Circuit Challenge 5

Consider the circuit shown below.

       Core Circuit of a Bandgap Reference
        Core Circuitry for a Voltage Reference

Observation
Practitioners of the electronics arts (particularly those who design and use voltage references) will recognize the schematic as a basic building block for bandgap references.  (Note:  The circuit could have been inverted, thus permitting the use of PNPs.)

Assumptions
Assume VBE1=0.57V at the design center.
Assume IC1=IC2=100μA at the design center.
Assume VIN=1.25V at the design center.

The Challenge
Determine the approximate value of R1.
Determine the approximate value of R2.
Sketch the transfer characteristics of IC1 & IC2 versus VIN, for 0V < VIN < 1.5V.

For a comparison of your results with the author’s results, click here.