CMOS Voltage References: An Analytical and Practical Perspective

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Bandgap Voltage Reference

The bandgap voltage reference circuit is one of the most commonly applied voltage reference circuit that theoretically outputs a voltage equal to the bandgap voltage of the semiconductor used. One of the first bandgap voltage reference circuits was presented by Robert Widlar of the National Semiconductor in 1971 (Widlar, 1971), and is known as the Widlar bandgap voltage reference circuit. The Widlar bandgap voltage reference circuit was implemented with the conventional junction isolated bipolar technology where the equivalent circuit is shown in Figure 5.1 in Chapter 5. The Widlar bandgap voltage reference circuit generates a stable low temperature coefficient reference voltage at 1.23 V (i.e., the bandgap voltage of silicon at room temperature derived in Exercise 1.3). This early implementation of a bandgap voltage reference circuit was successfully applied in the National Semiconductor’s voltage regulator integrated circuit LM113, which proved capable of achieving an output voltage with low temperature coefficient. Since then, it has been applied in many voltage regulator integrated circuits to generate the internal reference voltage.

3.1  Widlar Bandgap Voltage Reference Circuit

The basic idea of bandgap voltage reference circuit topology is the mutual compensation of a PTAT term (V_PTAT) and a CTAT term (V_CTAT) to pursue a reference voltage with zero temperature coefficient. The compensation can be achieved by a simple weighted sum between these ...