present invention can effectively reduce the DC offset VOS due to the input offset of the operational amplifier. Considering the input offset VOS of the op amp OP in Figure 1, equation (1) will be rewritten as: VOUT = VEB3 + VT × lnN × R2/R1 + VOS × R2/R1 (10)

Therefore, the input offset VOS of the operational amplifier OP in Fig. 1 amplifies the ratio of R2/R1. Referring to Figure 2, considering the input offset VOS of the op amp OP, equation (9) will be rewritten as: VREF = VEB4 + VT × lnN × R2/R1 - VEB1 × R2 × R4/(R1 × (R3 + R4 + R5)) + VOS × R2/R1 (11)

Since the term -VEB1 × R2 × R4 / (R1 × (R3 + R4 + R5)) is added to the equation (11), the voltage VREF of zero temperature coefficient is obtained. Therefore, the amplification factor of the input offset VOS of the operational amplifier OP in the present invention can be reduced as compared with the prior art.

The technical and technical features of the present invention have been disclosed as above, and those skilled in the art can still make various substitutions and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be construed as not limited by the scope of the invention, and the invention is intended to be

200‧‧‧Gap reference circuit

22‧‧‧current source unit

24‧‧‧voltage circuit

M1, M2, M3‧‧‧ PMOS transistor

OP‧‧‧Operational Amplifier

Q1, Q2, Q3‧‧‧ bipolar transistor

R1, R3, R4, R5‧‧‧ resistance

Claims (7)

A bandgap reference circuit comprising: a first current source; a second current source; a third current source; an operational amplifier electrically connected to the first to third current sources; and a first bipolar transistor An electric pole connected to the first current source, and a base and a collector electrically connected to a ground voltage; a voltage dividing circuit electrically connected to the first bipolar transistor Between the emitter and the base, the voltage dividing circuit provides a first voltage and a second voltage proportional to an emitter-base voltage difference of the first bipolar transistor; a second bipolar a transistor having a base for receiving the first voltage, having an emitter electrically connected to the second current source, having a collector electrically connected to the ground voltage; and a third bipolar transistor Having a base for receiving the second voltage, and a collector having an electrical connection to the ground voltage; and a first resistor electrically coupled to the third current source and the third bipolar Between one emitter of the crystal. According to the energy gap reference circuit of claim 1, further comprising: a fourth current source electrically connected to the operational amplifier; a fourth bipolar transistor having a base and a collector electrically connected to the ground voltage; and a second resistor electrically coupled to the fourth current source and one of the fourth bipolar transistor Between the emitters; wherein an intersection of the fourth current source and the second resistor provides a bandgap reference voltage. The bandgap reference circuit of claim 1, wherein the voltage dividing circuit comprises: a plurality of resistors connected in series between the emitter of the first bipolar transistor and the base to provide the a voltage and the second voltage; wherein the voltage level of the first voltage is higher than the voltage level of the second voltage. The bandgap reference circuit of claim 1, wherein the voltage dividing circuit comprises: a plurality of resistors connected in series between the emitter of the first bipolar transistor and the base to provide the a voltage and the second voltage; wherein the voltage level of the first voltage is lower than the voltage level of the second voltage. According to the gap reference circuit of claim 3, wherein the resistance of the resistor of the voltage dividing circuit and the resistance of the first resistor are adjusted to change the first current source, the second current source, and The temperature coefficient of the current of the third current source. According to the energy gap reference circuit of claim 4, wherein the resistance of the resistors of the voltage dividing circuit and the resistance of the first resistor are adjusted to change the first current source, the second current source, and The temperature coefficient of the current of the third current source. The bandgap reference circuit of claim 2, wherein the voltage dividing circuit comprises: a plurality of resistors connected in series between the emitter of the first bipolar transistor and the base to provide the a voltage and the second voltage; wherein, the voltage level of the first voltage is lower than the voltage level of the second voltage; and wherein the resistance of the resistor of the voltage dividing circuit, the resistance of the first resistor The value and the resistance of the second resistor are selected such that the voltage level of the bandgap reference voltage is lower than the voltage level of a bandgap reference voltage.