Analog and mixed signal techniques for low voltage bandgap references

Bandgap reference sources are well known and widely used building blocks of most integrated circuits. They provide a precise DC voltage output for biasing in analog integrated circuits. Precision reference voltage is essential for defining full-scale values of input and output voltages in data-converters, measuring instruments, etc. The full bandgap of Silicon being approximately 1.1V a circuit designed to generate this output will require a DC supply voltage greater than this value. Modern short-channel CMOS processes use 1V power supply and hence a fractional bandgap voltage generator becomes necessary. Many analog designs use differential representation of input and output signals. These would require differential reference sources with well-defined common-mode levels as well. Novel circuits are presented that uses the inverse function technique. The circuits provide an output-voltage equal to the bandgap-voltage having a low output-resistance and allows resistive loading. It does not use resistors or operational amplifiers. Thus the design is suitable for fabrication in any digital CMOS technology. For low current and lower power of operation, the circuit produces a sub-bandgap of 0.9V suitable for portable applications.;A new digital bandgap reference that provides programmable reference voltage output is presented. It uses the same idea as in any analog bandgap circuit except that all the three analog operations namely differencing, scaling and addition are done in the digital domain after converting the operands (that is analog junction-diode voltages) into numbers. Digital signal processing provides both precision and programmability. The computed result is converted back to obtain the analog output voltage. The voltage drop across one of the current-biased diodes is used as reference in performing both the analog to digital and digital to analog conversions. Both of these conversions are done in a short time period to ensure that a reference voltage remains constant. Thus the reference voltage value cancels and becomes immaterial. It also becomes easier to address issues like curvature correction in the digital domain. Simulation results are presented.