NPN band gap voltage reference

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to the sole FIGURE, NPN bandgap voltage reference circuit 10 is illustrated as comprising operational amplifier 12 and bandgap cell 14.
Bandgap cell 14 is generally known in the art and includes first and second transistors 16 and 18 the emitters of which are coupled together through resistor 20.
The emitter of transistor 18 is connected through series resistor 22 to power supply conductor 24 at which is applied a ground reference potential.
The collectors of transistors 16 and 18 are coupled respectively through load resistors 26 and 28 to a source of direct current operating potential.
However, in most, if not all, prior art bandgap cells realized in integrated circuit form the collectors of transistors 16 and 18 are connected in series with respective high gain PNP transistors which source current to the collectors and not through only load resistors 26 and 28.
The bases of transistor 16 and 18 are connected together such that the base to emitter of transistor 18 is in parallel with the base emitter of transistor 16 and series connected resistor 20.
In operation, the currents sourced through load resistors 26 and 28 to the collectors of transistors 16 and 18 are set equal to one another such that the two transistors are operated at difference current densities due to the fact that transistor 16 has a emitter area which is ratioed with respect to the emitter area of transistor 18, i.
e.
, the emitter area of transistor 16 is N times the emitter area A of transistor 18 (where N is any positive number).
Since transistor 16 has a larger emitter area it is operated at a lower current density than transistor 18 such that a voltage, .
DELTA.
V.
sub.
BE is produced across resistor 20 that has a positive temperature coefficient.
The voltage between the base and emitter of transistor 18 has a negative temperature coefficient.
The positive temperature coefficient voltage developed across resistor 20 produces a current therethrough that has a positive temperature coefficient and which flows through resistor 22