Circuit Challenge 5

Consider the circuit shown below.

       
        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 V_BE1=0.57V at the design center.
Assume I_C1=I_C2=100μA at the design center.
Assume V_IN=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 I_C1 & I_C2 versus V_IN, for 0V < V_IN < 1.5V.

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