An alternative case for voltage references are those that produce a voltage Proportional To Absolute Temperature or PTAT. These can be useful for compensating other BJT circuits, or just useful as-is.
The LM3900 supports PTAT references by use of nVbe biasing, very often useful for biasing AC amplifiers. The DC voltage swing involved over temperature is small over the usual (e.g. commercial) temperature range, so the effects on AC circuits are minimal. But the ability to set specific ranges of voltages is handy. This topic is covered in Section 3.3 of AN-72, and specifically Figure 14.
The engineering notebook results for a +1Vbe and +2Vbe design are shown below. This work was done while developing the LM3900 antilog generator.
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