Low-voltage CM0S bandgap reference voltage source design - Power Circuit - Circuit Diagram

0 Introduction Reference voltage sources are widely used in power conditioners, A/D and D/A converters, data acquisition systems, and various measurement equipment. In recent years, with the rapid development of microelectronics technology, low voltage and low power consumption have become one of the important standards in today's circuit design. For example, in some systems that use batteries, the supply voltage is required to be below 3 V. Therefore, as a voltage reference source for one of the circuit core functional modules such as power conditioners, A/D and D/A converters, it is inevitable to operate at a low power supply voltage.
In traditional bandgap reference designs, the output voltage is often around 1.25 V, which limits the minimum supply voltage. On the other hand, the parasitic BJT of the common collector and the common-mode input voltage of the operational amplifier also limit the low-voltage design of the PTAT current-generating loop. In recent years, some literature has attempted to solve this problem. To sum up, the former problem can be achieved by a suitable resistor divider; the second problem can be achieved by a BiCMOS process, or by a low threshold voltage MOS device, but the process difficulty and design cost will increase.
Based on the above considerations, this paper first analyzes the traditional bandgap voltage source principle, and then proposes a relatively low-cost and high-performance low-voltage bandgap reference voltage source. The low-voltage CMOS is designed by current feedback and first-order temperature compensation technology. A bandgap reference circuit allows its circuit to operate at lower voltages. This paper introduces the design principle of this bandgap voltage reference source, gives the simulation results of the circuit, and analyzes the results. The circuit was simulated based on CSMC 0.5μm Double Poly Mix Process and the ideal result was obtained.

l Low voltage COMS reference voltage source design
1.1 Traditional Bandgap Reference Source Figure 1 shows the principle of a bandgap reference. The base-emitter voltage VBE of a bipolar transistor has a negative temperature coefficient and its temperature coefficient is typically -2.2 mV/K. The thermal voltage VT has a positive temperature coefficient and its temperature coefficient is ten 0.085 V/K at room temperature. Multiply VT by a constant K and add it to VBE to get the output voltage VREF:

The temperature coefficient of equation (1) is differentiated from temperature T and substituted into VBE and VT to obtain K, which makes the temperature coefficient of VREF theoretically zero. VBE is less affected by changes in the supply voltage, so the output voltage of the bandgap reference is also less affected by the power supply.

Figure 2 is a typical CMOS bandgap voltage reference source circuit. Base-emitter voltage difference ΔVBE of two PNP tubes Q1, Q2:

Where: J1 and J2 are the current densities flowing through Q1 and Q2. The action of the operational amplifier places the circuit in a deep negative feedback state such that the voltages at node 1 and node 2 are equal. which is:

From Figure 2:

Through the mirroring of M1 and M2, I1 and I2 are equal, and combining (4) and (5) can be obtained:

Where A1 and A2 are the emitter areas of Q1 and Q2. Comparing equations (5) and (1), the constant K is:

In the actual design, the K value is expressed by the formula (7).
The traditional bandgap reference structure can output a relatively accurate voltage, but its supply voltage is high (greater than 3 V) and the reference output range is limited (1.2 V or more). To achieve an accurate reference voltage below 1.2 V at a supply voltage below 1.8 V, the reference source structure must be improved and improved.
1.2 Circuit design of low voltage COMS reference voltage source This design is based on CSMC-O. 5μm-CMOS process (NMOS threshold voltage is 0.536 V, PMOS threshold voltage is -0.736 V). The low-voltage bandgap reference source circuit designed by first-stage temperature compensation and current feedback technology is shown in Figure 3. The current of the low-voltage bandgap reference is used not only to provide the current required by the reference output, but also to generate the current source bias voltage required by the differential amplifier, simplifying circuit and layout design.