A voltage source includes first and second pn junctions which conduct the outputs of respective current sources to establish respective base-emitter voltages V.sub.be1 and V.sub.be2 at respective nodes; V.sub.be1 and V.sub.be2 can each be generated with a current I or a current N*I. An amplifier A1 has its non-inverting input connected to the second node and its inverting input connected to the first node through an input capacitor; a feedback capacitor is connected between the inverting input and a third node. Switches are connected between A1's inverting input and A1's output, between the third node and A1's output, and between the third node and a circuit common point. A control circuit operates the switches and current sources during first and second operating phases to selectively produce a temperature independent output voltage or a temperature dependent output voltage.