A simple bandgap reference based on VGO extraction with single-temperature trimming
Bandgap references are widely used in analog and mixed-signal systems to provide temperature-independent voltage or current reference. In traditional bandgap structure, the base-emitter voltage VBE of a diode is used to generate a complementary to absolute temperature (CTAT) voltage, which reduces as temperature increases. The base-emitter voltage difference ∆VBE between two diodes with the same current but different emitter areas supplies a proportional to absolute temperature (PTAT) voltage. With the proper adjustment of the coefficients of VBE and ∆VBE in a voltage summer, the temperature dependency of the summed voltage can be mostly canceled out and the output voltage can achieve a relative temperature-constant property. However, even though the linear terms of temperature-dependent components in PTAT and CTAT expressions can be canceled out, there are still some high order terms left, which still affect temperature dependency. For this reason, a first-order bandgap reference with only PTAT and CTAT linear term compensation cannot achieve a sufficiently low temperature coefficient (TC), normally ranging from 10ppm/°C to over 100ppm/°C. To achieve higher precision and lower TC, the high order terms also need to be considered and compensated by some techniques. This thesis study describes the development of a high order bandgap structure, including the initial thinking, design flow, equation derivation, circuit implementation, and simulation result.